Digital Photography Tips and Techniques

Nikon CLS Advanced Wireless Lighting, Part IV

picmax — Sun, 15 Nov 2009 06:36:13 +0000

After going through the boring parts of the series (Part I, Part II, Part III), in which I described the “secrets” of Nikon CLS Advanced Wireless Lighting, I will discuss some real world examples this time using Nikon CLS Advanced Wireless Lighting. The examples are intended to show some of the common issues people may have seen.

To run the test, I mounted a SB-800 Speedlight on one end of the Nikon SC-28 TTL Remote Cord, then mounted them on a light stand using the 1/4″ thread of the SC-28. If I connect the flash to the camera’s accessory shoe, I can use the available flash modes offered by SB-800, such as TTL/BL, TTL, etc. I can also disconnect the cable from Camera and set the flash as a remote unit that I can control using the camera’s built-in flash as master. This setup allows me to run the test without moving either the flash or the camera.

The first image was taken using Nikon D200 in Commander mode and a SB-800 as a remote in TTL mode. The camera was at f/2.8 and with 1/30s shutter speed. Flash sync mode is set to front curtain on the camera.

The second image was also taken using the same camera and flash setting. Did you notice the big difference?

The second image shows a slightly brighter overall scene and much brighter shadow on the right. The extra shadows of the book shelf in the image indicate that there was a second light source contributing to exposure. If you have followed through the previous articles of the series, you won’t be surprised to know that the extra light is from the camera’s built-in flash that I used as the commander unit. The remote flash trigger pulse is supposed to happen at the same time when the shutter is open and the remote flash fires.

In many cases this extra light can be a problem. The trigger flash is typically quite weak but can still be very noticeable when the flash-subject distance is short or the ISO sensitivity is high or there is highly reflective surface in the field of view. In rear curtain sync mode with shutter speed slower than 1/2 second, the remote flash triggering is done with a series of pulse (we explained this in part III). It will appear much brighter and get captured by the camera. To prevent the problem, Nikon has provide the Nikon SG-31R IR Panel for Built-in Flash you can mount on the hot shoe. It has a plastic panel that is opaque to visible light but allows infrared light to pass. Remote flash units can function perfectly fine with infrared signal.

The following image was taken in with the SB-800 off camera in TTL mode using a SC-28 connection. The image appear to be significantly brighter than the first one. To match the brightness I had to add a 2/3 stop exposure compensation to the first image. The question is, why would wireless TTL and wired TTL lead to different exposure?

Actually I am not the only one seeing this problem. The same problem (underexposure in wireless TTL mode) has been observed by many. Here are just a few examples I found at photo.net:

And there are a few more I found on Nikonians.org:

Answers that people could get from Nikon is like the following:

“…… There will be a slight exposure difference when the flashes are used off camera wireless because the camera uses a slightly different calculation with off-camera flash than when on-camera……”

If the difference is intentional, we can safely assume that the Nikon had good technical reasons for such a difference. We may never know the exact reasoning behind this. If you are really curious, here is what I think may be the reason. A flash attached to a the camera’s accessory shoe is often the only light source or the main light source when it is set to contribute to the exposure. The flash should point to the subject. So the camera needs to make sure the flash in TTL mode provide the exposure level expected to be normal by most users. With remote flashes in TTL mode, the camera has no way of knowing where the remote flashes are pointed at or what the intention of the photographer is. It could be providing the main light but it could also be providing the background light, or fill light etc. Without knowing what the photographer wants it to be, it will be foolish for the remote flash to try to bring the exposure of the main subject to the standard level. If the remote flash is not pointed at the subject, it may mean a blown-out region somewhere. The only practical and safe decision it can make is to make sure no regions illuminated by the remote flash are overexposed. Due to the typical auxiliary nature of the remote TTL flashes (Check out the Nikon SB-800 flash shooting techniques guide by Nikon) it probably makes sense to intentionally underexpose with the remote TTL flashes.

The decisions for the remote flash output amounts are made entirely by the camera. Nikon may choose to change the behavior if they want to and there are good reasons to do so. Actually I haven’t seen much complaints like this lately. Perhaps newer cameras are different now.

Another argument for the wireless TTL underexposure goes like this: the camera determines the output for each remote group based on the reflected light of the pre-flash of that particular group independently of other groups (for example, the test here). To avoid overexposures in the overlapping flash illumination areas, the output for remote groups are intentionally underexposed.

This is obviously wrong and it is easy to prove. I took the following shots with the camera in Aperture Priority exposure mode and Front Curtain flash sync mode. I used two remote flashes that pointed to the same area. In the first image, I triggered both remote flashes (one in Group A and one in Group B) in TTL mode. In the second image, Group A flash was left on in TTL mode. Group B flash was turned off. In the third image, only Group B flash was left on in TTL mode. Group A flash was turned off. There is some degree of variation in exposure but the overall exposures are very similar. If the camera indeed determined the flash output amount for a remote group based on its pre-flash only, I’d expect the image taken with both groups in TTL mode (the first image) would be much brighter (+1 stop). It was not the case.

The following image is the 2nd image above with +1EV exposure compensation done in Capture NX2. It is much brighter than the 1st image (Both Group A and B flash in TTL).

Recap

The trigger flash from commander unit does contribute to exposure, which is a problem in many cases. You can avoid the problem by using Nikon SG-3IR IR panel or use a dedicated wireless commander SU-800.
Wireless TTL flash tends to underexpose compared to wired TTL flash. The design may be logical.
Camera analyzes the reflected light of pre-flash from all remote groups then determine the flash output amount for each remote group.

Nikon CLS Advanced Wireless Lighting, Part III

picmax — Wed, 11 Nov 2009 06:21:11 +0000

In the first two parts (Part I, Part II) of the Nikon CLS Advanced Wireless Lighting series, I have showed many examples of the pulse communication sequences but didn’t go into details about them. In part III, I will discuss the detailed coding scheme used by Nikon CLS Advanced Wireless Lighting system.

From the previous examples we know that there are several command types the master flash unit emits to control the remote flash units. To avoid interference, the optical pulse sequences start with a channel indicator so only remote flash units belong to the specified channel react to the commands. This channel indicator always contains 3 pulses. After examining the distances between pulses, I found that all the distances are results of a unit distance multiplied by integers, except for the channel indicator pulses, which contains 1x, 1.5x, and 2.5x unit distances between pulses. It appears that the optical wireless communication uses a hybrid coding scheme. After the channel indicator, the pulses confirm to simple binary format, pulse for “1″, no pulse for “0″. So it is quite easy to figure out what’s going on.

Remote (group) setting command

This is the command the master sends to setup the remote flashes. It has the following format:

[Channel][0110][bbbb]

“0110″ is the command code for the remote setting. “bbbb” represents a 4-bit binary code for the modes. There are four modes available: Off (1000), TTL (1001), AA (1010), and M (1011). If there are more than one groups configured, the 4 bit codes representing the modes are simply concatenated together. The following is an example for Ch #1, Group A in M mode, Group B in TTL mode.

Pre-flash command

This command is used to instruct a particular remote group to emit the pre-flash (upon receiving the pre-flash trigger). It has the following format:

[Channel][bbbb]

“bbbb” is the 4 bit code representing a specific group. Only three groups are supported: A (1001), B (1010), and C (1011). After this command, the master unit sends out the pre-flash trigger (a simple double pulse). If the camera doesn’t detect sufficient reflected light, it will ask for a 2nd pre-flash with another pre-flash trigger (double pulse). Upon receiving it, the remote unit(s) in the specific group should fire a stronger pre-flash. The process is repeated for all groups that need to do pre-flash, including all groups in TTL and AA modes.

Final flash amount command

This command is used to tell all remote groups how much light they should emit. It has the following format:

[Channel][0101][bbbbbbbb]

“bbbbbbbb” is 8-bit binary number. The amount data for multiple groups are concatenated together. If there is just one group, the number may be shorter than 8 bit since zero bits are not transmitted. However if there are more then one group configured, the amount data for the first group(s) is always 8 bit (padded with dummy bits).

For manual mode, the code format for each output level is shown below.

For TTL mode, the amount data should be a guide number (GN). I didn’t attempt to decode it yet.

After sending the amount data, the camera then sends a final flash trigger (a single pulse). The remote unit should emit the specified amount of light at that time. Again, the remote units won’t sit and wait forever, it will time-out if the final trigger doesn’t arrive for some reason.

Special case

The details above should cover typical uses of Nikon CLS Advanced Wireless Lighting System. One exception is in Rear Curtain sync mode with shutter speed slower than 1/2. The communication sequences are slightly more complicated. The command code for final flash amount is “0111″, instead of “0101″ for typical cases. The 2nd difference is the final flash trigger. It is no longer just a single pulse, but a command like the following:

[Channel][0111]

The remote flash fires the final flash after a short period of delay after receiving the command, before the shutter is closed on the camera. The reason for the elaborate scheme is to make accurate flash syncing possible when the exposure time is long and individual flash units may have slightly slower or faster timers. One other benefit of using a complex command as the trigger is to avoid mis-firing caused by fireworks or other stray lights that may happen during a long exposure. With a Rear Curtain and short exposure or Front Curtain mode, using a simple single pulse trigger is not a problem.

Phew…the boring part is finally over. If you find this interesting, great. If not, we will actually see some photos taken in the next part.

To be continued…

Nikon CLS Advanced Wireless Lighting, Part II

picmax — Tue, 10 Nov 2009 04:50:11 +0000

In the Part I of the Nikon CLS Advanced Wireless Lighting series, I described the very simple and inexpensive setup I used to capture Nikon CLS wireless flash sequences and showed you some captures of the simplest form of wireless flash communication. I then detoured to talk about some trivias about the Nikon non-wireless i-TTL flash process. Going back to the series again, I will talk about the flash sequences with remote flash(s) set to TTL mode.

All the tests below were conducted using the built-in flash on a Nikon D200 in Commander Mode. The flash sync mode was set to Front Curtain. The exposure mode doesn’t really affect the results if the shutter speed stays within the sync speed limit of the camera, which is 1/250s. The sequences are slightly different in Rear Curtain flash sync mode with shutter speed slower than 1/2 second. I will get to it later.

The first example was made with the D200 built-in flash in Commander Mode, Ch. 4, M: Off, Group A: TTL. There was no actual remote flash.

I labeled each of the pulse groups (blue lines). The first group is the remote setting command, which tells each remote group (in this case only one group) which mode it should be in. The available modes are Off, TTL, AA, and M. The second pulse group is the pre-flash command, which tells a specific remote group to get ready to fire a pre-flash. After that, the master unit sends out a pre-flash trigger low signal (the 3rd pulse group). If the remote flash unit detects the command, it fires the pre-flash after a short delay. Since there is no actual remote group in the test, there is no pre-flash from the remote unit captured. But I will show you examples later with remote flash actually turned on. If the camera finds that the pre-flash too weak, it will ask for a 2nd pre-flash from the same remote group. That is the 4th pulse group labeled as preflash trigger high. The remote unit should then fire a stronger pre-flash. The intensity of the 2nd pre-flash is pre-programmed in the flash. There is no communication between the master and the remote on how strong the 2nd flash needs to be. The 5th pulse group contains the flash output amount data the camera calculated for the remote flash. After a relatively long delay, the camera instructs the master flash to send the final flash trigger (the 6th pulse). If there were actual remote flash, it would emit the main flash in sync with the trigger signal. The possible reason for the long delay is to let the flashes recharge after the communications just in case the final output requires full power.

The following graphs show the zoomed-in views of the pulses.

If you compare the remote setting, pre-flash CMD, and remote flash output amount pulse groups, you will find that the first three of them are the same. That is the indicator for the channel (Ch. 4 in this test). By sending out each command with the channel information, Nikon CLS wireless flash system allows photographers to avoid interference between flashes by using different channels at the same location.

The following is an example with two remote groups A and B. Master was still set to off in the test. No actual remote flash.

Compared to the first example, the difference is the extra three pulse groups for instructing remote group B to do the pre-flash. The next graph shows two captures: the top one is the same as the one above, the bottom one is with two remote flashes for group A and B turned on but pointed away from Camera’s field of view. You can see peaks immediately after the pre-flash trigger pulses.

This is a zoomed-in view of the pre-flash command, trigger pulses, and the actual pre-flashes for group A. The first pre-flash has low intensity, the 2nd pre-flash has higher intensity.

The following communication and pre-flashes were captured with the remote flashes pointed to the field of view of the camera lens. There is only one pre-flash for each remote group.

The next graph shows all the examples above put together.

Well, if you have gone so far I hope you have not been bored to death. Knowing those boring details probably won’t help you make better photos. It is just for the curious mind.

Nikon i-TTL Flash Trivia

picmax — Mon, 09 Nov 2009 07:04:39 +0000

I started the series of posts about Nikon Advanced Wireless Lighting (see Nikon CLS Advanced Wireless Lighting, Part I) but quickly realized that there are some interesting aspects of the non-wireless intelligent through-the-lens (i-TTL) system as well.

The i-TTL system typically works like this: immediately before firing the main flash, the flash fires a series of pre-flashes. The reflected light from the scene is detected by the camera. Combined with other information from the camera’s 3D Color Matrix metering system, the camera determines a proper flash output and fires the flash.

Nikon’s i-TTL has two modes: Balanced Fill-Flash mode and Standard mode. The Balanced Fill-Flash mode automatically balances the output of the Nikon Speedlight and the scene’s ambient light while the standard mode ignores the background and tries to bring the scene to a standard level. The standard mode is automatically activated when spot metering is selected.

How many pre-flashes?

The answer is one or two. As shown in the following graph, the last pulse is the final flash output. The first one or two is (are) the pre-flash.

The tests were conducted with a Nikon D200 with its built-in flash unit and a SB-800 Speedlight mounted on hotshoe. With the built-in flash I normally see two pre-flashes. The 2nd one appears to be weaker than the first one. If I put the lens cap on so the camera won’t detect the reflected light from pre-flash, there is only one pre-flash. In that case, the final flash appears to be at its maximum power. With a SB-800, it is a different story. I normally see only one pre-flash. If I put the lens cap on, I see two pre-flashes, the 2nd one is stronger than the first one. I cannot quite figure out the reason for the behavior with the built-in flash. The SB-800 behavior makes sense: if the first pre-flash is too weak, camera asks for a second one with higher output power.

How fast is the pre-flash to final flash process?

It is pretty fast. Normally the whole sequence takes about 0.1 second or less. Still I hear complaints about pre-flash causing closed eyes in photos. I guess people can really close eyelid faster than 0.1 second.

FV Lock

With flash value lock button pressed, the camera performs the pre-flash sequences but does not fire the final flash actually take the photo. The calculated flash output amount is used for the flash output when the shutter is pressed. I observed the same pre-flash behavior as above.

Red-eye reduction flash sync mode

On the D200 I have, the red-eye reduction flash sync mode simply turns on the focus assist lamp for a short period of time one second before the flash to cause pupils in subject’s eyes to contract. With a SB-800, the flash emits three short pulses for this purpose. Notice this delay between the last red-eye reduction pulse and the pre-flash is only about 0.4 second. The last two pulses in the graph above are the pre-flash and the final flash.

Modeling flash

When the depth-of-field preview button is pressed, the camera by default cause flash (built-in or shoe-mount) to emit a modeling flash, which is 70 short pulses within ~one second.

Commander mode TTL

If I set the built-in flash to Commander Mode and within Commander Mode sub menu set Built-in to TTL mode with both Group A and B set to Off, the flash sequence behaves just like when I set the built-in flash to TTL mode.

Aperture Auto (AA) mode

Some people offered AA mode as a solution for closed eye problem saying AA mode has no pre-flash. This is untrue. It still has pre-flash but the delay between pre-flash and final flash is much shorter. The following graph shows a comparison between AA mode and TTL mode. I guess no human eye can close faster than 50ms.

Auto FP High-Speed Sync

If you are not familiar with high-speed sync concept, please read this. In this mode, the flash sends out very fast pulses. The total duration of the pulses are longer than the shutter speed. In my test, when shutter speed is 1/4000s, the pulses lasted ~1/200s. The pulses are too fast for the maximum 96KHz sampling rate I used to resolve.

Nikon CLS Advanced Wireless Lighting, Part I

picmax — Sun, 08 Nov 2009 09:04:29 +0000

Nikon Creative Lighting System (CLS) is a complete lighting solution with the latest Nikon Speedlight flashes. The system consists of the following core functions: i-TTL Balanced Fill-Flash, Flash Value Lock, Auto FP High-Speed Sync, Advanced Wireless Lighting, Multi-Area AF-Assist Illuminator, and Flash Color Information Communication. For a quick descriptions of each functions and CLS basic capabilities, please check out this Nikon support link.

Advanced Wireless Lighting allows photographers to control their Nikon Speedlight flashes from a distance without wires. Compared to other wireless trigger or optical slaves, the Nikon system make it very easy to control up to three remote flash groups that can have unlimited number of flashes per group. For each group, you can remotely setup the flash in TTL, Auto Aperture (AA), Manual modes, or turn it off completely without the need of walking up to the flash or running any wires.

Nikon makes great camera systems but often failed to explain the technologies behind them to the public. For the Advanced Wireless Lighting system, Nikon offers some vague description as usual. The following was from the Nikon support link.

(Advanced Wireless Lighting is the) method of controlling multiple wireless flash units. The Master sends out a very small light pulses to provide the Remotes and they communicate back subject exposure readings before the main exposure.

Are you satisfied with this? I was not. So I tried to find out more about Nikon CLS Advanced Wireless Lighting. While I was doing searches on Google, I found quite a few interesting posts in which people have tried to capture the sequences of wireless interactions between the master flash unit and remote flash unit. In this Nikonian post (free registration required), Hal Byron Becker tried to capture the flash sequences by turning the time domain signal into space domain signal. In this article, Alson van der Meulen tried to record the communication sequence of Nikon SB-800 using an oscilloscope.

Thanks for a good tip here (see the comment section), I was able to setup a cheap but effective optical signal capturing system using a $0.87 photodiode, a RadioShack cable with 3.5mm stereo audio plug, a desktop computer with a on-board Realtek sound chip (other sound cards should work), and a free audio editor and recorder software Audacity. The following is the picture of the photodiode soldered to one end of the audio cable. If you want to try this yourself, you need to make sure the polarity is correct.

The plug goes into the microphone jack on the computer. Using sampling rate of 96000Hz (44100Hz works OK), I was able to record optical pulse communication initiated by the master flash unit. The following screen capture shows some example recordings I made using a Nikon D200 and its on-board flash in Commander mode. I set the master to off (”–”), Group A to Manual 1/128, and varied the Channel from 1 to 4. There was no actual remote unit.

You can clearly see three distinct groups of pulses. This is the zoomed-in view of the first group of pulses.

This is the zoomed-in view of the 2nd group of pulses. I aligned the pulses on the left so it is easier to see the differences.

In both pulses groups, there are differences only for the first three pulses. For each test, the first three pulses for the 1st and 2nd pulse groups are the same. Since all I changed was the channel number, it makes sense to assume what the first three pulses are used to indicate channel number so only remote flashes in the same channel would respond to the information sent in the subsequent pulses.

To find out more about the coding scheme, I did some more tests. In the first test, I set Master to off, Group A to M: 1/64. In the second test, I set Master to off, Group A to M: 1/128, Group B to M: 1/128. In the third test, I set Master to off, Group A to M: 1/128, Group B to 1/64. All cases used Ch. 4. The following shows the comparison of these tests and the previous single group test case (Master to off, Group A to M: 1/128, Group B to off, Ch. 4).

From the first pulse group, you can see 3 more new pulses that are simply duplicated when Group B is added in manual mode. Changing the flash output level does not cause change to the pulses in the first pulse group.

From the second pulse group, you can see more pulses when Group B is added with the same output of 1/128 as Group A. Changing output level to 1/64 caused the change to the last a few pulses in the 2nd pulse group.

In all the tests above, the 3rd pulse groups at the far end is the same: just a single pulse that is used to trigger the final flash emission from the remote unit. When there is an actual remote unit, the trigger pulse is indistinguishable from the final flash emission from the remote flash.

Without getting too much into the detailed schemes of communication, we can be pretty certain about how this simplest case of Advanced Wireless Lighting works. The first bunch of pulses has the channel indicator and some information about remote groups but does not have anything about the amount of flash output. The second bunch of pulses has the same channel indicator and carries the information for the amount of flash output for all remote groups. The third pulse group (just a single pulse) is the trigger pulse.

To be continued…

The Flickr App Garden

picmax — Wed, 04 Nov 2009 13:59:43 +0000

Part of the reason for Flickr’s enormous popularity is their open API that supports a large number of so-called Apps, which are third party software that make your flickr experience more fun and useful.

In the past, there was no centralized location for Flickr Apps. Users had to look for them on the web. Developers had to promote their apps using their own websites. It all changed yesterday. Flickr has made a home for these third-party apps called App Garden.

The App Garden does not automatically list all the apps created using Flickr API. Developers have to submit them. There aren’t many apps there yet one day after its launch but we can be certain it will change soon. You may want to check out the five cool apps picked by ReadWriteWeb.

More about Flickr App Garden

Umbrella vs. Softbox

picmax — Thu, 29 Oct 2009 05:20:35 +0000

If you are not limiting yourself to natural light photography, at some point you may start to consider flashes or strobes and various light modifiers for them. Umbrella and softbox are two of the most commonly used light modifiers for portrait photography. People are quick to notice that umbrellas are typically much cheaper than softboxes. Does it mean you get what you paid for?

Most likely not.

They are simply different and have their unique characteristics. I have seen both being used in professional studios and the results are all fantastic.

Umbrella is cheaper and easier to carry and setup than the softbox. You can get a decent one for less than $20. You only need a umbrella holder (Shoe Mount Multiclamp) and a light stand to complete the setup.

Umbrella is more versatile. You can use shoot through or bounce. Some people think one way is better than the other , others think it is just the opposite. The end results aren’t that drastically different and some of the differences can be attributed to the differences in the umbrella or the ways they are used.

Umbrella spreads light across a larger volume and is suitable for group shots. The softbox on the contrary has a more defined light and is suitable for individual portrait unless you can get very expensive large softbox. If you want better light control, go with softbox. If you don’t mind the light spill, which sometimes creates more uniform lighting in confined spaces, go with umbrella that is more flexible. If you can afford it, get them both and use the best one for the task.

Here are some interesting links that may help you to decide.

Video: Umbrella of softbox in studio
Article: Softbox vs. umbrella
Article: Umbrella vs. Softbox: a quick comparison
Article: Another quick comparison: Shoot through umbrella vs. bounce w/ cover
Article: How an umbrella works

Personally I have decided on umbrella long time ago and have gotten some good results. I do have a softbox coming just to get some hands-on experience on the differences between umbrella and softbox.

Windows 7 Saga

picmax — Sat, 24 Oct 2009 03:38:18 +0000

Windows 7 was officially released on Thursday October 22, 2009. I pre-ordered it from Amazon back in June when there was a promotion. Vista Home Premium to Windows 7 Home Premium cost only $50 back then. Now it is $120.

Amazon was nice enough to send me the upgrade Yesterday, the official release day. I started the upgrade process last night. First I ran the Windows 7 Upgrade Advisor to make sure I didn’t have hardware or driver issues. In a few minutes I was notified that I was all OK except that I should uninstall a couple of applications such as Apple iTunes and VMWare Player then reinstall them after the Windows 7 upgrade. I did that. The upgrade process took quite a while to preserve my 750K+ files so I went to bed. By the morning it was all done. During upgrade, the installer told me that my computer would need to restart a few times. It was all done without me acknowledging it with a click.

Just like what I heard all along, the new Windows is nice. It is uncluttered, snappy, and user friendly. My softwares all appear working. The only thing I found not working is Nikon Capture NX 2. Somehow the software thought my installed version was an expired trial version. Not a problem, I just had to re-enter the license key. If you don’t have the license key, you may be in trouble. Even if you have backed up the files, the key is likely hidden in the Windows registry.

I had little time to play with it before I had to go for work. Unfortunately things turned ugly by the time I got back from work. I saw an unresponsive dark monitor screen. I tried to power off the computer by holding on the power button. It did power off. But I was not able to power it on again.

This may not have anything to do with Windows 7 upgrade. It looks like the power supply is dead.

I really want to get the computer up running again. It contains all the photos I have ever taken. I have backup copies of them on an external drive. However they are in an archive format that I cannot easily access.

Update: The problem was indeed caused by a dead power supply. Replacing the power supply wasn’t a challenge but it did cost me $50 and a trip to BestBuy. At the end, I think the upgrade is well worth it.

New Camera Promises to Capture Every Moment of Your Life

picmax — Tue, 20 Oct 2009 12:32:43 +0000

A UK-based firm is launching a camera that you can hang from your neck and promises to capture every moment of your life.

The camera, called ViconRevue, can be configured to take photos every 30s. However it is not just a timer controlled point & shoot camera, it has multiple senses. It has a built-in accelerometer and light sensors to detect when a person enters a new environment and takes a photo automatically. An infrared sensor detects the body heat of a person in front of the wearer and the camera snaps an image of the person automatically. If you have seen an automatic toilet or urinal, you know how it works.

The camera can hold 30,000 images onto its 1-gigabyte memory. If it captures a photo every 30s, that is good for over 10 days. The question is, can the battery handle it?

Don’t think this as a toy. It was a results of Microsoft research that can help people with memory loss issues. For example it helped a person who had suffered encephalitis that permanently affected their ability to recall recent events. There are other possible applications as well, such as life logging and others.

Do you want one? The bad news is that it is not yet available as a consumer electronics gadget but primarily a research tool. It is not cheap either at ~$820. The good news is that the price will go down as the product enters large scale manufacturing and a consumer version is made sometime in 2010.

[New Scientist via AllTop]

Nikon D3S Offers Speed Upgrade, Movie Mode, and Insane ISO

picmax — Wed, 14 Oct 2009 13:03:41 +0000

Nikon has not disappointed us when it comes to releasing new high end DSLR cameras. The new D3S is not an exception. The D3S redefines what is possible with a six-figure ISO sensitivity for stills and video capture while enhancing overall performance.

The D3S features a Nikon designed 12.1 megapixel FX-format CMOS sensor with 8.45 micron pixels. For image sensors, the pixel size does matter. Larger pixel offers better signal-to-noise ratio and larger dynamic range. The D3S has a standard ISO range of 200 – 12800, expendable downward to 100 and upward to an eye-popping 100400. The high ISO enables the D3S to capture images in darkness that is beyond the capability of human vision.

The 1280×720 24fps HD movie capture seems to be inferior to Canon’s 1080P offering but it is sufficient for the targeted professional users. The D-Movie mode supports full aperture control, exposure control, and contrast detection auto focus. The motion JPEG codec makes it easy to extract JPEG frames.

The in-camera post processing capability is a great feature. It is not about the silly art filters you can find on point-and-shoot cameras. D3S allows RAW editing. You can change JPEG compression, Size, White Balance, Exposure Compensation, Picture Control, Noise Reduction, Colour space and Vignette Control settings. Instead of downloading the images first then editing on the computer, the in-camera post processing capability allows the basic editing in the field before the images are transferred.

The D3S is speedy. It powers up in 12 ms with shutter lag 41 ms and mirror black-out 74 ms. It can shoot 9 fps in FX mode and 11 fps in DX crop mode. The buffer is expended to allow 48 frames in consecutive shooting.

The D3S offers great flexibility. D3S offers several different crop modes (up to 1.2x) for different lenses or for convenience so no useless pixels are recorded. Picture Control allows pre-defined picture styles. Coupled with Nikon’s RAW editing software such as Capture NX, the users can quickly get the desired output image without extensive post processing. Live View and Quiet Shutter modes make it easier or possible to shoot in certain situations. Dual card slots allows users many options in saving their images and videos. Users can record two full CF cards of data sequentially, record the same data onto two cards for backup, record RAW and JPEG simultaneously onto separate cards, transfer data from one card to another, and use one slot for stills and one slot for D-Movie recording.

Smoke Photography

picmax — Tue, 13 Oct 2009 12:20:20 +0000

The mysterious smoke fascinates many photographers. If you are one of them, you may be tempted to take your own smoke photos. It is not difficult at all. The following video tutorial shows you how to setup the equipments, take the photos, then edit them in Adobe Photoshop to achieve some cool effects.

Adobe Photoshop.com Mobile App for iPhone

picmax — Sat, 10 Oct 2009 13:34:17 +0000

The popular Apple iPhone has a very crude camera application and there is no way to edit the photos on the phone after you take them without third party applications. There are quite a few good photo editing applications available at Apple App Store that are not very expensive. But why not use a free application from the big name software company Adobe if you have only the most common editing needs? It gets even better than just editing: by signing up for a free photoshop.com account, you get 2GB of free storage for online photo sharing and storage.

Photoshop.com Mobile lets you quickly edit photos using simple gestures: most editing can be done by nothing more complicated than tapping and dragging your finger across the screen.

Editing features

Basics: Crop, Rotate, and Flip
Color: Exposure, Saturation, Tint, Black and White
Filters: Sketch, Soft Focus
Effects: Vibrant, Pop, Border, Vignette Blur, Warm Vintage, Rainbow, White Glow, Soft Black and White

For the first three groups of editing functions, you can adjust the photo to your taste. The effects are pretty cool but there is no adjustment options for them. After editing your photo, you can save the edited photo. The software saves a copy so your original photo is safe. If you select the Save and Upload option, the photo will be saved on your phone and a copy is uploaded to your Photoshop.com account. You have the chance to edit the photo description and select the online album before the file is actually uploaded.

Sharing

Browse your photos stored online at Photoshop.com.
Choose existing photos on the phone or take new photos to share on Photoshop.com. You cannot share them anywhere else (Facebook, flickr, etc) directly.
You do not need to sign up for the free account if you only need the editing functions.
You cannot edit photos stored online.

The Photoshop.com Mobile application is simple and easy to use. For people with sophisticated editing and other social network sharing needs, you may have to look elsewhere. For people who might be disappointed by this application, please remember, it is not Photoshop for iPhone, it is Photoshop.com Mobile for iPhone.

Users of Windows Mobile based phones can download the application directly from Adobe.

Focal Length of Wide Angle Lenses

picmax — Wed, 07 Oct 2009 01:54:44 +0000

Have you ever wondered why wide angle lenses such as Sigma 10-20mm f/4-5.6 EX DC HSM doesn’t have the problem with its rear element getting too close to the image sensor of your DSLR camera?

Well, this is a reasonable question if your understanding of optics is not much beyond the simple thin lens model you learned in high school. Photographic lenses are not thin lenses. Even the simplest prime lenses are constructed with multiple lenses in multiple groups. These are called “thick lenses”. The effective focal length of the thick lenses are no longer the distance between the last optical element to the rear focal point (called back focal length). To make the wide angle length work on SLR cameras, the back focal length of the lens needs to be longer than the effective focal length so the mirror doesn’t hit the lens when the shutter is release. On the opposite, for telephoto lenses the back focal length needs to be shorter than the effective focal length. This is typically achieved by putting a concave lens (or negative lens group) or convex (or positive lens group) at the front for wide angle and telephoto lenses, respectively.

The modern day wide angle lenses were mostly inspired by the old but clever design called retrofocus lens design pioneered by a French engineer (a little more history can be found here). If you compare the original retrofocus lens and the aforementioned Sigma wide angle lens, you can notice the similarity. The Sigma lens used a group of concave lenses instead of single concave lens for the front element in the original design.

If you are interested in digging into lens design, there are many good books, for example, Applied Photographic Optics by Sidney Ray. However you can learn quite a lot without spending a dime from free online resources by using search engines.

Is the Inverse Square Law a Myth?

picmax — Mon, 05 Oct 2009 02:28:18 +0000

People who are familiar with flash photography know the inverse square law, which states that illumination from any light source falls off with distance. For a point light source, the intensity of light is inversely proportional to the square of the distance from the source.

This is a law based on physics principles, specifically in this case, energy conservation. As energy radiates from a point source, it spreads out to an area that is proportional to the square of the distance from the source. Hence, the radiation passing through any unit area is inversely proportional to the square of the distance from the source.

Like any physics law, there is a specific set of conditions the inverse square law can be applied. One of the key phase here is “point light source”, which typically means something infinitesimally small in mathematical term.

The flash head cannot be a point light source, right? Well, the bare flash head is quite small. It can be a good approximation if the subject is far away from the flash. If you put the flash behind a softbox or umbrella, the light source is essentially the entire surface of the softbox or umbrella. We typically do not use the softbox or umbrella very far away from the subject. So you cannot consider the softbox or umbrella as a point source. Will the inverse square law fail then?

Yes and No. If you blindly apply the inverse square law using the distance between the subject and the softbox (or umbrella), the law fails especially when the distance to the subject is short compared to the dimension of the softbox. However if you think the surface of the softbox as a collection of tiny point light sources, the law continue to apply and the intensity of the light at the subject is result of being illuminated by the collection of point light sources that have various distances from the subject.

Someone tried to bust the inverse square law myth and failed. The tests contained numerous errors, such as measuring the light intensity off the axis, using the pixel values as intensities, ignoring the gamma correction done by the camera, etc. When the experiment was done right, the myth was un-busted.

Nikon Reveals Five Rules for Sharing Photos

picmax — Tue, 29 Sep 2009 13:18:45 +0000

Nikon conducted research by polling people and found out that consumers love to share photos (Is that really a surprise?). In the digital age, the smallest scale of sharing is perhaps crowding around the camera’s LCD screen. The 2nd scale is sharing photos on a TV screen or on any appropriate surface using the Nikon Coolpix S1000pj with a built-in projector. The largest scale of photo sharing is sharing online, which profoundly overcomes the limit of time and space for photo sharing on an unprecedented level. The proliferation of social networks and increasingly powerful search engines mean that once a photo is shared online, you may never have the complete control on where the photo may end up.

Due to the nature of online sharing, it potentially has more impact. They are really nothing more than common senses, but the five rules for sharing photos online (Photo Netiquette) published by Nikon are good reminders.

Don’t post embarrassing pictures of other people without their permission
Ensure that you are happy for the pictures you choose to be on the web for all to see
Remember that your boss, family and friends may look at your pictures, so don’t post any inappropriate images
Don’t endlessly post picture of yourself – you’ll come across as self-obsessed, rather than interesting
Think about the impact your photos will have on other people before you share or project them

[via Amateur Photographer]

Bounce Flash Tips

picmax — Sun, 27 Sep 2009 22:48:18 +0000

Perhaps one of the first tips you learned about flash photography is to use bounce flash indoors. The reason is quite simple: direct on-camera flash produces unflattering photo and it also creates a hard shadow on a wall behind the subject. By bouncing the flash light off the ceiling or walls, you can create a natural-looking photo with soft shadow. Bouncing the flash effectively creates a much larger light source that can wrap the light around the subject. Bouncing also changes the direction of the light so the shadow is thrown down behind the subject instead of directly behind the subject.

Basic bounce flash tips

Ceiling bounce works out better because the shadow is thrown lower behind the subject. Wall bounce from the side of the subject can product a more visible shadow on one side of the subject and uneven side-to-side illumination on the subject. Ceiling bounce is possible when the camera is hold in portrait orientation by setting the flash head title angle to 90 and rotate the flash head to point to the ceiling.
The optimal title angle for bounce flash is greater 45 degrees. This reduces the amount of the light from flash head directly illuminating the subject. When shooting at a downward angle, try to title the flash head greater than 90 degrees (points backward so the flash head points to the ceiling). On most flashes, this can be done by rotating the flash head 180 degrees.
Bounce flash works best with surfaces with neutral white or high reflectance. Watch out for color cast if the wall has colors.
Bounce flash doesn’t work well if the ceiling is too far or too close. Too close, the effective size of the light on the bounce surface is too small to be effective. Too far away, the light loss is too great. Nikon flash manual recommends 1-2 meters or 3.3-6.6 feet between flash and the reflecting surface.
Bounce flash causes significant light loss (2-3 stops), make sure the photo is not under exposed. Use larger aperture or higher ISO if necessary.

Bounce flash with diffusion dome (Omni Bounce)

Diffusion dome is a white plastic cover that goes over the flash head. It is also commonly known as Omni-Bounce. It works by spreading the flash light to much larger spaces around it, causing light to bounce from many surfaces simultaneously. The end result is a nice evenly lit scene. Nikon recommends using the diffusion dome in bounce flash application. Here what is said in the SB-800 user manual.

By attaching the provided Nikon Diffusion Dome over the flash head, you can diffuse the light even more when doing bounce flash, creating extremely soft light with virtually no shadows.

Well, it doesn’t seem so in practice. You can still get hard shadows. Using the diffusion dome is against another important rule of bounce flash: avoid illuminating the subject directly from the flash. With the diffusion dome on, there might be too much light directly illuminating the subject.

To illustrate the problem. I ran a series of tests using Nikon D200, SB-800 Speedlight, and Nikkor 50mm f/1.8 D lens. I mounted the flash on the camera then took test shots with the flash head at 45, 60, 75, and 90 degree angles and the following flash setups: 1) with the diffusion dome, 2) without the diffusion dome, 3) without the diffusion dome but with the built-in bounce card pulled out, 4) without the diffusion dome but with both built-in bounce card and wide flash adapter, and 5) with the diffusion dome and built-in wide flash adapter.

The test result clearly shows the best approach to achieve complete shadow-free on the wall behind the subject: you want to reduce the amount of light directly illuminating the subject. That means not using the diffusion dome, or bounce card, or the wide flash adapter, all of which can put more direct light on the subject.

One note of caution: You can avoid the shadow behind the wall by reducing direct light, but you may create shadow on the subject from the bounced light. For example, shadow under the subject’s nose or chin. So sometimes it is a trade-off you need to consider.

Nikon’s mistake

The following is taken from Nikon SB-800 instruction manual. The illustration on the left shows you the softer shadow cause by the bounced light with the diffusion dome but the manual forget to show you the shadow created by the direct light from the flash!

Don’t bounce if it is not possible to bounce

We talked about this a while ago: Don’t use bounce flash setup if you cannot bounce.

Digital Photography Links – September 25, 2009

picmax — Fri, 25 Sep 2009 23:14:51 +0000

There is just a hint of Autumn here but we can expect to see the colors of the Fall at full display soon. It is a great time for photographers, not just for landscape but also for outdoor portrait.

Fall foliage shooting tips – The post is two years old but should still be relevant. Also check out the polarizer tip.
Fall foliage status – Check out the status of fall foliages across the United States.
Nikon Coolpix S1000pj with Built-in Projector is shipping. Be the center of attention at your next party.
The free PhotographyBB Online Magazine has published its 20th issue. The September 2009 issue features many post-processing related articles and other great tips. It will be a fun read for your weekend.
Ansel Adams Meets Apple: The Camera Phone Craze in Photography – Have fun with your iPhone using the $2.99 Best Camera application.
Quick Tips for Capturing the Perfect Dusk Photo – A video tutorial on how to take photos at dusk. Learn what exposure mode, focus mode, white balance, ISO, file format to use for the best results.
Follow us on twitter – We send out tweet when a new post is published.

Google Picasa 3.5 Released

picmax — Wed, 23 Sep 2009 13:57:16 +0000

Google has released an updated version of the free photo editing software Picasa. Version 3.5 adds a great new feature called Name Tags that was originally only available in Picasa Web Albums. The new version has also improved tagging , import/export, and enhanced geo-tagging with integration of Google Maps. Check out the following video to find out what’s new in Picasa 3.5.

Update [September 24, 2009]:

Since I installed the 3.5 update, Picasa has been busy scanning my photos to identify faces. After about 24 hours, it is only about 20% complete (I have a very large collection). I initially named about 20 people. Picasa automatically creates album for each individual. After that, Picasa scans my photo collection then come up with suggestions of photos with the same person in them.

My first impression is that Picasa has amazing ability in identifying faces. It doesn’t matter if the face is only tiny part of the photo, out of focus, blurry, under/over exposed, or partially hidden, they are detected. Even faces in the photo within the photo and statues are detected. The automatic face recognition isn’t perfect though. It seems more accurate for adult faces but not so for baby or toddler faces. Now I am in the process of confirming thousands of faces that Picasa isn’t sure about the identity.

In Tools->Options->Name Tags settings panel, there are some options you can tweak for Name Tags. However there is no clear documentation for what they exactly do so I just used the default values.

Capture NX: Image Dust Off

picmax — Tue, 22 Sep 2009 12:30:47 +0000

Image Dust Off is a very useful feature supported by Nikon Capture NX and NX2 NEF raw converter/editor. You can take a reference photo (feature-less white wall) in supported cameras and used it to automatically retouch subsequently taken photos in Capture NX/NX2 to remove the spots in your photos caused by dust particles on the image sensor. Dust spots tend to show up more clearly if you shoot small apertures (high F numbers). Macro and landscape photographers probably find this more of a problem than portrait photographers. If you’d like to learn more about Image Dust Off, please check your Capture NX/NX2 user manual or the help file.

In order for this automatic process to work as expected, the photos you want to edit should have the same dust pattern as the reference photo. To make sure, you need to take a reference photo for each shooting session. For Nikon DSLR cameras that has sensor-shake dust removal function, it gets tricky. You cannot use the dust reference photo taken before sensor cleaning to retouch the photos taken after sensor cleaning. Nikon recommends you to take the dust reference photo after each sensor cleaning. If you have setup the camera to clean the sensor automatically at each startup/shutdown, you may not realize that the dust reference photo is rendered invalid each time you switch off/on the camera. This is clearly documented in the instruction manual of your camera but how many of you actually read the manual throughly?

Nikon TTL/BL Flash Truth and Myth

picmax — Mon, 21 Sep 2009 13:10:34 +0000

One of our readers, Desmond, is a curious person. He found out through his tests that some of the common understandings of the Nikon TTL/BL flash mode may not be accurate and some facts even appear to contradict the voice of an expert. For example, Russ said that “… TTL-BL does not work correctly when the background is darker than the subject.” However the tests from Desmond showed it worked just fine.

You can read the complete tests results and his conclusions at his blog or watch the following Youtube video for his demonstration.

At beginning, I was a little skeptical. However the test results are pretty hard to dispute. Perhaps the conclusions are wrong but there has to be a better explanation of the results.

We should all blame Nikon who never seems to have come out with a clear technical explanation of how the Creative Lighting System (CLS) including TTL-BL mode works. What Nikon tells us is the typical nebulous description such as “…Balanced Fill-Flash is performed. The flash output level is automatically adjusted for a well-balanced exposure of the main subject and background.” (SB-800 Instruction Manual).

What are your thoughts on this? We’d like to hear from you. Please use the comment box below or click on the contact link above.

Better Ways to Carry Your Camera

picmax — Sun, 20 Sep 2009 14:01:17 +0000

The standard way of carrying your camera is using the shoulder (neck) strap that comes with almost every camera. It has a lot to be desired. When I am out with my family, the camera would want to swing or roll wildly whenever I bend down to do something. Even during normal walking the camera bounces around and wants to slip off my shoulder. It requires one hand constantly on the camera to make sure it is secure and leaves another hand to do very limited things. For outdoor photographers, the shoulder strap just won’t work well for biking or hiking. I am sure many people have similar complaints. Recently, I have noticed a few products that can nicely solve the problems, for a price.

HoldSLR

This is a collapsible SLR camera carrier constructed with steel wire and spring supported fabric boot. You can hang it on your belt or your back pack chest strap. The camera lens goes into the boot and the body rests on the coated wire frame holder. It also comes with a weather cover for the camera. The following is a Youtube video in which inventor Kelly Zunker demonstrates the HoldSLR camera carrier.

Also check out the video testimonial from a wedding photographer and see it in action on a mountain bike.

Price: $75.95
Potential problem: If you go through all of the videos you may notice that none of the lenses has lens hood on. My feeling is that it may be slightly inconvenient to slide the lens with a lens hood into the boot.
Find out more: HoldSLR

Cotton Carrier

Cotton carrier is a vest-like chest harness you can wear comfortably. It distributes the weight of the cameras nicely and allows you to carry two cameras effortlessly. You screw a camera insert into the tripod socket at the bottom of you camera and the insert slide into the receptacle on the harness and locks in place with a 90 degree turn. Watch the following video to see inventor Andy Cotton show you how easy it is to get the camera on and off.

The design of the Cotton Carrier is one size fit all. Check out this instruction video to see how to adjust and use the carrier.

Price: $139.00
Potential problem: Attention-grabbing head-turning design.
Find out more: Cotton Carrier Camera System

Spider Holster

They call this Spider Revolution. It is a pocket sized holster made of steel and aluminum that goes on to almost any belt. You mount a camera pin into tripod socket and the pin slide on to the holster. You have the option to lock it in place or leave it free for quicker access. The Spider Holster completely removes stress from your back, neck, and shoulder and put the weight on your hip. The design is very beautiful (product photos on flickr). Check out the following video to see inventor Shai Eynav introducing the Spider.

Price: TBA (coming this Fall)
Potential problem: Get a stronger belt or carrier a backup just in case. Not for low-rise jeans. Not sure how to use this with a tripod. Update [September 20, 2009]: my concerns have been addressed by Shai’s comment below.
Find out more: Spider Holster

Are there any other better camera carriers? I’d like to hear from you. Please use the comment box below to share you comments and recommendations.

Correct Exposure

picmax — Sat, 19 Sep 2009 14:38:50 +0000

Nowadays, camera manufacturers want you to believe their cameras are very sophisticated precision digital instrument that can take great photos effortlessly. There is some truth in the marketing literatures, but they don’t typically tell you at the same time that their cameras can also produce garbages if the users fail to use them properly. I admit, this is really not necessary for them to do so in the marketing materials and most camera manuals do come with such warnings. The matter of the fact is that many people have some unrealistic expectations from their cameras that cost them hundreds if not thousands of dollars.

When it comes to the very basic aspect of photography, exposure, the common complaints we heard is that the camera doesn’t product correct exposure. People can typically notice the obvious problems such as blown out skies, dark faces, grey snow, pale green leaves, etc.

Sometimes exposure problem is not very obvious because untrained eyes would think the exposure is OK if they can make out all the details. There are also elements of personal preferences: some like bright photos, others prefer darker ones. The definition of correct exposure various as a result.

We are not talking about your personal preferences or creative decisions that you can make about exposures, for example, high key and low key photos. The subject is: why does the camera sometimes fail to produce correct exposure in automatic exposure modes?

First, the scene may contain larger luminance range (dynamic range) than the camera can handle. The camera is forced to make a decision based on pre-programmed preference or information such as color, focus distance, and focus spot. The results is undesired exposure at some parts of the photo.

Secondly, the built-in exposure meter in the camera can be fooled. It doesn’t matter how intelligent or sophisticated they are. “3D Color Matrix”, “iFCL”, “1005 pixels RGB”, “63 zone” are just some of the fancy words used by big name camera manufacturers. All in-camera exposure meters have a fatal flaw: they are reflected light meters. They make decision based on the light intensity reflected from the scene. When the scene doesn’t reflect a statistically averaged 18% (or 12-13% as later studies found out) of the incident light, or the scene itself contains light sources (lamps, the Sun, sky, mirror reflections of flash, etc), the build-in reflected light meters will be fooled into incorrect exposure.

To obtain consistent exposure using reflected-light meter like the one in your camera, you can use a grey card, or compensate the exposure. The amount of compensation can be determined based on your experience or trial and error. You can also take multiple shots with various exposure compensation (exposure bracketing).

Another way of obtaining consistent exposure is to use an incident-light meter which measure the amount of light falling on the subject. The reading is not affected by the reflectance of the subject.

The following is an example of the exposure problem.

The photos were taken using a Nikon D200. I used aperture priority and matrix metering mode for the photo on the left. Exposure compensation was set at 0EV. The camera decided an exposure of 1/80s F/4 at ISO400. The photo on the right was taken using exposure of 1/200s F/4 at ISO400 in manual mode based on incident light reading from a light meter. The second photo accurately captured the late afternoon scene in my backyard. The first photo showed over-exposed pale leaves.

Picasa Uploader for Facebook

picmax — Thu, 17 Sep 2009 13:19:27 +0000

Picasa is a free photo management and editing software from Google. It is well integrated with Google’s own Picasa Web Albums photo sharing site but it doesn’t have restrictions that prevent it from being used for uploading photos to other photo sharing sites. For example, we have talked about uploading photos to Flickr using Picasa.

The same can be done for Facebook as well. Here is a uploader plugin for Picasa that allows you to upload photos from Picasa to your Facebook account. Installation is a simple 1-2-3 and the usage is also straight forward. The Facebook uploader works under Windows and Mac but the Linux version of Picasa is not supported.

My Eyes Only Photo Creator Sees Future in iPhone

picmax — Sun, 13 Sep 2009 14:00:42 +0000

Remember the iPhone/iPod Touch application My Eyes Only Photo we talked about a while ago? The application allows you to encrypt sensitive images to safe guard your privacy.

Today I saw an inspiring story on The Arizona Republic about how the application’s creator, Joe Michels, started his Plan B as he saw jobs disappeared at his former employer’s firm. After spending a few months worth of nights and weekends writing his first iPhone application, he succeeded. When the development team he had supervised at his former job was laid-off, and his old boss was on his way out, Joe already had his Plan B on a firm ground.

He thought he made the right decision to quit his job last Fall.

My Eyes Only Photo was his second iPhone application. It was released this summer at $3.99 (currently $1.99 at App Store). There isn’t an exact dollar figure to show us how well it does but sales right now “are enough to make a good living” according to Joe’s words in the article .