What is maximum flash sync speed? What does it really mean? When and why it is important for flash photography? To answer all these questions, let’s start by looking at the basic camera component related to flash photography.
The shutter
Most SLR cameras have a focal plane shutter. It consists of two shutter curtains (typically called 1st/2nd or front/rear curtain). When the shutter release button is pressed, one curtain will travel across the sensor and the second blade follows the first one after a period of time. Depending on the exposure time, there may or may not be a moment when the entire sensor area is fully exposed to the light. At short exposure time, a slit formed by the two shutter curtains will travel across the sensor, exposing the sensor by scanning through it. By reducing the slit width, the shutter can effectively produce a shorter exposure time otherwise impossible due to the limit of the mechanical shutter movement. The image below illustrate the shutter operations at long (top row) and short (bottom row) exposures.
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What is depth of field (DOF)? Here are some definitions. People seem to have formed some customary notions about this term but may not really understand it. Examples of them are:
- Lens with shorter focal length (wide angle lens) has more depth of field (or less background blur) than a lens with longer focal length (telephoto lens)
- Camera with larger sensor has less depth of field compared to camera with a smaller sensor
- Depth of field can be calculated precisely from a formula and it won’t change from person to person
- …
While these are true to some degrees, or in certain circumstances, it is not the case for all situations. If you are still confused by this subject or just want to refresh your understanding, please read the excellent article by Paul van Walree.
As Paul pointed out, the depth of field has a lot to do with human perception. Viewing conditions, distances, visual acuity, etc have significant impact on depth of field. When comparing depth of fields, it is very important to establish a comparison framework, otherwise the comparison will be meaningless. For example, wide angle lens has the same depth of field as telephoto lens when the subject is framed the same (with different perspective due to different subject-camera distance). It is also quite eye-opening to know that the lens design also affect the depth of field: some lenses with longer focal length may yield more depth of field than a lens with shorter focal length.
I hope you enjoy the reading. For more information on depth of field:
Posted in
Tips and techniques on October 9th, 2007.
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The imaging sensor technology has been advancing rapidly in recently years. However the sensor dynamic range (DR) is still not quite wide enough to be comparable to human eyes, let alone capture the high dynamic landscape scenes.
Have you been struggling to expose the sky properly but the main subject or foreground turned out too dark? Or you managed to expose the main subject but the sky was completely overexposed and appeared washed out? You were disappointed and frustrated, and wondering if the big name camera manufacturer’s next $8000 product is what you need… You are not alone with these dynamic range challenged landscape photography situations. Here are some tips that may help you out without breaking the bank.
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Posted in
Tips and techniques on October 5th, 2007.
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When shooting in dim light conditions or at night, one may intend to shoot a long exposure to capture the beautiful streaks of lights from the traffic, or render the flowing wafer surface silky smooth. One way to achieve the long exposure is to shoot at small exposure such as f/22. The small aperture also helps to achieve large depth of field (DOF). If you use auto exposure, the correct shutter speed may exceed the camera’s longest exposure limit (30 seconds on many cameras). To obtain accurate exposure, you will need to meter at a wider aperture such as f/2.8 to ensure the shutter speed is within the camera’s specified limit. Once the correct exposure is determined, you can then stop down the lens and increase the exposure time accordingly to compensate. [Inspired by this discussion.]
Posted in
Tips and techniques on October 4th, 2007.
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The zoom (during exposure) effect is a classic special effect technique that can be traced back to early film photography era. By zooming the lens during a long exposure (typically 1/4s to a few seconds), photographer can create dramatic radiating streaks from center of the frame. This is a great technique to accentuate motion or create tension in photographs. Here are three different ways to achieve the classic zoom effect today. Read More…
Plastic milk jug for the shell, a piece of packaging material for the reflection liner, some gaffers tape, rubber bands, and some tissue paper - these are all you need to make this DIY diffuser. See more pictures of this setup and a test shot. The result is not bad at all for for this easy do-it-yourself (DIY) portable softbox.
It was full moon again the day before yesterday. I setup my Nikon D200 with Sigma 100-300 f/4 and a Sigma 1.4x TC on a tripod in my front yard and took some moon shots. One of the test I did was trying to find out if the “sunny f/16″ rule can be used for the full moon exposure.
Since I was shooting at ISO200, the exposure should be 1/200s and f/16 according to the “sunny f/16″ rule. However I didn’t want to shoot at f/16, so I opened up the aperture by two stops to f/8. Correspondingly, I increased the shutter speed by 2 stops from 1/200s to 1/800s. As shown in the picture above, the moon taken using the “sunny f/16″ rule looks a little bit dark but it retains the details of the moon surface. I then shoot an 1EV/step bracketing series. 1/500s and f/9 is a third stop stop overexposure than the “sunny f/16″, 1/250s and f/9 is 1 and 1/3 stops overexposure, and 1/125s and f/9 is 2 and 1/3 stops overexposure. Which one is the perfect exposure? 1/125s and f/9 is definitely not. The details in the highlight was blown out. The final conclusion may be dependent on personal taste. It is probably somewhere between the “sunny f/16″ and approximately 1 and 2/3 stops more exposure.
Just like all other “rules”, this test is only relevant to my specific test conducted at the specific time and location under the specific atmospheric conditions using my camera and lens. When it comes to your own full moon shooting, you may find that the perfect exposure is off more or less depending on various factors. For more detailed moon shooting tips, please read my previous post .
Posted in
Tips and techniques on September 28th, 2007.
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Multi-Flash Fun by Green Destiny
Stroboscope photography refers to the technique of photographing a moving subject with camera’s shutter open to yield multiple stationary exposures of successive movement phases, with pulsed flash illumination or mechanical devices that intermittently allow the light passing into the camera.
Nikon D200/SB800
A good write-up of this technique is by Professor Andrew Davidhazy of Rochester Institute of Technology titled Introduction to Digital Stroboscopic Motion photography. The article also contains a link at bottom that links to a article on film-based stroboscopic photography and details of do-it-yourself stroboscopy using a mechanical stroboscope.
The most challenging part of this technique is to get the exposure right. If each single frame has correct exposure, the overlapping parts of the photo will most likely be overexposed. As shown in the example on the left, the moving finger received much less exposure compared to the stationary hand. Having the subject in a different position for each exposure is the key to avoid this problem.
Another tip is to use a dark background and make sure the pulsed flash contributes the most exposure not ambient light.
Details on how to setup stroboscopic photography using pulsed flash vary depending on the camera and flash makes and models. For users of Nikon SB-800 AF Speedlight, you may find this article useful. Sigma EF-500 DG SUPER is compatible with many cameras and it also offers the multiple pulse flash capability.
Posted in
Flash photography on September 23rd, 2007.
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