Tuesday, November 6, 2007

Additional Musings on Flash Photography


Violet Darter series 2007_8-1
Originally uploaded by Dalantech.
I really struggled with flash photography when I first started shooting macro –and if the truth were told I’d have to say that I still struggle with it from time to time even today. Macro, defined as life size and higher magnification, is really a form of stop motion photography. No matter what you use to steady the camera there is still going to be movement. Vibration from the mirror, the wind blowing the subject or your tripod, etc. is all going to create minor displacement that wouldn’t normally be a problem for any other type of shooting. But when the image frame, at life size, is only 22.5 millimeters wide on a 1.6x crop factor camera it doesn’t take much movement to make an image look soft…

The key to getting good at flash photography is to understand how the flash works. I’m sure I’ve said this before but I’ll say it again: The intensity of the light that your flash produces does not change –ever. No matter what the exposure is the intensity of the light that the flash produces from frame to frame is always a constant. The only thing that does change is the duration of the light –darker scenes require the flash to turn on longer than lighter ones.

You’d think that getting more distance between the flash and the subject would be a good thing, but the duration of the flash has to increase to give you a correct exposure. Reflections become more of a problem because the light has more time to bounce off of shiny surfaces. Plus it gets more difficult to freeze motion since the light is on longer –there is more time for you, or the subject, to move.

I can’t tell you how much time I spent trying to get the flash away from the subject thinking that it would make the light less harsh and improve the quality of my images… *sigh*

So how do you get a short flash duration and at the same time reduce reflections? Get the flash heads close to the subject, and then experiment with the angle of the flash heads. The flash duration will be low, so freezing motion and getting sharp images won’t be an issue. As for reflections; sometimes all it takes is a minor change in the angle of a flash head to cut most, if not all, of the reflections out of a scene. The image above is an example of getting the flash heads of the MT-24EX close to the subject and using one flash head as a fill light (positioned over the top of the dragonfly).

I tried experimenting with using the flash head that’s over the subject for the main light source and the other as a fill flash for the shadows by setting the ratio control on the MT-24EX to make the overhead flash twice as bright as the fill light. Here’s the result:

RRS Flash Bracket Test 1-4

If you look at both of the images with this post you’ll see that the bottom photo doesn’t have as much detail in the eyes because the shadows are too strong. Also since the camera is metering for the entire scene the flash head that’s over the subject has to be on a lot longer to get the scene properly exposed (due to the distance and the angle of the overhead light source). I knew the flash duration was high because it was taking too long for the flash to recycle after each frame. So I went back to using the flash heads at equal power and the struggle continues… :)
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