Thursday, March 6, 2008

Getting use to the 40D

Like most of the gear I write about on this blog this is not a review –I’m not qualified to give you an in-depth review of any camera body or lens because I haven’t used them all. Instead I’m going to tell you about the problem that I had in switching from the Xti (400D) to the 40D.

The Xti’s light meter consistently under-exposed everything and I was use to it. No problems with raising the exposure in post by about -1/3 (if necessary) because colors naturally saturate when you under expose with a digital camera, and since I cut my teeth on Fujichrome Velvia back in the film days I liked the effect that under-exposing has.

Unfortunately, at least for me, the 40D’s light meter is very accurate –sometimes a little too accurate. Images are either dead on, or a little over-exposed and the level of over-exposure depends on how much natural is available. The end results are what seem to be inconsistent exposures when shooting flash macro at 0 FEC –sometime it works, and when it doesn’t the area in the scene that’s blown out varies.

Like an idiot I switched cameras and immediately changed my style by shooting at ISO 200 instead of staying at ISO 100 and it made the problem worse…

I didn’t think that going from ISO 100 to 200 would make much of a difference –it’s just one stop and when shooting flash macro I’m usually 3 or 4 stops below ambient anyway. But for every one stop change in exposure the amount of light coming through the lens either gets cut in half or it doubles (depends on the direction of the change). In going from ISO 100 to 200 the amount of light coming through the lens from the flash stayed the same –the flash duration simply dropped in half (which was my motivation for going to ISO 200 in the first place since it would be easier to freeze motion with a faster flash). But the amount of ambient light coming through the lens DID double, and that’s what was causing my inconsistent problems with blown highlights in my images.

Sure, I could set the FEC to -2/3 and continue to shoot at ISO 200 with no blown highlights. But the subject would be too dark and I’d loose too much detail. So at ISO 200 I can set my FEC to -1/3 and deal with some minor over-exposure in the highlights or drop down to ISO 100 to eliminate it. I still have to set the FEC to -1/3 at ISO 100, but I don’t think it’s a metering issue with the camera: I’m using the MT-24EX and when you shoot with two light sources one of them is bound to cause problems depending on the scene. If I were using a single flash head I could probably set the FEC to 0…

The photo I’ve attached to this post was taken at ISO 100 with the FEC set to 0 and there is some minor blown highlights in the background –you can’t see it because I adjusted the exposure in post to pull it out. As long as the blown highlights are minor, and not on the subject, it’s an easy fix. This next shot was taken at ISO 100 and -1/3 FEC and the exposure was dead on:

Fly at 4x

Moral of the story: If you run into a problem then blame yourself first, and not the gear…
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