7D servo focus in different conditions...

Looking for feedback from 7D users who shoot fast action:

Do you find that the camera focuses better in overcast conditions and/or when the contrast in your scenes is lower?

Not at all. Higher contrast, better focus.

I never heard otherwise.

Well, you'd think that might be the case.
I shot about 3000 frames (fast-moving motorcycles on a road course, with a 600/4.0 IS lens) this past Sunday.

When the conditions were cloudy, the focus was pretty good, with about a 75% keeper rate.
When the weather improved (very bright, sunny, harsh and contrasty light), the keeper rate fell through the floor. I shot for an entire hour and afterwards, inspection revealed that only about 20% of the shots were in focus in the sunny sky conditions.
I did not change my technique with the weather.

This pretty much jives with what I saw a couple weeks ago, when I shot a similar event under cloudy skies, and the focus worked quite well.

I can't explain it, but I suspect it has to do with glare fooling or otherwise slowing the AF tracking.
I'm hoping someone else has seen similar results with their 7D.

In any case, I obviously can't count on my current combination (7D + 600/4.0 IS) to perform in bright conditions. I'm wishing I'd kept the combo I was using last year (D300 + 400/2.8 VR), which performed as well as I could have hoped.

High contrast leads to faster focusing. If you do this test at home, and try to focus on something that has one solid color, i.e. - white door, your AF will keep on hunting and hunting. Then focus on just the handle, and recompose.

aboss3 wrote in post #10202893
High contrast leads to faster focusing. If you do this test at home, and try to focus on something that has one solid color, i.e. - white door, your AF will keep on hunting and hunting. Then focus on just the handle, and recompose.

Your statement is not backed up by your proposed test.
In your test, you propose focusing on something with virtually no contrast at all to begin with.

I have obviously not very clearly explained my observations. I'll summarize:

Cloudy conditions, less contrast = better results; more in-focus shots
Bright conditions, LOTS of contrast = worse results; more OOF shots.

I'm off to dig up a few examples...

I have the same results with my 40 and 50d with either a
400 2.8, 500 f4 or my 600 f4. The auto focus drops focus 50% of the time in bright conditions. I am looking at the 7d because of the slow focus settings that is similar to the Nikon D300 which helps the focusing issues. I was shooting Osprey`s fishing for the last 2 weekends and my keeper rate was less than 20% for the action shots. In bright indirect conditions the keepers go to 80+%.

I think it's similar to shooting a mirror. The mirror won't be in focus, but what is reflected in the mirror will be. Same with objects of varying distance reflecting off your subject in bright, contrasty light. Try to focus on highly reflective surface and you're more likely to get in focus what is reflected from that surface.

Let's try this as a comparison.

First, we'll look at the "good" set - that is, where the photos - while not "tack sharp" - are at least good enough to sell.

These six photos were shot in cloudy/overcast conditions, using a 7D in manual exposure mode, AI Servo focus mode, with a Canon 600/4.0 IS lens. Here are two sets of three consecutively-shot photos, taken on two consecutive laps.

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Now let's look at six photos that were taken when the weather improved, using identical camera settings (but manual exposure adjusted for brighter conditions):

These are two sets (one of four consecutive frames, and one of two), taken within maybe fifteen minutes of each other. They're ALL out of focus and most customer won't buy them.

My conclusion: The 7D is "full of fail" when it comes to tracking focus on a fast-moving subject in bright, contrasty conditions.

Anyone want to debate this?

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What focus points were used? It seems like nothing in the second set of photos is in focus. The second set looks like you were closer,is that so?

TAZorich wrote in post #10209553
Let's try this as a comparison.

First, we'll look at the "good" set - that is, where the photos - while not "tack sharp" - are at least good enough to sell.

These six photos were shot in cloudy/overcast conditions, using a 7D in manual exposure mode, AI Servo focus mode, with a Canon 600/4.0 IS lens. Here are two sets of three consecutively-shot photos, taken on two consecutive laps.

The rider isn't in focus at all. Neither is the rider in the sunny conditions either. Your photos aren't really making your case because BOTH sets are OOF, and honestly I wouldn't buy any of them.

Looks like the lens is being back focused and needs an adjustment.

I've got a straight sequence of 23 frames in 3-4 seconds from my 7D and 100-400 of a BIF in bright sunshine and I'm happy with the focus on all of them. Slideshow of unedited files here....

http://picasaweb.googl​e.co.uk …eshow/547232777​2032749074

I agree, it looks backfocused to me.

Try microadjusting to get better, sharper results.

I might be wrong (and probably am) but isn't the focusing more dependent on the contrast of the subject than what the weather is doing? Yes, I know that bright sunlight should create more contrast but you would have to test identical subjects under the two different lighting conditions with identical settings to really see what is going on. To my thinking, if you are using a small focus area pointed at a solid color area of the subject then the AF is going to have some difficulty regardless of whether it's cloudy or sunny. I usually use Point Expansion and have not seen any difference in focusing between cloudy or sunny.

mrgooch:
The center focus point (only) was used. Yes; both sets are uncropped/unedited, and I was indeed a bit closer to the riders in the location from which I shot the second set, because of the physical distance from the outer wall to the track surface.

MrGreen:
They are indeed a bit back-focused (the rear wheel is usually sharp in photos out of this combo), but the lens is not back-focusing at all on a static subject. I don't know that an adjustment will help - and if I adjust it, won't it then make static subjects OOF? The truth seems to be that the 7D + 600 combo is too slow to track focus accurately on these kinds of subjects. Fortunately, photos like those in the first set are decent enough that my customers are still buying them in numbers; over the last couple events, it's been 15 to 20 Rider CD's a day at $50 each, plus prints and single image files. Sales are lower than they were last year (when I was using a better-performing combination of gear), but the sales numbers are still making my events worthwhile.

As for the posted photos "not making my case"...are you failing to see how much worse the second set is? In any case, your participation is appreciated, but you're not helping to answer the question: Why does the autofocus perform more poorly in the brighter and more contrasty conditions?