Canon 7D - soft focus when using Al Servo mode

Has anyone come across this problem on Canon 7D? I recently did a photo shoot of Prairie Chicken "booming" in WI, and came back with almost all soft images. I used Al Servo mode and high speed continuous drive with tripod mounted 400/f4 lens + 1/4x II TC on a sturdy tripod with IS II on. Images taken with the same setup with IS off, one-shot and single frame modes are sharp as usual. I have noticed this is the case whenever I use the al servo mode. I am wondering if it is due to operator error or a problem with the focusing system in al servo mode. I am wondering if I should send the camera for service. Thanks for your feedback.

Ravi, do you only have this problem in AI servo? I use my 7D with a 400/5.6 and found that I needed to do significant micro-adjust on this lens, but I had the issue in every AF mode.

Ravi- What were the conditions like at the time of shooting? Unstable air caused by heat variation can cause shimmer and the AF will not work in these cases. This can happen for example if the sun is coming up and heating cool ground, and many other scenarios.

It was early in the morning w/ temps around 25-30 degrees with frost on the ground. There was some fog for 20 minutes or so when the sun came up. During that time, all the images were soft and could see the fog in the images. Otherwise, the air was clear. I didn't microadjust the lens and the TC. That could be a problem too. I have taken pictures of another bird the morning before with one-shot AF and single frame mode with the same lens/TC combo with crisper images. I have never done any microadjusting, so I can try it next time I rent the lens. Thanks for the ideas.

like Ian, I micro adjusted mine after comparing it to another camera..made a huge difference..and I did it on a lens by lens combo basis

Agree with others here regarding micro-adjust. My 7D + 600F4 IS is at +9 and 7D + 600 F4 IS + 1.4x III is at +3.

My 7D with 600mm f/4 was -10, huge difference after micro adjustment..

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Originally Posted by Ravi Hirekatur

It was early in the morning w/ temps around 25-30 degrees with frost on the ground. There was some fog for 20 minutes or so when the sun came up. During that time, all the images were soft and could see the fog in the images. Otherwise, the air was clear. I didn't microadjust the lens and the TC. That could be a problem too. I have taken pictures of another bird the morning before with one-shot AF and single frame mode with the same lens/TC combo with crisper images. I have never done any microadjusting, so I can try it next time I rent the lens. Thanks for the ideas.

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AF micro-adjust could be the answer but Ravi implied that this happens when AI-Servo is on, so it doesn't happen all the time. If it were a AF micro-adjust issue he would see the problem all the time.

Ravi- the conditions you describe are exactly the sort of occasion I might expect to see unstable air, shimmer, and soft images. Fog is an indication that you have air pockets whose temperatures are cold enough to be below the dew point. When the sun comes out it does not heat evenly and you will be shooting through pockets of cool and warm air. And by the way, to the naked eye the air might look perfectly clear to you but this does not mean you will not have a problem with shimmer. If you suspect a problem like this, the best way to test it is to mount your gear on a tripod and focus on a stable target like a tree trunk or fence post some distance away. Turn on Live view and set to maximum magnification and have a look. Shimmer/unstable air will cause the Live view image to shift in and out of focus completely on its own. The degree of shimmer problem depends on the amount of air you shoot through so take a look at your images and see of the closer ones are better than the ones farther away.

I agree with John on this and I have photographed from the same blinds you speak of. It very well could have been caused by heat refraction. Did you take any video? The problem can easily be seen in a video. You will see the shimmer while viewing video or as John stated in live-view. I have noticed that when heat refraction is a problem, the background bokeh looks somewhat different...hard to describe...not as smooth.

What does not make sense is that you say that one-shot images looked good. It shouldn't matter if its in one-shot or ai... most images will appear blurred due to the effect. I would do some test images in a controlled environment to see if the camera does have an issue.

Also, if microadjust was the issue, it will not matter what mode you are in AI or One-Shot.

Fun to watch those Prairie Chickens, although I enjoy Sharp-Tailed Grouse on the lek just as much or more!

Alan

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Originally Posted by John Chardine

AF micro-adjust could be the answer but Ravi implied that this happens when AI-Servo is on, so it doesn't happen all the time. If it were a AF micro-adjust issue he would see the problem all the time.

Ravi- the conditions you describe are exactly the sort of occasion I might expect to see unstable air, shimmer, and soft images. Fog is an indication that you have air pockets whose temperatures are cold enough to be below the dew point. When the sun comes out it does not heat evenly and you will be shooting through pockets of cool and warm air. And by the way, to the naked eye the air might look perfectly clear to you but this does not mean you will not have a problem with shimmer. If you suspect a problem like this, the best way to test it is to mount your gear on a tripod and focus on a stable target like a tree trunk or fence post some distance away. Turn on Live view and set to maximum magnification and have a look. Shimmer/unstable air will cause the Live view image to shift in and out of focus completely on its own. The degree of shimmer problem depends on the amount of air you shoot through so take a look at your images and see of the closer ones are better than the ones farther away.

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Yes Alan, exactly. Here is an example of a day I had a few years ago, shooting Piping Plovers. The water was cool and the sun was hot, and you are shooting close to the ground. Notice the pattern in the OOF specular highlights. That is a sure sign of shimmer. I managed to salvage a few images from that day when the subjects came close.

Shimmer could be it, but I don't understand why it wouldn't affect the images when in One Shot.

Which focus point(s) are you using and which one was at critical focus when in AI Servo? When in One Shot you'd be composing and focussing until pleased and then pressing the shutter button, but in Servo perhaps the focus point was switching to another, closer, area of the subject (if using multiple points)...e.g. breast, or wing. Do you have any part of the images perfectly sharp or are they all uniformly soft like John's example?

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Originally Posted by Daniel Cadieux

Shimmer could be it, but I don't understand why it wouldn't affect the images when in One Shot.

Which focus point(s) are you using and which one was at critical focus when in AI Servo? When in One Shot you'd be composing and focussing until pleased and then pressing the shutter button, but in Servo perhaps the focus point was switching to another, closer, area of the subject (if using multiple points)...e.g. breast, or wing. Do you have any part of the images perfectly sharp or are they all uniformly soft like John's example?

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Good point Daniel, if Ravi is using expansion points instead of simgle point, the 7D may being focusing the wing and not the head...

How do you micro adjust??

Alan, It was an otherworldly experience to watch the prairie chicken display, dance, fight and mate. Unfortunately, I didn't take any video. I will have to try next year.
John, I think the problem could be shimmer, microadjustment or the al servo mode problem or all of the above. I am going to test the camera on both modes and compare images. Dan, I do not see any particular area in focus in the images. They are uniformly soft. I did use multiple focus points.
I am posting one of the "better" of the lot, if that helps to figure out the problem. I can not rule out operator error (camera not firmly attached to tripod head, etc.), as I am not very experienced in handling large lenses. The same evening, I took images of canada geese - pretty much static compared to prairie chicken with same settings (al servo, tripod mounted, etc.) with the same result (soft images). I will also post an image that I took the day before with one-shot mode. This is a great discussion. Thanks for everyones input.

Another question regarding microadjustments. If I microadjust my 100-400 lens at 400 mm (which I am more likely to use, will it affect the sharpness at other focal lengths?

The image I am posting is a straight conversion from RAW to JPEG without any adjustments, cropping, NR or sharpening.
Canon 7D + 400 f/4 + 1.4x II TC
Tripod mounted
F/8, 1/200, ASA 800, no flash
multiple focus points, Al Servo, high speed continuous shutter release

All good points raised here so far. From the posted shot, my first gut reaction is that the SS is too slow if these birds were moving at all. I would guess that would have had the greatest affect. My guess is that your one-shot shots were probably used for more stationary stuff. That said, 7D bursts aren't the best and often have 2-4 shots OOF anyways especially in busy environment like this shot was. Still the SS is too slow for my liking. I wouldn't expect anything good at those focal lengths and 1/200.

I'm with Geoff, I think that the SS may be too low. The bird might not be covering a lot of distance, but the shaking involved is quite fast. I think that you needed to be at or above 1/1000-sec for these subjects.

Geoff and David,
I think you are right on low SS. the bird was also shaking while doing the display. I am attaching another image taken at 1/1000. slightly sharper, but still soft. I am beginning to think that the problem is due to low SS for the movement of the birds and microadjustment. I will test both one-shot and al servo modes under live view and post my observations. This is very good learning for me.

Same settings as above except
f/5.6, 1/1000, ISO 800

Could you post one of the one-shot shots that you thought were sharp? I see a defined focus plane in the grass that seems to be close to the right plane that the bird is on but it is hard to tell at this size of image how sharp things are. Obviously, even at 1/1000 his moving neck feathers are still blurred from the movement. It still seems strange that one-shot would be drastically different from AI Servo if you were shooting the same subject in both modes.

Looking at it at 175%, I can't find any totally sharp spot, so I'm thinking that even 1/1000 was too slow for a vibrating bird. ISO 1600, here we come...

I tested both modes on stationary objects. both modes come out equal. I am attaching the shots here.
I think there are two issues here - one, the bird shaking its feathers constantly while displaying. the shutter speed need to be higher.. David nailed it. The other, microadjustment. I used a prime lens, which needed microadjustment. i don't have the lens now, so I can not test it after microadjustment. However, I tried to compare Al servo with one shot mode with 100-400 lens and it turns out that the sharpness in both modes are almost equal. I think my confusion arose when I compared a static image of an owl taken at one-shot mode to the dynamic image of the prairie chicken that was not only moving but also vibrating. This exercise really helped me understand the concepts. Thanks everyone for the discussion.

Attached image - tripod mounted, f/5.6, 1/15, ISO 800, remote shutter release, IS on
Left Image on AI servo. Right image on one-shot mode. In both modes, central sensor is activated and is on the same spot. Images at 100% @ 240 dpi