AI Servo Focussing

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dancook

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Dan
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I'm using AI Servo and back button focussing for street photography, using the smaller single AF point.

I'm constantly shooting still and moving subjects, and need to be ready for both.

I'm shooting wide open 200mm @f2 and find that sometimes I'm missing focus. I'm concerned with the AI servo and BBF that it continually tries to focus, and can miss critical focus.

I don't know what went wrong here..

FQ2A0528 by dancook1982, on Flickr

Just took some photos of a colleague - AI Servo holding BBF took multiple photos whilst following his eye. Checking the preview screen on my camera it shows a red focus square over his left eyelid (so the one on the right!) However when reviewing the image, attached, it isn't in focus.

View attachment 11292

Oh 10 photos, a few of them did not have focus where the red square appears.

Is there a problem with my technique? as I said It feels like the lens does tiny-hunts with BFF held - and perhaps I catch it when it's moved itself OOF.

I also had it on continuous shutter.
 
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Are you being hypercritical here?

Your mono shot looks fine to me and when enlarged on my iPad, the only area very slightly out of focus is the tip of his nose and hair growth above his top lip which using single point focus I'd expect.

The shot of your colleague is, to me again an ok shot. The blurring I see is his right eyelash. Everything else appears ok to me. I'd add that I get the impression he's just blinked. What shutter speed was used?
 
BMD said:
Are you being hypercritical here?

Your mono shot looks fine to me and when enlarged on my iPad, the only area very slightly out of focus is the tip of his nose and hair growth above his top lip which using single point focus I'd expect.

The shot of your colleague is, to me again an ok shot. The blurring I see is his right eyelash. Everything else appears ok to me. I'd add that I get the impression he's just blinked. What shutter speed was used?
Click to expand...

1/320 shutter speed

I suppose I need more controlled testing, I thought maybe there might be a known issue with AI-servo "micro-hunting" in and out of focus on stationary subjects.

The street one looks pretty soft to me, maybe it's just his closest eye being slightly OOF ruining it for me.

I did manage to get camera shake at 1/500 in this photo, so I am prone to being too quick to take the shot.

FQ2A0503 by dancook1982, on Flickr
 
Which body are you using? I use a 1Dx and there was a firmware update earlier this year which amongst other things, updated and added too the AI Servo.
 
Checked your firmware? although I don't think its a camera issue
 
BMD said:
Checked your firmware? although I don't think its a camera issue
Click to expand...

1.2.3 - latest firmware.

I will have to do some tripod mounted tests in good light, I probably am expecting too much.
 
Try taking the shots closed down a stop or 2, the dof is very very small when you are at F2. if you shot at F4 or F5.6 your camera will get the speed and ISO right if you are set on Auto ISO and more of the subjects face will appear in focus, there be more pleasing to the eye and appear sharper, the background should still have a soft out of focus look to it. It appears that by shooting at F2 for to throw the background out, you are only getting a very small portion of the subject sharp in focus.

If you use an IPAD look for the app called 'simple dof' its free and will help give you the distance of focus you need
have fun.
 
i'm not sure it's possible to stop down the 200mm f2, I don't think i've seen it done.. :D

I will have to give it a go..
 
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