Acceptable focus accuracy?

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parsley

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I've read through some threads on focussing, where it's been reassuring (sounds like we're all in the same boat) that Canon xxxD cameras and maybe others too can be a bit hit and miss depending on how strict our requirements are.

I mostly shoot landscapes, but would like to be able to shoot wildlife too if possible. For landscapes I'm not too fussed (plenty of time to adjust, high f numbers), but for wildlife, accurate af would be good.

Sorry I can't show pics yet - my web connection is running slower than dial-up currently - but will try later. I set a scene up with a contrasty target almost parallel to sensor plane, more than covering the centre AF point, and a ruler next to it.

The three lenses I've tried (50/1.8, kit 18-55, and sigma 50-500 on EOS 550d ) all typically got the centre focus point about 1-1.5 cm out (too near) at 1.5 m. At f/1.8 that's enough for the subject to be somewhat blurry. (I also found the centre AF point seems to have a somewhat large area and it can be distracted by things a bit beyond the box).

With the 50-500 at 500mm, 8 m from subject, wide open (f/6.3?) it gets the subject just about within the sharp zone. Not centred axactly, but with maybe 10-20% sharp beyond it.

Is this about all I should expect :) anyway? I don't really want to try swapping cameras. (Who gets the returned one, who pays postage etc.?)

Thanks for any comments
 
These sound like consistent af problems, in that all your lenses are front focussing. I had some af issues, but they were hit and miss and indeed down to the conditions. Time to return the camera for calibration perhaps?
 
Are you sure that the DOF isn't just the 1/3rd infront and 2/3rds behind thing making it appear slightly front focussing?
 
Thanks for both of these. I should have said that at 8m the 500mm was focussing beyond the target - I'd also thought initially that it was always front focussing so maybe a camera issue.

I'll do some more tests and have a think.

Have any of you got xxxD-level cameras which focus really accurately?
 
My trusty 3 year old 400D has no such focusing issues, in fact, I do some pretty demanding stuff for a consumer camera, I've just returned from a horse jumping event using AI servo all day (with a lens which I know not to be the fastest to focus) and I pretty much have a 95% keeper rate! All my lenses are Canon though, I don't know if that helps in terms of body / lens harmony?!

I note most new prosumer models have a micro focus facility, suggesting not all cameras will come out of the factory with absolutely perfect AF! It might be that your body needs some very minor adjustment, but that will most likely have to be carried out through Canon?
 
Thanks - glad to hear yours works so well. I was just about coming round to the view that they're all a bit iffy, but clearly they aren't. But live view is a nice compensation for landscapes.
 
No problems with my 40D, with Canon lenses and with my Sigma 10-20mm. Does make you wonder, as Jim suggested, if perhaps not all cameras come out of the factory spot on. You might find this is similar with other brands as well. Anyone know of issues with other makes?
 
parsley said:
Have any of you got xxxD-level cameras which focus really accurately?
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could be dodgy AF on your unit. my 350d from way back was great. in a bizarre experiment, i used a macro lens to shoot a fashion show, and it worked!



granted, my white balance and exposure control weren't fantastic then, but the AF was accurate :D
 
My 40D is a hit and miss with some lenses (well all of them except 70-200mm f/4L, and also perfect with the others at closer distances). So was my old 30D and some 400Ds. At least 1Ds mk2 is 100% spot on every time - perfectly perfect. I hate to say it but with Canon 1-series is the way to go.
I must point out that am extremely picky and I do pixel peep. I guess I would find some flaws in most other xxxd and xxd cameras even if the current owners are happy with them.

I also must point out that the OP has lenses with strong character. 50/1.8 is known to be very soft wide open, but improves a lot by f/2.8. Personally, I'd use it as f/2.8. Kit lens has it's own flaws so best to use it at f/8-11 and not at the extreme ends. Finally the Sigma is generally soft lens. There is no cure other than 500mm prime.
 
daugirdas said:
My 40D is a hit and miss with some lenses (well all of them except 70-200mm f/4L, and also perfect with the others at closer distances). So was my old 30D and some 400Ds. At least 1Ds mk2 is 100% spot on every time - perfectly perfect. I hate to say it but with Canon 1-series is the way to go.
I must point out that am extremely picky and I do pixel peep. I guess I would find some flaws in most other xxxd and xxd cameras even if the current owners are happy with them.
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Thanks for sharing your experience.

daugirdas said:
I also must point out that the OP has lenses with strong character. 50/1.8 is known to be very soft wide open, but improves a lot by f/2.8. Personally, I'd use it as f/2.8. Kit lens has it's own flaws so best to use it at f/8-11 and not at the extreme ends. Finally the Sigma is generally soft lens. There is no cure other than 500mm prime.
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"Cheap" might be another word :) . I found my 50-500 was sharpest at about f/10 at 5 m. Currently trying to shoot a good landscape including the moon.
 
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