60-250 af fine adjustment issues


Puggy

Link Posted 05/07/2016 - 14:56
Hi all

Thought I'd ask here before taking any further as I'm really not sure if I maybe over playing my expectations.

A few months back I purchased a used 60-250 from SRS. I almost exclusively shoot motorsport now. First time out I was rather disappointed with the results but I put it down to getting used to the extra weight and size of the higher quality lens. Second time out was no better so I went about trying to adjust the af point.

I printed out and assembled a chart set up in the garden and with the k3ii firmly on a tripod went about some tests.

What I found is that I cannot achieve an adjustment that works at different apertures. At f8 a plus 5 adjustment is correct but at f16 that would result in a bank focused image so a different adjustment is required. Nothing would help at f4 the lens just seems much softer than I expected wide open.

Also although it doesn't show in images there is a big black speck on one of internal elements, too big to be dust it looks like maybe metal swarf.

Do you think this should be returned under warranty? I have a couple of weeks before I need it again but am not in a position where I have any backup kit.

Thanks in advance

Pete Aldridge

Puggy

Link Posted 05/07/2016 - 15:02
As if that post is not long enough will add that I regularly shoot mf so I'm not talking about camera failing to keep up with target but If making quick adjustment I like to switch to af to confirm focus is where I want it, for instance focus on the end of some armco or kerb before switching back to mf.
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johnriley

Link Posted 05/07/2016 - 15:25
Firstly, a black speck would not normally show on images. It would have to be huge to make any difference. Black is good because it won't cause flare spots. However, a large speck isn't what we'd expect to find in a new lens.

I think we need to look at technique here, as I'm a bit baffled as to why we would use MF and then switch to AF to confirm it. Might as well use AF and then lock it in with a half press on the shutter release. As for shifting focus, many lenses might shift a bit at different apertures and zoom settings, but an average correction should be close enough to be satisfactory. Motor sports are not that close that major errors should occur. Your actual selection of the point you are focusing on might have more relevance.

It's difficult to be totally sure without being there, but I'd start with basics first. Try using AF on some general subjects, maybe in the local park, and then see if they are sharp. If not, something is seriously amiss. Don't forget to watch the shutter speed is fast enough as well and make use of SR if appropriate. SR may not be appropriate for motorsport as it takes time to lock on, which will delay the focus on rapidly moving objects.

Hope some of the above helps you to start the process of narrowing this down.
Best regards, John

johnriley

Link Posted 05/07/2016 - 15:26
Another thought. If using AF to focus on a point, use centre point only. Maybe your camera is choosing different points every time it focuses?
Best regards, John

Puggy

Link Posted 05/07/2016 - 16:31
Hi John.

Thanks for your thoughts and prompt answer.

Maybe I didn't explain what I meant very well with regards to switching between mf/af. Take for instance shooting through the fence at oncoming cars coming out of the chicane at Donnington the ideal shot is the car on two wheels as it clips the kerb. No need or want to be in af but as it's quite some distance away I use the confirmation in viewfinder to confirm focus. Camera remains in mf so that nothing changes, camera doesn't get confused by fence etc. There should as you say be a significant in focus area but on review the entire area oof and the faces of spectators some 50ft back are sharp. I didn't have the same issues using same technique with cheap 55-300.

When I do use auto focus I only use back button and only use the cross point focus points and only in single point mode. Don't have same problems panning (when wrong it's definitely my fault!!) . I normally decide between mf/af depending on the track, which corner etc

You did answer my question though that I am expecting too much for an adjustment to work across the lenses range. Thanks

Feel free to have a look at some of my stuff

link

Kind regards Pete A
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johnriley

Link Posted 05/07/2016 - 16:39
Can't actually see the images Pete, you'd need to change the privacy settings or send out a Friends request.
Best regards, John

Puggy

Link Posted 05/07/2016 - 16:47
Ah. That is an album on a closed group Doh! Linked it because had a decent selection.

This is my page link. Rather a lot to troll through though!

If that doesn't work I'll sort a link out when not on a phone

Thanks
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JohnX

Link Posted 05/07/2016 - 18:31
AF fine adjustment with a zoom is always a compromise, but in any event it should always be done at the widest aperture.

With a zoom, either (a) set af adjustment at the point in the zooms range that you use most often, (b) determine what's needed at the min, max and middle of the zoom range and average the adjustment setting, or (c) determine af adjustment at various main focal points throughout the zooms range, note the adjustment required at each point and adjust the setting in real time once you know what focal length you require.
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