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04-26-2010, 12:58 PM   #1
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Help with K-7/DA* 300mm AF adjustment

So, I have this issue, and perhaps not as critical as it may seem, but it is just lefting me wondering if indeed there is an AF "misadjustment" on this particular set-up:

- K7 with DA*300/4 ... no TC.

I find that when I shoot "Distant View" (as per Photo ME section "Camera" ... "Subject distance range", the subject always shows softness. It is not usually very sharp.
On the other hand, anything within 50 feet usually is dead-on, and sharpness also.
I would like to know if even I need to check for AF adjusting in this case.
Well, I suppose this wouldn't hurt to give it a test, right?

In that case ... I have another problem.
I have tried all sorts of focusing charts and manners to adjust AF on my K20D, and that helped. But I never tested it for the DA*300/4-k7 combo.
I realize this has been much talked about, and explained, but to me, adjusting AF on a 300mm telephoto lens is not that easy.
If anyone would be willing to tell me exactly what is the best way to do it, I would appreciate it a lot. Those are the parameters I have problems with:
1. The distance between the subject and the camera/lens.
2. The aperture ... F4?
3. The actual target(s) to use.
I might be forgetting something but those are the issues I have before proceeding to test, if need be.

Cheers and hoping someone will be patient enough to get me through this AF test ... if needed.

JP

04-26-2010, 04:15 PM   #2
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Post moved from the articles section to the lens section. The articles section is more for contributions than for questions, and I have a feeling that here, your question might just be answered a bit faster. Thanks

Adam
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04-26-2010, 04:42 PM   #3
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QuoteOriginally posted by Adam Quote
Post moved from the articles section to the lens section.
Thanks Adam, I think that was a right move.

QuoteOriginally posted by jpzk Quote
I find that when I shoot "Distant View" (as per Photo ME section "Camera" ... "Subject distance range", the subject always shows softness. It is not usually very sharp.
On the other hand, anything within 50 feet usually is dead-on, and sharpness also.
This may hint to a problem with the lens. I don't know the lens and don't know for sure but it doesn't sound right to me.

However not that a rule of thumb for a general adjustment AF is that the distance should be at least 50 x the focal length of the lens. In your case that's 49.2 ft. Why don't you try to optimise sharpness for 50ft and beyond?

QuoteOriginally posted by jpzk Quote
Those are the parameters I have problems with:
1. The distance between the subject and the camera/lens.
2. The aperture ... F4?
3. The actual target(s) to use.
1. See above. I don't know the CF distance for your lens but I hope you don't have to settle for bad performance closer than 50ft. If you do, there might be a problem with the lens but other DA* 300 owners are in a better position to help with this question.

2. Typically one uses the widest aperture possible in order to get a good reading of where the centre of sharpness is exactly. However, due to a possible "focus shift" on aperture change, you may want to optimise for the aperture you work with the most. If the latter is fine after a "wide open" adjustment, everything is OK, of course.

3. If the standard charts don't work, e.g,. because you don't see the rulers anymore, then print your own version. The main thing is just to make sure you that the AF system only sees one target spot (set it to manual AF point selection and make sure the centre AF point sees nothing but your target) and that you have some ruler like structure within the image as well.

A good alternative to tilted focus charts is to use a flat target and perform a series of shots, each time using a slightly different AF adjustment. Refocus after each adjustment and do multiple shots for each setting to allow for small deviations in AF performance. The sharpest shot in the overall series tells you which AF adjustment you need (keep notes as to which images used which AF setting).

Hope this helps.
04-26-2010, 04:50 PM   #4
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Is it safe to assume you've updated your firmware on the K7? I seem to remember a similar issue a way back where the IS was interfering with getting a sharp shot, slower shutter speeds, and long focal lengths. IIRC either an official or one of the silent updates cleaned this up.



04-27-2010, 01:56 PM   #5
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QuoteOriginally posted by Class A Quote
Thanks Adam, I think that was a right move.


This may hint to a problem with the lens. I don't know the lens and don't know for sure but it doesn't sound right to me.

However not that a rule of thumb for a general adjustment AF is that the distance should be at least 50 x the focal length of the lens. In your case that's 49.2 ft. Why don't you try to optimise sharpness for 50ft and beyond?



1. See above. I don't know the CF distance for your lens but I hope you don't have to settle for bad performance closer than 50ft. If you do, there might be a problem with the lens but other DA* 300 owners are in a better position to help with this question.

2. Typically one uses the widest aperture possible in order to get a good reading of where the centre of sharpness is exactly. However, due to a possible "focus shift" on aperture change, you may want to optimise for the aperture you work with the most. If the latter is fine after a "wide open" adjustment, everything is OK, of course.

3. If the standard charts don't work, e.g,. because you don't see the rulers anymore, then print your own version. The main thing is just to make sure you that the AF system only sees one target spot (set it to manual AF point selection and make sure the centre AF point sees nothing but your target) and that you have some ruler like structure within the image as well.

A good alternative to tilted focus charts is to use a flat target and perform a series of shots, each time using a slightly different AF adjustment. Refocus after each adjustment and do multiple shots for each setting to allow for small deviations in AF performance. The sharpest shot in the overall series tells you which AF adjustment you need (keep notes as to which images used which AF setting).

Hope this helps.
Thanks!
OK, first thing is that I do shoot a fair amount at 50 feet or less; however, there are those times when I need to have sharp focus beyond that.
I can't really settle for a soft AF at 50 feet nor at 100 feet. Perhaps I am demanding too much? The point is that I wish I could have sharpness on the whole range, not just at a pre-determined distance.
Anyway, I am going to get out there and test it really good, according to your suggestions, and I will report back.
I appreciate your time for replying.

JP
04-27-2010, 01:59 PM   #6
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QuoteOriginally posted by JeffJS Quote
Is it safe to assume you've updated your firmware on the K7? I seem to remember a similar issue a way back where the IS was interfering with getting a sharp shot, slower shutter speeds, and long focal lengths. IIRC either an official or one of the silent updates cleaned this up.

Hi Jeff.
I presently have firmware v.1.03 on the K7.
I am not sure whether any "silent" update(s) would help at all.
I assume this is the latest update.

JP
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