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11-02-2018, 12:02 PM   #16
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Sigma 100-300 F4 APO EX DG with poor AF

Sorry posting a similar post, but after investigating a bit more I have more information, so I was hoping a new post with a more refined information would be allowed. I tested my sigma at 100, 200, and 300 at f4, f8, and f11 for each of the focal length and I noticed that the part of photo that was closer was more in focus. I adjusted the AF Fine Adustment on my k-50 to Apply One -10, and while its better its still not perfect as you can see in the pictures. Does anyone have any suggestions? I don't think I can go beyond -10 unless there is a trick I dont know about? I have full resolution pictures on drive: Update your browser to use Google Drive - Google Drive Help . I can upload the pictures on to here if that would be preferred, just not sure how to do batch cropping in lightroom. Its an old lens, so definitely not still under warranty.

11-02-2018, 01:52 PM   #17
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A bigger adjustment is possible with debug mode.

Debug focus adjustment various pentax models. - PentaxForums.com
11-02-2018, 07:13 PM   #18
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Iíll give it a try. Does fine tuning it affect all focal lengths equally? I was messing with it at about 8 feet but hadnít tried it 40+ feet. Also I couldnít find k50 can you debug the k50?
11-02-2018, 07:17 PM - 1 Like   #19
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QuoteOriginally posted by nmcleod1993 Quote
Does fine tuning it affect all focal lengths equally?
Unfortunately it does, so if you correct for a 280mm focal length that will, in all probability, throw out focus at 135mm. That is the nature of global lens adjustments.

I wish Sigma allowed for focus adjustment VIA the lens dock with all current and legacy glass.

11-02-2018, 08:33 PM   #20
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QuoteOriginally posted by Digitalis Quote
Unfortunately it does, so if you correct for a 280mm focal length that will, in all probability, throw out focus at 135mm. That is the nature of global lens adjustments.

I wish Sigma allowed for focus adjustment VIA the lens dock with all current and legacy glass.
So is there really any fix besides just having it in focus at one focal distance? Or just always shoot at f8?
11-02-2018, 08:46 PM - 3 Likes   #21
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QuoteOriginally posted by nmcleod1993 Quote
So is there really any fix besides just having it in focus at one focal distance?
You could average the adjustment and shoot at f/8 all the time, that way the focus shift will be just enough to keep your subject within the plane of focus. This will be problematic if you shoot distant subjects or close up subjects.

I seem to have been very fortunate with my copy of the Sigma 100-300mm f/4 APO EX DG, even on the K10D - which under normal circumstances, has no option for AF adjustment, it worked fine.


Yes, the lens is very sharp - there is a slight drop in contrast @ 300mm f/4, however stopping down to f/5.6 delivers consistently high performance across the entire focal length range - with one caveat being:


The Sigma lens does experience diminished performance at the minimum focus distance at focal lengths over 100mm, so it is best to use a macro lens for close ups.



Pentax K5IIs - Sigma 100-300mm f/4 APO EX DG - 1/250th ISO 2500 f/5.6


Pentax K10D - Sigma 100-300mm f/4 APO EX DG - ISO 200 1/180th f/4 off camera AF540FGZ + 1/2 CTO Gel used.

Last edited by Digitalis; 11-02-2018 at 11:59 PM.
11-03-2018, 01:47 AM - 2 Likes   #22
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I use mine a lot, particularly for aircraft shots, usually around F5.6 or F8 and its always been a super sharp lens over several bodies, K10 / K5 / K5ii / K3 / K1


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11-03-2018, 10:57 AM   #23
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I guess I'll tune it for far distances at 300 and see where it takes me, thanks everyone I really appreciate the feedback.
Nathan

11-05-2018, 10:21 AM   #24
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QuoteOriginally posted by Digitalis Quote
You could average the adjustment and shoot at f/8 all the time, that way the focus shift will be just enough to keep your subject within the plane of focus. This will be problematic if you shoot distant subjects or close up subjects.

I seem to have been very fortunate with my copy of the Sigma 100-300mm f/4 APO EX DG, even on the K10D - which under normal circumstances, has no option for AF adjustment, it worked fine.


Yes, the lens is very sharp - there is a slight drop in contrast @ 300mm f/4, however stopping down to f/5.6 delivers consistently high performance across the entire focal length range - with one caveat being:


The Sigma lens does experience diminished performance at the minimum focus distance at focal lengths over 100mm, so it is best to use a macro lens for close ups.



Pentax K5IIs - Sigma 100-300mm f/4 APO EX DG - 1/250th ISO 2500 f/5.6


Pentax K10D - Sigma 100-300mm f/4 APO EX DG - ISO 200 1/180th f/4 off camera AF540FGZ + 1/2 CTO Gel used.
Could sigma fix a problem like this? I really like the lens, and would pay to have it fixed, I just don't know if its fixable?
11-05-2018, 01:37 PM   #25
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The Sigma 100-300mm f/4 has been discontinued for a considerable length of time, Legacy glass is a very low priority for manufacturers.

If sigma re-released the lens [ which I hope they do, it is superb] A user defined focus limiter would be a must-have feature for this lens. Along with AF adjustment Via the Sigma Lens dock.
11-05-2018, 03:37 PM   #26
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So you donít think that it could even be fixed if I sent it to there service and repairs? That stinks

QuoteOriginally posted by Digitalis Quote
The Sigma 100-300mm f/4 has been discontinued for a considerable length of time, Legacy glass is a very low priority for manufacturers.

If sigma re-released the lens [ which I hope they do, it is superb] A user defined focus limiter would be a must-have feature for this lens. Along with AF adjustment Via the Sigma Lens dock.
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