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Focus shifting with different focal length.

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tzk1810 View Drop Down
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Post Options Post Options   Quote tzk1810 Quote  Post ReplyReply Direct Link To This Post Topic: Focus shifting with different focal length.
    Posted: 02 January 2021 at 08:29
Hi, guys and ladies in this forum greeting.

Just as the title said, I got a Sigma 70-200mm EX DG OS HSM (2010) and use it along with my a77ii, and I realise that the lens got a front focusing shifting problem. Then I tried to calibrate it myself using the AF micro-adjust. I had set +5 for the 200mm end but when I zoom out back to 70mm again it went front focusing again. I am very frustrated as I tried many methods to fix but none of them works. And Sony camera is lacking AF micro-adjust on multiple focal lengths. So is there anyone know how to fix this problem?

Or I should just sell the lens and buy another Sony 70200 instead?
Thank you.
 



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bigsi View Drop Down
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Post Options Post Options   Quote bigsi Quote  Post ReplyReply Direct Link To This Post Posted: 02 January 2021 at 09:53
As far as I know there is no way around it, I have the same lens and just ended up calibrating it for the focal length I used most often, 200mm. Mine was ok at shorter lengths, though whether that was down to sample variation or I dont have as critical eye as you I dont know!
I imagine the sony 70-200 would be built with tighter tolerances but I've never owned one, maybe someone else can help there, though if it suits your photography maybe a minolta 200mm 2.8 is the only other alternative?
It will be interesting read what others recommend as its something thats bothered me also.

Edited by bigsi - 02 January 2021 at 10:05
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tzk1810 View Drop Down
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Post Options Post Options   Quote tzk1810 Quote  Post ReplyReply Direct Link To This Post Posted: 02 January 2021 at 11:09
yeah that really sucks because now the f2.8 on 70mm are just useless. I need to slow down to at least f5.6 to get my shoots right in the DOF.
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stiuskr View Drop Down
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Post Options Post Options   Quote stiuskr Quote  Post ReplyReply Direct Link To This Post Posted: 02 January 2021 at 12:01
There's a couple options, you could split the difference and micro adjust at 135mm and see if you get acceptable results throughout the range. If time is not a factor in getting the shot you could dial in at one end, record/memorize the setting for the other end and adjust when needed with just a couple button presses.
Rob Suits Jr.
a99M2 a99 a77 a700 KM7D|Min24/2.8 Min35/2 So50/1.4 So50/2.8 Min85/1.4G Tam90/2.8 Tam180/3.5|Tam17-50 CZ24-70G2 KM28-75D So70-200G1 So70-300G So70-400G1| SonyF60 AD200R2
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pegelli View Drop Down
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 02 January 2021 at 12:18
I had a similar problem with my Minolta 80-200/2.8 HS

Only I lucked out and on my A850 doing +3 microadjust was good all the way from 80 to ~180, only the last steps to 200 mm needed up to -7 (so a big jump)

So maybe the first thing to do is to check microfocus adjust through the whole range and see if there is one setting that works for most of the lens.

What I did is use the standard setting of +3 and only zoomed until 180. When I needed more and didn't have time I cropped, when I had time I changed the setting to -7 and set it back when done. It was a cumbersome process (especially not forgetting to reset back to +3) but it was better than nothing.

Hope you will get it sorted
Mind the bandwidth of others, don't link pictures larger then 1024 wide or 960 pix high, see here
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TomV View Drop Down
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Post Options Post Options   Quote TomV Quote  Post ReplyReply Direct Link To This Post Posted: 08 January 2021 at 04:01
The main issue is that Sony does not assure that MFA will work with non-Sony/Minolta lenses.

I had the latest Tamron 70-200 that did not adjust at all with MFA. I also had the 28-300 PZD that had a knee at about 70mm that caused a problem since the wide and tele end points of MFA assume a monotonically increasing/decreasing slope to calculate intermediate focal length corrections. The slope was shallow from 70 to 300 and had a diff of about 2 between them. The drop from 70 to 28 was about -5. I sold both lenses.

I now have more Tamrons, the latest SP series that are supported by the Tap-in Console. I have determined that each lens works as expected for MFA with my a99ii without the need for the Console. Go figure.
The are the Tamron 45mm, 90 mm macro and 150-600 G2 (2 copies). I am particularly impressed with one of the 600s where the MFA for 150 is -2 and 600mm is -7. The values selected by the camera for intermediate focal lengths are the same values I would have used based on the work I did characterizing the lens, thus I set the Tap-in Console values to 0.

My Sigma 50-500 late-model zoom (also OS) was a sweet lens that required the MFA to be different by only a unit or two, I do not remember any issues with it.

It seems Tamron has caught up with their latest lenses to the Sony MFA software.

I would fully characterize the MFA for each labeled focal length of the lens to determine if you can indeed choose a meaningful value. If using that value does not yield good results with your a77ii (a 1 MFA value per lens design) then maybe you will choose to purchase a Sony/Minolta lens.


 



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LAbernethy View Drop Down
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Post Options Post Options   Quote LAbernethy Quote  Post ReplyReply Direct Link To This Post Posted: 08 January 2021 at 12:33
Maybe, Maybe not. Is the Sigma 70-200mm EX DG OS HSM the only lens giving you trouble? Is the a77II the only camera with a problem?
My a77II has been an AF problem child since I updated the Firmware, the SAL70200G included.
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