Sigma DG 120-400 APO HSM OS AF mystery...

Started 5 months ago | Discussions thread
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chronhunter
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Sigma DG 120-400 APO HSM OS AF mystery...
5 months ago

So, I have a perplexing AF issue with my lens. It is an A-mount on a Sony A77. I have had it for over a year. A couple months ago it stopped autofocusing. I checked all the possible combinations and settings on both the lens and the camera (there are many way to cancel AF with the A77) and could not find the problem so I sent the lens off to Sigma. A couple weeks and $140 later I got the lens back... it still didn't work. I called Sigma and let them know they said they had tested it and it was repaired (new circuit board) and functioned fine prior to shipping. I took the lens to my LCS and tried the lens on another A77 body... It worked just fine! I went back home and it still wouldn't work on my body. BTW all my other AF lenses worked and work flawlessly on my body. At that point I called Sony, after a couple of minutes they brought up the "release shutter without lens" setting, a setting I have enabled since I use non chipped Samyang lenses all the time. This had never been an issue before so I was skeptical but of course changed the setting a viola... it worked the lens AF system suddenly came to life and "AF" not "MF" showed up in the display for the first time since the repair. A little annoying (now I needed to change this setting every time I swapped lenses and never had to before) but the lens AF fully functioned. That was a week ago and while shooting today the AF system stopped functioning again (even with the "release shutter without lens" setting disabled). So... I went back to the LCS with my body this time and started swapping lenses with bodes trying every combination. My body would AF with every lens I threw on it (Sony or third party) but refused to work with my Sigma and the Sigma worked fine yet again on the other A77 body (and even an A7 with and E-mount adapter). Before you ask the firmware levels are the same (1.07) and all the settings are exactly the same. One other interesting tidbit is the other A77 body focused fine with the "release shutter without lens" setting enable or disabled just as mine used to.

Sorry for the ridiculously long post but I'm hoping with the level of expertise on these forums my mystery can be solved!

Thanks for taking the time to ponder this

 chronhunter's gear list:chronhunter's gear list
Sony SLT-A77 Sony DT 16-50mm F2.8 SSM +3 more
Sigma 120-400mm F4.5-5.6 DG OS HSM Sony SLT-A77
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