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06-08-2016, 07:48 PM   #1
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Help required for Focus Issue

I purchased my 645Z 2 days ago. I am an experienced photographer traditionally using a Canon 5DMkiii and 7DMkii plus an extensive range of Canon lens.
Finally I gave up on Canon producing a Sensor with a high megapixel count, excellent ISO performance (low noise) and wide Dynamic range.
On the 645Z I am using SMC D FA645 55mm F2.8 AL (IF) SDM AW and HD DA645 28-45 F4.5ED AW SR Pentax lenses.
The problem I am trying resolve is the slow, inconsistent or non existent focus when using the AF button with the shutter button AF turned off. Its a random problem, sometimes its Ok other times it just doesn't work.
Any ideas to help me please. Thanks

06-09-2016, 01:03 AM   #2
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I'm around two months into the Z (also a frustrated long term Canon user) and I have it set up the same as you (AF on the back) but haven't experienced any problems.

06-09-2016, 02:00 AM   #3
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Same here, back button AF, disabled on the shutter, 55mm f/2.8. It focuses faster and more accurately than my Canon 5D II ever did. I don't expect it to be as fast as a 7D II or 5D III though.
06-09-2016, 02:56 PM   #4
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Back AF Button is fine

I have been using the back focus button successfully for two years. It sounds your camera may have a defective AF switch or wiring. If you have access to another 645Z Body, you might want to try to isolate the problem to your camera.

06-11-2016, 03:01 PM   #5
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it sounds like your button is intermittently not working.switch back to half press AF and see if AF operates consstently.
good luck
06-12-2016, 05:55 PM - 1 Like   #6
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Original Poster
Thanks everyone for your responses, they are greatly appreciated.

I have discovered that some of the issue was my set up on the camera but with that resolved It still happens. Its such a pain to send away a new camera for repair I will persist for awhile and see if its still a usage issue or is in fact an intermittent problem with the back AF button. As suggested by mikeSF I have switched back to back to both rear AF and shutter buttons able to focus. I will use the rear button first and if that doesn't work I will try the shutter. If the shutter AF works then it points to a problem rear AF button. Took a few night street shots to test the Dynamic Range and was very pleased. The detail I could pull from shadow was terrific. I am very happy I made the move to Pentax medium format. Thanks again everyone.

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