77 Limited won’t autofocus, sometimes flashes F—

narual · 05-21-2023, 11:46 AM

I just had a buyer test my 77mm, and it was weird. It wouldn’t AF until he switched to manual and back, maybe he moved the focus on manual, not sure. But it would autofocus once and then stop til he did it again. He says it would stop AF as soon as it hit infinity.

His K1 showed an aperture in live view, but the viewfinder showed F—

I’ve had my k3 not recognize assorted lenses in the past, including my 31mm but it was always something where removing the lens and replacing it fixed it. It’s never happened to me with the 77 but I don’t use it much, hence selling that one.

Anyone have any ideas? I’ll test it on mine when I get home in a couple hours. Weird. Good thing neither of us had to drive very far.

**ProfessorBuzz** · 05-21-2023, 12:37 PM - **1 Like**

It needs to be on the A setting. Or the contacts on the camera or lens are dirty OR it didn't seat properly.

narual · 05-21-2023, 04:03 PM

No, those are all fine. (I just cleaned the contacts on both and other lenses work fine).

I just reproduced it on my camera and with more time to experiment, it works fine until you try to focus past about 20 feet, manually or AF, everything between the minimum 2.3 ft or so and ~20 feet, it can read the aperture and the AF works, any distance past that, it goes to F— and AF stops working until you manually focus it closer.

It’s really freaking weird.

Edit - of, and if I put the lens on focused to infinity, it asks me the focal length like it would fit a manual lens.

**UncleVanya** · 05-21-2023, 07:38 PM - **1 Like**

I wonder if there's a cable that's getting stretched and losing contact? What a bummer.

James O'Neill · 05-22-2023, 07:51 AM

Originally posted by UncleVanya

I wonder if there's a cable that's getting stretched and losing contact? What a bummer.

Sounds like that. All the symptoms are "lost electrical contact" but I've never known the contact to be lost as the lens moves back and forth. Sounds like a visit to a repairer lies ahead.

narual · 05-22-2023, 09:00 AM

Yeah, I was looking at the exploded lens view and the only thing I could think of was the part labeled contact brush. Googling that shows it’s also called a focus brush.

Last time I opened a len, the aperture pin springs went everywhere, so I’m not doing that again, especially not on one like this - I’ll have to wait til I can get it fixed or sell it as damaged. That sucks

Thanks, everyone!

05-21-2023, 11:46 AM	#1
narual Veteran Member Join Date: Jun 2013 Location: South Bend (Notre Dame), Indiana Photos: Gallery \| Albums Posts: 1,988	77 Limited won’t autofocus, sometimes flashes F— I just had a buyer test my 77mm, and it was weird. It wouldn’t AF until he switched to manual and back, maybe he moved the focus on manual, not sure. But it would autofocus once and then stop til he did it again. He says it would stop AF as soon as it hit infinity. His K1 showed an aperture in live view, but the viewfinder showed F— I’ve had my k3 not recognize assorted lenses in the past, including my 31mm but it was always something where removing the lens and replacing it fixed it. It’s never happened to me with the 77 but I don’t use it much, hence selling that one. Anyone have any ideas? I’ll test it on mine when I get home in a couple hours. Weird. Good thing neither of us had to drive very far.

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05-21-2023, 12:37 PM - 1 Like	#2
ProfessorBuzz Loyal Site Supporter Join Date: Feb 2018 Posts: 1,903	It needs to be on the A setting. Or the contacts on the camera or lens are dirty OR it didn't seat properly.

05-21-2023, 04:03 PM	#3
narual Veteran Member Join Date: Jun 2013 Location: South Bend (Notre Dame), Indiana Photos: Gallery \| Albums Posts: 1,988 Original Poster	No, those are all fine. (I just cleaned the contacts on both and other lenses work fine). I just reproduced it on my camera and with more time to experiment, it works fine until you try to focus past about 20 feet, manually or AF, everything between the minimum 2.3 ft or so and ~20 feet, it can read the aperture and the AF works, any distance past that, it goes to F— and AF stops working until you manually focus it closer. It’s really freaking weird. Edit - of, and if I put the lens on focused to infinity, it asks me the focal length like it would fit a manual lens.

05-21-2023, 07:38 PM - 1 Like	#4
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,472	I wonder if there's a cable that's getting stretched and losing contact? What a bummer.

05-22-2023, 07:51 AM	#5
James O'Neill Veteran Member Join Date: Apr 2023 Posts: 351	Originally posted by UncleVanya I wonder if there's a cable that's getting stretched and losing contact? What a bummer. Sounds like that. All the symptoms are "lost electrical contact" but I've never known the contact to be lost as the lens moves back and forth. Sounds like a visit to a repairer lies ahead.

05-22-2023, 09:00 AM	#6
narual Veteran Member Join Date: Jun 2013 Location: South Bend (Notre Dame), Indiana Photos: Gallery \| Albums Posts: 1,988 Original Poster	Yeah, I was looking at the exploded lens view and the only thing I could think of was the part labeled contact brush. Googling that shows it’s also called a focus brush. Last time I opened a len, the aperture pin springs went everywhere, so I’m not doing that again, especially not on one like this - I’ll have to wait til I can get it fixed or sell it as damaged. That sucks Thanks, everyone!