K-3 poor autofocus fix
I've been having focus accuracy issues with my Pentax K-3 for a while now. Seems like it has slowly gotten worse. Today I was testing the 20-40's AF in low light and was really disappointed. On a whim I put it on my K10D and it was MILES better. I thought that just can't be right. So I figured the AF sensor must be dirty. While reading about how best to clean it I stumbled upon this Reddit post:
Could you take a look at your secondary mirror? Is it clean? Might have found a reason for AF inconsistency on some bodies.
byu/sdhov inpentax
TL;DR: the AF mirror (which rests just below the main mirror) gets some residue on it, oil or dust, I'm not sure. Here's a link to what it looks like.
I lifted the main mirror and sure enough that was my K-3's problem! It looked just like that image, only worse.
It's like I have a new camera now - it can focus even in low light again! I bought it used so it may have always been like this and I just never noticed. I have no idea. But it's better now and I thought I'd share. Some more searching showed that this may be a common issue for the K-3, so I thought I'd share here for the other K-3 owners. It's probably worth checking with other models and brands as well if you notice a degradation of AF performance.
Testing it against my K10D again I see I still have more cleaning to do, the K10D is still better. But the improvement in the K-3 is noticeable. I can't believe how accustomed I got to the poor AF performance! Frog in boiling water, I guess.
Congratulations that you got that sorted out. Well done.
Could you please explain with which technique you cleaned the secondary mirror?
Thanks a lot!
E.
This is awesome! I didn't even know about this AF sensor. I just cleaned my K-3 image sensor the other day and that gave me the warm-fuzzies. Now I'm off to check the AF sensor....
Quote from EckyH on August 2, 2022, 4:37 pmCongratulations that you got that sorted out. Well done.
Could you please explain with which technique you cleaned the secondary mirror?
Thanks a lot!
E.
Thanks! I wasn't certain if a solvent of any kind might damage it, so I just used a microfiber cloth. I may try solvent later. Right now it looks perfectly clean, but depending on what the residue was (people seem to think it's oil), it may take a bit more effort than a quick wipe with a cloth. But this is what I did:
Gently and slowly lift the main mirror up towards the top of the camera. You will see a smaller secondary mirror under it and toward the back (it's attached to the same pivot). If you keep moving the main mirror up this secondary mirror will flip up also. Just move the main mirror back down a little and the secondary mirror will flip back down.
It is a very tight area, so I used a microfiber cloth wrapped around a q-tip and gently wiped it clean.
Quote from grover on August 2, 2022, 4:47 pmThis is awesome! I didn't even know about this AF sensor. I just cleaned my K-3 image sensor the other day and that gave me the warm-fuzzies. Now I'm off to check the AF sensor....
Yeah, I learned a ton today. I had no idea where the AF sensor was, or about the secondary mirror that directs the image to it. The AF sensor itself is on the bottom of the mirror box - it's just chilling on the bottom in there looking up into the secondary mirror. Initially I was cleaning this trying to fix my AF issue. For a lot of people this is the cause - a hair or dust etc gets on this sensor and causes issues. Then I stumbled up on that post about the secondary mirror and sure enough, "there's your problem."
Let us know what you find! I'm curious if this is a problem with all/most K-3s, and possibly other models too.
