I recently got a Praktica BX20 and discovered that it most likely has some kind of issue with focusing. After a test roll it became apparent that the focus I see in the viewfinder doesn't match with what I get on the results. The actual focus is further away than what the viewfinder shows. I did a basic test by attaching an old matte screen from another camera on the film plane and sure enough, there's a fairly significant difference between the focus I see there and in the viewfinder. Then I made a 1mm scale on the lens and measured the offset, then took some test shots by focusing through the viewfinder and then turning the lens by the measured amount before taking a photo - and those were perfectly in focus.
Unfortunately I only have this one lens and body in the Praktica B system which isn't perfect to make sure but with the testing I've done I'm 99% certain the problem lies with the body and not the lens. Now the question is, what is the most likely cause? I don't see anything obviously wrong from the outside. The mirror seems fine, the matte screen sits in place the right way down. One thing to mention is that the camera had an old sticker from a service place so it's possible that it was opened and put together incorrectly some time in the past. I thought about having a look inside but a BX20 disassembly video I found on youtube makes it look like you have to basically take the whole camera apart to get to the prism and focusing screen and I'd prefer to avoid that if I can. Plus the focusing screen in the BX20 is glued in so I'm not sure if there even is any way for it to be adjusted.
Does anyone have any other ideas what could be the cause and what else could I check/try? Sending it out to a professional isn't financially worth it but I'd really like to fix it as the camera works perfectly otherwise, which isn't something you can take for granted with B series Prakticas - their electronics weren't exactly the most reliable.
Unfortunately I only have this one lens and body in the Praktica B system which isn't perfect to make sure but with the testing I've done I'm 99% certain the problem lies with the body and not the lens. Now the question is, what is the most likely cause? I don't see anything obviously wrong from the outside. The mirror seems fine, the matte screen sits in place the right way down. One thing to mention is that the camera had an old sticker from a service place so it's possible that it was opened and put together incorrectly some time in the past. I thought about having a look inside but a BX20 disassembly video I found on youtube makes it look like you have to basically take the whole camera apart to get to the prism and focusing screen and I'd prefer to avoid that if I can. Plus the focusing screen in the BX20 is glued in so I'm not sure if there even is any way for it to be adjusted.
Does anyone have any other ideas what could be the cause and what else could I check/try? Sending it out to a professional isn't financially worth it but I'd really like to fix it as the camera works perfectly otherwise, which isn't something you can take for granted with B series Prakticas - their electronics weren't exactly the most reliable.
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