Viewfinder focus / diopter issue (Mamiya 645 FK402 finder)

[howstrange]

Hi - so I'm really having problems nailing the focus with my Mamiya 645 and the FK402 mirrored viewfinder. Even with an 80mm 1.9 (so lots of light coming into viewfinder), shooting at say 5.6/8, im getting a lot of shots out of focus. When I'm focusing, I can get the focus within about 90% accuracy, but the final 10%, it really looks the same to me when i tweak the focus a tiny bit left and right and i pretty much have to guess.

Here's the thing - i wear contact lenses which give me 20/20 vision. Even without the contact lenses, my sight is okay - the contact lens is -2.25 strength.

However to get the viewfinder at its sharpest, i have to set the diopter as far minus as it can go - so -5%! This can't be right can it? Maybe something is wrong with my viewfinder so its misaligned, and im still not seeing the image as sharp as i should even with this extreme adjustment, hence the problem seeing minute focus changes in the viewfinder.

But if I'm wearing my contact lenses that give me 20/20 vision i should be able to perfectly with 0 diopter, is this right? Or does looking through a viewfinder via contact lenses not work like that?

If its a matter of a broken viewfinder, is there any way i can fix it , or a place i can being to be repaired? (I'm in Germany)

 

[jwd722]

This link may/may not help:

http://photo.net/medium-format-photography-forum/00aUH5

 

[pagonzales]

I removed the diopter that my waistlevel finder had since I couldn't focus with it while wearing my glasses. No problem now since it's been removed. This is using a mamiya 80 1.9 and a 1000s body with WLF.