Did I just ruin focus on my new Mamiya C220?

[madeleineostoja]

I just got a new Mamiya C220, and did something very silly. It stank of cigarettes and the focusing screen was dirty, so I took the whole thing apart for a thorough clean.

When I took the screen assembly off the paper shims sandwiching the nameplate bracket fell out, but I replaced them when I put it back together. Now the stupid part, when I was cleaning it all I thought I’d give that nameplate bracket a clean, and I thought I was wiping off gunk, but I was actually wiping off a gummed on paper shim. I stopped once I realized, after it had already been torn up a bit.

Would such a small change have ruined focusing? Is there some way I can check?

 

[keytarjunkie]

Is the focus still correct at infinity? You can of course check by shooting a roll of film, especially up close and wide open. You could also try placing a piece of ground glass on the film plane with the back open. See if the viewing lens and the taking lens are focused on the same spot (again, up close and wide open will help to reveal this). Then you can adjust the viewing screen if necessary.

 

[madeleineostoja]

I’ve heard of using ground glass to check focus before, I might try that. I don’t have ground glass handy, but I think you can use wax paper? Would that be accurate enough, just taped to the film plane and focussed to infinity, then compare to the viewfinder? If infinity is dialed in could I assume the whole thing is calibrated correctly?

 

[retinax]

Just put the torn shim back where it was, why would a tear matter? Just make sure it doesn't double up anywhere. The do a test roll, focus could have been off from the start, it's good to know anyway.

 

[pete.mod]

I’ve heard of using ground glass to check focus before, I might try that. I don’t have ground glass handy, but I think you can use wax paper? Would that be accurate enough, just taped to the film plane and focussed to infinity, then compare to the viewfinder? If infinity is dialed in could I assume the whole thing is calibrated correctly?

I used to make a "ground glass" screen out of a cd case. Cut out a square from the transparent plastic, use fine sandpaper to dull the surface, face the dull part toward the lens and you have a cheap way to check focus.

 

[madeleineostoja]

Ooh that’s a great tip, I never thought of just dulling some plastic with sandpaper. I’m sure we have some around somewhere. Thank you!

 

[OlivierAOP]

You can also use a piece of glass with frosted scotch tape stuck on it.

I would recommend a loupe to inspect the ground glass. I've also used a digital camera with macro lens and live-view, it's very effective.

If both ground glass test and focusing screen agrees, you'll be good.

 

[madeleineostoja]

Update: I did the focus check trick with wax paper, and it was a touch off, so I added an extra tiny shim with tracing film, and it’s now perfect. I feel very accomplished haha. Thanks for the tips!!