Mamiya C33 Focusing Screen Query

[Steve Smith]

My father has recently bought a fair amount of Mamiya C33 and C330 parts which means he now has a C330 and C330S. Out of the remaining parts I have put together for myself a C33 with 80mm lens and I have taken the best (least marked) of the C33 focusing screens.

My question is about spacing of the focusing screen. I thought that the 80mm lens was at infinity focus with the bellows at minimum extension. i.e. wound right back to the body, but the focusing screen only shows infinity focus with the bellows out about 2mm.

In between the screen and the body is a black fibre strip with three holes and there are two washers spacing off the other two screw positions.

Am I missing something or does winding the bellows rack right in actually focus past infinity?

Thanks,


Steve.

 

[Ian Tindale]

Racking the bellows all the way in is not related to the lens being at infinity. The infinity focus point of the bellows is different across various lenses. Take a 135mm lens, and you'll find that infinity focus involves racking the bellows out quite significantly.

 

[Ian Grant]

You need to get a piece of ground-glass, take the back off focus the lenses at infinity on the groundglass, obviously you need the viewing screen/viewing lens to match the focus of the ground-glass/taking lens.

Ian

 

[Steve Smith]

I did do the ground glass test yesterday (quickly) and I thought it was focusing at infinity fully racked in. Doing it again this morning and being a bit more critical, it does appear that infinity focus for this lens is slightly forward on the rack.

Time for a test roll of film wide open to see if I'm getting what I am expecting.

Like I need another camera!!


Steve

 

[grahamp]

The film plane to lensboard plane with a particular lens will be the same for all models of the camera. If you can prise one of the C330's from your father, get some measurements. The screens on these cameras have to be shimmed to align them to the film plane distance.