Lens mounting depth on lensboard - critical?

[StephenT]

I recently purchased a Sinar F with a Schneider-Kreuznach Super Angulon 90mm/f8 Technica in a Compur shutter. It has Linhoff on the barrel. The lens is definitely coated, but it does not have a focusing lever to open the shutter - I have to use the B setting to lock the shutter open for focusing (never seen this before - all my other large format lenses have that capability).

The shutter goes from B to 1/500.

It came mounted on a Sinar board, but the retaining ring was on the front element (actually the shutter, of course), and was screwed all the way forward on the shutter. Normally, I believe the retaining ring is found on the interior side of the lensboard, but this lensboard hole is just a bit too small, so it has to be installed on the shutter assembly on the exterior side of the board. The rear element is then screwed into the shutter and the retaining is used as a "spacer" to limit how far the rear element can be screwed into the front element.

Removing the lens, it appeared to me that the rear element could protrude dangerously close to the aperture blades. Remounting the lens, I did not screw the ring all the forward on the shutter, but left plenty of room so the rear element would have plenty of space between it and the aperture blades.

Is the entire length of the lens/board/shutter a critical dimension? Are all lensboards the same thickness? It seems to focus fine from what I can tell on the ground glass, but I believe there might be design limits on the distance between the front and rear elements.

At a maximum aperture of f8, it's a little hard to tell on the ground glass what may lie in the periphery of the image circle.

Has anyone had an experience like this?

Any input would be appreciated before I start experimenting.

Thanks.

Steve

[ic-racer]

Front/rear cell spacing can affect field flatness.

[Jac@stafford.net]

I cannot picture the retaining ring situation you have there. Can you make a snapshot or two of it?

I am guessing that you have a Compur "P" shutter. There is a button on top that on other Compurs is a self-timer actuator. On the "P" that button should open the shutter for focusing.

Give it a try!

Cock the shutter, then push the button towards the camera. Then press the cable release. The shutter should stay open. To close the shutter, recock it.

[StephenT]

I cannot picture the retaining ring situation you have there. Can you make a snapshot or two of it?

I am guessing that you have a Compur "P" shutter. There is a button on top that on other Compurs is a self-timer actuator. On the "P" that button should open the shutter for focusing.

I'll take a pic of the assembly and post it later today.

No, there is no button on top. In "googling" compur shutters, apparently this is not uncommon but is not the norm. I think I have an older shutter than the lens. There is a website somewhere that will relate the serial number of the lens with it's manufacturing date, and I'll try to find it again.

I'm hoping that the field flatness issue will be minimized with stopping down. I seem to recall that a good rule of thumb is f22/32 or so - smaller apertures may produce unsharpness due to diffraction. Would anyone like to give their input on that?

Thanks for the input.

Steve

[Jac@stafford.net]

Quite puzzling.
Does your shutter have this little switch?

[StephenT]

Quite puzzling.
Does your shutter have this little switch?

Nope........no switch, no lever, no button. The lens is beautiful, and the shutter is very nice and works very well. The speeds are right on, the ones I can test, anyway.

f8 to f64 aperturbe - don't think I've seen an f64 before.

[StephenT]

oops.........."aperture."