Changing shutters?

[Ed Bray]

I have a query that I would appreciate the answer to.

If I had a 210mm f5.6 Symmar in a No 1 Compur shutter and later purchased a 210mm f5.6 Apo-Symmar in No 1 Copal shutter would I be able to do a straight swap of the shutters and would everything remain the same (barrel distance, aperture)?

TIA

[IanG]

Straight swap would be fine.

Ian

[Sevo]

A Symmar (convertible) or Symmar-S? The latter is very, very like the Apo-Symmar (cynics say the only difference was the name change). The convertible is older and a more different design - I'd proceed more careful there, even though my shuttered ones seem to have the same aperture scale. In either case, measure the total lens height with a precision caliper before and after - if there is a difference, you may need to rearrange the shims (it is hard or impossible to tell which shim compensated cell and which the shutter tolerances - the latter ought to stay with the shutter, the former ought to be moved).

[Leigh]

The proper depth of a Copal #1 shutter, measured from the front face to the rearmost surface, is 22mm.

If you move lenses between shutters, the first thing to do is measure that dimension on each of the shutters.
Your measurements should have an accuracy of at least 0,1mm.

If the measurements for the two are the same, then move any shims along with the cells.

If the measurements differ, you have a problem and should not proceed without further guidance.

- Leigh

[Andrew]

I've just tried a swapping two similar lenses of nominally equal focal length [210mm]
to convince myself it was OK I focused infinity, swapped over the cells and measured the amount of readjustment needed to refocus infinity
in my case there was a tiny difference that amounted to about 3mm which for a 210mm lens seems insignificant
I think that makes my aperture scale in error by about 1.5%

addit
Leigh, does this fit correctly with our previous discussion?

[Leigh]

in my case there was a tiny difference that amounted to about 3mm which for a 210mm lens seems insignificant
I think that makes my aperture scale in error by about 1.5%

A 3mm (~1/8") difference in infinity focus is huge in terms of the shutter geometry.
It may indicate that the cell spacing is not correct.

The aperture scale is not related to the infinity focus position at all.
It's a function of the apparent aperture (entrance pupil) and the optical focal length (which is invariant).

- Leigh

[Andrew]

it was a swap of a newish 210 g-claron for an older "dagor" style g-claron so it is a different design
but if they're both nominally 210mm optics... ?

[Leigh]

OK. You said similar, so I thought you meant similar.

If they were different designs then the flange focal lengths could be quite different.
My lens database shows modern 210mm lenses with FFLs from 177mm to 223mm.

- Leigh

[Andrew]

yeeees... so if you swapped cells and found that you had to rack the standard backwards or forwards by 46mm to refocus infinity then I think anyone woud expect a problem with the aperture scales being incorrect

what if I swapped a nominally 300mm rapid rectilinear into the shutter of a nominally 300mm plasmat and found that focus was perfectly maintained ?

[Ed Bray]

A Symmar (convertible) or Symmar-S? The latter is very, very like the Apo-Symmar (cynics say the only difference was the name change). The convertible is older and a more different design - I'd proceed more careful there, even though my shuttered ones seem to have the same aperture scale. In either case, measure the total lens height with a precision caliper before and after - if there is a difference, you may need to rearrange the shims (it is hard or impossible to tell which shim compensated cell and which the shutter tolerances - the latter ought to stay with the shutter, the former ought to be moved).

It is a Symmar convertible and an Apo-Symmar (no L).

There is nothing wrong with either shutter, I just prefer the more rounded aperture of the Compur to the pentagon design of the Copal aperture.