how to work out shims

[brighamr]

out of interest

how is the need and thickness of shims calculated ?

my guess is set the camera to infinity i.e. 450mm extension on 450mm lens then see if its in focus
but how would you measure so precisely

and how would you shim for macro ?
my 210 macro sinaron has a shim that is 0.1mm is my vernier gauge is to be believed

best

robin

[mdarnton]

I think you misunderstand shims, but will leave the explanation to someone else. Your macro does not have a shim because it is a macro.

[Doremus Scudder]

Are you referring to spacing rings used in mounting lenses to a barrel or shutter? If so, they are used to precisely position the lens elements at the right distance from each other and the aperture so that the lens is properly in focus. To determine what shims are needed, if any, and their size and position, one needs a sophisticated optical bench and very precise measuring equipment. It's not something that can normally be done at home...

If you're referring to something else, then you need to elaborate a bit so we understand.

Doremus

[ic-racer]

The lens spacing with the shims will let you control flatness of field for infinity and closeup. Closing the aperture can also change focus, so you might need to expose film at working apertures, rather than try to examine the edges of the ground glass with the lens wide open to find the best lens spacing for your purposes.

[Dan Fromm]

OP, where is this shim you mention? If it is between a cell and the shutter, it is there to compensate for a slightly off-specification cell. If it is between the back of the shutter and the lens board, it is there to provide clearance for the diaphragm's actuating lever.

[brighamr]

thanks for the replies

the shims i’m referring to are the ones between cell and shutter
in the case of my 210macro it’s in a Sinar DB shutter
but it’s the same sort that’s in a copal or compur shutter

best

robin

[Bob Salomon]

thanks for the replies

the shims i’m referring to are the ones between cell and shutter
in the case of my 210macro it’s in a Sinar DB shutter
but it’s the same sort that’s in a copal or compur shutter

best

robin

But not necessarily the same thickness. That will vary from none to some depending on the specific shutter and lens.

[Dan Fromm]

thanks for the replies

the shims i’m referring to are the ones between cell and shutter
in the case of my 210macro it’s in a Sinar DB shutter
but it’s the same sort that’s in a copal or compur shutter

best

robin

If it came with the lens it is what's needed. The only thing you have to do is not lose it if you move the lens to another shutter.

[Tin Can]

Also possible any shim has already been lost

New user will not know



If it came with the lens it is what's needed. The only thing you have to do is not lose it if you move the lens to another shutter.

[brighamr]

so getting back to my actual question

"how is the need and thickness of shims calculated" ?

I'm quite happy with my lenses some of which have shims and some do not

best

robin

[Bob Salomon]

so getting back to my actual question

"how is the need and thickness of shims calculated" ?

I'm quite happy with my lenses some of which have shims and some do not

best

robin

On an optical bench.