Imagon 250mm + Compur 3 f5.6?

[olk]

Hello,
is it possible to use the Imagon 250mm with an Compur 3 shutter with f5.6 (the Imagon is equipped with a H5.8 sieve aperture)?
The Compur 3 usually shipped with the Imagon 250mm has no f-scale and opens the iris fully (f4 or f3.5).
I'm concerned that the aperture for the f5.6 version influences the H5.8 aperture.
best regards,
Oliver

[Mark Woods]

I only use the disks for the aperature.

[olk]

Yes, but what if I have to replace the original Compur 3 shutter with the f5.6 version? I open the iris to its max. e.g. f5.6.
Does this work together with the h5.8 disk? Or will it reduce th arperture too much?

[Bob Salomon]

Yes, but what if I have to replace the original Compur 3 shutter with the f5.6 version? I open the iris to its max. e.g. f5.6.
Does this work together with the h5.8 disk? Or will it reduce th arperture too much?

As long as the aperture is fully open it will work and you will be at 5.8 without a disk or with the disk with the largest center hole with all of the peripheral holes open.

[olk]

As long as the aperture is fully open it will work and you will be at 5.8 without a disk or with the disk with the largest center hole with all of the peripheral holes open.

Thank you, that's what I'd like to know.

[peter brooks]

Surely the physical size of the wide open aperture on the shutter has to be at least the same as the physical size of the disk?

I know that the Imagon 'h' stop measurement is not the same as the 'f' stop but due to the arrangement of the smaller (closable) holes on the disk the light is gathered over a relatively larger area?

(Having said that I don't know the comparative openings of the two shutters in question).

[jga]

Hi,
I uploaded 3 pictures of a Compur 3 shutter, I think it is easier with pictures...

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So, first of all, the scale of the shutters is relative to the lens they mount, so if you reuse the shutter from a different lens, the scale will probably be off anyway. You can see that in this case the scale is fixed with a couple of screws, one can remove and mount a different one.

234713
234714

The second and third pictures show that there is a limit screw in this group of holes, that limit the maximum aperture. The lens in this case is a Symmar-S 240mm f5.6, and the maximum aperture of the shutter is too big for it, so it has the limit screw.

So, what I think is, if you have a limit screw in your shutter, remove it, you don't need it. Also, you may want to remove the aperture scale, since it is just misleading (if you can, it might be printed directly in the shutter). Also, it is possible to remove the complete aperture mechanism of the shutter from the bottom, without disassembling anything else.

Good luck!

[olk]

So, what I think is, if you have a limit screw in your shutter, remove it, you don't need it.


That helped! Thank you!