Aperture scale for 300mm Symmar-s

[Amfooty]

I have a 300mm f/5.6 Symmar-S mounted in a Compur Electro 3, but it has two aperture scales listed. As far as I know it isn't a convertible lens. Are the apertures still accurate? It looks to be the same scale on the convertible 240/420mm Symmar.

[Amfooty]

the two lenses side by side.

[Bob Salomon]

No, that lens was probably put in a different shutter. Those are not the scales for a Symmar-S and probably are not the scales for a 300mm. Why not contact Schneider and see if they might still have the correct scales. They probably don't as Prontor Werke discontinued this shutter decades ago and discontinued all shutters more then 20 years ago. Otherwise check with Bob Watkins at Precision or with SK Grimes about having a correct scale made.

[Amfooty]

Thanks for the reply. Is there anything I could do in the meantime to figure out the correct apertures?

[ic-racer]

Search for 'convertible' lenses. Lens cells with busted or no shutters are sometimes very inexpensive. For example you can look for the 135mm/f5.6:235mm/f12 lens elements for the one shutter, etc.

[Amfooty]

Search for 'convertible' lenses. Lens cells with busted or no shutters are sometimes very inexpensive.

I very much like the Symmar S. Just want to get the exposures correct on the shutter I already have.

[Amfooty]

Since the scale looks the to be the same on both shutters, could I just set up a simple ratio to figure out what f/8 would be on the 300mm using the f/8 on the 240mm?

[Bob Salomon]

Since the scale looks the to be the same on both shutters, could I just set up a simple ratio to figure out what f/8 would be on the 300mm using the f/8 on the 240mm?

If you have an exposure meter with a microscope attachment you could easily meter a gray card through the gg (must have a Fresnel screen for this to work properly and you need to figure out what the light loss is when metering through the gg/Fresnel) then you can easily determine what the actual exposure is at each marked stop on the scale and be able to mark the scale for the actual stops.

[Jim Jones]

The f/number can be determined by measuring the apparent aperture through the front lens cell and calculating it. To create a scale, calculate that apparent aperture diameter, set the shutter to that diameter, and mark it with the f/number. When doing either of these procedures, the parallax error can be reduced by observing the aperture diameter from a distance, or shifting the eye by about the diameter of the aperture. A temporary scale can be improvised with white tape on the shutter body. This can be protected by a layer of transparent tape.