Hugo Meyer Convertible- converting mm aperture to typical f-stops!?

jonw · Feb 25, 2006

I recently picked up a nice Hugo Meyer triple convertible- 240mm, 540mm, 420mm. It is truly a sharp lens, even when converted. However, it has the aperture settings in mm, i.e., 34, 24, 17, 12, 8, 6, 4, and 3. How do I prepare a chart to convert it to typical f-stops? Your assistance is truly appreciated. Thanks. Jon

Donald Miller · Feb 26, 2006

I believe that if you divide the focal length in mm by the aperture in mm that you will have the F stop of the lens.

Ray Heath · Feb 26, 2006

g'day jon
Donald is quite correct
the relative aperture is calculated by dividing the focal length by the diameter of the hole to be used

ie the amount of light transmitted by a known sized hole varies depending on the focal length

also, the same f number on any lens transmits the same amount of light regardless of the focal length, what varies is the size of the hole

jacobus · Feb 26, 2006

This method is correct when using a single component behind the shutter, since in this case (only) the actual iris diameter will work as the effective stop. If you combine both cells to one lens, the front lens will magnify the iris diameter, which means that you have to calculate stops on a different basis, the entrance pupil.
To find its diameter just hold the lens at arm's length in front of you and measure the diameter of the round spot with a caliper. Dividing it by the focal length will give you the stop number. You certainly know that calculating from one stop to the next is simply done by multiplying each diameter with factor 1.4. Hope this helps and isn't too redundant.
Uli

jonw · Feb 26, 2006

Thanks for all of your great responses, both here and via pm's. I can now make a chart to go with my Hugo Meyer Triple Convertible and head out with the old Dorff V8. The only downside is that I need a flange/retaining ring for it. The barrel is almost 52mm or slightly larger than a copal 1 retaining ring. If anyone has one, please send me a pm. Thanks fellow APUGgers! Jon

jacobus · Feb 26, 2006

Jon,
which Meyer triple lens is it: a Plasmat, an Euryplan or an Anastigmat? I have some data sheets copied from older Meyer brochures. So if you want to have some additional information, send me am PM ...
Uli

sanderx1 · Feb 26, 2006

jonw said:
I recently picked up a nice Hugo Meyer triple convertible- 240mm, 540mm, 420mm. It is truly a sharp lens, even when converted. However, it has the aperture settings in mm, i.e., 34, 24, 17, 12, 8, 6, 4, and 3. How do I prepare a chart to convert it to typical f-stops? Your assistance is truly appreciated. Thanks. Jon

Assuming lots of stuff, you cnvert these to the aperture numbers / f stops by dividing with the focal length. Beware however that these are relative numbers you get, and that "real" numbers for the f-stops easily be as much as a full f-stop different, possibly more.

Donald Qualls · Feb 26, 2006

And this thread illustrates why I'm a member here at APUG, long after leaving another photographic forum in disgust.

I was going to do exactly this job for a Polaroid Prontor Press shutter after removing the baffle that, originally, made it usable only with the (no longer present) original 127 mm Ysaron (soon to be home to a pre-War 13.5 cm f/4.5 Skopar). Now I know how to correctly measure the aperture, without having to ask (or do it wrong, not realizing that the front lens in fact affects things). And I can similarly make a conversion chart for "converted" use of the front or rear groups of my 150 mm Componon, which has a correct aperture scale for the full lens but not for the converted forms.

Excellent...

jonw · Feb 27, 2006

jacobus said:
Jon,
which Meyer triple lens is it: a Plasmat, an Euryplan or an Anastigmat? I have some data sheets copied from older Meyer brochures. So if you want to have some additional information, send me am PM ...
Uli

It is the Anastigmat. I have 3 sheets of 4x5 drying now and assuming the pictures can be scanned, I will post them... But, my initial viewing indicates that they are very sharp...and will be improved now that all you great APUGgers have helped me determine the proper aperture f-stops so that future photographic efforts with this barrel lens will improve.
Jon

Ray Heath · Feb 27, 2006

yeh guys, great info
my idea of focal length divided by aperture diameter does only work for a single lens element, this comes from my recent experiences designing and building a simple lens camera

i now recall that i read in an old book that to accurately measure the diameter of the aperture - shine light through a very small hole into the back of the camera, place frosted glass/paper etc across front of lens, measure the easily seen cicle of light, this then is the diameter of the opening after the lens does it things such magnifying and causing the light rays to travel straight
i don't actually understand the last bit but give it a try

and Sanderx 1, if all measurements are accurate there should not be an expectation that the real stop is something else
in fact the term 'relative aperture' means the amount of light passed relative to the focal length
ie a particular f number on any lens passes the same amount of light as that same f number any other lens, because the f number is related to focal length, so what actually changes is the size of the hole

sanderx1 · Feb 27, 2006

Ray Heath said:
and Sanderx 1, if all measurements are accurate there should not be an expectation that the real stop is something else
in fact the term 'relative aperture' means the amount of light passed relative to the focal length
ie a particular f number on any lens passes the same amount of light as that same f number any other lens, because the f number is related to focal length, so what actually changes is the size of the hole

I meant to say "relative to wide open", my bad. The size of the hole != the aperture. As a trivial example, consider the Schneider 150mm f/4.5 Xenar that "fits" a 33mm hole in a #1 shutter with a mere 30mm hole ;-) 210mm f/5.6 Xenar fits an even larger hole. And Xenars don't really even try to have a large aperture.

Ray Heath · Feb 27, 2006

sanderx1,
now i'm confused
these calculations are not a consideration of the size of the hole that the lens mounts in
they are the size of the hole created by the aperture inside the lens

sanderx1 · Feb 27, 2006

Ray Heath said:
sanderx1,
now i'm confused
these calculations are not a consideration of the size of the hole that the lens mounts in
they are the size of the hole created by the aperture inside the lens

And? The maximum size of the "hole" aka aperture aka iris opening in the "#1" size shutter is 30mm. The size of the maximum aperture / iris opening is not the same as the lens maximum aperture, and by diving the focal length by iris opening size you don't necessarily get the lens maximum effective aperture. It can be considerably larger. Or conversly, it can be quite a bit smaller. It depends on the optical design.

Still confused on the Xenars having a 37mm aperture in a shutter that has a 30mm maximum iris opening?

Hugo Meyer Convertible- converting mm aperture to typical f-stops!?

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