How do you create an aperture scale for a lens?

[Helen Bach]

... and sometimes what we hope are precise or accurate methods may not be as precise or accurate as they might appear and we may as well use an approximate method. A caveat with the method of measuring at the film plane is that angle of incidence may affect the light meter reading more than it affects exposure of the film. A spot meter pointed at the ground glass and aligned with the lens axis may be over-influenced by rays close to the lens axis, thus taking too little account of rays coming from the periphery of the exit pupil when the lens is wide open.

Best,
Helen

[sully75]

Here's the lens in question:



Any thoughts about its worth? I'm happy playing around with it right now.

2nd photo I took with it:

[sully75]

the aperture scale on the bottom is homemade. Not sure if that's obvious or not!

Just put it next to another camera and looked at the amount of light coming through the ground glass. Not too scientific. Thanks for all the suggestions. I'm sure either way will be better than what I've done so far.

It's an old speed graphic, I'm not sure how accurate the shutter is to begin with...

[sully75]

I forgot that there was a stop between 8 and 16 initially.

[cowanw]

the early German (usually marked for aperture) and all "American" branded dynars (which is what you have if the focal length is given in inches) are all f6. The later (German branded) dynars are all f5.5, and nearly always marked as such. If yours is not marked for f-stop, I would assume f6.

cheers

Tim

Although, the cover of the 1927 Voigtlander Lenses
Catalog shows a Dynar of f5.3. doesn't list any though.

[sully75]

I'm considering selling this lens. Not sure what it might be worth. Could anyone give me a reasonable asking price?

Thanks!
Paul

[sully75]

Divide the common aperture nos. into 165 to get aperture diameter in mm. ie. 165 divided by 8 is 21. A 21mm hole is your f8. 165 divided by 11 is 15. A 15mm hole is f11, and so on. I think Dynar's are f6.3

Hi Jim,

I'm finally actually working on this lens. By your method, do I measure the aperture with the cells in or out? The opening of the aperture with the cells out appears to be f8. With the cells in it looks more like f6ish.

Thanks
Paul

[BradS]

You folks always strain at gnats in these discussions, and you are of course correct. But in the practical world of getting some pictures made, the errors we live with in our meters, + or - 15-18%, and in our shutters, + or - 30% plus the human error in our zone calcs + or - unknown%, make the pupil error of no consequence at all really. Just get a ruler and start making some photos with it. You'll be very very close doing it the way I outlined.

Jim (who has made 1000's of decent negatives the non-perfectionist way) Galli

Here's some sane advice that's worth heading. Would that we had more folks as interested in making photos by whatever method that's proven to be "good enough".

[BradS]

Hi Jim,

I'm finally actually working on this lens. By your method, do I measure the aperture with the cells in or out? The opening of the aperture with the cells out appears to be f8. With the cells in it looks more like f6ish.

Thanks
Paul

You measure with the optic in place, looking into the front of the lens.

[c.d.ewen]

Jim (who has made 1000's of decent negatives the non-perfectionist way) Galli

But Jim, unlike you, the rest of us put our glasses on to make pictures.

Sully75: If you're obsessive and can't follow the sage "good enough" advice, check your work this way: mount the lens, focus the camera at infinity, and lock everything down. Take the camera into the darkroom. Take a piece of cardboard, poke a pinhole throught the center of it, then tape it to the center of the GG. Hold a piece of photo paper up against the front of the lens and a flashlight against the cardboard and turn the flashlight on for a bit. Develop the paper and measure the resulting circle. That's your entrance pupil opening. Divide it into the focal length and you've got your f/stop.

If you're truly obsessive, you'll now worry that you don't know the real focal length of the lens. If this happens, see a doctor.

Charley