210mm f/9 Graphic Kowa - Image Circle

[Old-N-Feeble]

Kerry,

Do you know if there's a way to determine optical construction without having to disassemble the groups?

BTW, I often visit your lens pages... great stuff there.

Mike

[Dan Fromm]

Do you know if there's a way to determine optical construction without having to disassemble the groups?

PMFJI. Counting reflections is a start. Use a point source or a single lamp. An air-glass interface makes a strong reflection, a glass-cement-glass interface makes a weak one. Weak reflections can be very hard to see.

Think about it and you'll see that Kerry's two lenses -- 6/6 sort of perhaps double Gauss and 6/4 plasmat -- are easy to tell apart.

[Old-N-Feeble]

Thanks, Dan. I checked again and could only see 4 reflections in each set of cells... all strong reflections. This time I used a small very bright LED flashlight from about 3 feet away. I tried very hard but could not see any weak reflections.

I don't know if this helps but, other than the mounts, the front and rear groups look identical and seem to have identical individual focal lengths.

[Zaitz]

Well I won't be much help with my images. They are probably not the best to tell corner sharpness, pre-sunrise dark corners... I do have one that is very sharp throughout but it was focused closer so not at infinity. I also have one from Great Sand Dunes NP but would need to re-scan it at higher resolution. Sorry for that. I have a couple getting developed but won't see those for a week unfortunately. Those might be of more help.

[Old-N-Feeble]

Thank you, Zaitz. I'm in no hurry. Please post your results as they filter in through your normal routine.