Your Oldest Lens

[Steven Tribe]

I couldn't find the site last night! I'll try and remember the search words.
He included an analysis of FL, radii, whether they were crown/flint or flint/crown (yes some did use the reverse system!), convex or concave pointing forward. He included ****ograms of the light coming through which showed the presence of irregularities in the homogeneity of the glass (really cool images) and more.

[eddie]

*wolf whistle*

oh la la! what an old baby!

i love it.....can i have it? har har har!

i would not clean it or polish it.

[cowanw]

Send it to the 11th province: I think not!
Regards
Bill

[Steven Tribe]

I still can't locate the website I mentioned earlier. I'll post if google comes up trumps.
Having done a bit of reading, it appears to be the general optical historian view that the Chevalier lens is a front achromat taken from telescope production. Perhaps the "concave forward" is just because the telescope cell, when screwed into the back of a tube, would be that way around! This explains also why it performs so poorly below F16 as there is a restrictive stop in the telescope tube. It was the basis of the "French landscape type". Petzval modified the achromat using maths to push performance up to about F10 before the image is dramatically corrupted.

[goamules]

Maybe you are looking for Kingslake's book. The part on Petzval Here. And yes, it does say he basically used a telescope type doublet to start his design.

[Steven Tribe]

No, this was a modern study.
I have checked my surviving early telescope achromats and I can't get down to F.5 as Kingslake says. I have a F6.6 and an F9. I have a day or night as well and judging the distance to the erector lens and the barrel diameter, this must have been an F9 as well - the big difference here was the absence of limiting stops as in the usual type daylight telescopes. These stops was at the front end of the first extension - In the illustration I have pushed the draws in to show the stops.

[Steven Tribe]

This is an update to a mail I made on the 2nd November!
The optical investigations of the old telescope achromats were rochigrams and focograms.
The study can be found at the Adler Planetarium website under the Dioptrice project.

[rjmeyer314]

CZ Jena Tessar, c. 1958-1960. Relatively speaking, it's a young whippersnapper!

The Tessar was designed by Paul Rudolph in 1902.

[dsphotog]

I have a CC Harrison lens (#7129) that is on a c. 1855 camera, Would one of the experts, please remind me the formula for calculating focal length & f number?
Also if the lens age can be determined by the serial number.
Thanks

[john wood]

A Busch Pantoskop that, though designed in the 1860's I've read, was made...dunno, in the '60's as well, or maybe later on. Maybe Miguel or Ole know...