Metrogon cell spacing revisited HELP

A frightening thought...

Knowing that the aerial lenses came as matched cells, I just realized
that I think I have seen serial numbers on the shutter body on one
also.

What if each shutter housing is spaced for each lens pair? I hope this
isn't so, because there were apparently (judging from the surplus
market in Metrogon's) more lenses made than cameras. The aerial camera
manuals had procedures for changing the lenses, and I know one didn't
need a new shutter! I guess we can dismiss the above paranoia...

But I could have some issues with the 6" Metro I put together from
unmatched cells...maybe that's the one that needs a focussing tube!

I hope that the fixed mechanical nature of each half of a Metrogon cell
pair reduces the difficulty of getting the spacing right as Brian
experienced. The only think I am finding a little shaky to measure is
the depth of each meniscus. I have an accurate depth caliper
(calibrated every 3 months, 4 decimal places (inches) with a needle
point, but I'm not using an x-y table to position the lens...I'm taking
repeated measurements to find the deepest part...so I'm probably going
to throw away any data past the 3rd decimal place. Measuring the flange
hwight etc was no problem.

So, Brian, did you accomplish the 250 mm Topogon with more brain than
brawn? I imagine radical meniscii are not easy to find. Maybe you have
the right contacts to get such glass without giving up body parts in
exchange.

Working with available optical emlements (found glass) sure puts a
damper on one's experiments!

M

"So, Brian, did you accomplish the 250 mm Topogon with more brain than
brawn? I imagine radical meniscii are not easy to find. Maybe you have
the right contacts to get such glass without giving up body parts in
exchange.


Working with available optical emlements (found glass) sure puts a
damper on one's experiments! "

I ground and polished the lenses myself according to my own design. I
suppose it sounds like alot of work, but the experience has really paid
dividends over the years in my career as a designer. The glass blanks
themselves were very inexpensive since I used SK16 and F2 for the
design. Years later I discovered that you could achieve a very nice
Topogon/Metrogon design using even cheaper glasses: BK7 and a light
flint such as LF7. Such a design would have the added bonus of not
requiring AR coatings for chemical protection of the glass. SK16 is
cheap and easy to work with, but it stains very rapidly after
polishing.

The main difficulty was the outer positive elements which had very thin
edges. I wound up making them sharp-edged by cementing the concave
side to a sacrificial glass blank. Unfortunately, the resulting
razor-edge is unbelievably delicate, and I watched the first element I
made gradually crack completely in half over the course of about an
hour. Fortunately, this only happened to me once! I also had
difficulty mounting the elements since there was no room. I wound up
cementing the lens elements into metal cells using ordinary UV curing
optical cement, and this has held up well over the years.

Brian
www.caldwellphotographic.com

Wow, yow, & Great Googly-Moogly!

I bet it still was no small feat.