View Full Version : Glass placement critical in old brass lenses?

Jon Wilson
28-Mar-2008, 22:20
I understand the principle of how individual cells in a barrel need to remain constant for the barrel lens to retain the same focus. However, I periodically see some ebay sellers take the glass cells out of a brass barrel lens. This raises a flag of concern for me. How confident should I be that lens which have been removed and reinstalled in a brass barrel has had its cells properly reinstalled? Or in other words, is it necessary for the glass in old brass lenses, e.g., Voightlander or Dallmeyer barrel lens, which have been removed be reinstalled in the barrel precisely for the lens to work as designed? Is the alignment of lenses critical in the old brass barrel lens?

Ole Tjugen
28-Mar-2008, 22:49
That depends a lot on the actual type of lens!

For a Petzval to be as sharp in the center as it can be, the spacing is important. But not so much that you can't dismantle one for cleaning - and besides, in the century or so since it was new it is very likely that someone has done just that.

A normal Aplanat is less critical, a RR even less so. But a wide angle Aplanat is supercritical, even more so than many modern lenses!

And then there's centering...

Jon Wilson
29-Mar-2008, 10:12
Thanks Ole, that is what I suspected. I appreciate you pointing out the degree of precision required in removing and reinstalling the old glass...especially as to a wide angle Aplanat. Would your answer be the same as to the "newer" lens, e.g., Verito, Vitax, Versar, and other similar lens which are in either a barrel or studio shutter?
Thank you. Jon
BTW, how did your exposures with that small protar I sent you turnout?

Ole Tjugen
29-Mar-2008, 15:16
I admit to not knowing very much about Veritos or Vitaxes - or indeed most other lenses beginning in "V". :)

In my experience the "better" the lens, the more obvious is any offset from optimum. I happen to have a WA Rectilinear and a WA Aplanat of approximately the same focal length, and have "played around" with them a little and discovered that there was no way I could get the RR as sharp over a wide field as the Aplanat was, but it took very little misalignment to make the Aplanat's sharpness drop drastically

The WA Protar seems to be at least partly inspired by the WA Aplanats, and shares the same demands for accurate spacing. Fortunately drastic misspacing is clearly visible, and fine tuning can be done with a good loupe (awaiting confirmation by exposing film, of course).

My problem at the moment is that I have a big stack of exposed but undeveloped film. I started in my new job two weeks before I expected to, which meant that lots of stuff was just left dangling. And I haven't really caught up since... I'm hoping that the next few months will be slightly less "interesting" than the past seven months have been, so I can finish up all the various projects that should have been done last year.