Looking at the 127 Tominon, First element is pretty close to plano-convex with flat side toward iris Second element is double concave with more concave side toward iris Third (rear) group is cemented doublet with side toward iris being approx. flat, and rear facing side convex. Looks like a Tessar to me, but there's sure a lot of coverage. The 127 has room for significant movements and I have a 105 Tominon with exact same construction that just covers 4x5 wide open. Looks at least ok in the groundglass right to the corners @f8. I wouldn't expect that from a Tessar design. ----- Original Message ----- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx> To: <pure-silver@xxxxxxxxxxxxx> Sent: Sunday, March 13, 2005 12:01 PM Subject: [pure-silver] Re: Tominon, Ysaron > > ----- Original Message ----- > From: "Gene Johnson" <genej2@xxxxxxx> > To: <pure-silver@xxxxxxxxxxxxx> > Sent: Sunday, March 13, 2005 9:58 AM > Subject: [pure-silver] Tominon, Ysaron > > > > I've done some picture taking lately with a 127mm version > > of each of these. I'm kind of impressed. Both of them > > behave exactly the same as far as I can tell, in that they > > are none too impressive wide open, but sharpen > > dramatically when stopped down, being pretty good by f5.6 > > and by f8 are fairly amazing (folks, I spent 20 bucks each > > for them) with serious resolution and very good contrast > > and cover 4x5 with good sharpness all the way to the > > corners at f8. > > I've learned that they were probably from an MP-3 copy > > camera. They have the standard one cell on either side of > > the iris and are not the front mounted barrel lens type. > > Has anyone else tried these and gotten the same results? > > > > Richard, I was cleaning the glass in a Tominon this > > morning, and I swear the center element (Tessar type > > construction) has a very very slight brown cast. Could > > these things have some kind of wierd Aero-Ektar kind of > > glass in them? > > > The lens is probably optimised for whatever distance it > was used at in the Polaroid camera. I think these are > Tessars so its likely they have some coma or oblique > spherical (look the same but come from different sources) > which blurs the image as you move away from the center. Both > are reduced by stopping down. > I don't know why the center element should be brown. If > its radio active you might be able to tell by laying the > lens on a bit of fast film for a day to see it it fogs the > film. Aero Ektars had one element made of a glass with both > Lanthanum and Thorium in it. Thorium was added to some of > the early rare earth glasses to raise their index. It was > either not known at the time how radio active it was or else > it was thought that the lens performance was more important > than either stability or safety. Thorium has not been used > in optical glass for a few decades but these lenses may be > old enough. There are other ingredients in glass which can > be unstable and cause staining so its not certain these are > radioactive. > Tominon lenses seem to be pretty common on the used > market. I don't have one so I have no idea of how they > actually perform. > You can help me by seeing if you can determine the lens > construction from reflections. I am not certain they are > Tessars. > > --- > Richard Knoppow > Los Angeles, CA, USA > dickburk@xxxxxxxxxxxxx > > ============================================================================ ================================= > To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there. > ============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.