8" Dallmeyer Pentac f/2.9 - Any Users?

[Jason Greenberg Motamedi]

I have been looking for a 10" or 12" Pentac for more than three years, and have yet to find one, or even hear of one. Apparently they were made, but must be pretty rare. On the other hand, a 12" f/2.9 lens would be huge. I have a 13.5" f/3.5 Eastman Anastigmat which weighs 12 lbs; the 12" pentac would be larger!

I also recommend getting the Vade Mecum. It is full of holes and inconsistencies, but it is by far the best source on lenses we have.

[Øyvind Dahle]

"Brown discoloration due to radiation damage from Thorium glass cuts out at least a stop of light, effectively making the lens f/3.5"

At this link: http://www.largeformatphotography.in...ic/249393.html

it was stated:

"Incidentally, I read on usenet that at least some of the colour centers in some of the radioactive lenses can be bleached by leaving the elements exposed to sunlight. If you are using these lenses and want to get close to their original performance, this might be worth a try.

--Struan Gray, 2002-03-26 06:19:57 "

So try the sun or UV-light! Please report back any change

Øyvind

[Struan Gray]

Øyvind: several people have reported success in bleaching their browned Aero-Ektars. There is yet another active Aero-Ektar thread on photo.net's LF forum right now, in which Micheal Briggs summarises a whole bunch of previous threads, and provides links to them.

www.photo.net/bboard/q-and-a-fetch-msg?msg_id=009mU2

[Jason Greenberg Motamedi]

Øyvind,

I got rid of my 7" Aero-Ektar some time back, so I can't try the sun treatment and retest.

I did bleach an earlier model of 9x9 Aero-Ektar, a 352mm f/3.5. After three weeks in the sun it lost most of its tea colored strain, but retained a distinct and strong yellow color. For aerial photography this yellow color would be an advantage, working kind of like like a UV filter, but for my purposes--using a blue sensitive alternative process--the color cast was a huge disadvantage.

[David A. Goldfarb]

Just to add another fast 5x7" lens to the list, I just received a Schneider 21cm/f:3.5 Xenar in barrel. The serial number dates it at 1925-28, but it looks like it's had an aftermarket coating added, and there's a sticker from Burke and James, who used to perform that service. It seems to be a standard tessar type.

Just holding it up and seeing what kind of image it projects on the wall, it looks pretty sharp in the center wide open, dropping off visibly in sharpness toward the edges of the image. I'll make a lensboard for it and try it out on my 5x7" Press Graflex, and will report back.

[Dan Fromm]

Jason, you might want to set your monster out to bask some more.

I have three tessar-type TTH process lenses that seem, pending a visit to Michael Briggs' geiger counter, to have radioactive rear cells. I'm not sure which element. All three arrived with yellowed rear cells, one so yellow that shots on EPP with it had a distinct yellow cast. After a month under a 20w BLB tube, all were clear. Shots on EPP with the bad 'un now show proper colors.

Cheers,

Dan

[Jason Greenberg Motamedi]

Thanks Dan, I will try using the black light bulbs and see what happens. Maybe, while I am at it, I should dig out my fuzzy "black light" posters from the 70s, to fully appreciate the effect.

[Cole Seaborn]

I read this entire thread with interest as I was doing some research on a Dallmeyer Pentac 8 inch f/2.9 (coated), that recently surfaced in my inventory. It was very helpful to read your comments, as I had no idea as to it's history, or value, prior to coming across this site. I have listed it on ebay, and will gladly email a link to anyone who cares to contact me

[markcornelison]

I bought one on a nice Speed Graphic that the seller had refurbed. Images have a razor thing DOF, but great backgrounds.

[Tin Can]

I have one, and wonder how powerful a UV lamp can I use to fix the brown?

I never used it as it looks so bad...

But it was the first lens I tried to use for LF and I had no idea how to get it into focus.

My camera didn't close up enough...