i've had alook in the vademecum but cant find any manufacturers with the initials a.m. anyone heard of them?
its a pretty big lens. in aluminium (thats what we call it here) the front of the barrell is 84mm across. it has a 20 blade aperture. non coated
engraved on the side is - a.m . 14a / 3140
serial no. is - uu278196
The AM Engraving means Air Ministry. Many of these lenses were made under license for the Air Ministry in the UK during WW II and perhaps before.
The lens design is a triplet originally made by Dallmeyer who named them Pentac.
The demand was so high that Dallmeyer contracted other companies to make these lenses and those don't show the name of the company just AM.
Lenses where used for Aerial photograhy. The 14" is more rare than the 8" 2.9 of which i have one, a late Dallmeyer now monuted in a #5 Alphax great wide open and quite sharp stopped down. Some of the AM lenses did not quite perform as the Dallmeyers but you could have one of the better, go shoot some photos and have fun.
Jan, odds are that it is a 14"/5.6 Dallmeyer Serrac (tessar type) in Air Ministry dress. The contract number (3140) is not the one (3254) under which TTH made 14"/5.6 Aviars for the Air Ministry. According to the Vade Mecum, "UU" is the code for Dallmeyer. I've seen, didn't buy, a 14"/5.6 Serrac, own a 14"/5.6 Aviar.
It can't be a Pentac, Pentacs are f/2.9 and the OP's lens is f/5.6.
And Pentacs aren't triplets, they are heliar types.
Steve, there's an easy way to tell a tessar (Serrac) from a heliar (Aviar). Count reflections from a single light source. A tessar will have four strong, no weak reflections from the front cell and two strong, one weak, from the rear cell. A heliar will have four strong, one weak from one (usually the front) cell and two strong, one weak, from the other (usually the rear). Ole, I know that heliars are supposed to have the central singlet in front of the diaphragm, but I have an Apo Saphir with the central singlet behind the diaphragm (I identify the rear cell as the one that has no engraving on the trim ring, the front has the one that has engraving on the trim ring).
An air-glass interfaces produce a strong reflection. A glass-cement-glass interface produces a weak reflection, and weak reflections can be hard to see.
Cheers,
Dan
Dan, Thanks for the correction. The 5.6 should off course be enough to tell that it isn't a Pentac. Lesson, no advice until after the first two cups of coffee.
Is it correct that a triplet has two strong reflections from the front and one strong from the rear?
Dan, My Cooke made Aviar's are dialyt type. And well loved.
Jim, thanks for the correction. I blew it. Its the Pentac that's a heliar type. Ouch!
Jan, I've had my coffee already. Two cups, in fact. No such excuse for me.
About reflections. Each air-glass interface makes a reflection. One singlet, two reflections. Two singlets, four reflections. That's why coated lenses transmitted light better than uncoated ones.
Dan, more coffee. You did write that the Pentac was a Heliar type first.Jim, thanks for the correction. I blew it. Its the Pentac that's a heliar type. Ouch!
thanks a lot guys for the advice. i never even thought of the air ministry. it does seen to be a tessar type - 3 reflections from the back. 4 from the front.
the vademecum seems to be a bit ambiguouse. it mentions a no name 14" f5.6 but above this it says "serial no.s begin with uu or vv if original dalmeyer. does anyone one know if both prefixes are dalmeyer factory, or just the vv.
both
WWII Aerial photography lenses were very much in demand at the time, and are quite often very poorly documented. They were military secrets as well, which made the documentation even better hidden.
There were also a bewildering number of different types: If anyone knows anything about a Schneider Göttingen Aerotar 30cm f:5.5 except for the fact that I own one, I would be glad for any information.
BTW - it seems to be a 3-3-2 Heliar derivative with a negative triplet in the middle!
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