20", f6.3. Any info?

[Math]

Seems to be an aerial lens, but I have no knowledge about it. Wayy too large to mount on any of my cameras, so I doubt it'll see any use, so I'll also have to ask.. Is it worth anything? I doubt it though. Makes for a nice doorstop...
Also came with a 8" f2.9 (Pentac?) but sadly, I found out AFTER buying that the rear element was completely missing. Talk about mistakes! :p So if anyone happens to have a rear pentax 8" f2.9 element laying around.

http://img194.imageshack.us/img194/6389/20inch.jpg

[Dan Fromm]

Any other engraving on the trim ring or barrel?

Also what is that flange on the front of the barrel?

Many aerial cameras have three pins at the front, spaced 120 degrees apart, to accept bayonet mount filters. Does this lens have 'em?

[Steven Tribe]

Looks like a Ross Xpres 20" from the 20/30's - the type that often have EMI (extra maginal illumination?) written on them. They don't have the usual order contract no. (!4a/xxxx) on them. According to VM there are 2 versions - 1 +1 / 3 and a plasmat type with 1+1+1 / 1+1+1.

[Math]

There's no EMI written on the lens, however, there IS a contract ref no.: 14a/2320.
The serial on the front is No173049. There is also an extra engraved arrow in the barrel. There are no pins for filters, and the front flange is non removeable. There is however a screw thread for filters, but I'm not sure it's ment for filters.

[Dan Fromm]

Thanks for the reply. The 14A/ identifies the lens as ex-MoD. Both Ross and Dallmeyer sold 20"/6.3 lenses to the MoD during WWII. The serial number (does it have a prefix, e.g., RR or VV?) fits WWII-era Ross, eliminates Dallmeyer if P-H Pont's chronologies are correct.

If a Ross, the lens could be a 2/2 telephoto or one of the Xpres types described by Steven Tribe. Count reflections and then you'll know.