low-profile FED lens choices?

I have a FED-2b with the Industar-26m.
What are my options for a low-profile lens? I gather that an "Orion-15" is one choice. Are there others? I don't care much about focal length or speed - the priority is to make the overall camera 'thinner', for clandestine concealment.
-Pete

Industar-22 is collapsible 50mm/3.5.. Industar-50 is a also pancake-style lens 50/3.5 as well..

Why not a collapsible Fed 50/3.5? There were Fed-2b's fitted with it... (I guess the Russar is far too expensive, and the finder adds some extra bulk!)

Thanks folks. Correct me if I'm wrong, but the collapsible lenses are only "functional" when they're extended, right? To clarify what I want: it would be a lens that is focused at infinity, and the total thickness is short.
Pete

Oh, and I should mention that I'm only interested in cold-war-vintage options.
Pete

You can supposedly use this lens:

http://www.ebay.com/itm/INDUSTAR-69-2-8-28-Russian-Wide-Angle-Pancake-Lens-M39-/170791978802?pt=Camera_Lenses&hash=item27c3fec732#ht_4495wt_1139

Industar-69 is from Chaika camera, it does have standard M39 mount but I believe the focus on it is non standard it may need some modification to focus to infinity on FED-2.. I'll let the lens experts here provide more info on compatibility...

Cheers,
Vlad

Now that I think about it I think I-69 vignettes like crazy on full frame rangefinders because it's made for half-frame Chaika.. if that's something you're looking for... And from what I remember in terms of what focus issues it has on full frame rangefinders - is the backfocus on Chaika is slightly off..

It appears that the I-50 may be a reasonable choice for me...

Pete, but keep in mind that flatter version is for Zenit mount and not rangefinders.. the rangerfinder one is as big as Jupiter-8.

vlad.

Russar 5,6/20mm, Orion 6/28mm... They are the shortest.
The Jupiter 12 is too a good choice: more voluminous but less expensive.

Of course, the Fed 4,5/28mm. But it is quite impossible to find and was made too early for you (1938).

Jacques.

The Industar-22's spring loaded locking tab will catch on the FED-2's vulcanite. The lens mount is set rather low, and there will be no rear clearance for the lens's locking pin. There was an I-10 collapsible made specifically for the FED-2. Their locks clipped on the front part so there is no protrusion in the rear anymore.

I-69 were made for 18X24 halfframe Chajka cameras... they will vignette terribly on the 24X36 format. And this is not just dimming- the black areas are non-image areas, so there is nothing there which can be corrected later. Stopping down the lens will not help. More details here:
http://www.zorkikat.com/industar-69-28mm/265/