A new 'thread'....

Yes, this brief post refers to the Leica thread which has come to be known as 39 mm or LTM (for Leica Thread Mount). Not that one is likely to be able buy a brand new taking lens with this type of mount as they are now mostly found in smaller enlarging lenses, a (very) few reissues of classic lenses and the Cosina ranges.

There is a vast stock of taking lenses in this fitting which can, mostly, be adapted to Leica M mount or in some cases digital cameras  even, if in some cases, only for close up use. This field is truly is vast going back almost 100 years to say nothing of the large Russian/Ukraine/USSR ranges.

I recently had need of a 105 mm enlarging lens and had a late TTH (Taylor, Taylor & Hobson) in my stock, made near here by Rank in the last batches of the 1960's. I wished to enlarge some  6 x 9 negatives and was ready to fit it on to my 6 x 9 enlarger flange when I found it would only turn about one half of a turn before jamming. At this point it became clear that it did fit another flange I had, but had never used. From various other sites I found that Leica screw thread is 39 mm and 26 t.p.inch. Rather a strange definition for a precision engineering company but explained by the background of Leitz in Microscopes which commonly used such threads in Whitworth form over many years. Close examination of the TTH showed it was of 1 1/2 inch diameter and  24 tpi. with a heavily relieved 'lead in' to the thread. I have come across these 'almost right' fittings in the past on an US Leica look-alike, the Perfex, with 39 mm in a very fine thread.

Needless to say, there is no question of the TTH being 'wrong' in any way, it is simply using UK standards for a UK lens!

If you find one do not think of forcing it onto a flange by brute force!