are there 2 types of M42?

[johan_de_groote]

I have been playing with a Sankor 135/3.5 lens for 35mm. It belonged to my

father and he used it with the Praktika MTL3. So it must be a M42. Or so I

tought until I played with it and found that I can screw off the alu ring at

the base. It is possible this is a lens that he used with the Edixa he had

before the Praktika (and before I was born).

 

But the strange thing is, the thread on the lens itself is also 42mm diameter

but the pitch is different! Normal M42 is 1mm pitch (so I always tought) but

this lens has 42mm diameter screw with a 0.65mm(?) pitch. The exact pitch is

difficult to measure but it is clearly finer than M42.

 

Are there 2 different 42mm threads?

 

I searched a bit about Sankor but it mostly turns up in relation to cine and

projection.

[christian_kolinski]

Sounds like a T2-mount lens.

T2 is 42x0,75mm.

[dan_fromm2]

T-mount. The difference between T-mount and T2 is not in the lenses but in the mount adapters.

[dan_fromm2]

T-mount. The difference between T-mount and T2 is not in the lenses but in the mount adapters.

 

The huge difference between T-mount and Praktica/Pentax is register. T-mount flange-to-film distance is 55.00 mm.

[johan_de_groote]

The adapter that is on the lens changes the register by +1.8mm (again rough and ready measured).

[donnie_strickland]

As Dan says, that thread is for a T-mount (42 X 0.75). You can get different adapters to screw onto the lens, which will allow you to use the lens with almost any brand of camera mount. As you have seen you have the adapter for M42 (or 42 X 1.0).

[JDMvW]

The Praktica/Pentacon screw mount (origin on the Contax S, later adopted by Pentax) was 42x1. Why in heaven's name Tamron later adopted a 42x0.75 screw mount for the T mount series is uncertain, but a decision to be cursed. It's good you discovered it was not the same mount, as many have permanently damaged both lens and body by forcing them together and stripping the threads.

[John Farrell]

Just to confuse things, there are two variants of M42x1 lenses, Praktica (Pentax etc) and Edixa (and early Yashica M42). If you screw an Edixa or early Yashica lens onto a Pentax, the focussing mark doesn't end up at the top. Th register may be slightly different.

[dan_fromm2]

But JDM, T-mount register is 55.00 mm. Pentax/Praktica is 45.46 mm. Think of the joy of using a lens that has to have 9.44 mm of focusing travel just to reach infinity.

[JDMvW]

I wasn't suggesting that Tamron make it so their lens would fit directly on to a Praktica--I was indicating that Tamron should have chosen something other than 42mm to avoid the problem of ignorant mismatching.

 

If it had been 42x1.0 at least it would not have done damage, of course, but no question of using it at infinity focus without an adapter.