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Telyt to Telescope - internal thread spec.


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I have an old pre-APO 400mm f5.0 Telyt which I am planning to convert to a telescope. To do that I need to unscrew it, set aside the rear focussing section and connect an adapter to the front section which holds all the glass. My problem is that I'm not sure as to the thread specification where the two halves join. (I don't mean the LTM thread at the back which is a mixture of metric and imperial - diameter 39mm, Whitworth thread, 26 turns per inch pitch).

 

 

Where the two halves join I have measured the male thread on the rear of the front section. It looks like 64mm diameter (I measured 63.9mm) and either 34 tpi or 0.75mm pitch (I measured 34.25tpi = 0.742mm) . So just what is the specification of that screw thread? Any pointers to who might know?

 

 

Why can't I just adapt an eyepiece to the rear LTM? Because the LTM flange to focal plane is 28.8mm, too short to fit in a right angle "diagonal", eyepiece and adapter. That needs about 55mm.

 

Once I can nail down the thread spec. I will need to find a machine shop to make the adapter as it certainly won't be off the hook. Suggestions welcome.

Edited by LCL999
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I have an old pre-APO 400mm f5.0 Telyt....

Why can't I just adapt an eyepiece to the rear LTM? Because the LTM flange to focal plane is 28.8mm, too short to fit in a right angle "diagonal", eyepiece and adapter. That needs about 55mm....

Wait a moment... if the lens you have is the "old" Telyt 40cm f5, consider that it was made to be mounted on Leica LTM bodies WITH THE VISOFLEX I DEVICE in the middle, for reflex viewing and focusing : to say, its flange to focal plane distance is 91,3 mm : 28,8 (Leica LTM body) + 62,5 (Visoflex I) that is lot of space for any enyepiece you can design (and, of course, Visoflex I in itself is such).

 

See here an illustration of Telyt 40cm f5 on Visoflex I (post #13): http://www.l-camera-forum.com/topic/29125-telyt-400-on-viso/

 

Things are similar for the other more modern Telyts (like the 400/560 f5,6 and f6,8), with the slight difference that they were designed for Leica BM bodies (27,8 mm flange distance) with Visoflex II/III (41 mm), so with a total flange distance of 68,8mm

Edited by luigi bertolotti
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I am not sure why you would bother. The APO correction of this lens is poor and the resolution average in the centre and very soft in the corners  (I have had this lens and still have the 400/f5.6. For what the machine shop costs, you could buy a Chinese spotting scope with zoom eyepiece, that probably would be a better performer. I keep meaning to get round to selling my 400/560 Telyt/Televit kit with pistol grip, shoulder stock and boxed Visoflex III because I just never use them since I got Contax 300/f4 and 600/f6.3 mm Tele-Tessar lenses which I can use with a Novoflex adapter straight onto my M240. They are a different world from the old Telyts. 

 

I was always concerned with the Telyt kit, especially if you had the 560mm head on, that some policeman would decide you were using an RPG7 rocket launcher, shoot first and ask questions later, given that an elderly deaf man in the UK, was shot dead for carrying a table leg.   :ph34r:

 

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... Once I can nail down the thread spec. I will need to find a machine shop to make the adapter as it certainly won't be off the hook. ...

 

I think its a good idea. Even E. Leitz has accepted a foreign ocular* on their lenses.

Here one of my Modifications for M: Telescope Okular TO-R  to M *  (prototype TO-M)

 

(* Link with Images,  german part of the forum.)

 

Wish you every success in your efforts - Thorsten

 

Addendum: Even the APO-Extender-M {#11} (;-) remains useable. 

Edited by Dao De Leitz
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Wait a moment... if the lens you have is the "old" Telyt 40cm f5, consider that it was made to be mounted on Leica LTM bodies WITH THE VISOFLEX I DEVICE in the middle, for reflex viewing and focusing : to say, its flange to focal plane distance is 91,3 mm : 28,8 (Leica LTM body) + 62,5 (Visoflex I) that is lot of space for any enyepiece you can design (and, of course, Visoflex I in itself is such).

 

See here an illustration of Telyt 40cm f5 on Visoflex I (post #13): http://www.l-camera-forum.com/topic/29125-telyt-400-on-viso/

 

Things are similar for the other more modern Telyts (like the 400/560 f5,6 and f6,8), with the slight difference that they were designed for Leica BM bodies (27,8 mm flange distance) with Visoflex II/III (41 mm), so with a total flange distance of 68,8mm

Luigi

 

Of course you are quite correct. I feel like a fool because I've used the Telyt with a Visoflex. Obviously lots of room. Somebody told me there was not enough room and I just did not stop to think.

 

Now I'm looking for an LTM to T-mount adapter. After an extensive search of the net have found nothing. I did note that lots of advertisers offer "M39"  with 1mm pitch claiming it to be the same as LTM. The true 26tpi is just enough different to wreck both threads, or so I'm told.

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... I did note that lots of advertisers offer "M39"  with 1mm pitch claiming it to be the same as LTM. The true 26tpi is just enough different to wreck both threads, or so I'm told.

I should be quite confident that a thread stated as "M39" does fit a Leitz screwmount... see these references :

 

http://en.wikipedia.org/wiki/M39_lens_mount

http://photo.net/leica-rangefinders-forum/00Bifg

http://www.rangefinderforum.com/forums/archive/index.php/t-106042.html

 

Is a fact that, albeit some area of uncertainess if one goes in depth about standards, "M39" in the optical world is generally applied to the Leica Screw Mount (LSM) mount.

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I often find these sorts of issues, being of Leica interest, as well as astro.

 

You want something like this, or the other way round?

 

http://www.ebay.com/itm/Leica-fit-L39-39mm-LTM-screw-thread-T2-mount-for-rangefinder-/371333262594?pt=LH_DefaultDomain_3&hash=item56752fed02

 

Having just looked and found this, I recognized the Vivitar box and realised I have this same adaptor.

 

But I think you are wanting a fitting with a female M39 thread, and a male M42x0.7, correct? While I'd have the check my Vivitar adaptor, I fear it is "the other way round", typical.

 

I'll keep looking, and PM you if I find anything.

Gary

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Taking the insert part of a cheap l39 to anything adaptor e.g.

http://www.ebay.de/itm/Leica-L39-M39-Mount-Lens-to-Sony-NEX-NEX3-NEX5-Adapter-/250821451991?pt=LH_DefaultDomain_0&hash=item3a661fa0d7

and mounting this into the end pice of a cheap t mount lens should solve the problem.

Edited by duckrider
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