Telyt ∞ adjustment

[k-hawinkler]

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Correctly adjusted M-bayonet lenses are spot on for infinity focus as well.

For 200, 280, 400, and 560 mm Telyts on Visoflex III and M9, what is the expectation for proper ∞ adjustment?

Should it be on the infinity mark? Or should it leave some play for thermal expansion or contraction of the Telyts in question?

 

Thanks, K-H.

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[jaapv]

A totally different situation - the focussing is SLR style - so any inaccuracy of the lens is automatically compensated for, as long as your Visoflex is adjusted properly - which most are. In general many long lenses adjust beyond infinity

[Michael Geschlecht]

Hello K-H,

 

To add to what Jaap said: By allowing the lens to focus beyond infinity it makes it easier to rack back & forth when visually focussing just before infinity.

 

Best Regards,

 

Michael

[k-hawinkler]

Thanks Jaap and Michael,

 

Well, that's how my long Nikon lenses work as well.

It's just very convenient, when it's getting too dark to focus, to be able to rely on the ∞ setting.

 

Best, K-H.

[k-hawinkler]

I would like to rephrase my question to:

 

"Is thermal expansion and contraction of a Telyt severe enough so that it requires wiggle room in order to be able to focus at ∞ for a variety of temperatures?"

"Or, has the Telyt, through use of appropriate materials, been managed to a degree that the stop can be set at ∞ without limiting the ability to focus?"

 

If the latter case were true, I would have the Telyt set that way and would be able to focus at infinity with a hard stop.

 

Best, K-H.

[jaapv]

Well, the follow-focus Telyts don't have distance markings anyway and setting to infinity might work with the 200 and maybe even 280 - but expansion will take place. All materials will expand when heated, except ice when melting, so there is probably no possibility to counteract this effect with choice of material.

[Robert_M]

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This discussion of thermal expansion effects is true in theory, but I don't believe any user will see it in actual use. Let's work the numbers.

 

Most metals have a CTE of about 20 ppm per degree C. Specifically, AL=23, brass=19, Stainless 17, and Mg 26. I'll take the 280mm Telyt as an example and figure on about 250mm nominal length between the optics and focal plane. For environmental extremes, let's assume 30 deg C temperature range. That works out to a length change of the system of about 0.15mm.

 

The thread pitch on the 280 lens seems about 50mm per turn. The above length change then works out to about a 0.7mm change at the focus scale on the lens focus ring. (I'm going by memory on a few of these dimensions, so the numbers are rough). I'd contend that most of the users will have a very difficult time seeing a change in focus on the ground glass focus screen to that precision when focusing at infinity and moving the focus ring back and forth by 1/2 mm. If you can do that, you eye sight is superior! Certainly beyond my 20/20 corrected eye sight (with contact lenses).

 

So my recommendation (and my action) is contrary to the above posters. I adjust the infinity point as near as possible on my 280 Telyt v3 to be exactly at infinity on the scale. I do this on the M9 by taking shots with slight focus changes and then enlarging to 1:1 on the screen.

 

The focus ring on the 280 Telyt is made to allow this adjustment. There are 3 set screws on the focus ring which set into a brass groove under it (on the ring that actually turns the focus stage). By loosing these screws, one can adjust the scale on the lens without moving the lens.

 

I do NOT recommend doing this unless you are adventurous and know what you are doing! But this is something that a service tech could easily do. But having given that caution, it is not a difficult task if you are mechanically inclined.

 

Anyway, my 280/4.8 v3 is spot on at infinity. And living in the desert SW USA, I have clear, still skies which allow me to focus on rocks and trees at 10 km away (nearby mountain range). At infinity, I can see features down to the gsd (ground sampling distance) corresponding to the pixel pitch on the sensor.

 

BTW, thermal expansion IS a major issue for very large optics. And there are specific materials used for certain applications in that field. Invar is a special Ni-steel which has a CTE of 1 ppm/K. SiC is also low. And Carbon Fiber composites can be designed with almost 0 CTE. Also, there are special glasses and ceramics used in large mirror manufacture with near 0 CTE (ie, Zerodur, and ULE).

[Robert_M]

Another practical example occurred to me. I have a very clean 135/4 tele-elmar lens from the last series with removable lens head. Using it as a rangefinder lens, it is incredibly sharp at infinity when looking 5-10 km distant. The limit in resolution is the sensor pixel pitch on a clear day here.

 

Now, I can take the exact same lens head and mount it on the correct visoflex focus helicoid and visoflex III. The viso helicoid is made to focus past infinity so that various lens specs can be accommodated (there is a tolerance in the exact focus distance). So to focus at infinity, one must use the glass screen and not just an end stop. It is hard to get as precise of an infinity focus with this arrangement than the carefully calibrated end stop of infinity on the rangefinder mount.

 

And let me assure you that the viso screen is calibrated correctly. And, I also can check these statements by focus bracketing and then checking the 1:1 image.

 

Bottom line is that one can not focus as accurately at infinity with the glass screen as optical lab equipment can be used to preset and calibrate the lens at an infinity stop.

[k-hawinkler]

This discussion of thermal expansion effects is true in theory, but I don't believe any user will see it in actual use. Let's work the numbers.

 

Most metals have a CTE of about 20 ppm per degree C. Specifically, AL=23, brass=19, Stainless 17, and Mg 26. I'll take the 280mm Telyt as an example and figure on about 250mm nominal length between the optics and focal plane. For environmental extremes, let's assume 30 deg C temperature range. That works out to a length change of the system of about 0.15mm.

 

The thread pitch on the 280 lens seems about 50mm per turn. The above length change then works out to about a 0.7mm change at the focus scale on the lens focus ring. (I'm going by memory on a few of these dimensions, so the numbers are rough). I'd contend that most of the users will have a very difficult time seeing a change in focus on the ground glass focus screen to that precision when focusing at infinity and moving the focus ring back and forth by 1/2 mm. If you can do that, you eye sight is superior! Certainly beyond my 20/20 corrected eye sight (with contact lenses).

 

So my recommendation (and my action) is contrary to the above posters. I adjust the infinity point as near as possible on my 280 Telyt v3 to be exactly at infinity on the scale. I do this on the M9 by taking shots with slight focus changes and then enlarging to 1:1 on the screen.

 

The focus ring on the 280 Telyt is made to allow this adjustment. There are 3 set screws on the focus ring which set into a brass groove under it (on the ring that actually turns the focus stage). By loosing these screws, one can adjust the scale on the lens without moving the lens.

 

I do NOT recommend doing this unless you are adventurous and know what you are doing! But this is something that a service tech could easily do. But having given that caution, it is not a difficult task if you are mechanically inclined.

 

Anyway, my 280/4.8 v3 is spot on at infinity. And living in the desert SW USA, I have clear, still skies which allow me to focus on rocks and trees at 10 km away (nearby mountain range). At infinity, I can see features down to the gsd (ground sampling distance) corresponding to the pixel pitch on the sensor.

 

BTW, thermal expansion IS a major issue for very large optics. And there are specific materials used for certain applications in that field. Invar is a special Ni-steel which has a CTE of 1 ppm/K. SiC is also low. And Carbon Fiber composites can be designed with almost 0 CTE. Also, there are special glasses and ceramics used in large mirror manufacture with near 0 CTE (ie, Zerodur, and ULE).

 

 

Hi Robert,

 

Many thanks for the great feedback. You sound like an astronomer from Kitt Peak or a similar good site for observations. I am in Los Alamos, so we are practically neighbors.

 

Based on your feedback, I would divide the Telyts into two groups.

 

• There are the 200 and 280 mm Telyts with distance markings. Provided your information is correct (I have no reason to doubt it) then those Telyts should be adjusted with ∞ spot on. That certainly would be more accurate than using my aging eye sight.

 

• AFAIK, the 400 and 560 mm Telyts don't have distance markings. However, those Telyt heads used with the Televit grip could be adjusted (set for ∞) with a stop knob on the grip for drastically varying temperatures.

 

Thanks again.

 

With best regards, K-H.

[k-hawinkler]

Another practical example occurred to me. I have a very clean 135/4 tele-elmar lens from the last series with removable lens head. Using it as a rangefinder lens, it is incredibly sharp at infinity when looking 5-10 km distant. The limit in resolution is the sensor pixel pitch on a clear day here.

 

Now, I can take the exact same lens head and mount it on the correct visoflex focus helicoid and visoflex III. The viso helicoid is made to focus past infinity so that various lens specs can be accommodated (there is a tolerance in the exact focus distance). So to focus at infinity, one must use the glass screen and not just an end stop. It is hard to get as precise of an infinity focus with this arrangement than the carefully calibrated end stop of infinity on the rangefinder mount.

 

And let me assure you that the viso screen is calibrated correctly. And, I also can check these statements by focus bracketing and then checking the 1:1 image.

 

Bottom line is that one can not focus as accurately at infinity with the glass screen as optical lab equipment can be used to preset and calibrate the lens at an infinity stop.

 

 

Hi Robert,

 

Thanks for these excellent points. I have the TE 135/4 as well and use it on my M9 and with an appropriate focusing mount and adapter on Nikon cameras. Your feedback clearly suggests to use the properly adjusted TE 135/4 as an M-bayonet lens and not as a Visoflex lens for ∞. I had been practicing this already. I find I can get pretty good focus on my M9 using the combination of the 1.4x and 1.25x magnifier.

 

Of course, for macro work, this lens works very well on the Bellows II and Visoflex III.

 

Thanks again.

 

Best, K-H.

[jaapv]

It is indeed excellent for macro. I find the lens easy to focus on both M9 and M8 without any magnifier, in fact it focusses better without for me.

[Robert_M]

I recently picked up a used 200mm f/4 Telyt lens to play with on the Visoflex III with M9. The lens is very clean optically but the focus ring needs some adjustment. The ring can go about 5 mm past the infinity mark. A quick check of the lens focusing shows that it is the ring which needs adjustment so that the stop is at infinity, not beyond. Someone must have severely mis-adjusted this in the past.

 

I've previously adjusted my 280mm f/4.8 v3 lens for proper infinity adjustment (as I mentioned above). Thought I'd do the same with this 200mm lens. However, the construction is different on the 200mm lens and it is not really obvious how one does the adjustment. Does anyone have a service manual picture blowup of this lens and how to disassemble? Or, can anyone tell me how to disassemble the focus ring?

 

I'm guessing that one needs a pin-spanner type tool to remove the chrome ring at the bottom of the focus know (marked with the distance scale). Will that then expose screws to free up the focus know proper (to allow adjustment of the knob)?

 

Any help would be appreciated. Thanks.

 

RM

[tobey bilek]

On my 200 &280, infinity is infinity and I never had a problem.

 

The lens does not rotate past infinity.

[UliWer]

Same for my 4/200 an 4,5/200.

[Robert_M]

Yes, I believe that is how it should be! In fact, I've done some careful exposures and find that the distance indicator ring should be adjusted very slightly (about 1-2 mm to the left of infinity). But my question remains: Does anyone know how to adjust???? How to disassemble???

 

RM

[ho_co]

Robert, sorry, I'm no lens technician. But I do want to add another point on thermal expansion, in support of what you said.

 

To my knowledge, Leica never used a "thermal expansion" argument to explain any peculiarities on any Viso lenses. The first company I remember doing that was Canon, with their 400/2.8 IIRC.

 

In other words, Leica kept the lenses more compact for quick hand-held work. With the 400 and 560 Telyts, they did this with simple optical designs and very direct mechanical designs. By keeping the diameters relatively small (f/5.6, later f/6.8), they had no need to annoy the photographer with focusing "past infinity." Infinity stop and optical infinity were the same on all, without slack. (The macro and bellows mounts are a different story.)

[Washington]

Thanks all for this fascinating and very informative thread. I really have nothing to add

and it was more fun to listen than speak.

Odd tool it would be to grab the .056’’ hole on the beveled distance scale ring on the

200 Telyt! But, that may be the way …. I just don’t know either. Cheers!