A sharp and small 270 mm lens combo for M mount

[onasj]

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As many of you know, Komura offered a 2x teleconverter for Leica M lenses.  It has a poor reputation, largely because lenses and aperture settings that pass image circles of large diameter through the teleconverter result in muddy, low-contrast, fuzzy images.  But for two lenses in particular, the 90/2.4 (Summarit) and the 135/3.4 APO, it turns out that the Komura teleconverter can work quite well, even wide open, resulting in 180 mm and 270 mm lenses.

You lose two stops of light with any 2x teleconverter, but fortunately the outstanding high-ISO performance of current M cameras—especially the M10 Monochrom—make this limitation much less of a constrained than it would otherwise be.

The Komura teleconverter also needs a bit of... tinkering to improve its focusing performance.  I replaced the too-thin M39-to-M mount adapter that it comes with (causing back focus) with a Fotodiox Pro M39-to-M mount adapter, which not only looks better, but allowed me to carefully sand the back of the Fotodiox adapter until the rotation of the teleconverter was proper when mounted on an M camera, and until it was focusing more accurately with the rangefinder.  Note that critical focus when using this teleconverter is best done with live view and focus peaking.

Attached is a 100% crop of an image taken at 270 mm (135 APO + Komura) on the M10 Monochrom at ~2 m focusing distance, f/3.4 setting on the lens (wide open).  I was surprised how sharp the middle 2/3 of the field turned out to be, even wide open.

135 APO @ f/3.4 setting + Komura 2x teleconverter:

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(More in the next post)

Edited April 5, 2020 by onasj

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[onasj]

And here is the same shot, showing the same tiny 100% crop, but setting the lens aperture to f/5.6:

135 APO @ f/5.6 setting + Komura 2x teleconverter:

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While it is a bit sharper than the "wide-open" image, they are both very sharp to me.

(More in the next post)

[jaapv]

Yes - we've been there before

 

 

[onasj]

And finally, since many 2x teleconverters turn out to result in images of no better quality than the normal image cropped, here is the 135 APO at f/5.6 with NO Komura teleconverter, resized in Photoshop to 200%, then cropped to approximately the same size as the above photos.  The Komura still turns out to be better, somewhat to my surprise.

Trying any lens other than the 90 Summarit or 135 APO yielded much worse results.

135 APO at f/5.6 with NO teleconverter, enlarged to 200% then cropped as above:

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Edited April 5, 2020 by onasj

[onasj]

And here's what the entire 270 mm frame looks like, for reference:

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Perhaps the best feature of this combination is its size; the Komura 2x teleconverter is about the same diameter as the 135 APO, and adds only rough 1 inch to the length of the lens.  They are no longer manufactured but you can get new old stock or used ones for ~$300 online.

 

Edited April 6, 2020 by onasj

[james.liam]

Why put an APO lens on a non-APO TC? 

Want a 360 f/6.4? Then put the 180 R Telyt APO with a 2x APO extender on an adapter to the M. You're showing B&W images but my guess is that color images won't stand up to the test on the Komura. 

[jaapv]

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As shown in my short try-out. With colour images a crop is far better than the converter. The only use of that converter was for slide film.

[luigi bertolotti]

5 hours ago, james.liam said:

Why put an APO lens on a non-APO TC? 

Want a 360 f/6.4? Then put the 180 R Telyt APO with a 2x APO extender on an adapter to the M. You're showing B&W images but my guess is that color images won't stand up to the test on the Komura. 

It's my goal... wasn't it that the 2xAPO is far from being cheap. 😒  (btw... I wonder why somone like CV or chinese doesn't make a 2x for M.... i think it could be succesful... but maybe it's really an out of fashion accessory,,,) 

PS : 360 f 6,8... indeed... same of the last long Telyts... 😉

Edited April 6, 2020 by luigi bertolotti

[james.liam]

3 hours ago, luigi bertolotti said:

It's my goal... wasn't it that the 2xAPO is far from being cheap. 😒  

PS : 360 f 6,8... indeed... same of the last long Telyts... 😉

It is indeed far from cheap but then again, the lenses are far from cheap too. Sticking in junk in between a great lens and a great camera makes little sense.

Yes, my math is off with all the Wuhan virus about. Hope you are well in Brescia, Luigi. 

[onasj]

11 hours ago, james.liam said:

Why put an APO lens on a non-APO TC? 

Want a 360 f/6.4? Then put the 180 R Telyt APO with a 2x APO extender on an adapter to the M. You're showing B&W images but my guess is that color images won't stand up to the test on the Komura. 

Because the only Leica mount lens I have longer than 90 mm is the 135 APO.

Color images are fine with the 135 APO and 90 summarit and this teleconverter.  I used the M10 Monochrom because its higher resolution makes for a more rigorous sharpness test.  If Leica would have released the M10-R I would have used that instead...

[pgk]

If I remember correctly, most teleconverters were available to be used for any lenses, but some were intended for use with specific lenses only and these were called 'matched multipliers'. I don't know how the Komura was intended to be used but my guess is that, in effect, it happens to work optimally with the 90 Summarit and 135 APO. This is probably because of the placement of its optics relative to those of these two lenses. That said, unless the Komura has good coatings, it will probably drop contrast due to the increased glass/air interfaces being added into what is effectively a long lens, so will probably work well enough in good, reasonable contrast conditions but may well not be so good in poorer conditions. I wouldn't write off a cheaper, older teleconvereter because it may well work well with some lenses under certain conditions. Teleconverters were intended for use with longer lenses and in the case of the Komura the only M focal lengths which it would have been intended for use with would have been 90 and 135.

[ardbeg]

While a bigger setup, combining, for example, a 180/2.8 non-APO R lens with a 1.4X R TC, and R to M adaptor will get you to an effective ~250mm f4 at an "affordable" in Leica terms price point. The APO 180/2.8 is of course better but also more expensive.