APO 75 focus tab scale question

[otho]

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I recently bought AA75. Perfect quality image, no focus shift at all - no back or front focus. Love this lens!
My question concern distance scale on focus tab. Red colour marked little decentering of inscription in my copy (form left: CV Ultron 21, AA75, AA90).

 

 

Decentering on AA75 is slightly biggest, than on other lenses (my LUX 50 Asph. FLE haven't any visible decentering). Infinity mark is in the right place. I searching on internet, but without results in that theme.

Is it normal / standard behaviour of AA75?

[rodoleica]

I recently bought AA75. Perfect quality image, no focus shift at all - no back or front focus. Love this lens!

My question concern distance scale on focus tab. Red colour marked little decentering of inscription in my copy (form left: CV Ultron 21, AA75, AA90).

 

 

Decentering on AA75 is slightly biggest, than on other lenses (my LUX 50 Asph. FLE haven't any visible decentering). I searching on internet, but without results in that theme.

Is it normal / standard behaviour of AA75?

On my Apo-Summicron-M 1.2/75 Asph, serial N° 4044602 I see exactly the same decentering. What is the reason ?

[jdlaing]

It's not decentering. It just focuses a little shorter that the minimum marking.

you boys are a little obsessive.

[otho]

you boys are a little obsessive.

:)

Thanks

[spydrxx]

Infinity is supposed to line up...the rest is more or less close enough. Jdlaing hit it on the head.

[adan]

In the distant past, Leica only guaranteed calibrated rangefinder focusing to the shortest engraved distance (feet or meters), but allowed a little extra movement.

 

Thus the paper specs list the engraved distance as the minimum focus - in the case of the 75, 0.7 meters

 

It is not "decentered" - it just means the lens actually focuses to 0.67 meters or so. Just think of it as a little extra close-up gift from Leica.

[otho]

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Thanks a lot

[otho]

Another question: when focusing to nearest distance, the focus ring is bit stiff and little bit noisy. Is it normal according to FLE mechanism?

[a.noctilux]

Our Apo-Summicron-M 75mm has smooth and silent focussing at all range.

[otho]

I mean, when I quickly turn focus ring to minimum distance, there is some subtle noise like air drawn by that lens. My AA 90 or Lux 50 asph. haven't symptoms like AA75... It doesn't affect image quality at all.

[otho]

Above case take place especially when I focusing APO 75 lens vertically (with lens hood on top).

[adan]

Some subtle noise is natural (take the caps off the backs of your 90 and 50, and focus them near your ear....). There are moving parts inside, after all. They rub against each other. Mine is about equal to the noise from my 90 Elmarit or 135 Tele-Elmar, on average.

 

Turning to minimum distance increases the internal volume of the lens, (rather quickly due to the short focus throw - distance on the focus ring from infinity to 0.7 meters) so it most certainly is sucking in air as it "grows" and breathes. Mine is louder when the back opening is covered (on body or with lens cap) and air is sucked through the narrow crack. But air is likely drawn in through all the "seams" around the aperture and focus rings.

 

(The Fuji-X 18-135 expands massively when zoomed, and is weather-sealed - so it actually has three little pin-hole air vents built in near the base, so that suction/vacuum won't interfere with the zoom movement. Some Canon zooms acquire horrible internal dust problems because of all the air they suck in and out when zoomed).

 

The focus helical for the 75 ASMA has more threads/teeth/ribs than most other M lenses, 1) for the long travel needed to get down to 0.7 meters, 2) for the additional threads needed to move the FLE, and the focus cam on the back (see cutaway view below from Leica spec sheet). More threads = more surface area to rub.

 

Focusing the lens pointed vertically puts more force on the helical thread surfaces, since you are "lifting" the weight of glass and brass against the force of gravity. Again, more "normal force" causes more friction causes more noise.

 

The threads are lubricated, and lubrication wears out eventually. It may just be time for a re-greasing. But some noise - in excess of simpler lens constructions, is normal.

 

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[otho]

Thanks a lot for detailed answer.

[otho]

A few technical informations about APO 75 & generally behaviour of focusing ring in case of Leica-M FLE lenses:

 

http://www.l-camera-forum.com/topic/176588-got-a-new-summilux-35mm-fle-stiff-focusing-ring/

 

http://www.l-camera-forum.com/topic/163991-focusing-accuracy-from-an-operational-point-of-view/

 

http://www.l-camera-forum.com/topic/145011-summicron-75-jerky-focussing-at-low-temperatures/