Focusing accuracy from an operational point of view

[wda]

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Leica cameras are renowned for their ability to produce extremely sharp images, when desired, and for their mechanical qualities. Many threads major on lens performance. I would like to raise the operator angle.

 

I have used M-cameras for nearly fifty years and still own my original M3 and 50mm Summicron. Progression through later models has peaked with an M9 which is more sensitive to focusing accuracy. Generally any focusing failures or reduction in expected sharpness I have attributed to user-error. However recently I have begun to suspect another factor, viz. lack of appropriate frictional resistance within the focusing mechanism.

 

Two lenses in particular have aroused my suspicion; a current 28mm Elmarit and a current 35mm Summicron when used at full, i.e. maximum aperture. (The effect is obscured once the lenses are stopped down to normal working daylight apertures). At first I thought that it was a classic camera rangefinder error and was preparing to return the camera for recalibration. I might still have to do so. But yesterday I noticed how easy it is to dislodge the focus setting between the act of focusing and actually taking the photograph. Only a minor disturbance takes the lens focus setting away from the correctly focused position. So this raises the question, how much friction should there be in the focusing mechanism of Leica lenses?

 

Clearly it depends on the lens construction. Some complex mechanisms exert their own intrinsic ‘braking’ during focusing with certain lenses requiring rather more force to focus. However the two lenses mentioned above, 28mm and 35mm current, have extremely light focusing and it is very easy to disturb a setting inadvertently.

 

I would welcome members’ thoughts and experiences on this issue, in particular with smaller lenses such as those cited. (I have no such problem with my 75mm, 90mm or 135mm lenses). Thank you.

[Lindolfi]

A very important issue you raise there. Apart form miscalibration and from not overlaying the images in the rangefinder correctly, focus errors may occur due to offset movements from the correct focus due to a low friction of the focus ring.

 

The focus friction of the lens however is not the only issue that influences possible faults. There is also the focus hand, the fingers, the orientation of the fingers, the other hand, the arm postures and whole body posture that influences possible focus errors. Then there is movement control issues and tremor of the fingers and hand. All in all it is a complex matter. I'm trying to say there are ways to make focussing with a low friction lens like the 35mm summicron easier. For instance lean the base of your left middle finger to the housing of the camera, so that you remove any unwanted movements of the hand from the focus action. You can even press the second segment of you middle finger to your index finger, to further reduce unwanted movements. Experiment with it to reduce errors would be a way to go. Hope this is of use to you.

[TomB_tx]

Certainly a valid observation that it is easy to nudge the focus unintentionally. I've also use Ms since the 1960s, and I think a lot comes down to technique. Once you move to a TTL meter (M5 and up) you tend to tweek the exposure more just before capture, while with external meters you generally set exposure first and then just handle focus and framing. The more you do after focus, the more chance of bumping the focus off.

A good lens has very little "stiction" - meaning the "break-away" friction from fixed position is no greater than the moving friction of the focus mechanism. That makes it easier to make fine adjustment, but also easier to shift it unintentionally. A lens with stiction stays in place better when set, but but can be hard to set exactly.

I've experimented with different types of grease when cleaning and lubing old lenses, and I prefer a lighter TFE grease for low effort and no stiction, which is what Leica now uses. Others do prefer a stiffer action, and a camera tech can easily switch to a different lube if you want it stiffer.

[01af]

However recently I have begun to suspect another factor, viz. lack of appropriate frictional resistance within the focusing mechanism.

Resistance sure is an important factor but there's another factor compromising effective focus accuracy that is at least as significant, if not even more so—focus throw.

 

Too many clueless users are confusing shorter focus throw with quicker focusing, so Leica feels encouraged to shorten new lenses' focus throws more and more. The culmination of this distressing development so far is the Apo-Summicron-M 75 mm Asph lens which is so ridiculously short to focus it's next to impossible to adjust it in really fine increments. With this lens, I developed the habit to do the fine-adjustment by swaying my body a bit back and forth rather than trying to turn the ring. Furthermore, the focusing ring is so stiff it's almost jerky.

 

When the focus ring's resistance is just right, i. e. not too stiff and not too light, then an extremely short focus throw will tend to be less of a problem (albeit 'less' is not the same as 'not at all'). For example, the Summarit-M 75 mm's focus throw is almost as short as the Apo-Summicron's but still it's easier to focus due to optimal resistance. However the Summilux-M 75 mm is yet easier and quicker to focus due to the long focus throw. Sure—switching from 0.8 m to infinity will take an extra second ... but typical focusing from one shot to the next is much quicker when the coordination of hand, rangefinder, and eye is so much more relaxed due to a longer focus throw.

 

I really wish Leica would stop making these ludicrously short helicoids and return to the ways they did it ten or twenty years ago.

[pico]

David, I was thinking of exactly that yesterday while using the Canon 50mm F/.95. This particular one has stiff (not jerky) focusing and I believe it actually helped! Once in-focus I could more confidently move the camera. OTOH I got a Summilux 35mm V2 and with the locking tab I mess-up sometimes because it slips (rather, I let it slip.)

 

(The other Canon 50mm F/.95 is much more free to turn. Variances prevail.)

[stephan_w]

I made several tests on several lenses, most from 50-90 mm range, on a 3 m distance. Each lens was focussed 10 times, at random. The results surprised me: All lenses varied +/- 5 cm in focus, which can be seen as an user - error.

 

On the other hand, our "M-AF-System" is only as good as the eyes behind the camera. Well, I still will continue to use Summiluxes, but sold my Nocti.

 

It maybe not a bad advise to test our own focus abilities.

[Lord Fluff]

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Apo-Summicron-M 75 mm Asph ...... the focusing ring is so stiff it's almost jerky.

.

 

FYI, I have this lens too and the focussing is smooth and with correct gentle resistance throughout the range - sounds like that one needs looking at.

[wda]

I made several tests on several lenses, most from 50-90 mm range, on a 3 m distance. Each lens was focussed 10 times, at random. The results surprised me: All lenses varied +/- 5 cm in focus, which can be seen as an user - error.

 

On the other hand, our "M-AF-System" is only as good as the eyes behind the camera. Well, I still will continue to use Summiluxes, but sold my Nocti.

 

It maybe not a bad advise to test our own focus abilities.

Stephan, I went through this routine during my long period of fruitless diagnosis and found similar results to you. The tabbed lenses seem to be more vulnerable to accidental 'nudging' between focusing and exposure. I am now modifying my grip to minimise this trait.

[Stateowned]

i must say its not too bad..

 

i think the variations you are talking about are more important when using a summilux/noctilux lens or lenses with higher focal points then 50mm..

 

with my 28 cron i rarely have a miss.. the natural DOF makes sure the bit i want is nice and crisp.. ofcourse i cant be off by miles but a its got some play..

 

the 50mm cron i just purchased is a bit more tricky so i have yet to figure that out.

[Guest #12]

I have read a couple of complaints about the S-lenses being "too stiff due to the weather-sealing."

[wda]

Thank you #12. I would not like my lenses to be too stiff to focus. I think mine are about right, but two need care not to nudge the focusing tabs especially when holding an M vertically.