M9 + Lens Focus Setting

[tobey bilek]

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The two distances to check are infinity and I meter from the sensor/film plane. Those are the two calibration points and the only two distnces that need checking.

 

Get one of the aluminum meter/yard sticks at Home Depot and set the 18" mark at one meter from the sensor.

 

A star is good for the infinity check. The moon has issues because of atmospheric causes aberations. People use it, but I never do.

 

Both lenses and bodies can be off. They can both be off in opposite directions thus cancelling each others error, Therefore what you believe to be perfect may not be perfect.

 

They can both be off in the same direction and the error is too greater than either.

 

With only one camera body, there is no way to tell if it is correct or not unless you have a known "perfect" lens.

 

You may end up having to have the whole kit checked.

[jaapv]

Stephen, a number of the newest Leica lenses are diffraction limited wide open. The first lens Leica managed to produce was the Apo-Telyt R 280/4.0, followed by the Apo Summicron M 90 asph and the R modular system. I have no information on the following designs, but I would not be surprised if the Summicron M 75 and Summilux M 50 asph were in that group as well.

[hoppyman]

The point of this example was to show the accuracy of the focus adjustement of my lenses on my cameras. The sharpest plane is on the stem which is exactly where I focused. The flower is slightly inclined towards the camera (the stem's not vertical) so that the plane of the top of the stem is just behind the plane of the centre of the flower. The elements of the flower itself show the area of acceptable DoF well, I think.

 

So you're welcome to question my artistic judgement on where to focus it was just shot as an example. I'm not convinced that the plane of sharpest focus belongs in the centre of the acceptable DoF of the largest aperture though (nor that Leica designs/adjusts them that way). That is personal and anecdotal though. We need to sit with Peter Karbe over a coffee and get educated.

Same lens at f/4 or so

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If the camera and lens are adjusted to account for near and far limits of DOF, and you focused on the stem...best focus would be on the stem. If the DOF is averaged, best focus would be in front of the stem by an insignificant amount. In any case, in this example the difference is only 0.039mm (near limit is 694.812mm and far limit is 705.266mm; CoC=0.03mm).

 

I have always assumed that for practical reasons, when adjusting lenses/cameras, best focus is taken to be the midway point of the DOF. This is what I have heard second-hand about Leica practices. In most cases it wouldn't matter; in the rather extreme case of the poster's 21 at f/1.4, 1.0m, the difference between the two adjustments is about 9mm. So the question is not altogether unimportant.

[Guest trond]

The focal point of a decent lens can be close to the diffraction limit which would be a few micrometers at most at largish f/values. It would be interesting to know how close Leica glass is to the ideal.

 

Dear Steven

 

I believe to have heard that there is a common consensus, that current state of the art lens design can cope with a pixel pitch of around 5 micron on a 35mm full frame sensor.

 

I think also Peter Karbe mention 5 micron in Michael Reichmann´s video interview with Peter.

 

This means that we are a-okay for M10, but need new lenses for M11

 

I have tried the Canon 7D, which has a pixel pitch of just over 4 micron. It is quite clear that even expensive Canon L-lenses cannot cope with the resolution of this sensor.

 

I think we are very far from reaching the diffraction limits, at least on the fast Leica lenses. The Airy disk diameter of a f1.4 lens on a 35mm system, is only 1.9 micron. If we again use 2X the pixel pitch as the limit for sharpness, this means that diffraction will not be reached until we get a 250 megapixel sensor on a 35mm system!

 

Erwin Puts, in his recent test of the resolution of a high resolution B&W film, using the 24 mm Elmar, measured the resolution to be in the range of 160+ lp/mm. This is more than double the linear resolution of the M9 sensor.

 

Best regards

 

Trond

[Guest mc_k]

...I'm not convinced that the plane of sharpest focus belongs in the centre of the acceptable DoF of the largest aperture though (nor that Leica designs/adjusts them that way). That is personal and anecdotal though. We need to sit with Peter Karbe over a coffee and get educated.

...

 

thanks, that would be good info. My comments had to do with how adjustments get done, nothing else. This issue came up when the M8 came out--the two ways of splitting the depth of field was said to explain why more cameras were back-focusing than front-focusing. That is, users tested one way and Leica adjusted another. (Not my opinion, but that of others.)

 

If you're using something like one wine bottle for a target, obviously you're testing for the plane of best focus. With a ruler or chart it is not always so obvious. Sometimes someone posts a test, and 3-4 people read it differently; I have seen this happen more than once.

[SJP]

Hi Trond,

 

Thanks for the info re. diffraction that is achievable. As you seem to be one of the rare species that actually likes this sort of stuff I thought I should post a link to my scribblings on this matter here. I wrote this a few years ago to sort this stuff out to my own satisfaction - discusssions on crop, effective focal length & what have you were all over the place at that time.

 

pdf file comments & suggestions are welcome

excel thingy for DoF and IR focus (password is "leica" if you want to look under the hood)

 

Enjoy

Stephen

[Guest trond]

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Dear Stephen,

 

I am just back from San Francisco, more than 20 hours on an airplane is not my kind of fun!

 

Yes, I think these things are interesting, I am an engineer and super geek

 

I will read your documents with interest.

 

Best regards

 

Trond

[SJP]

Strength:D, as said comments or points requiring clarification are welcome

[Guest trond]

There is a parallel discussion going on in this forum on the same topic in the thread below:

 

http://www.l-camera-forum.com/leica-forum/leica-m9-forum/115034-rangefinderproblems-new-m9s-8.html

 

This cased me to loose a little faith in Leica´s quality procedures.

 

What different posters seem to have experienced with their lenses focus calibration seem nearly like a random process to me.

 

At least in the past before computer assisted calibration like the one shown in Michael Reichmann´s video from the M9 factory tour.

 

I think this explains why so many Leica users hav had to send their lenses back to Leica for calibration.

 

Hopefully this problem will become history with the introduction for the computer assisted focus calibration now at work in Solms.

 

Best regards

 

Trond

[SJP]

Maybe the lenses are OK and the users need calibration:D

 

More seriously, focussing with a rangefinder is not easy and kind of grows on you, so I would not at all be surprised if there are minor differences between camera's. The first camera that allowed immediate feedbck is the M8 (OK OK there was an Epson) and so it was the first time you could check immediately, not always confirming perfect focus. I understand that it is advisable to focus from infinity downwards, without "hunting for focus". this may imply that there is a certain amount of play in the whole mechanism, in fact it is amazing there is so little focus play as it stands.

 

When I first got my TE90/2.8 I had a hard time focusing the thing, now I am just fine, but no adjustments were required except my brain and the lens getting acquainted (apparently, I have no other explanation).

[Guest trond]

Maybe the lenses are OK and the users need calibration:D

 

Probably a bit of both!

 

I always check out a new lens using the LensAlign Pro, which I find to be very accurate and straight forward to use, compared to shooting a real subject.

 

I have also experienced that there is a certain amount of play or slack in the focus mechanism, both on manual focus and AF lenses. However, much less so no Leica lenses, which to my experience is really tight.

 

Even so I have found that focusing from infinity towards the subject, gives the most accurate and repeatable results.

 

For calibrating an AF lens this is absolutely necessary in order to get reliable results.

 

I recently tested the new Canon TS-E 24mm f3.5 II. This manual focus lens puts the focused distance in the camera EXIF data, with a resolution of one micron.

 

Those Japanese engineers must have a really strong ego and self confidence!

 

However, I calibrated the lens at 25X the focal length i.e 0.6 meters, by mesuring the distance from the camera film plane mark to the LensAlign focus target.

 

The camera EXIF shows a distance of 597mm, which I think is quite incredible!

 

I think it would be possible for Leica, in a future M camera to put such kind of electronically assisted manual focus in the camera.

 

Best regards

 

Trond