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Noctilux focussing tolerance with M9


IkarusJohn

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Some of you will recall the advice of many here (Edmond Terakopian for one) that if you buy a Noctilux 0.95 to use with an M9 it is worth getting the lens calibrated to that specific camera.

 

My M9P went off to Solms to have the sensor looked at, so I took the opportunity to send the Noctilux with it. I thought some of you might be interested in the response from Leica:

 

We do not expect any difficulties in general. But as the M9 Sensor is the most powerful sensor in class a’ 1/1000 mm within the tolerance can be seen on the photo. It is a can not a must. I am positive.

 

For my purposes, I find that reassuring.

 

With the rush to higher resolution, more detail, better high ISO performance in each new camera model, there is a risk that we pixel peep, chimp and generally get too excited about marginal differences in gear at the cost of the quality of the final image.

 

I will be very happy to get my own camera and lens back, and to return the loaner kindly provided by the local importer.

 

Cheers

John

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No, this is not quite the issue.

 

Both lens and camera were adjusted to the standard. The issue, discussed previously, is that there are tolerances within that standard (as evidenced by the quote above). Due to the razor thin depth of field of the Noctilux wide open, and particularly at close focusing distances, the entire plane of best focus can fall outside the tolerance of the camera's calibration.

 

Put another way, both lens and camera may meet the calibration standard, but the tolerances of both are such that the lens may not focus correctly. So many people recommend that the Noctilux and M9 should be calibrated together - they will both remain within the tolerances set by the standard - what is required is a fine adjustment.

 

I did comment that I hoped that any adjustment would not cause problems with my other lenses - I'm assured not.

 

The quote simply comments that if you look for it, you might be able to detect a 1/1000 mm deviation from exact focus - in other words, don't go looking for it.

 

My sensor did turn out to be faulty and has been replaced.

 

Cheers

John

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1/1000th of a millimeter-, 0.001mm, or 1micron. Within the band of near-Infrared light. The 50APO Summicron is stated to be 125LP/mm, which would require a 0.004mm (4micron) wide pixel to resolve. The width of the pixel on the KAF-18500 is 0.0068mm, 6.8micron.

 

I'm sure that the test equipment used at Leica to align the detector can measure 0.001mm differences. Using the camera with Photographic lenses, even pixel-peeping- I'll settle for getting the shim within 0.01mm.

 

7187990803_f89606e9ff_c.jpg

Dewdrop, 1936 CZJ Sonnar 5cm F1.5, wide-open by anachronist1, on Flickr

 

7600463728_4968da317e_z.jpg

100% crop, F1.5, 1936 Sonnar converted to Leica Mount by anachronist1, on Flickr

 

This conversion was pretty close.

Edited by brianv
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I am not sure the shim correlates 1:1 to an object in close range. My understanding is the ratio unfortunately favours a greater shim accuracy requirement, the focus patch has to move from say 1m to 500 effectively with a few mm of movement via a twist of the lens barrel. I am also not sure how linear it is, I suspect not very.

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For a 50mm (51.6mm) LTM lenses: the movement of the optics is 1:1 with respect to the RF cam. Later M-Mount 50mm (nominal) lenses use an indexed cam that is "almost" 1:1 to correct slight differences from 51.6mm. Positioning the shim accurately for a 50mm lens is equivalent to shimming the detector. For lenses other than 50mm- it is not 1:1.

Edited by brianv
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Also have they said anything about the faulty sensor? Why it was faulty?

 

No idea. It looked like something sprayed across the top of the sensor had baked on. Here is the report:

 

Physical work comprised:

Replace sensor

Adjust sensor

Adjust range finder

Clean range finder

Adjustment of all parts

Cleaning and end control

 

I will test all my lenses when I get the camera back - probably a few weeks away as it needs to clear German customs.

 

Cheers

John

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A difference in the placement of the sensor by 0.001mm for a 50mm (51.6mm) Leica lens, or the change of the main shim of a 51.6mm makes a difference of ~0.08mm in focus at 0.9meters.

 

 

at 0.9m- perfect focus.

1/51.6mm= 1/(900mm)+ 1/(backfocus)

0.019380mm= 0.001111mm+ 1/(backfocus)

0.0182688mm= 1/(backfocus)

Backfocus= 54.7380mm

 

Add 0.001mm to back-focus,

 

Backfocus= 54.739

1/51.6= 1/(distance)+1/(54.739)

0.019380= 1/(distance)+ 0.0182651

1/(distance)= 0.00111133

distance= 899.819mm

 

The focus of the lens would change by 0.081mm when the shim is increased by 0.001mm.

 

This is the formula for focal length. I use it to in this manner to compute the change in the thickness of a shim that a lens requires to correct the focus.

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1/1000th of a millimeter-, 0.001mm, or 1micron. Within the band of near-Infrared light. The 50APO Summicron is stated to be 125LP/mm, which would require a 0.004mm (4micron) wide pixel to resolve. The width of the pixel on the KAF-18500 is 0.0068mm, 6.8micron.

 

I'm sure that the test equipment used at Leica to align the detector can measure 0.001mm differences. Using the camera with Photographic lenses, even pixel-peeping- I'll settle for getting the shim within 0.01mm.

 

 

This conversion was pretty close.

 

The Leica factory visit video showing M9 construction and testing shows and discusses this....

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Took a couple of test shots in the office - not ideal; no tripod, ugly fluoro lighting. I guessed 45 degrees hand held, set the shortest focusing distance and rocked back and forth till I was pretty sure the centre line was in the best plane of focus.

 

Here it is at f/0.95. A second image at f/2 was crisper (obviously) - I'm happy.

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