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Visoflex with M8


Michael Jones

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I have been using the Visoflex III on my M8 with a 280mm Telyt.

At medium distances, I have had no focus issues that I could detect.

However, this weekend while trying to capture some bald eagles in the

wild, I noticed that when close to infinity focus at full aperture, the focus

is definitely off. I have to move the focus of the lens more toward infinity

to get a sharp image on the M8 sensor. Has anyone else experienced this?

Is it some change in sensor distance vs. Film Ms? The Viso is not coupled

so it seems to be a matter of distance to the focus ground glass vs. Distance

to the sensor. Any thoughts or method to correct this?

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Michael,

 

If you have no focusing problems at medium distances, the ground glass / sensor / lens flange distances must be correct. By the nature of its design, it is impossible for the Visoflex / camera combination to focus correctly at one distance and be off at others.

 

The 280 Telyt distance scale will turn past infinity, to allow for expansion in high temperature environments. The only answer to your issue I may have is that you inadvertently turned the focusing mount to full stop, past the infinity mark. This will of course render objects at infinity unsharp, because you would have in effect focused ‘past infinity’.

 

Best,

 

Jan

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Jan,

 

Thank you for your insight. Based on your post, I retested the visoflex / lens combination again at middle distances at light levels to use the full aperture. I discovered that indeed, I had the same focus problem at middle distances! I did not notice this before because all of my shots were in bright sun and I was using a smaller aperture so DOF was probably covering the error.

 

After some very careful testing and study, I determined that when the Visoflex is in focus, the focal plane for the camera is actually shorter than the actual sensor distance. I came to this conclusion because if I back the camera away from the Visoflex even a millimeter or two, the focus gets worse, not better. So, I theorized that if the ground glass were a mm or two further from the mirror, that would move the focused image to the actual sensor position.

 

Studying the mounting of the ground glass, I discovered that Leica has placed several shims of different thickness under the ground glass mounting frame. I was able to remove this frame and count 3 shims, each of a different thickness to properly bring the image to correct focus. I replace the assembly but left a space of 0.5mm as if I had another shim in place just as a test. PERFECT ! The image on the ground glass and the image from the camera are finally identical! So, I must shim the ground glass up about 0.5mm to make this work properly on my M8.

 

The chance of finding extra Leica shims is probably not very good but if anyone has a Visoflex III in very poor or incomplete condition, I could use the shims! In the meantime, I am searching for material to try and make my own using one on the Visoflex III as a pattern. Amazing what a difference a half millimeter can make.

 

Best Regards,

 

Michael

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If the Visoflex was correctly assembled in the first place, it seems extremely unlikely that the relative positions of the lens flange and focusing screen could have shifted enough to require a 0.5mm correction.

 

But you would get very much the same symptoms if the mirror is out of adjustment and doesn't lower quite as far as it should into the viewing position. I think it would be a good idea to check that before shimming the focusing screen.

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If the Visoflex was correctly assembled in the first place, it seems extremely unlikely that the relative positions of the lens flange and focusing screen could have shifted enough to require a 0.5mm correction.

 

But you would get very much the same symptoms if the mirror is out of adjustment and doesn't lower quite as far as it should into the viewing position. I think it would be a good idea to check that before shimming the focusing screen.

 

Yes, it is highly unlikely that the front to rear flange to screen distances of the Visoflex are not correct. The mirror and the shims are the only variables in the set up and I would also make certain first that the mirror is all the way down before adjusting the shims. Short of taking my Viso III apart again, I don't recall there being shims below the screen. If I recall, there are springs above the screen to hold it in place.

 

The mirror stop in the mirror box is an excentric (?) screw, which would also adjust the mirror's resting position. So there seems to more than one way to skin this cat....... I would start checking the mirror - fortunately, on the M8 you have an 'instant replay' and you can check the final image with the the one on the screen quite easily.

 

Good luck,

 

Jan

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Thank you all again. I will fill in a few pieces of information. To answer Luigi, yes, it is the later version of the lens and mounts directly to the Visoflex. I agree with the statement that it would be very unlikely that the screen to mirror and mirror to focal plane distance would be incorrect during manufacture of the Visoflex. The shims in my unit are three different thicknesses! To me this means Leitz was very precise in its adjustment of screen distance. The shims are virtually invisible with the unit assembled. Look for a very thin (about 1/2 to 1mm) black area just below the chrome mirror assembly. With a 10X magnifier, I was able to see this before disassembly confirmed it.

 

With regard to the mirror adjustment, it is important in this optical arrangement that the mirror be precisely at a 45 degree angle to the surface of the screen which is 90 degrees from the focal plane. If the angle (mirror stop) were not correct, a point in the center of the focal plane with the mirror up would not appear in the center of the ground glass with the mirror down. The mirror seems to be correctly aligned in my Visoflex and working properly.

 

I believe it is possible for all M cameras to have small variation in flim to lens flange distance or sensor to lens flange distance. The rangefinder is adjusted at the factory (or some of you have done it yourself :)) to correct for these small variances. When you use a Visoflex, you do not use the rangefinder at all and so the only adjustment is in the Visoflex itself. I am not sure but I can imagine people sending the camera and Visoflex back to Leitz to have their system fine tuned the way some do today with their lenses and M bodies!

 

I am almost finished fabricating my shims and hopefully will be able to test again by the weekend. By the way, I really like the Visoflex and the interesting photographic possibilities it brings to the M8 for a very reasonable cost.

 

Regards,

 

Michael

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With regard to the mirror adjustment, it is important in this optical arrangement that the mirror be precisely at a 45 degree angle to the surface of the screen which is 90 degrees from the focal plane. If the angle (mirror stop) were not correct, a point in the center of the focal plane with the mirror up would not appear in the center of the ground glass with the mirror down. The mirror seems to be correctly aligned in my Visoflex and working properly.

 

I'd be interested to know how you measured this. I couldn't think of a way of doing it at home. Or does "seems" imply that it looks OK to the naked eye?

 

 

I believe it is possible for all M cameras to have small variation in flim to lens flange distance or sensor to lens flange distance. The rangefinder is adjusted at the factory (or some of you have done it yourself :)) to correct for these small variances.

 

Not really. Yes, each rangefinder is individually adjusted as it's assembled (or when the camera is overhauled). Yes, there's a tolerance allowed in the distance between lens flange and sensor or film rails - but it's tiny, a matter of microns, to cope with the tiny depth of focus of fast wide-angle lenses. The purpose of the rangefinder adjustment is not to compensate for an out-of-tolerance flange-to-sensor distance (that's adjusted by shimming the sensor or lens mount on digital and film Ms respectively): it's to adjust the rangefinder so that it works accurately with any (correctly adjusted) lens.

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John, to answer your question about measurement of the mirror position, yes it was by visual observation of two things. 1. an object in focus at the top of the screen also appears in focus at the bottom, the left, and the right. 2. An object centered in the photo is also centered on my screen. I believe both of these could not be true if the mirror were not in the proper position.

 

With regard to the rangefinder adjustment, I agree with your statements. I am not the expert on this but it would be interesting to know if Leica changed the sensor to flange distance on the M8 camera compared with a film M. For example, a lens could work on both film and the M8 even if the sensor to flange distances were different IF it were compensated for in the design of the M8 rangefinder during manufacturing. I just do not know if this is the case but an interesting thought to me none the less.

 

I found it interesting that Leitz produced shims in three different thicknesses to adjust the screen on the Visoflex. They are not simple shims either. By that, I mean they have two locating holes for alignment with pins on the screen carrier, they have holes to clear the four screws that hold the carrier to the top of the Visoflex and they have the center cut out to frame the screen field of view. It was "fun" duplicating these on brass stock 0.025mm thick! I pressed two layers of the brass between 3mm thick aluminum sheets. Traced the original shim on the aluminum and worked on the sandwiched assembly, sawing, drilling, reaming, and filing....lots of filing. When finished, I separated the layers and cleaned up the finished shims. To reduce the internal reflections, I put my brass shims in between the originals that were, dark, unpainted steel.

 

I am happy to report that I have lost all patience and decided to finished the task this evening instead of waiting for the weekend! I have tested the 280mm at full aperture with the Visoflex and am very happy to report that to my eye, the focus on the screen now matches the image:) No more Focus Bracketing!

 

Regards,

 

Michael

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John, to answer your question about measurement of the mirror position, yes it was by visual observation of two things. 1. an object in focus at the top of the screen also appears in focus at the bottom, the left, and the right. 2. An object centered in the photo is also centered on my screen. I believe both of these could not be true if the mirror were not in the proper position.

 

This is one of the situations where I would rely on instruments rather than appearances. It's one thing to say "appears in focus", another to - for example (a) set the camera up so the film plane is precisely parallel to a focus chart; (B) focus on a target near the top of the frame and mark the position of the focus ring; © defocus; (d) focus on a target near the bottom of the frame; (e) see whether the focus ring is exactly at your mark; (f) repeat several times to ensure you're getting consistent results.

 

With regard to the rangefinder adjustment, I agree with your statements. I am not the expert on this but it would be interesting to know if Leica changed the sensor to flange distance on the M8 camera compared with a film M. For example, a lens could work on both film and the M8 even if the sensor to flange distances were different IF it were compensated for in the design of the M8 rangefinder during manufacturing. I just do not know if this is the case but an interesting thought to me none the less.

 

It cannot be the case. M lenses have to focus at infinity when you turn the focusing ring to infinity regardless of whether the rangefinder is correctly adjusted or indeed whether the camera has one at all (M1, MD, MDa).

 

Sometimes it's important to remember that the calibrated distances are flange to film rails (film Ms) and flange to sensor (digital Ms), while the ones that affect the image are, respectively, flange to film and flange to sensor. The film does not lie perfectly flat in the gate, so the distance from flange to film is not the same as the distance from flange to film rails.

 

To put it another way, the specified distance from lens flange to film rails (on the one hand) or sensor (on the other) may be different but this is purely to ensure that the film (on the one hand) and sensor (on the other) are the same distance from the flange. It's not an arbitrary design decision.

I am happy to report that I have lost all patience and decided to finished the task this evening instead of waiting for the weekend! I have tested the 280mm at full aperture with the Visoflex and am very happy to report that to my eye, the focus on the screen now matches the image:) No more Focus Bracketing!

 

Congratulations!

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