Linhof Master Technika and fresnel lenses

[KenM]

I recently purchased a 2-year old Master Techinka. Great camera, but the one thing I don't particularly like about the camera is the fresnel lens that is installed in it. I find it somewhat difficult to focus, due to the ridges on the fresnel. So, I'm thinking of replacing it.

I'm a touch concerned about the fresnel focus shift that I've seen discussed here. If I remove the fresnel/glass protector and replace it with a plain ground glass (or a Boss screen, or a Maxwell Bright screen, or a ... ) do I have to do anything (send it away for servicing?) to adjust the back? Or, am I worrying to much about it?

What I also found interesting is that the fresnel doubles as the ground glass - the user-side of the fresnel is frosted; I had initially thought that the fresnel butted up against the 'ground' glass, but when I took the glass off I was surpised to find that the 'ground' glass wasn't - it's clear!

My guess is that to replace the fresnel/protector combination with a plain ground glass, you would need the ground glass to be exactly the same thickness as the fresnel, and you would install it with the ground side towards the user, instead of towards the lens - this would insure that the ground side of the glass would be in the same plane as the 'ground' side of the fresnel. I would therefore still need a protector glass to ensure that the ground side of the glass didn't get damaged.

Anyone care to comment?

[Eric Rose]

The book Way Beyond Monochrome has a great illustrated section on how to check your GG and film holder/Grafmatic alignment. They also tell how the GG should be put together. If you want I can lend you my copy. I even have it downtown today. Let me know, it's the only book I didn't pack!

Eric

[KenM]

Already have the book, but thanks anyways buddy.

[Bert Otten]

Hello Ken,

Less than a year ago I replaced the groundglass in my Technika MT 2000 with a Bosscreen (a Dutch product). Being concerned about a possible focus shift I checked it with a large aperture picture of a ruler, photographed at an angle, using film in a Sinar film holder and in a Fidelity holder. It appears that the focus is exact because of the correction strips on the Bosscreen. From this test it also appeared that the fidelity film holders have quite a variation in the position of the film in the camera because of non-flatness. At working apertures of f8 and higher this is no problem. The variation is less than 0.3 mm. So when your groundglass is mounted with an accuracy of 0.1mm to 0.2 mm or so, it is not limiting. Now the good news is that it is great to work with a Bosscreen, since there is no grain and the contrast of the image is much better. You can appreciate the image much better. Moving your head about under the cloth lightens up the dark corners with a 47 mm lens. A big improvement and as long as you don't change the settings of the tiny screws for the depth position of the ground glass, the focus is fine.

All the best, Bert

[Bob Salomon]

You don't have a fresnel screen you have the Linhof Super Screen with the Overlay.

The standard Linhof gri is the CM Grid screen 021815 and the linhof Fresnel is 022522. To use them you would take off the SuperScreen and the Overlay. Place the 021815 gg on the shims, ground side down, replace the hold down clamps at either end and place the frenel under the silver sliding clamps that are held on by the center screw on the hold down clamps.

However, since you have the Super Screen installed your camera may be missing the silver fresnel clips. In that case you would have to get new ones from service. In the US they can be reached at 973 808-9626.

As to a shift in focus there will be none, with or without the fresnel, if you follow the instructions above. There would be a focus shift if you were installing the fresnel under the gg. Linhof has not placed the fresnel under the gg for a couple of decades.

[KenM]

Thanks for the response Bob. However, I do have one question - when you say you place the ground side of the replacement glass 'down', do you mean that the ground side of the replacement glass is oriented towards the lens? That's the reverse of the super screen, where the ground side points towards the user. To me, this would place the focusing plane in a different position than with the super screen, yes?

No, I don't have the sliding clips - the only silver clips on my back are the small center clips holding the protector in place. I'm not sure I want a fresnel anyways, so this may be a non-issue.

Lastly, there is some deflection in the super screen - it's bowed in the center towards the lens. This is not a good thing, that's for sure, so I may be looking to get the super screen replaced pronto.

[Doug Dolde]

I bought the Linhof fresnel for my MT2000 and am extremely happy with it. It's quite bright and easy to focus. Install per instructions, on the back of the GG under the clips.

[Bob Salomon]

The grain or ground side of the GG faces the lens. So does the frosted side of the Super Screen. That places the imaging forming surface in the same place with both systems. But it is always possible that the previous owner installed the screen upside down.

The silver clips holding the protector in place are the fresnel clips. And you really will want a fresnel screen to even out the coverage on the ground glass. Any camera system you now have; 35mm SLR, medium format SLR, etc utilizes some type of field lens (fresnel) to make the screen bright and even across the field.

If the Super Screen bowed it is either a very old one or they did not shim the sides as suggested by service. Being a plastic material with all that unsupported length on the sides it could bow under high heat conditions. On the other hand the wax layer in the Boss Screen has its' own unique problems with extreme heat or cold. A glass ground glass simply can't bow - but it can crack or shatter- and a fresnel laying on top of a gg can add a bit of protection to the gg. Although the fresnel can be fairly easily scratched.

So every system has advantages and drawbacks.

[KenM]

Ah! In my case, the frosted side faces the back of the camera, so I guess it's been installed incorrectly. That also means that I've been focusing incorrectly. My negatives have been pretty sharp, but the stuff I've been shooting of late has been pretty planar, so stopping down will fix that. I'll flip the screen around and see what difference that makes.

The shims are in place, BTW. Perhaps heat caused it to warp.

[Bob Salomon]

"The shims are in place,"

Not the 4 silver metal shims. The shims that may be missing are more like wooden match sticks on the sides of the screen. Not in the corners.

[Eric Rose]

Gee Ken I bet all your pics came out backwards LOL.

[Brian Ellis]

When I bought a BosScreen for my Technika V I let Marflex or Steve Grimes, I forget which, install it. I think the cost was about $50 and it gave me a lot of peace of mind to have someone who knew what they were doing add or remove shims where necessary, test it properly, install it properly, etc.

[KenM]

Well, I flipped the Super screen around, and made a few test shots with a couple of lenses wide open. Checked them on the light box, and they're tack sharp.

My only nit is that when inspecting the corners for focus, the Super screen's grooves are *very* noticeable. Granted, I'm using an 8x loupe and should be using something a bit less (like a 4x), but still - wow. Regardless, I'll hang with this for a while, and see how it works out.

I'm going to run one more test, one that I thought of after I had dumped my developer - take a shot of a extremely receeding plane, such as a ruler, and focus on on mark without using tilt. If the negative plane is correct, then that one spot should be in focus - if anything else is in focus, then the negative is not in the same plane as the focusing surface.

Thanks for the comments guys. They were all very helpful.

[Bob Salomon]

"My only nit is that when inspecting the corners for focus, the Super screen's grooves are *very"

That sounds like you have a loupe that does not have an adjustable eyepice or it has not been properly adjusted if it is adjustable.

You want to adjust your loupe so it is set to the ground (or frosted in this case) side of the screen.

To do this remove the lens, point the camera at a light source and adjust the eyepiece till the grain of the gg is in sharp focus. Then replace the lens and focus. Now the grooves should be far less trouble and your eye is focused on the actual image forming layer.

If your loupe does not have adjustable focusing then you should get one that does.

[Ron Bose]

This is a very useful thread, I've had the same issue with my Technikardan 45S.

I bought it used and it has a Superscreen in it, placed with Fresnel side closer to the lens. This seems to be a common mistake !! I'll turn it around and test it, then do the same with the regular Linhof GG I've just bought ...