Linhof Technica III ground glass positioning

[dwtruax]

I recently made the plunge back into LF with the purchase of a Linhof Technika III, Version 5. It is in great shape but I thought the ground glass needed a little tidying up, so I disassembled it, cleaned the glass and fresnel lens . . . and promptly forgot how they were assembled. My best guess is that the glass was on the outside (photographer's side) with the shiny side out and the frosted side nearest the lens, and the fresnel was inside of that with the coarse side closest to the lens? Am I right?:confused:

 

[resummerfield]

The fresnel rings or rough side should face the gg.

But I don’t think the Technika came from the Linhof factory with a fresnel. I may be wrong, but I’m guessing your fresnel was added later. In that case, the fresnel could be placed either in front of (on the lens side) or behind the ground glass.

If it is behind the ground glass, which is most likely because it would not change the focal plane, the order, starting from the lens side, is: ground glass rough or matte side, ground glass shiny side, fresnel ringed or rough side.

If it is in front of the gg, which is the more traditional method, the gg would have to account for the thickness of the fresnel for proper focal plane positioning. The order, starting from the lens side, should be: fresnel shiny side, fresnel ringed or rough side, gg rough or matte side, gg shiny side.

I’m not familiar with the version 5 of the Tech III, but on an earlier Technikas that I have seen, the gg was mounted under a hold-down bar mounted on the inside of the frame (toward the lens) which was screwed to the frame. The gg was mounted under this hold-down bar, with the spring under the gg pushing between the gg and the frame. I hope this makes sense. The order would be, starting from the lens side: hold-down bar, gg rough or matte side, gg shiny side, spring clip, frame back.

If the Technika came from the Linhof factory with a fresnel, then disregard the above. It must only be reinstalled as per the factory.

And finally, I hope you watched for small shims which may have been placed under the hold-down bar for proper spacing.

 

[dwtruax]

Thanks for the help

Eric, thanks for the thoughtful reply. It appears that at a minimum I had the fresnel reversed. I was careful about disassembly, despite my boneheadedness once I got to cleaning the glass, so I'm certain there were no shims. There were, as you note, two springs at the bottom of the assembly (away from the lens). The tips of these had a bit of rust, and that seemed to match marks on the shiny side of the ground glass. Therefore, I assume my ground glass was farthest from the lens. And there are two hold-down bars closest to the lens. Whether this is the way it was assembled at the factory, it appears I can only guess.

Can I assume that if the ground glass is in the wrong position it will show up as unfocussed negatives or transparencies? Is this best tested at a wide aperture?

Well, time to load up some film and give this baby a test drive.

Thanks again.

 

[resummerfield]

Film testing would be the best and easiest way to test. I took a piece of white mat board about 2 feet long and drew black vertical lines at 1 cm intervals, with the center line much darker and longer. Set this mat board about 3 or 4 feet away, and oriented at about a 70 or 80 degree angle to the lens axis (for reference, at 90 degrees you would not see any lines, and at 0 degrees all lines would be at the same focal plane). This places the vertical lines at different distances from the camera. Zero all camera adjustments, and focus on the center dark line and shoot at wide aperture. The neg will show one line sharper than the others; hopefully it is the center line.

If the actual focus plane is farther away than what the gg indicates, you need to move the gg closer to the lens. I would suggest a shim between the hold-down bar and the frame back, to space the hold-down bar (on which the fresnel/gg sits) away from the frame and closer to the lens. Start with a shim about 1/3 the thickness of the fresnel. If you can’t measure the fresnel, start with a 0.020-inch shim (a very thin washer). Then check again.

If the actual focus plane is closer than what the gg indicates, put the shim between the fresnel and the hold-down bar and check again. To protect the fresnel, I suggest putting a piece of vinyl tape, such as electrical tape, over the shim. If you need to shim this way, watch that there is sufficient room to fit the shim and the fresnel/gg sandwich between the hold-down bar and the frame back. You may need to have a slight amount of metal machined from the frame to allow the additional thickness of a fresnel.

The tips of my springs went toward the metal frame, with the spring center bow touching the gg. This allowed the spring tips to fit over a ridge on the metal frame, which was probably there to position the spring. But it shouldn’t matter, so long as it fits tight. Good luck!

 

[dwtruax]

test worked great

Eric, thanks for the simple but elegant method to test for the plane of focus. I used your method and the focus seems fine without the need for shims. Whew. All is copacetic.

 

[HenrikB]

Hi,

for what it's worth, I have a Tech III as well and they did not come with a fresnel back then. I have had a fresnel added, as well as a new brighter gg, and the fresnel sits BEHIND the gg (looking from the lens). Since the back was never designed for this, the fresnel had to be shimmed into the open "frame" behind the gg and is thus slightly smaller in size; if you just piggyback it with the gg you will offset the focal plane and it will not match your film plane. I had a very experienced Linhof mechanic doing this for me, as neither the gg or the plastic fresnel conform of the current standard (Tech V) size, so they had to be machined... without getting the debris into the fresnel...

Anyway, end result is a great old camera with a wonderfully bright screen - at least a 2-3 stop improvement from the original gg - that works wonders with wideangles. I almost never use a dark cloth.

Good luck with a great camera, and let me know if you need more info.

/Henrik