Focus screens for rangefinders

[Jockos]

Hi all!

i've been looking at some rangefinder adjustment tips, and i saw this interesting setup with a DSLR focus screen and a loupe.

I'm looking into making one of those for myself, but I have a few questions.

Since rangefinders work best on vertical lines, wouldn't a split image screen work best? I'm guessing microprism is out of question?

Should the screen be placed directly onto the camera over the inlet or should it be shimmed somehow?

Has anyone done this themselves, and if so; did it work?

What does the pros use? only lasers and xrays?

Cheers!

Joachim

 

[rxmd]

Don't bother too much with DSLR focusing screens, a good loupe is more important. If anything, a plain old matte screen, matte sticky tape or a CD case roughed up with sandpaper will do, too, as long as it's reasonably flat. Hold it flat against the film guide rails, the matte side needs to sit where the film emulsion would sit.

 

[Jockos]

I tried tape, but I found it a bit hard to determine if its not going into the camera, if you know what I mean?

I assume you have no experience with focus screens?

 

[rxmd]

I tried tape, but I found it a bit hard to determine if its not going into the camera, if you know what I mean?

I assume you have no experience with focus screens?

No, but I don't see what they would add.

 

[t6un]

As in slr's, the split image works best for quick and rough focussing confirmation. If you need to see the actual sharpness of the image the plain ground glass is still needed. Microprism is a compromise between them by accuracy and the ease of use.
Theoretically, the darker the ground glass is, the better and in the test conditions it's easy to compensate for with target illumination.
That said, I use the frosted tape over a thin glass plate that rests on the inner rails of the film gate.

 

[sevo]

No, but I don't see what they would add.

Planarity - errors in the order of 20µm already can be critical. It is pretty hard to place tape that accurately, and near impossible to verify that it is not moving about to such an extent.

Sevo

 

[ruby.monkey]

An SLR focussing screen would do sweet Fanny Adams for rangefinder focussing.

 

[Jockos]

Thanks for your replies everyone!

t6un: so i should be looking for something similar to the Canon precision matte EG-S?
never tought of placing the tape on glass, I'll give that a go first!

 

[ColSebastianMoran]

i've been looking at some rangefinder adjustment tips, and i saw this interesting setup with a DSLR focus screen and a loupe.

Jockos, I've used this with a second camera to check infinity focus.

With two cameras pointing lens to lens, both focused at infinity, the focal plane of one should be perfectly in focus on the other.

It's a do-it-yourself collimator, and I've done this to verify that one of my cameras had infinity focus wrong. Adjusting focus is a little harder; I leave it to the pros with their better equipment.

You want three things all at the same time:
- Infinity subject focused perfectly on the film plane
- Rangefinder or other focusing aid indicating "in-focus"
- Distance mark on the lens barrel at "infinity"

 

[Rob-F]

An SLR focussing screen would do sweet Fanny Adams for rangefinder focussing.

Is Fanny related to Ansel?

 

[Rob-F]

A screen from a Nikon F, F2 or F3 would add a fresnel screen and a magnifier. The trick will be holding it in place, maybe just a couple of rubber bands, top & bottom, around the entire camera.

I could see where a plain matte variety, such as the "B" screen could work, particularly to calibrate the vertical component. A split pea such as the "A" screen might work for distance calibration.

Positioning exactly on the film plane is the rub.

A screen for the FE/FE2/FA would also work, and might be easier to use, as they are just a thin piece of plastic that would be easier to hold in place than the thick and heavy F/F2 type.

 

[Sarcophilus Harrisii]

A friend and I made our own ground glass for focus checks from some sheet glass cut to the right size for 35mm and 6x6 film rails, and aluminium oxide we sourced from a friendly local optical manufacturer. They work well when placed across the film rails, the rest of the procedure is as the good Colonel (or is it Col?) suggests.
Regards,
Brett

 

[nikon_sam]

I've done this with a screen from an Olympus OM camera and used it to check the focus on an Olympus 35-SP...
Matte side towards the lens, placed on the film rail and taped to stay in position...
I've tried tape but like you said it could bow in towards the lens...tape on glass would work...

 

[Sonnar Brian]

I use a negative strip from the start of film, so it is transparent. I put strips of scotch tape over it. I use a Loupe with a glass reticule at the plane of focus. It acts as a pressure plate with the film strip.

 

[L David Tomei]

I haven't seen this mentioned here on RFF but surplus fiber optic faceplates are pretty cheap and are by far the most accurate tool for setting the focus at the film plane (within a few wavelengths). Simplest as well.

Ciao.

David

 

[rxmd]

I haven't seen this mentioned here on RFF but surplus fiber optic faceplates are pretty cheap and are by far the most accurate tool for setting the focus at the film plane (within a few wavelengths). Simplest as well.

Hm, how would that work? From what I understand, they just transfer the image from one side to the other; would you just install it in place of the film and look at the other side with a loupe, like you would with a ground glass?

 

[L David Tomei]

The image would be "captured" at the film plane by the faceplate optical fibers and then would be visible on the opposite surface. I happen to use a 3:1 taper which provides a larger image, but a loupe can be used to view the image. It's a real image similar to any computer display screen with each fiber providing a pixel.
It's a simple setup and the focus is sharp and precise, unlike ground glass. The sharpness or precision of the image displayed at the faceplate surface depends on how small the optical fibers are. The smaller, the better.

There are a lot of these coming out since they had been used for quite some time in optical equipment that is now being salvaged and sold. 35mm x 6mm faceplates can be had for $5 from surplus parts dealers.
David