Position/orientation of ground glass in Graflok focusing screen?

Donald Qualls · Apr 5, 2021

I've got a ground glass on the way to go in my Graflok focusing screen (which came without one), and I notice in the repair manual for a Pacemaker Speed/Crown that there's supposed to be a Fresnel panel in the screen as well -- but because the item numbers and parts list in the manual I downloaded are crossed up a bit I'm not certain which item is which, and the only camera I have that I'm sure has a Fresnel is my Kodak Reflex II. In that camera, the Fresnel is between the lens and the ground glass -- but the camera is built to have this setup, so the focus is calibrated for it (I know, I did the calibration on this when I freed the stuck focusing thread years ago).

On my Speed (an Annie being converted to Graflok) I need to focal plane to match what will be in the film holders and Grafmatics -- and I don't have a Fresnel panel.

Do I need a spacer, need to hunt for (or improvise) a Fresnel panel, or will the ground glass focus at the correct plane if I just install it textured side toward the lens in the focusing panel?

BrianShaw · Apr 5, 2021

Keep looking for the fresnel. Search eBay for “Ektalite”. They show up from time to time and are well worth it.

BTW... my Anniversary Graphic was upgraded with Graflock back. That makes for a very versatile camera!

BrianShaw · Apr 5, 2021

... or this:

https://www.ebay.com/itm/4x5-Graflo...-/254276575125?_trksid=p2349624.m46890.l49286

Donald Qualls · Apr 5, 2021

Okay, I've saved a search for "Ektalite" -- unfortunately, Kodak seems to have used/reused that name for at least four or five different, and seemingly much more common (now) products. Laser pointers, microfiche readers, projectors. And the search always want to turn it to "Ektralite" which is the last generation of quality 110 cameras they produced. I'm a little tight this pay cycle, so I'll grab that spacer (which is in my Ektalite search) next payday (hopefully they'll still have some by then).

BrianShaw · Apr 5, 2021

Kodak didn’t make life easy for us the way they used and reused names!

Mal Paso · Apr 5, 2021

On the Graflok back on my Cambo the glass inserts from the rear, ground side toward the lens. resting on the rim of the opening which is the focal plane. The Fresnel lens is on top, or to the rear. Both are held with the same spring clips.

Been a long time since I held a press camera.

BrianShaw · Apr 5, 2021

Graflex sets it up differently. The fresnel is between the ground glass and the lens, with the grooves and ground surfaces together (in the middle).

hsandler · Apr 5, 2021

If it’s a Graflex Graflok focus panel, you need a spacer. The order starting from the lens side is Ektalite field lens (fresnel) with etched side away from the lens, then ground glass with ground side against the fresnel. For many view cameras international backs not designed for a fresnel, any aftermarket fresnel goes on the photographer side of the ground glass.

Donald Qualls · Apr 5, 2021

Right, so same setup as in my Reflex II then (and seemingly in most if not all viewing screens originally designed with Fresnel panels). And a simple frame spacer (i.e. shims under the ground glass panel) would have to be thinner than the spacer linked above, because the glass is optically only about 2/3 its physical thickness (due to refractive index).

If a proper Ektalite panel doesn't turn up in the next couple weeks, I'll go ahead and get that spacer, so I can use the camera with the conversion Graflok back (though I mainly use this one with the RF; if I'm doing tripod and ground glass I bring my Graphic View).

Dan Fromm · Apr 5, 2021

Donald, be very careful and measure even more carefully. I suggest this because my 2 Crown and 1 Pacemaker Graphics have Graflok backs with focusing panels that weren't made for fresnels (Ektalites). Their GGs sit on bosses. So do the GGs for Graflok focusing panels made for fresnels. The difference is that the focusing panels made for fresnels have lower bosses. To add to the confusion, the low bosses are high ones milled down; both styles of focusing panels have the same casting number.

This confusion happened because when the Graflok back was first offered the Ektalite screen was an option. Not all buyers chose to pay for it.

Donald Qualls · Apr 5, 2021

Dan Fromm said:
Donald, be very careful and measure even more carefully.

So, there's a standard depth from the front surface that bears on the mount (where the DDS frame would go) to the plane of focus -- I should be able to measure this off an existing DDS, except I don't know where my dial caliper (with its built in depth probe) is stored. It's going to be a difference of .040 to .060 inch, though (1 to 1.5 mm) representing the thickness of the Ektalite panel -- which is big enough and accessible enough (when I dismount the hood for access to the ground glass frame) to measure with eyeball and millimeter scale.

What's the correct setback between front surface and film plane?

Dan Fromm · Apr 5, 2021

I don't know if off the top of my head but there's an ANSI standard.

Nodda Duma · Apr 5, 2021

Setback from surface of your film holder to the septum is 5mm for 4x5

Donald Qualls · Apr 6, 2021

Nodda Duma said:
Setback from surface of your film holder to the septum is 5mm for 4x5

Excellent. That should let me verify whether my focusing frame has the short lugs (for the Ekalite) or the long ones (ground glass only).

Nodda Duma · Apr 6, 2021

Keep in mind that if you include thickness of glass/fresnel in your distance calculations, multiply measured glass and plastic thickness by 1.5. You are actually measuring optical path length, so you need to factor in the index of refraction.

Donald Qualls · Apr 6, 2021

Nodda Duma said:
Keep in mind that if you include thickness of glass/fresnel in your distance calculations, multiply measured glass and plastic thickness by 1.5. You are actually measuring optical path length, so you need to factor in the index of refraction.

Yes, as I noted above, the glass is only equivalent to 2/3 its thickness, optically -- but I'm only looking for whether the ground glass supports in my focusing frame are machined for ground glass only (5mm from the reference surface) or for the Ektalite panel plus ground glass (should be visibly less than 5mm). I can almost do that without even a scale, but since I have a handy millimeter scale on my person any time I'm dressed (my Leatherman), I'll use that.

BrianShaw · Apr 6, 2021

Would pictures help? This is the Graflock back that was adapted to my Anniversary Graphic.

Donald Qualls · May 1, 2021

Well, having exchanged the Pacemaker Graflok back replacement I got from 20th Century Camera for one newly made to convert an Anniversary (and hoping it'll hold in place; the screw holes look oversize for the heads of the original screws) (EDIT: Yep, it went on, with near-zero tolerance in the screw holes, but once they were all lined up, they went in), I went to install the ground glass in the focusing panel I purchased -- and found it won't fit. Not just an issue related to the Ektalite field lens; the ground glass I have in hand is too big for the machined pocket in the panel -- and the panel doesn't quite match the description I'm finding on the Graflex.org FAQ pages, either (hood is a friction fit rather than held with clips, ground glass is held by a frame a half inch deep instead of the two swallowtail clips in the above photos).

Which is probably because it's a Graflok focusing panel & hood for a Polaroid MP4, says the clearly visible nameplate inside the hood.

I've tested it; it latches and unlatches correctly on the Graflok conversion back, and the depth from the contact surface to the ground glass step is correct at 5mm, so it will work (albeit with undersize viewing area) -- but I'll need a smaller ground glass. The actual dimension of the ground glass pocket is about 79x105 mm -- was the MP4 a 3x4? I could still return the focusing panel (clearly described as for a Pacemaker in the eBay listing), but I haven't seen a lot of Graflok focusing panels going by, and the ones I've seen were either complete back mounts for some other brand (Sinar, etc.) or a different size (there's a 3x4 on there now).

I'm confident I can get a ground glass to fit this MP4 focusing panel; I don't know that I'll use the ground glass all that much anyway (the RF works and is calibrated for the lens I usually use, and I expect to use this camera mostly with Grafmatics and the upcoming Lomograflok instant back and RF). I suppose a "hedge my bets" option here is to get a ground glass that fits the MP4 back and keep looking for a correct Graflex 4x5 Graflok focusing panel, and plan to sell the MP4 panel on once I find a correct one.

Opinions?

reddesert · May 1, 2021

I'm not exactly following what parts you have or what the desired end result is. However, if you have an unusual size focus panel and need a ground glass, rather than continuing to try to find GGs that fit, consider making your own ground glass. It is pretty easy and you can make any odd ball size, make smaller GGs to use for focus testing cameras, and so on. You can also make a ground glass that is finer ground than standard older commercial glasses. Basically you just need some glass (picture frame or window glass will work), a glass cutting wheel, sandpaper to smooth the edges, and 600 grit silicon carbide powder. You can get the silicon carbide online or at stores that cater to jewelry and rock hobbyists/artists. My local shop sold me a 1 lb box of grit for $8 - that's enough to make a hundred ground glasses. The hardest part for me is getting a nice straight clean break.

BrianShaw · May 1, 2021

reddesert said:
The hardest part for me is getting a nice straight clean break.

Fresh glass breaks cleaner than old glass.

Donald Qualls · May 1, 2021

reddesert said:
I'm not exactly following what parts you have or what the desired end result is.

Okay, I can understand that. I have an Anniversary Speed Graphic that came to me with a common Graphic (aka "spring") back. I've installed a conversion Graflok back produced by 20th Century Camera (largely 3D printed, but with metal parts where it matters). I bought a Graflok focusing panel (with no ground glass) and hood that was sold as for a Pacemaker, but turns out to be off a Polaroid MP4 (hence, despite fitting correctly on the Graflok mount, has much smaller than 4x5 pocket for ground glass) and I purchased a very nice grid-engraved 4x5 ground glass that would probably be a correct fit in a Pacemaker focusing panel (I should check whether it'll fit my Graphic View's spring back).

I'm not confident of being able to cut the ground and engraved glass to a smaller size -- first, it'll mess up the framing markings (6x6, 6x7, and 6x9, plus another off-center appr. 8x8 cm square), and second I'd expect the break to try to follow the engraving.

Window or picture frame glass is likely to be too thick for this, though too thick (as long as it's not WAY too thick) is better than too thin, and finding twenty minutes to install a cut-to-size ground glass is much easier than finding a couple hours to cut and grind the glass myself (and I'm very familiar with that operation, having made an 8" telescope mirror back in 1998).

shutterfinger · May 1, 2021

A 1948 Pacemaker Crown Graphic with a retro Graflok back that has a ground glass only ground glass is 4.817 inches X 3.948 inches. It just fits between the retaining clips bosses and between the top and bottom edges of the opening.

Donald Qualls · May 2, 2021

@shutterfinger That sounds right, and is probably the same as the grid-engraved ground glass I bought. The pocket I have is much smaller than that, in inches it'd be 3.11 x 4.13 inches. I presume this is sized to match the image area of 3x4 Type 100 pack film; although the MP4 could also accept a 550 (4x5 pack film) back, there would be little enough difference that the more economical film would have been more commonly used. In trying to verify that, i found a sale page for an MP4 "kit" (bunch of accessories plus the camera body itself) that included three twin-packs of 667.

I found an eBay seller who offers custom cut ground glass and they listed a piece to my size when i asked about it -- that's on the way now (if it's tight, I can sand the edges on fine wet-dry paper). Since the Annie has only very limited movements (front rise, shift -- bed drop is all or nothing and not really very useful for tilt because it's too much) and I have a view camera if I anticipate needing rise, I can live with the undersize ground glass until I can find an actual Graflex focusing panel, or a compatible one from another brand, and compose with either the optical viewfinder (which has parallax compensation) or the wire frame finder after focusing with the Kalart.

Position/orientation of ground glass in Graflok focusing screen?

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