Mirror clearance on 2x3 Graflex SLR ?

[Sam_PNW]

Does anyone know or could helpfully measure the minimum distance between the mirror and film plane on any of the 2x3 Graflex (Auto, Junior, etc) SLR's? Specifically I'd like to make a smaller version of the "Aero Ektar + Graflex" combo. I measured the lens I'm considering (Uran-27, 100mm f/2.5) and it looks like it needs ~75mm from the rear element to film plane in order to hit infinity. I read elsewhere that there's approximately 3" between the mirror and film plane on the Graflex Jr, so it might work without having to modify the mirror.

Thanks in advance for any help or advice.

 

[shutterfinger]

A 1920 Graflex catalog gives the minimum focal length of lens accommodated as 4 inch for the Jr. with a fixed back; the RB Jr. as 5 1/4 inch.
http://piercevaubel.com/cam/catalogs/1920graflexlp376.htm
The RB Series B introduced in 1923 uses a 5 1/2 inch lens. http://piercevaubel.com/cam/catalogs/1923graflexlp324.htm
Focal length of these lens is measured fro the aperture blades to the film plane when focused at infinity as the rear nodal point is near there.
The mirror is longer on the RB models to cover the 3 1/4 distance in portrait orientation.

https://graflex.org/RBGraflex/

 

[Dan Fromm]

I have a Uran-27 mounted on a 2x3 Pacemaker Graphic board. It sits entirely in front of the board, to which it is held by a threaded ring that screws into the lens' rear tube. My 2x3 Pacemaker Speed Graphics' minimum extension is 61.9 mm. The lens just barely makes infinity on that camera.

In short, it won't work on a 2x3 Graflex SLR. As far as I know there are no "normal for the format." let alone shorter, lenses that will work on any Graflex SLR. It would be nice, but ...

 

[Sam_PNW]

Interesting. My copy of the Uran-27 easily makes infinity on a 4x5 Pacemaker Speed, and I’m pretty sure I measured 75mm from the rear of the lens cell to the ground glass, but I could be mistaken. I’ll re-check that tomorrow.

I read in this thread that there’s 3” clearance for the mirror on a Junior:

https://graflex.org/helpboard/viewtopic.php?t=3182&sid=12c16fe57b6f8634796f0fc27dbdd861

 

[Dan Fromm]

Interesting. My copy of the Uran-27 easily makes infinity on a 4x5 Pacemaker Speed, and I’m pretty sure I measured 75mm from the rear of the lens cell to the ground glass, but I could be mistaken. I’ll re-check that tomorrow.

I read in this thread that there’s 3” clearance for the mirror on a Junior:

https://graflex.org/helpboard/viewtopic.php?t=3182&sid=12c16fe57b6f8634796f0fc27dbdd861

How did you attach y'r Uran-27 to y'r 4x5 Speed? The lens' barrel is too fat to pass through a 2x3 Pacemaker's lens throat, so I had to mount mine entirely in front of the lens board. 4x5 Speeds have larger lens throats.

So, I know with reasonable precision the rear of barrel-to-film plane distance. That's what matters when putting a lens on an SLR.

Slight correction. I just put my U-27 on the 2x3 Speed. It focuses ~ 5 mm through infinity. I just checked, the 4x5 Pacemaker Speed's minimum extension is 66.7 mm. No to be impolite, but, um, yeah, so what?

 

[Sam_PNW]

I mounted in a temporary fashion - gaff tape and aluminum tape to light proof. The lens cell does fit through the opening in the front standard on the Pacemaker Speed 4x5, I added a pic below. But this means the rear cell is recessed approx 12mm - this is where I made my measurement error. I’ve since unmounted / un-taped it, but I held it up and focused on some trees 100’ away trough a window (it’s raining, best I could do) to re-check infinity and it’s 75mm from the front of the standard to the ground glass. So less 12mm gives 63mm for my particular copy. That agrees with your number within a reasonable margin of error.

By the way, my Pacemaker Speed has 60mm between the front of the lens board and the ground glass, at minimum.

https://imgur.com/a/TNEUz57

 

[Dan Fromm]

Have you considered using a 6"/2.5 Aero Ektar? Although most have fixed apertures, some were delivered with iris diaphragms.

6"/2.8 Elcan lenses with serial numbers beginning 138- won't do for you, they were made to cover only 6x6 and won't stretch to 2x3. Also, back focus is only 1.6 inches.

 

[Sam_PNW]

6” is rather longer than I’d want to use. I do have a rather rough 5”/2.9 Pentac, which might work.