View Full Version : inherent problem with crown/speed graphic GG?

12-Jul-2011, 14:33
Hi everyone
i have a crown and a speed graphic. looking at large prints made with these cameras, some of the time my focus shifted a bit forward, a few centimeters in front of where i focused (towards the camera). it was usually when the subject was not too far from the camera, let's say around 2 meters. I used a Caltar N-II 75mm and a 6x12cm Horseman back. i usually shot at around f/11-16.
however, when i ran a test (similar to this one - http://graflex.org/articles/sanz-cervera/) focus seemed ok, but i don't know if i made it 100% correct.

this week i made measurements with both cameras. both focusing screens have a Fresnel between the groundglass and the lens, the grooves side of the fresnel faces the groundglass and the frosted side of the groundglass faces the lens.
the measurements taken with a caliper were:

depth of the focusing back (from the camera) to the fresnel: 3.55mm
fresnel thickness: 1.85mm
total depth (from the camera) to the ground glass surface: 5.4mm

as i know, the standard depth for film holders is 5mm and the measurements from my holders confirm that.
if i reduce the film thickness (around 0.18mm) i get around 4.8mm depth (from the camera) to the film surface.
on my focusing back: 5.4mm
on the film surface: 4.8mm

this means that the film is closer to the lens by 0.6mm (0.0236 inch) more than the groundglass. this of course correlates to the finding on the prints: the focus ending up being closer to the camera than what i saw on the glass.

what is your opinion and experience with this issue?

12-Jul-2011, 14:41
I would check the infinity stops before the glass. Thats where the error was always on any of my graphics.

12-Jul-2011, 15:46
I do believe the fresnel belongs on the viewer side of the GG, not on the lens side.

- Leigh

12-Jul-2011, 16:07
A couple of observations:

1) the ground glass - fresnel configuration described by the Op is exactly how it is supposed to be for a Crown/Speed.

2) if the OP is focusing on the ground glass then, the position of the infinity stops is completely irrelevant. The position of the infinity stops only affects focusing with the range finder.

3) where the image is formed in a ground glass - fresnel lens focusing system isn't so straightforward as a when only the ground glass is used. Never-the-less, the geometry described in the OP is in essence:

depth of ground surface of ground glass: 5.4mm
depth of film in film surface holder: 4.8mm

with this geometry, we would expect to observe the actual plane of focus, on the developed film, behind the plane the was focused upon with the ground glass....(because the actual image distance is shorter than expected by 0.6mm, the actual subject distance must be longer).
Thus, if you focused on the king, the developed film might be actually focused on the queen BEHIND the king. --- is that what you observe in your tests? .

tom thomas
12-Jul-2011, 16:26
Leigh, on the later Crown/Speed 45 Graphics, the Ektalite (fresnel) lens is between the glass focus plate (GG) and the lens according to the illustrated parts listing in the service manual. The Users manual implies the same thing.

The groove side of the fresnel on my Graflex is facing the glass screen, ie the exposed plastic side facing the lens is smooth.
Check the positioning in this service manual.


I notice my focus is off at close range as Tal describes except mine focuses long, ie further away.

Check these photos, in the first one, I was focusing on the lens ring, yet the hand grip and the lens cap are in focus. The camera name plate is out of focus about an inch further in depth. I was about 4 feet from the subject.

In the photo of the railcar wheel carriage, same thing. I focused with GG on the grease cap, yet the springs about 2 inches deeper are in focus. Guess I'd better do some fine focus adjustments or just enjoy the soft "bokay" as many do. I was about 3 feet in this case. Result photo is a scan and crop of the larger neg.


12-Jul-2011, 18:14
No Leigh
The frensel is on the inside. The prisms touch the Ground surface of the glass.

I do believe the fresnel belongs on the viewer side of the GG, not on the lens side.

- Leigh

12-Jul-2011, 18:36
Frensels in general are a pain. Graflex did supply a metal frame the same thickness as the plastic screen. This located the GG in the same plane. On my Deardorff Triamapro I added a Grafloc Back. I shoot with a 57mm Grandagon, 75mm Centigor, A 120 Angulon and a 152 Ektar. I have to use 2 different Frensels for these lenses. Frensels have a Focal length that really should be matched to the taking lens. The WA lenses use a very fine frensel and the 152 uses a coarser one. (factory Stock Ektalite)
This Ektalite screen works fine for longer lenses.

Ivan J. Eberle
12-Jul-2011, 18:55
Graflex also made backs that properly had ground glass only. Is it possible that sometime in the past 40+ years a fresnel got assembled in the wrong rear half of a back (or that's something other than an original Ektalite/GG sandwich)?

edit: Scratch that theory... I reread the OP's post to say it's happening with two cameras.

Two other avenues come to mind:

First, you're having this problem with both cameras and one roll film back? Does a standard Lisco or Fidelity holder give you the same focus shift problem? The back may be the problem.
Secondly, 75mm lenses are notoriously difficult to focus. Are you using a loupe? Have you stopped down and looked at the focus to determine that the focus point doesn't actually shift (perhaps the lens was assembled wrong at some point, without a shim?)

Too, I've got the SAE film holder depth and tolerance etched into my brain... not the Metric equivalents.

12-Jul-2011, 20:09
You know, I think I'd do a precision focus adjustment. Big well lite wall with newspaper in the corners. Say a wall 16x20 feet. Put a full page in the corners and middle. Can you visualize this? fill the glass with this test at 8 feet high. take some loupe views and adjust. Can you read the print? The camera has adjustments on the front to square it with the glass.

16-Jul-2011, 05:56
yes BradS, you're right in all of your observations and comments.
as the focus issues i had were not consistent, i will have to repeat those tests again.

yes Ivan J. Eberle, logically the problem might be the back (even though i doubt a new horseman will be the problem rather than an old graphic with who knows how many previous owners etc).
but you're right, i'll have to run the tests also with my fidelity film holders as well.

in any case, i do intend to buy a technikardan pretty soon. i'm sure i will feel a lot safer and assured then.. :)
thanks again

16-Jul-2011, 06:10
You could also try the cameras without the fresnel, i.e. just the ground glass, and see if your focusing is more accurate.

16-Jul-2011, 12:51
no ari, that will cause a much more severe focus shift, these graphic GG NEED to have the fresnel there (or a frame or simple glass in the thickness of the fresnel).

16-Jul-2011, 14:12
Ah, I see; so maybe another poster was right, and your fresnel is not original, and of incorrect thickness.
My Toyo G came with the fresnel on the lens side as well. I got rid of the fresnel, bought an aftermarket GG out of China, and never had a problem with focusing or sharpness.
Good luck, it's a frustrating problem.