Question of Focus

[Lobalobo]

For a couple of years, I've shot Efke 25 B&W film in a wide-angle pinhole camera, developed the negatives (mostly) in D-76 (at 1:1 for 5 minutes of continuous rolling in tubes), then made contact prints on Ilford RC3 using (mostly) Dektol; I've been happy with the results even though the slow film and f/179 of the pinhole, combined with reciprocity failure, yields bright sunlight exposure times of 10 seconds, which means that I've never expected sharp focus. (Even buildings have soft edges because the flap-shutter, light wooden camera can't be held perfectly still throughout the exposure, or at least I can't do it or haven't tried.)

Recently, I tried to expand my process and so bought a Crown Graphic press camera, a Fujinon 135mm lens, a (moderately) heavy-duty tripod, and a focus loupe. I continue to shoot Efke 25 and process as above. I also used the (40+ year old) film holders that came with the camera. I used the old film holders because I worried, perhaps needlessly, that newer film holders would not match precisely the depth of the older ones.

The results were not good. Surprisingly, the decades old light meter that came with the camera worked fine; that is, the exposure is generally correct. But there is no sharp focus, not even at the plane of focus in the center of the image. (I rarely shot smaller than f/16 and thus didn't expect great depth of field on a 4x5 negative.) I'm not sure what is going on here as I spent some time with the loupe getting what I thought was sharp focus. Here are some possibilities I've considered: the old film holder isn't holding the film in the right place; ground glass focusing on a Crown Graphic isn't inherently sharp, even with a loupe; there is something wrong with the lens (though this should have prevented focus on the glass as well). Any of this plausible? Anything else I should look for and check out? Thanks in advance.

[nemo999]

As I recall, Crown Graphics could be ordered with a plain focusing screen or with a plain screen plus a fresnel. There were I believe two types of focusing screen frame with recesses of different depths to accept either a screen on its own or screen plus fresnel. If you have the latter type, the assembly sequence is first the fresnel screen, with the patterned side facing towards the back of the camera, and then the actual focusing screen with the matt side downwards (facing towards the fresnel). If you fit a single screen to this type of back, a sheet of glass of appropriate thickness must go in first to act as a spacer. A lot of people carry out this assembly incorrectly, so this should be the first thing to check.

[Lobalobo]

Thanks for such an informative answer, Nemo. Any idea how I can determine wither the camera was built to include a fresnel screen? (My guess is that this camera has not been altered since it was new more than 40 years ago, but I could well be wrong.) Thanks again.

[Phillip P. Dimor]

Well, i've found fresnel lenses in the graflok backs. The spring backs i've had are all plain ground glass. You can remove the focusing hood and unscrew the four screws located on the two ground glass retaining clips to pull up the glass carefully and see. Careful if it is a fresnel, they scratch very easily. Don't clean it with anything, or at least read up on how to clean it. I think it's better to not clean it but that's me.

Sometimes people put the fresnel in backwards or wrong and your focus will definitely be off. I have holders from 40/50+ years ago and ones that are relatively new (80s/early 90s). They both give me the same results from what I can tell.

[nemo999]

Thanks for such an informative answer, Nemo. Any idea how I can determine wither the camera was built to include a fresnel screen? (My guess is that this camera has not been altered since it was new more than 40 years ago, but I could well be wrong.) Thanks again.

I believe the fresnel option was available from the time the Pacemaker Graphic was introduced (I think 1947?). As I mentioned, the distinguishing feature is the depth of recess in the screen frame. If your camera back has just a simple screen and the retaining clips hold this snugly, it was probably made that way. Conversely, it is very unlikely that someone has omitted a fresnel screen that was meant to be there, since otherwise the focusing screen would be very loose (unless the retaining clips were bent inwards very hard). If you inspect your screen by unclipping it from the camera via the Graflok mechanism, you should be able to see whether a fresnel screen is present.

[Lobalobo]

Thanks to all. I haven't removed the glass but have now looked carefully, and I'm pretty sure that the glass is not fresnel and that the camera wasn't meant to take fresnel (as the glass fits snugly). So the mystery continues. Maybe I just didn't focus as sharply as I thought. (I use reading glasses sometimes for reading, but didn't for focus through a loupe because assumed that if the image looked sharp it was--that is, I've never heard of a lack of glasses making an image look falsely sharp.) Thanks again.

[bnstein]

If your focus is sharp with the loupe that tends to rule out the front standard being slightly out.

Possibilities that occur to me are then
1. your groundglass has been installed inside out.
2. your film holder is not up to par or out of synch with the groundglass register. check with another if you have one, or get a vernier and measure the gg register and the film holder register: they should be = (measuring gg register fairly contorted task)
3. there is focus shift as you stop down your lens. check focus again at taking aperture
4. your setup is in some way not quite stable enough and you are moving things as you insert the holder albeit this seems unlikely if this is a repeated offense.

[cowanw]

I would suggest you take a shot of a ruler lengthwise or something stretching away from you. If there is a focus shift or a back problem etc something along the ruler should be in focus. Make a note of the number you focus on and see if some number shorter or farther is in focus.

[Phillip P. Dimor]

The method Bill suggests is good; I do this to confirm focus with rangefinders (including the one on the crown graphic). I do shoot the ruler wide open.

[NavyMoose]

I have a Pacemaker Crown Graphic from 1962 and it has a fresnal glass in front of the ground glass. Geert from LF Forum made me a very nice GG with a lumigrid embedded in it.

The screws to remove the frame around the glass are very small and easy to lose. There are also very small washers it needs as well. Use a magnetic screwdriver, it will make life easier.