You sure got a lot of good feedback. I don't know the answer, but I would leave the fresnel off until you figure this out. Eliminate variables.
You sure got a lot of good feedback. I don't know the answer, but I would leave the fresnel off until you figure this out. Eliminate variables.
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OK - we can rule out the camera because you got the same results with two different ones.
We can rule out the lenses because you get similar results regardless of lens.
We can rule out the film holder/roll film backs because you get the same with whatever type you use.
We can rule out your eyesight/other human error because other people have used your camera and get the same result (assuming these people were familiar with view cameras).
Ermm... something wrong here - there is nothing left. That's all the variables covered. As these tests were done 7 years ago, I suggest you repeat them now, with all your lenses, because something does not add up.
Cheer, Bob.
Hi
Did you use differnet loupes or always the same? Did you maybe use a to stron loup for a fresnell screen?
You should not use a loupe with a frensel stronger then 4 times it gets really difficult to focus with a loupe for example 7x on a fresnell. I can do it but for critical focussing then I put the fresnell away on my Sinar and it is much easier to see if it is in focus.
This was a reason for me to switch from an Arca F-Line to a Sinar because on the Sinar I just take the fresnell away because it is behind the groundglass and it solved my focusing problems with the wider lenses, which I had with my Arca!
Good luck!
You've received a lof of advice, most excellent, some off the mark. Let me try to add a few ideas.
LF cameras are as WYSIWYG (What You See Is What You Get) at its gets. All that has to be done by the camera manufacturer to get this to work is to place the ground glass in the same optical position as the film and to have the visible edge of the ground glass coincide withe the edges of the film in the film holder. This really isn't that hard. Without a Fresnel lens, or with the Fresnel lens on the photographer's side of the ground glass, the correct optical position is the same as the mechanical postion, i.e., the ground side of the ground glass should be in the same plane as the film. Since Cambo has checked the camera, it seems likely that this is correct on your camera.
The filmholder manufacturer must make their holders within the depth spec. Are you using modern Fidelty/Lisco holders?
The 72 mm Super-Angulon XL lens is the shortest lens that I have. I am an experienced LF photographer and it is the most difficult to use lens that I have. Your focus problems may be due to the difficult of using these lenses -- I expect your 58 mm to be even harder to use. The difficulty is that, except on the optical axis, the light rays arrive at an extreme angle to the ground glass.
Finally, the lens manufacturer must design and produce a lens that doesn't shift focus as you stop the lens down -- this occurs in a lens with signifcant spherical abberation. I know of no modern lens with this problem. Certainly I don't have this problem with my 72 mm SA-XL. With my 110 mm Super-Symmar-XL, I find that focusing is difficult off-axis when the lens is wide-open because the image is not sharp enough off-axis & wide-open. The 110 SS-XL can be focused with the on-axis image wide-open, or off-axis by stopping down about a stop. This procedure might help when you use your 110 mm SS-XL.
Since your tests were done 7 years ago, I second the idea to repeat the tests from scratch. I further suggest that you start with by testing focus with your 210 mm lens as the easiest to use. I second the idea to make photographic tests. I suggest carefully using the lens on a bright sunlight day and focusing on a slant to a newspaper (as suggested by Leonard) or to a fence, or setting up a scence with objects just in front of and just behind the object that you focus on.
Some photographers think that depth-of-focus (the required accuracy in positioning the focus) is smaller for short focal length lenses. This is not true for photographying distant objects -- the equations (with reasonable, small approximations for distant objects) show that depth of focus depends only on f-number. So you can use your 210 mm lens to test the accuracy with which your camera can be focused, e.g., the accuracy of the position of the ground glass.
Incidentallly, I have measured with a depth micrometer and photographically tested the focusing of several modern LF camera and modern Fidelity/Lisco film holders. All have measured to be within spec and tested to have accurate focus. I think most of the focus problems from incorrect equipment are for old cameras and holders, or from a Fresnel lens or screen that has been incorrectly installed, removed or adjusted by an owner of the camera.
The correct adjustment of your loupe is to focus it on the ground surface of the ground glass. Without a lens on the camera, point the camera at a bright light and focus the loupe on the grain on the ground glass. Poor eyesight shouldn't cause a _consistent_ focus shift. It might make it difficult to judge the sharpness position and thus random shifts about the best focus. I suggest that you try the photographic tests several times and see if the focus shift, if any, is always the same. Even use the same test setup -- after taking a test photo, move the standard off focus and start focusing over again. Do you repeatedly get the same focus results on the film, or is the item in best focus different from attempt to attempt?
My preferred loupe powe is about 4x to 6x. Higher power than 6x usually doesn't help because of the grain of the ground glass and the dimmer image.
Re your final question: I have tested several modern LF lenses for image quality vs aperture and found their best performance, considering the entire 4x5 film, to be at about f22. The image was still excellent at f32, but was slightly softer. The image was significantly less sharp at f45. While the results will depend on the lens, no lens can avoid diffration effects. You might not notice the difference between f22 and f45 if you don't photograph the same object or if you aren't checking detail in an object at the distance of best focus. If you need the depth of field, f45 is usable, but I wouldn't try to solve focus problems by always stopping down to f45.
Let me expand a bit on one point Michael made.
The formula for depth of focus is
2 N c (1 + M)
where N is the f-number, and c the circle of confusion. For sufficiently distant objects, the magnification is so small that 1 + M is so close to 1, that you may as well drop the term M. In any case the result is not directly dependent on the focal length f.
The way the focal length comes into it is as follows. If u is the subject distance, the magnification is given by
M = 1/(u/f - 1)
So when the ratio of the subject distance to the focal length u/f is small enough, the magnification is large and the depth of focus is larger. Usually, u/f is considered sufficiently small for this to matter when it is less than 10, which by convention is called the close up range.
Since depth of focus is not directly dependent on focal length, it is puzzling why people often complain that it is more difficult to focus wide angle lenses. One reason, metnioned by Michael, is that off axis the rays are striking the gg obliquely. And, of course, at the same relative aperture, the image is dimmer. For relatively close subjects, the above analysis may also provide a partial explanation. For a subject 1 meter away from the lens, you are well within the close up range for a 250 mm lens but clearly outside it for a 75 mm lens, so you actually do have visibly more depth of focus in the former case than the latter. I think another reason is one's subjective expectations based on one's off camera perception of the subject space. One tends to see things in normal perspective just looking at the scene, so in some sense there is a predisposition to a "normal" focal length lens. What you see through a wide angle lens distorts that perspective, putting everythings further away, so to speak, and thereby subjectively expanding all distances, at least in the final print. So the same error, looked at purely in terms of the optics, looms larger in terms of one's expectations. With a longer lens, you would not be surprised that you were not able to focus to within a inch or two for a distant subject, but you are when using a wide angle lens and the subject is closer. But your defintion of "close" and "far" has to be modified with considerations of viewing perspective in mind.
Lots of responses, difficult to sift through what seems best. One thing I note is that nobody really said they have had the same problem, at least not to the degree I have experienced it, which tells me that my problem seems to be an individual problem, not a common one.
I have started with an investigation of the loupe question. After looking at several loupes from 2 different LF dealers here in Stockholm I discovered that there are no loupes that allow me to focus on the GG when not wearing my eyeglasses! I can never turn the focus ring far enough to get the grain on the GG sharp. I can of course keep looking for other models . . . but it appears to me that this is not going to be a solution, or even something I could test. And just generally speaking, I have to wonder if my focusing through the loupe wearing eyeglasses would really lead to an object 12 meters away appearing sharp, when in fact (according to what’s on the film) I am really focusing on an object 4 meters away. That’s very extreme. There must be thousands of more-than-slightly-nearsighted LF photographers out there who are managing alright keeping their glasses on . . . or?
If I can accept as givens that 1) I must wear eyeglasses while focusing, 2) my GG/fresnel setup is ok, since it is what the factory ships, and 3) All of my equipment is state-of-the-art (and I therefore shouldn’t really need to be fussing with grinding down film holders and loupes), then among all the suggestions that have come in, the only thing I can see to do at this point is to test again by photographing a newspaper at 45 degrees in the manner described, and see what happens with that. I am a little uncertain, however, about what I will learn that is new. . . . I will return about this later.
A question for Michael: What do you mean by focusing on-axis and off-axis? I don’t quite get this. Do you mean looking into the loupe straight on rather than slightly from the side?
Wow, lots of great ideas here. One thing to check, that I didn't see, is which way your groundglass is turned? The frosted side must be toward the lens for it to be in the same place as the film emulsion. Then the fresnel is behind, so the photographer looks through the fresnel, then through the clear side of the GG, to see the image on the frosted side of the GG.
Problems such as your own eyesight are not relevant with a frosted GG, because you are viewing a true image on the GG, not a virtual image in midair; poor vision won't affect what you are focusing on, only lessen the acuity with which you see it. (IOW, you'll see the best image through the loupe only when it is actually in focus; your bad eyes won't focus it any differently.)
Also, you've already confirmed that the fresnel is NOT on the lens side of the GG. That leaves (to my mind) only two things: either the GG is in backward, or it isn't located in the same plane as the film emulsion. The former requires you to flip the GG over, the latter either shims or removing some material where the GG seats until it IS in the right plane.
I'm pretty nearsighted, and I focus with my glasses on. I use either a Schneider 4x loupe or the Toyo 3.3x loupe.
"On axis" means "close to the center of the image circle" (i.e., the lens axis) and "off axis" means "out at the edge of the image circle." If you use a normal loupe off axis with a wide lens you won't see very much, because the light from the lens is striking the glass at an angle. If this is the problem, you might try a Silvestri tilting loupe, which is designed to address precisely this issue.
"On axis" refers to the axis of the lens. Imagine a line through the center of the lens and perpendicular to the lens board. That is the axis. If you could see the whole image circle, the center of that circle would be where the axis intersects it. If the camera is set up with no rise/fall or shifts, that will also be the center of the frame.
It is easy to correct a lens for optimal performance on or near the lens axis. As you depart from the lens axis, lens defects become prominent. Also, illumination drops off.
Michael S. Biggs: You mention that you also have difficulty in using your 72 mm Super Angulon XL. What exactly is the difficulty you are experiencing, and how do you deal with it?
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