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Tintinla
31-Oct-2006, 14:52
Hi:

I own both a Cambo 45SF and a Cambo 45NX. I also own and use a Zig Align for parallelism of the standards.

I recently made the following experiment: I align either of these cameras properly with the Zig Align, meaning one can see through the hole in the front standard mirror an infinity of circles perfectly aligned on the mirror sitting in the rear standard. The controls are tightened properly so that they keep this corrected position.

I now attach a metal wire around the lens to be used and fix the wire at two places on the front standard still set with the Zig Align. Since I use a Linhof to Cambo adapter as the front standard, these 2 places are the 2 metal "pieces" on which the lens rests. I let the lens hang freely from the wire and look again in the hole of the Zig Align. The weight of the lens invariably tilts the front standard forward, enough to throw off the alignment in that direction alone. Removing the lens reverses the process and the camera is realigned. This happens on both Cambos.

As said, the controls are pretty well tightened and tightening them more could endanger them. The NX is more sturdty than the SF and exhibits the exact same fluctuations of forward tilt. The NX has axial tilts and the SF base tilts.

As anyone gone through the same procedure on their cameras and Zig Align. We are talking here of a substantial tilt (substantial in the sense that if it were there to start with, you would definitely correct for it, at least for the ones who have come to trust their Zig Align).

Second, if you do have checked your alignment with the lens weighting on the standard, and have found the camera to remained aligned, could you mention the brand and model. I am considering the purchase of a Technika 2000 and of course would love to know if such a test had been run on that camera.

I live in the Los Angeles area and am available for carrying such a test if your camera mounts the Technika lensboard. The mirror that sits in the front standard for my Zig Align is installed in a Technika lensboard and is not removeable from there.

Thanks for your collaboration.

Alan Davenport
31-Oct-2006, 17:31
[just made a sidetrip to the website of the product in question. interesting, but not applicable.]

I use a small torpedo level to set the camera to level (enough) and to make the rear standard vertical (enough.) I've always found the normal detents and markings on the cameras close enough to set the front standard, since it's seldom that I don't use any tilts or swings.

I'm wondering what kind of photography you do, that requires the standards to be this closely parallel? Parallelism is a nice, theoretical starting point for the two standards on a large format camera, but unless you're shooting a flat piece of paper that is also parallel to the standards, it is only a starting point and not where you'll be when you release the shutter. If you're not using movements, maybe you should try a different type of camera that won't flex.

I'm sure there are applications that require this kind of hair-splitting precision. LF photography in the real world isn't usually one of them. This alignment thing sounds like another solution in search of a problem. Put it in the drawer and go take some pictures.

Whoa, hey, I just noticed that you only joined today. You're not here trying to plug your company's product, are you?

Brian Ellis
31-Oct-2006, 18:00
Thanks for posting this information. I'm always happy to learn from people who seem to enjoy testing because I hate testing myself. But I have to say that keeping the standards perfectly positioned to the degree you're talking about here seems a little overboard, at least for the kind of photography I do. I suspect that all the various things in LF equipment that can be off by a few micromilimeters either all balance each other out or, if they don't, it doesn't matter.

Tintinla
31-Oct-2006, 20:17
Hi:

No I am not trying to plug any product here. I don't sell any product either. I am just a photographer.

It is interesting to note that the kind of parallelism I am talking about is an absolute given in a Hasselblad, Mamiya and the like (and there must be some reason to that). Contax went as far as creating a vacuum back so that the film would be perfectly flat both on 35mm and 645. It is also known that some BetterLight scan back users are using a Zig Align and I am quite sure would not tolerate the kind of error I am seeing. I believe that this is a matter of how big you enlarge.

In any event, I plan to enlarge very big and I believe that at the degree of magnification I envisage, this kind of error will be visible, in particular on prints derived from wide angle shots. The problem I have mentioned is apparent with a Nikon 90mm F5,6 SW among other lenses.

Tintinla
31-Oct-2006, 20:18
Hi:

Sorry, I forgot to thank you both for your input. So, thank you. I much appreciate.

Ed Richards
31-Oct-2006, 20:39
Since front tilt only moves the plane of focus, I am not sure why it matters if the front standard sags a little - you are going to use swings and tilts to move the plane of focus anyway, and you can see what you are doing with a magnifier. Makes a big difference in an enlarger because everything is flat, but not in a view camera. Even in the flat paper example, you would just correct for sag as part of focusing.

Tintinla
31-Oct-2006, 21:41
Yes, I know what you are saying and probably have corrected for this in the past not knowing about it. It just would seem more natural to start with a definite zero position and then make adjustments.

Also, let's say the adjustment you require is now a front swing instead of a tilt. Can one still Scheimpflug if the plane of focus is tilted and swung at the same time?

It occurs to me that I have never enlarged bigger than 16 x 20 and my plan is to go quite a bit above that.

In any event, I was trying to see if some users had found either the same issue or found that their camera maintained good parallelism irrespective of the weight of the lens.

Thanks.

Oren Grad
31-Oct-2006, 22:30
The Zig-Align promotional material focuses its discussion on specific situations where lack of parallelism is most likely to cause problems: in enlarging and in copy photography.

Have you actually encountered any situation in which there was a sharpness problem that you attributed to a lack of parallelism in the camera? If so, under what conditions (subject, focus distance, focal length, aperture, etc.)?

Ed Richards
1-Nov-2006, 06:35
> Yes, I know what you are saying and probably have corrected for this in the past not knowing about it. It just would seem more natural to start with a definite zero position and then make adjustments.

Sure, if there were no costs involved. But to get a perfectly parallel system when loaded with a big lens one would have to use a heavy studio camera which would be very difficult to use in the field. I suspect a Sinar P2 does not sag much, but I would hate to tote one around. You have to look at the degree of sag you are dealing with - Zig-align is designed to detect problems that are well below the threshold of visbility in real photography - it does not affect sharpness because you are shooting three-D subjects. It only slightly shifts what is sharp, which is going to be impossible to see. In contrast, an enlarger is mapping one flat sheet to another, and even the slightest tilt puts most of the image out of focus.

Leonard Evens
1-Nov-2006, 08:21
In the real world, exact parallelism of the lens plane and film plane are impossible. If nothing else, the film won't lie perfectly flat no matter what you do. So it is always a matter of keeping the lack of parallelism within acceptable bounds. But what is acceptable will depend on the situation.

Shorter focal length lenses will yield more of a shift in the plane of exact focus. To some extent, when focused at the same distance, such lenses will compensate with greater depth of field at the same f-stop. On the other hand, it is harder to check focus at the edges of the field with such lenses. I've found at times that I ended up slightly out of focus at the edges when photographing a building facade with a wide angle lens, so in such situations, I try to be careful to maintain parallelism of the standards.

In many siatuions, just using the detent or zeroed positions is adequate for all practical purposes. In cases where parallelism may be critical, I think it is best to check it with the lens in place. Use of a levels should be adequate for the degree of accuracy required in large format photography, so I don't think more elaborate methods are called for. Check of tilt is best done with the camera level because that is when the lens weight will be relevant. Check of swing can be done with the tripod pointing down and the gg level. A torpedo level placed across the lens barrel can then be used to check allignment. Horizontal adjustment shouldn't be affected if the camera is returned to level.

Finally, checking on the gg glass will confirm that all is well. For example, when photographing a building facade which is plumb, you want the back vertical and parallel to the facade. The former is checked with a level and the latter can be checked by making measurments of the image on the gg. Distances which are equal in the subject plane should yield equal gg images. Then a check of focus across the field will confirm that all is well. If not, one can make small adjustments of tilt or swing as necessary. Some people prefer to do it entirely that way without worrying to start whether or not the standards are parallel. But I find that once I identify when the standards are parallel, I can leave them set that way for most of my pictures and then I don't have to make any adjustments afterwards. Overall, that saves me time.

C. D. Keth
1-Nov-2006, 08:37
Smaller formats, where you normally use short focal length lenses do have to be parallel, or much closer anyway. With such long lenses for LF, the depth of focus (this IS different than depth of field) is much deeper and parallelism becomes less important. It's a nice standard but in practice it's not thet big a deal, nor is it difficult to compensate for when you need to.

GPS
1-Nov-2006, 08:57
The most practical solution I see is to try to tilt the back standard to the parallel position but in such a case the Zig align probably won't work (as the standards are shifted now). That's the solution avoided by the mentioned "Hassy and Mamiya" with "locked" parallelism.

Tintinla
1-Nov-2006, 23:26
Hi:

I just wanted to thank you very much for your detailed and knowledgeable answers.

To answer one of the posts, no I have not detected a focus shift in my prints up to now. As said, I have not enlarged beyond 16 x 20.

As I am moving from a wet darkroom to a digital one, at least for the color work, I plan to have my chromes scanned on a Tango drum scanner at high resolution. I have a feeling that a lot of things that were acceptably sharp at 16 x 20 might be substantially less so at 40 x 50. I am quite aware that prints of that size are not usually viewed at the same distance, but personally, I like to inspect my prints at the same distance from 8 x 10 and up. That is where the Zig Align came in.

Not to push the point much further, but I am curious. Is it possible to use the Scheimpflug rule to obtain uniform focus when the plane of focus is both front tilted and swung? I once tried such an experiment in the field (and I don't remember why the situation required such an adjustment), on a particularly hot day in New Mexico, and after the better part of 45 minutes of futzing, I obtained an uniformly UNsharp chrome...

Anyway, thanks again for your input. I am quite impressed with the level found here.

Ed Richards
2-Nov-2006, 07:12
> Not to push the point much further, but I am curious. Is it possible to use the Scheimpflug rule to obtain uniform focus when the plane of focus is both front tilted and swung?

Some plane will be in focus, but it might be impossible to match it to anything in your picture.

You do not need to have a giant print to look for critical sharpness, just use a 10x loupe to look at the chrome. Depth of field issues are going to be much more of an issue with sharpness than alignment. Scheimpflug only solves the problem if you are taking pictures of soccer fields. In the real landscape there is likely to be stuff sticking up from the plane of focus that Scheimpflug cannot deal with.

Leonard Evens
2-Nov-2006, 08:56
Not to push the point much further, but I am curious. Is it possible to use the Scheimpflug rule to obtain uniform focus when the plane of focus is both front tilted and swung? I once tried such an experiment in the field (and I don't remember why the situation required such an adjustment), on a particularly hot day in New Mexico, and after the better part of 45 minutes of futzing, I obtained an uniformly UNsharp chrome...


This is discussed in Jim Stone's book on the view camera. You choose three points you want to lie in the plane of exact focus. They should not lie on a single line or be close to such a line. If the plane of exact focus is more horizontal than vertical, use a tilt first and then a swing. Otherwise use a swing first and then a tilt. Use two of the points as near/far points to determine the first movement, tilt or swing as required. Then use the second movement to bring the third point into focus. That may require going back and readjusting the first movement to keep the first two points in focus, so several iterations may be necessary. When you have the exact plane of focus close to where you want it, choose two points on either side of it that you want to be in adequate focus, determine the focus spread between them, and use the usual method to determine the f-stop that should work.

I must say that, because it is hard to visualize the three dimensional geometry, I am having a hard time figuring out exactly what happens from a theoretical point of view. Of course the Scheimpflug Principle plays an important role. But I will keep working on it, and if I come up with anything useful, I will post it.

Brent McSharry
4-Nov-2006, 01:48
Contax went as far as creating a vacuum back so that the film would be perfectly flat both on 35mm and 645.

I Just thought this point should be cleared up.

I believe there is an important difference between film flatness and parallel standards. Everyone likes film flatness whether standards are aligned and parallel or not, as the plane of focus will exacly match the ground glass (and of course our chosen depth of field will then extend in a predictable manner from this perfect plane).

Some of the large format astrophotography guys actually use battery powered fish tank pumps to generate suction, in their case so the film does not buckle or move during prolonged exposures (which would result in blurred images). Such a device might also be useful if one were to shoot 'wide open'.

Hope this makes sense

GPS
4-Nov-2006, 06:59
Brent, when you think of it, the first (the film flatness) doesn't exclude the other (the parallelism of standards). You want to have the film flat just so that the plane of focus - in the case of parallel standards - would exactly match the ground glass. And that is also the case for non parallel standards - if you like another plane of focus.