Focusing With A Chamonix 045-N

[IanBarber]

When using my Chamonix 045-N to do some close up still life subjects, I find that turning the middle focus knob only seems to Magnify the image on the glass and not really focus. To get a more precise focus, I have to slide the back backwards on the rails.

Am I doing something wrong here or is this the way you have to work it.

[Oslolens]

Two ways to focus: move the back or the hole camera. Arond 1:1 this will happen with any camera.

Sent fra min SM-G975F via Tapatalk

[Doremus Scudder]

With close up work, focusing by moving the lens stage moves the lens in relation to the subject a rather large percentage of the total distance, thus effectively changing the "camera-to-subject distance" and, thus, the size of the image. If your camera has back focus, you'll find using it alone or in combination with the front focus generally more satisfactory.

The ideal tool for close-up work is a monorail with focusing on both standards that are geared the same so one can move each independently, keeping the desired image size while dialing in sharpness at the same time. With your field camera, you'll have to approximate this as best you can with what you have. When I use my field cameras for close-up work, I find inching the tripod back and forth to adjust camera-to-subject distance while focusing a valuable tool.

Have fun!

Doremus

[IanBarber]

Thanks to both for your answers.

The Chamonix does allow you to move the rear standard back and fourth which appears to give me better results as the image size doesn't appear to change as much so this will be the way I will do it I think.

[Alan Klein]

I'm a new 4x5 user. My Chamonix camera can focus using both standards. Each standard can be adjusted individually. I didn't notice this change in size much. Maybe I haven't been paying attention with all the other procedures involved.

So when using long, wide angle or standard lenses for a subject let's say 50 feet away, or from let's say a subject that includes something near at 5 feet to subjects at the horizon, a typical landscape picture, what size changes occur using each of the standards to focus? What are the recommended procedures when you focus? What should I be concerned with?

[grat]

You're not trying to do extreme closeups, so moving the lens a bit won't affect things noticeably.

Even at 5 feet, the change in magnification will be tiny-- a 210mm lens has a focal length of 8.25 inches, so shifting a few mm in either direction won't be a big deal.

But when you're doing very close-up work, where the subject might only be 8" from the lens, now moving the lens closer, even by a millimeter or two, will result in a magnification factor because you're moving the optical system closer to the subject by a significant percentage.

I'm sure someone can explain the optics better than I can (actually, almost anyone. :) ).

[ic-racer]

For every lens, the magnification is set by the film to subject distance, not anything to do with the lens position.

If the film plane is closer to the subject than 4 times the focal length, no image can be produced no matter where you put the lens.

[GG12]

If the film plane is closer to the subject than 4 times the focal length, no image can be produced no matter where you put the lens.

Is this true? Never heard this before. Why is it the case?

[Tin Can]

Many use a Macro rail (https://www.google.com/search?q=Macro+rail&rlz=1C1CHBF_enUS850US850&sxsrf=ALeKk02slV5wrVXv1D-s7MUTX1amGbbZkw:1607863728320&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjomf6S_8rtAhUNrFkKHRzhCJQQ_AUoAnoECA0QBA&biw=1229&bih=608)for focusing close to subject,

Any Horseman 4X5 L has it built in, as it has 3 ways to focus, front, rear AND the bottom knob will move the entire camera forward or back but not change bellows draw

I am using this setup today, big image for clarity of setup, 210 mm lens

https://live.staticflickr.com/65535/50713217918_d62d64ac35_h.jpg (https://flic.kr/p/2kgmuSb)Macro (https://flic.kr/p/2kgmuSb) by TIN CAN COLLEGE (https://www.flickr.com/photos/tincancollege/), on Flickr

[ic-racer]

1/p + 1/q = 1/f

[Tin Can]

http://www1.lasalle.edu/~blum/p106wks/pl106_Lens.htm


1/p + 1/q = 1/f

[sharktooth]

For every lens, the magnification is set by the film to subject distance, not anything to do with the lens position.

If the film plane is closer to the subject than 4 times the focal length, no image can be produced no matter where you put the lens.


This is very interesting. I was suspicious at first, but after going through the math using the simple lens formula, it is indeed correct. The shortest possible distance between the film plane and the subject is 4 times the focal length. The distance from the subject to the lens, and the lens to the film plane will both be equal (2 times the focal length) at the shortest combined distance. You can still shorten the distance between the subject and lens, but the overall distance between the subject and film plane will be greater than 4 times the focal length.

If you're using a technical camera, like a Linhof Technika, you must ensure that the film plane is at least 4 times the lens focal length from the subject. For a standard 150mm lens, this means that the film plane needs to be more than 600mm away from the subject to enable focus by moving the front standard. This isn't intuitive, and probably explains some close focusing problems I've experienced in the past.

[Doremus Scudder]

ic-racer

While it is technically correct about magnification being determined by film-to-subject distance, you've left out important parts of the whole picture. Moving the lens in-and-out of focus changes the image size on the ground glass as well. Different focal length lenses will also change image size on the ground glass for a given position.

Now, usually we're only interested in in-focus images, so the effect of focusing (and lens choice, for that matter) has to be part of the total magnification/camera position picture

Moving the lens closer to the subject/farther from the ground glass will enlarge the image and vice-versa. I can change the image size on the ground glass without changing the camera position a whit just by changing the length of the bellows. Sure, there's only one position at which any give point in the subject will be in focus, but still, choosing where to position focus changes the image size and that choice is not always straightforward.

This situation is further complicated in close-up work with three-dimensional objects for which choosing a point to focus on is not clear. Focus on a far point; the image gets smaller. Focus on a near point; the image gets larger. It's a simple function of conical projection.

Finding the sweet spot between lens position and ground glass/film position to get the focus and the magnification desired is often determined by where we focus int he scene, how much depth of field we need, etc. and, lacking precise measurements and calculations, becomes a dance between positioning front and rear standards to get what we want on the ground glass.

Best,

Doremus

[ic-racer]

Thank you for you insight. I was just referring to focused images. Thus for a given lens and a given film to subject distance there is only one magnification (actually two, but they are reciprocal).

[sharktooth]

I've learned a lot from this thread that I didn't know before. The 4 times focal length min subject to film distance was completely new to me, and very useful. I also learned that you can maintain the magnification by setting the bellows to a fixed length, and focusing by moving the entire camera back and forth. This would be very useful for digital focus stacking, and explains why a macro focusing rail would be a real benefit (or a secondary rail as with the Horseman L).

Thanks to all.