Perspective Control in the Darkroom

[Studio1005]

Is it possible to do perspective correction when making a darkroom print?

If so, could someone point me in the right direction. I am building a darkroom and have a Omega D5500 enlarger that I want to use.

Gus

 

[mdarnton]

You do perspective control in the darkroom the same as in a view camera. Tilt the easel. Things closer to the lens are smaller, those farther, larger. Of course this throws everything out of focus, and stopping the lens down doesn't help enough.

What you need to do then is tilt the film. Parts of the neg representing the place on the paper that's closer to the lens need to be farther from the lens, and the other way around: the negative needs to be closer to the lens for those areas which are being imaged on the paper farther from the lens.

Think of what happens when you focus your camera: the closer your subject (the print) to the camera, the farther the film is from the lens (as the lens moves out to focus). Once you get this relationship in mind, you can start to figure out where the shim the negative carrier to regain the focus you lost by tilting the paper. The areas where you need to move the enlarger lens down (away from the neg) to get good focus, those areas of the neg need to be shimmed to be farther from the lens, so you don't have to do that refocusing. When every corner is in focus without refocusing, you're done.

This isn't hard, once you understand what's going on. The hard part is finding just the right shim for under the negative carrier, and getting precise focus. I used to do this with a micromega magnifier, that let me read focus right out to the corners. You w-ill also need to wrap something--a dark t-shirt, for instance, around the neg stage, because one you get the carrier all shimmed up, it will leak light like crazy.

Long, long ago Omega made a tilting carrier for the carrier to facilitate this. From the large format photography forum, for the D2 Omega:
"The "Distortion Correction Attachment" is catalog #429-080 and it has negative carriers for 35mm up to 4x5.

35mm #423-902
6x6 #423-903
6x9 #423-904
4x5 #423-905"

Search this page for "distortion" and you'll find the attachment about 3/4 of the way down: http://www.glennview.com/omega.htm If you click on the little catalog illustration, there's a picture showing what I was talking about, above.

 

[rodinal]

Yes, you can.
All you need is that your enlarger lens board allows tilting. If so, you can tilt the easel to correct perspective and then tilt the lens to correct the focus of the image.

This image was corrected that way (DURST M605)

 

[Dwig]

Yes, it is possible, but...

you need to be able to tilt 2 or the following 3 planes independently:

1. Negative stage
2. Lens board
3. Easel

#3 is easy, but the D5500 makes either of the other two all but impossible. Beseler, back in the day, would occasionally pitch their enlargers' (45MX, 23CII) ability to tilt the lens board as a feature advantage over the competing Omega models. I believe that at one point Omega offered a lens cone for their 4x5 models that had provision for tilting. Finding one now is a "needle in the haystack" class of project. If you are adequately skilled, making your own is a possibility.

Tilting the easel relative to the negative carrier's plane accomplishes the perspective correction/alteration. You then can't focus evenly across the whole print. Tilting the lens using the Scheimpflug principle will correct the focus problem. Without the lens tilt you can do very little adjustment before you can't get enough DOF to produce a uniformly sharp print.

 

[rodinal]

Yes, it is possible, but...

you need to be able to tilt 2 or the following 3 planes independently:

1. Negative stage
2. Lens board
3. Easel

Certainly you need to coordinate 1, 2 and 3, but need to control only one between 1 and 3 (and always 2 ). Control of 3 is always possible...

 

[Studio1005]

Thank you mdarton for the explanation and others for the discussion. My first thought was that a shift of the negative and easel relative to the lens would accomplish this but that sounds too easy. I can see now why tilting works.

This looks like a great forum with very helpful participants. I posted a few digital photos in the gallery and felt very welcome over there as well.

Once again, thanks for the help!

Gus

 

[Ronald M]

This is why I bought my Phillips 130.

Two other thoughts:
instead of focusing paper, I used a paper with grid for line up of elements that are to be parallel.

the other is one side of the picture is enlarged more that the other so the true projected image is a trapezoid from which we use a rectangle. the result being the higher magnification end makes a less dense image. So you need to do a burn from one end to the other to even things out.

If you are working from 35 mm, 5x, 8x, 11x, 16x all require 1 stop more exposure from the previous size . Therefore measure the two ends and decide how much to burn the wide end. If not 35mm, then you need to look up the increase based on magnification formula which I can not remember.

I highly recommend a view camera or shift lens rather than darkroom manipulation.

If you scan, there are programs that correct distortion and they do not generate exposure changes.