Focussing image on paper problem

game · Sep 23, 2005

Hi,
I am working on my colour darkroom. I've worked in B/W ones but not yet in a colour one. Something seems very impossible to me...

How does one focus and adjust the image on the paper underneith the enlarger when all is dark??

In b/W there is a red glas that makes sure paper is no lighted, but how this work for coloure?????

Please tell me, it must be quite simple but I can't figure it out.

Game

seadrive · Sep 23, 2005

Unless I'm misunderstanding your question...

If you are using a grain magnifier, you cut out a piece of unprocessed paper in the shape of the bottom of the magnifier, and glue it to said bottom. Now you can focus on the easel, without having a piece of paper in it.

gbroadbridge · Sep 23, 2005

Just use an old piece of paper (test strip, whatever) to do the setup, then replace with the real piece of paper in total darkness.

Flotsam · Sep 23, 2005

Yes, Don't focus directly on the unexposed paper. Focus on a blank sheet of paper and then with the lights and enlarger off, replace it with the unexposed paper that you will print on.

raucousimages · Sep 23, 2005

This is the same thing I do in B&W. It reduces the total time the paper is exposed to any light.

kwmullet · Sep 23, 2005

I've started to wonder if grain magnifiers are all they're cracked up to be. Paper tends to bow a it in the easel, and a grain magnifier placed on a spare piece of paper will depress that paper down to the surface of the easel. The paper you actually expose isnt similarly depressed, so I've always wondered if that results in adequate focus.

What are y'all's thoughts about whether using a magnifier, like the brim type sold in craft stores, to examine the projected image on a spare piece of the same type of paper instead of using a grain magnifier? Might that result in a more accurate examination of the focused image?

-KwM-

Neal · Sep 23, 2005

Dear Game,

Use a grain magnifyer for focusing. Simply place it on your easel after roughly focusing and cropping. Once set, turn the lights off, load your paper and proceed.

FWIW: In "Post Exposure", there is a chapter on focusing errors using grain magnfiers. In that chapter there is a reference to the method of placing the grain magnifier on top of a piece of paper to increase focusing accuracy. The author, Ctein, claims that the thickness of the paper is insignificant to the focusing accuracy. If you disagree with this position, keep a sheet of paper around to place the grain magnifyer on.

Neal Wydra

Donald Qualls · Sep 23, 2005

kwmullet said:
I've started to wonder if grain magnifiers are all they're cracked up to be. Paper tends to bow a it in the easel, and a grain magnifier placed on a spare piece of paper will depress that paper down to the surface of the easel. The paper you actually expose isnt similarly depressed, so I've always wondered if that results in adequate focus.

Another thought on grain focusers.

I don't have one, and can't presently afford one worth paying shipping to get. So, I do the best I can with what I have: I make sure I don't have my contacts in when I work in the darkroom, and to focus, I get my face very, very close to the easel (with the card that protected the first sheet of paper in the box in place of a sheet of "live" paper), look over the top of my glasses, and with my myopic eyeball I focus as critically as I can. I usually can't see grain in the projected negative image, but I can see the sharp image features. Perhaps its a coincidence, but I find that even with the head all the way up on my D2V, I can just reach the focus knob while I focus on the print surface.

And you know what? Every time I do this, I find I can see sharp, crisp grain in the resulting print, grain that's still sharp under an 8x loupe. I have no immediate plans to spend my paper budget on a grain focuser.

If you're not nearsighted, you're on your own; when I have my contacts in, even a pair of +2.75 diopter readers don't do as well (perhaps because 3/$10 readers have junk for lenses, or perhaps because my contacts are two years overdue for replacement and are getting pretty scratched up).

Mick Fagan · Sep 24, 2005

There is one major difference with colour negative as opposed to B&W negative enlarging, lack of grain.

With colour negs you have layers of dye to focus on, they are quite soft compared to the in or out of focus grain structure, from most conventional B&W films.

What I find is easiest for focusing with colour neg, is to find a colour change on the neg which could be a red changing to a blue, or find a building or face outline that has a contrast and colour change with the background, this makes it easier to focus with.

The hardest colour neg material I've used for focusing, is Kodak Ektar 25 professional, basically there is almost nothing to focus on, the film is as smooth as silk, so to speak.

I also think you should remove the filtration for focusing as it gives you more light.

In short it's the same as B&W, the only time you need the lights off, is when you have the paper on the easel.

Mick.

MikeS · Sep 24, 2005

Neal said:
FWIW: In "Post Exposure", there is a chapter on focusing errors using grain magnfiers. In that chapter there is a reference to the method of placing the grain magnifier on top of a piece of paper to increase focusing accuracy. The author, Ctein, claims that the thickness of the paper is insignificant to the focusing accuracy.

I would have to agree, I've used both a grain focuser, as well as a Bestwell magnifier (it actually has a groundglass in it, rather than focusing on the aerial image), and have tried both of them both with a piece of paper under them, and directly on the easel, and I've yet to see a difference in focus. Of course DOF might be having an effect, I usually print at either f16 or f22!

-Mike

game · Sep 24, 2005

off course! should have figured that out myself.
With B/W I used to use my won eyesight. I have a grain enlarger, altough it looks really cheap (a guy in this topic gave me the impression they cost). Guess there is cheap and expensive ones like in everything.
thanks for the explaining.

Game

Jerry Thirsty · Sep 24, 2005

kwmullet said:
I've started to wonder if grain magnifiers are all they're cracked up to be. Paper tends to bow a it in the easel, and a grain magnifier placed on a spare piece of paper will depress that paper down to the surface of the easel. The paper you actually expose isnt similarly depressed, so I've always wondered if that results in adequate focus.

-KwM-

I recently got a box of paper with a lot of curl to it and was having noticeable problems with keeping it flat on the easel. My $3 solution was to get a roll of Scotch 667 Removable Double-sided Tape from an office supply store and stick a bunch of pieces down to the easel. I'm using a two-bladed easel with the adjustable margin guide in the upper left corner, so I position that corner of the paper while holding the rest of the paper up off the easel, then press it down on the tape. The first few times you use a new piece of tape it usually pulls up with the paper when you take the paper out, but it peels off clean and you just stick it back to the easel. After a couple times doing this the top side becomes less sticky and the tape stays on the easel when you pull the paper up. It remains fairly sticky for quite a few uses (maybe 50 or so), but eventually you have to peel it off the easel and put fresh tape down. On a few occasions the tape has made it difficult to position the paper square in the easel and I've ended up with slanted borders, but generally it's not a problem.

Also, there is a recipe in the Darkroom Cookbook for making a sticky easel out of plywood, corn syrup, gelatine, and I forget what else, but it sounded like more work than I needed. Maybe if I were moving up to print sizes larger than my current easel and didn't want to buy a bigger one.

Jerry

kwmullet · Sep 24, 2005

well, I suppose the ultimate solution would be some sort of vacuum easel with glass to prevent newton's rings, since you'll be projecting the image through it, but that's a lot of noise and engineering to put up with when it might be sufficient to just focus on the surface of the paper.

I'm thinking a cool gadget would be something that looks somewhat like a grain focuser, but actually sits off the side from the easel and lets you point a magnifier at the projected image on the paper. That way, you could even check each of the corners.

One thing we haven't talked about that I've heard but never investigated is that lenses tend to focus differently at different apertures. In other words, if you focus wide-open at 4.5 or so, then close down to 11 or 16, you may no longer be at the point of optimum focus for your aperture. The focus at some random point within the depth of field range still isn't exactly the same as optimum focus.

Of course, the problem is that it's damned hard to focus critically at 11 or 16, especially if you've cranked your enlarger up a ways.

-KwM-

PeterB · Sep 25, 2005

kwmullet said:
One thing we haven't talked about that I've heard but never investigated is that lenses tend to focus differently at different apertures. In other words, if you focus wide-open at 4.5 or so, then close down to 11 or 16, you may no longer be at the point of optimum focus for your aperture. The focus at some random point within the depth of field range still isn't exactly the same as optimum focus.

Of course, the problem is that it's damned hard to focus critically at 11 or 16, especially if you've cranked your enlarger up a ways.

-KwM-

Can anyone elaborate on the existence OR not of this problem? If it is true then surely the vast majority of us aren't focusing optimally - assuming we focus wide open and then stop down to expose the print.

thanks
Peter

Ed Sukach · Sep 25, 2005

PeterB said:
Can anyone elaborate on the existence OR not of this problem? If it is true then surely the vast majority of us aren't focusing optimally - assuming we focus wide open and then stop down to expose the print.

thanks
Peter

I would fear not - the Optical Designers for the reputable Enlarging lens manufactures can be relied upon to take care of this.
There is NO inherent reason for a "shift" in focal length due to the reduction in aperture - unless another characteristic is ignored - that of "flatness of field". Eliminating rays toward the periphery of the lens would eliminate those that converge at a different focal length, thus appearing to change overall focus - but the truth is that there would be a general improvement of the image overall.

I have tested "a few" lenses, back in the pre-stone (actually "pre-laser) era of Optical Benches. I have seen diasters of many different "flavors", but never a focus shift of that type in a well-made Rodenstock, or Schneider, or Nikon, or Wollensak- or Kodak --- or Elgeet -- or .. lens.

Dave Miller · Sep 25, 2005

Can I be a teeny little bit controversial here, and suggest that we may be getting wound up over this apparent focusing problem unnecessarily. I suspect most of us stop-down two or three stops from wide open after focusing. I think that this provides a depth-of-field sufficient to hide all but the very worst focusing errors, certainly far more than the thickness of the printing paper. May I suggest that you try an experiment along the following lines: Set-up as if to print your maximum normal size enlargement, for me this would be 16x12, Focus as normal, and print a section on a 10x8. Then raise the paper, say a quarter of an inch by slipping something under your easel, magazine, piece of wood, whatever, and print the same section again. Develop, compare, and comment. I’m not suggesting that we should be slipshod over focusing, far from it, just that there are more important things to exercise our minds over.

Focussing image on paper problem

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