Talk about frustrating. I can't believe how long it took me to figure out that my grain focusser is out of focus. I didn't even notice that the focus is adjustable...

I tried using a loupe and that helped alot, but my confidence is shaken. Do any of you have a cool trick that will enable me to get on with reprinting (confidence restored) all the images I knew were sharper that the resulting prints indicated. (What a bummer)... t

-- tom meyer (twm@mindspring.com), March 08, 2000

Answers

The only problem I have ever had with focus with a grain magnifier not being sharp was until I put a piece of double weight paper on the bottom which now give me the reading as it would be on the paper itself. The other solution is to have your eyes checked, I looked in a grain focuser once and the black line was all spider webbed and I thought that it was broke, the salesman looked and said the line was straight, I looked and it was the spider web again, went to the doctor and my right eye was hemmorraging, so you might want to get a check up if the paper does not solve your problem. Regards, Pat

-- pat j. krentz (krentz@cci-29palms.com), March 08, 2000.

That's not it. The loupe correction wouldn't have helped that. Sorry to hear of your trouble.

Conrad told me about a method using an slr and a macro lens and then interupting the light path with the grain focusser. The only thing I have to figure is whether the angle of the focusser eyepiece will be a problem. I'm going to try it in daylight tomorrow a.m. and post the results here... t

-- (twm@mindspring.com), March 08, 2000.

As far as I know, a grain magnifier is the only easy way to get accurate focus on the base board, but you are reliant on the manufacturer getting the dimensions spot on for it to work properly. Like all bits of kit, there are good ones and bad ones. The worst one I've seen used a thin metal rod to give the point of focus for the aerial image. The rod wasn't blackened, and was so thick you could shift the focus considerably, depending on which part of the rod you focussed your eye on. The better ones have a proper engraved glass graticle. The graticle distance should be factory set and locked though. Are you saying yours is adjustable, Tom?

You could check the focus with a human hair taped across the enlarger negative carrier (assuming the carrier design allows it to lie in the emulsion plane). This gives an easy image to focus on the base board, and then check your grain magnifier against that.

I'd be interested to hear of a more elegant way of checking the focus too!

-- Pete Andrews (p.l.andrews@bham.ac.uk), March 09, 2000.

There are also focusing errors due to color. It turns out that focuing with blue light may give up a 10mm error due to chromatic aberations with the enlarger lens. Modern papers are such that focusing under white light is best.

There is also an error based on variable contrast papers being more sensitive to UV light than the eye is.

-- Terry Carraway (TCarraway@compuserve.com), March 09, 2000.

Here is another easy way to focus on the base board: Buy (or make) a focusing negative, i.e. a negative that that allow for easy focusing without any focusing aid. To make such a negative, use a piece of fully exposed, thus black, film, such as the leader. Scratch that using a needle. Then set the enlarger head to the height you need for your negative in question. Remove the acutal negative, and replace it with the focusing negative. Now focus. It is usually best to focus at full aperture, because there is almost no depth of field then, which would otherwise make focusing less accurate. (The only exception to this rule is a lens where the focus shifts upon stopping down.) Also, it if you use contrast control filters under the lens, you should put the filter in the path of the light when focusing.

As for chromatic aberration: I wonder if this is really a problem, particularly in the order of magnitude mentioned. Modern enlarging lenses are usually corrected to a high degree. Also, using the VC filters when focusing (either above or below the lens) should reduce this problem if it exists at all, because they absorb some of the spectrum.

As for UV light: I wonder if VC papers are in fact more sensitive to UV radiation than graded stuff. Actually, all photographic emulsions are more easily exposed by blue and UV light. You have to mix in sensitizers to extend their sensitivity to light with longer wavelengths, light toward the red end of the spectrum. Also, I think that enlargers with a light source that does produce a significant UV radiation usually have UV filters somewhere in their heads. Finally, I would expect VC filters to remove most of any existing UV radiation.

-- Thomas Wollstein (thomas_wollstein@web.de), March 09, 2000.

Thomas,

You should read Ctein's "Post Exposure".

I could give the details here, but he has charts and diagrams, including spectral sensitivity charts of some papers.

-- Terry Carraway (TCarraway@compuserve.com), March 10, 2000.

Tom, I would think that the first thing you need to do is focus a negative (preferrably one that has detail that is easy to focus) on your baseboard and then adjust your grain focuser to that. Projecting the image on a scrap sheet of whatever weight paper you use is required if you don't have a piece taped to the bottom of your grain focuser since the thickness will make a difference. The easiest way would be to borrow that $300 Peak grain magnifier from your rich friend's darkroom and compare against that. If, like me, your friends aren't that rich and/or don't have darkrooms, you can use your macro setup on whatever camera you have. First, draw a thin ink or pencil line on the paper on the baseboard (or on the baseboard itself if you are using the no-paper method). Set up your camera with the highest magnification macro thingie you have and focus on the line; the greater the magnification you can achieve, the greater your accuracy will be. Once you have the line in perfect focus, tape, tie and anchor everything so that it will absolutely not move while you turn off the lights and, using the pre-focused camera and lens to veiw through, focus your negative on the baseboard. What you are really doing is using your camera's close-up capabilities as a direct focusing magnifier. Once you have the neg in focus, put the questionable grain focuser on the baseboard and adjust it till it is in focus. This is usually done by moving the eyepiece and/or focusing mirror, I'm not sure how yours works. Check everything a few dozen times, and when you are satisfied with the focus tape, glue or otherwise fix your focusing magnifier in place. There you have it (whew), and it should be OK for years to come. Just to be on the safe side though, check everything with different negative magnifications to be double sure. Good luck, ;^D)

-- Doremus Scudder (ScudderLandreth@compuserve.com), March 12, 2000.

Oops, I detected an error in my reasoning! Even if you have a piece of paper taped to the bottom of your magnifier, you need to focus your camera on a piece of paper. Then after using the camera to focus the neg on the paper, remove the paper and adjust your grain focuser. Sorry if this causes any confusion. ;^D)

-- Doremus Scudder (ScudderLandreth@compuserve.com), March 12, 2000.

Buy a good magnifying glass, it will do the job as good as any grain focuser and is never out of calibration. If you want to still use the grain focuser, make the calibration with a good negative and lens combination using regularly the glass for re-checking. I have the 300 $ Peak, but feel always so doubtful with the calibraton image, that seldom when I use it, I'll still check the result with the magnifying glass. So you are not alone...

-- Jan Eerala (jan.eerala@itameri.net), March 12, 2000.

Here's a test you might find useful:

(1) Raise the easel 10mm above the table, by putting a 10mm-thick strip of wood under each side.

(2) Focus the enlarger on the easel, and make a print.

(3) Remove the strip of wood from one side of the easel, and add it to the one under the other side. The easel should be 20mm above the table on one side, and directly on the table on the other side.

(4) Without shifting the enlarger focus, make another print.

(5) Compare the two prints.

If the enlarger was correctly focused in step (2), the first print will be sharp all over, and the second will have the central strip in focus.

If the second print is sharpest somewhere other than the central strip, the enlarger was not correctly focused.

You may find the the second print is sharpest in the central strip, but one edge of the second print is sharper than the same edge of the first print. This indicates either an alignment problem, or that the lens has a curved field.

-- Alan Gibson (Alan@snibgo.com), March 15, 2000.