Help. Height of enlarger head affects contrast.

greenspun.com : LUSENET : B&W Photo - Printing & Finishing : One Thread

I have noticed that when I move the enlarger head up to blow up a print that the contrast decreases. I think that it is due to the light bouncing around in the room.

Has anybody else noticed this problem? Has anybody a solution besides painting the room orange or black?

Ken

-- Ken Heflinger (khefling@ichips.intel.com), July 28, 2000

Answers

I think this is normal. I often have to increase the contrast grade of my paper for bigger enlargements.

-- Ed Buffaloe (edbuffaloe@unblinkingeye.com), July 28, 2000.

It could also be the result of the extended exposure time to a slightly unsafe safelight. Try handeling, exposing, and developing a print in total darkness.

-- Bill Mitchell (bmitch@home.com), July 28, 2000.

Bill,

I am glad you brought that up. I did check my safelight using the "partially exposed" paper, the coins being placed on the paper at one minuite intervals and after 15 min there was no effect at all from the safelight. So I am sure the safelight is ok.

Any other ideas I can check?

Ken

-- Ken Heflinger (khefling@ichips.intel.com), July 28, 2000.


I'd print a step tablet to be sure the problem is real, as opposed to some apparent effect. Maybe you could drape a dark cloth in front of the potentially offending walls and see if that makes a difference. Looking at larger prints I've made, I seem to suffer from the same thing- dang, another thing to investigate!

-- Conrad Hoffman (choffman@rpa.net), July 28, 2000.

I have always assumed that I needed to increase the contrast grade as I moved the enlarger up & assumed it was 'general knoweledge.' Can't point to a reference off hand, but don't think there is anything wrong with your set-up.

chris

-- Christian Harkness (chris.harkness@eudoramail.com), July 29, 2000.



The more you enlarge an image, the less contrast you get. That is typical. I find I need to add about one-half grade of contrast just between 8x10 and 11x14. It makes no difference what size negative you use. Contact prints don't count, though, since they are a different process.

-- E.L. (elperdido65@hotmail.com), July 29, 2000.

The reason is because as you move the enlarger farther from the paper the grains get apparently farther apart and the lpm resolution of the lens gets less. So the sharpness downgrades and the image gets fuzzier. So you have to increase the contrast so the apparent internal contrast(black against white) sharpens the image. James

-- james (james_mickelson@hotmail.com), July 29, 2000.

You don't need to paint the entire room black, just the ceiling and walls immediately adjacent to the enlarger. When I built my darkroom I didn't do this and ran into problems with flare when the enlarger head was cranked up. A quart of flat black latex paint solved the problem for me.The rest of the darkroom, btw is glossy white mildew resistant bathroom paint,it stinks while it is drying but is very easy to care for.

-- Robert Orofino (rorofino@iopener.net), July 29, 2000.

This is normal. Ansel Adams references the effect in The Print. It's probably a combination of technical and sensory effects.

I have a negative that prints wonderfully at 5 x 5 inches. Anything bigger doesn't work, at least I haven't been successful at it.

Your idea about flare from the room is interesting. You could try total darkness to verify, but I suspect that is not it.

-- Charlie Strack (charlie_strack@sti.com), July 31, 2000.


This is normal. I increase filtration by 1/2 grade when I make a print larger.

-- Gene Crumpler (nikonguy@worldnet.att.net), August 01, 2000.


I think James Mickelson hit the nail on the head on this one. I've long suspected that as the grain structure opens up, as print size increases, the impression of apparent contrast decreases. Well said.

-- Sergio Ortega (s.ortega@worldnet.att.net), August 01, 2000.

Thanks for all the input.

At least I know that it is "normal" to see this effect .. whatever the cause.

Ken

-- Ken Hefilinger (khefling@ichips.intel.com), August 03, 2000.


Perhaps there is more significant reciprocity effect in printing papers than is generally known, (which is certainly true for color papers). It would be interesting to see if the same effect appears if the exposure times were kept constant.

-- Bill Mitchell (bmitch@home.com), August 10, 2000.

Bill,

Interesting idea. Next time in the darkroom I think I will try to keep the exposure time constant and see if that helps.

Does color paper show a color shift with longer exposure times?

Ken

-- Ken Heflinger (khefling@ichips.intel.com), August 10, 2000.


If this were a reciprocity effect wouldn't the picture be gaining in contrast and not losing contrast? The area that receives the least light (your highlights) would need an increase in exposure due to that lost sensitivity. The increased exposure would cause the shadow areas to go darker because the change would not effect areas that receive plenty of light and you aren't changing development. I don't think that the change that has been noticed in this thread is reciprocity, probably flair or I think it is more psychological than real. Seeing the image in a different size and not accounting for variation in viewing distance.

-- Jeff White (zonie@computer-concepts.com), August 10, 2000.


Moderation questions? read the FAQ