Uneven processing?

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I shoot alot of copywork, I am having trouble with reproducing artwork that is on white paper or off white paper. The problem is that I always have fall off on the edges and I can't seem to get an even burn while printing, how can I tell if the unevenness (is that a word)is from processsing, lens, enlarger etc. I would appreciate any help I could get.

-- K. Eck (eckk@wichitaartmuseum.org), March 01, 2000

Answers

Two quartz broad lights or reflector photofloods placed at 45 degree angles to the copyboard should do the trick. Then you need to use an incident lightmeter on the copyboard to make sure that the illumination is even (to within 1/3 stop) from corner to corner. It's tricky but it can be done. Make sure the lights are not too close to the copy.

-- Peter Hughes (leo948@yahoo.com), March 01, 2000.

I need to add that I am positive I have even lighting the problem is either processing, enlarging or my 4x5 lens, how can I tell which one it is?

-- K. Eck (eckk@wichitaartmuseum.org), March 01, 2000.

First you might make some contact prints (4x5 you said?) They will be big enough to evaluate your lighting, just in case. From there you should know if it is processing or your enlarger. If it is bad processing you should probably look at your agitation technique. I use the HP Combi tank and a gentle once-over inversion every minute -- my skies and even-toned subjects come out nice and smooth. If it seems to be the enlarger, check that your condensers are installed properly. If that checks out, check the alignment to make sure everything is parallel. As far as the lens goes, if it is a decent make of the right focal length for 4x5 (135-150mm or so) Then I'm not sure what to tell you.

-- Tony Brent (ajbrent@mich.com), March 01, 2000.

First, to verify even illumination, use a SPOT meter and meter the corners and edges. Except for flash meters, incident meters are useless! (Phil Davis not withstanding!) But it sounds like a lack of coverage from your enlarging lens. A 135 mm lens will NOT cover a 4X5 negative; you need a 150 mm. That should fix the problem. Uneven developing will show very uneven areas all over the negative, not just the edges/corners. Good luck.

-- Michael D Fraser (mdfraser@earthlink.net), March 01, 2000.

The light fall off you describe can be caused by a number of different things. The suggestions above are good and should be checked. Here are a couple of other things for you to consider as well: If you are shooting with a wide-angle lens on camera and the camera is relatively close to the copy work, there will be light fall off due to the relatively large distance difference from the lens to the center and edges of the film, respectively. This problem can be solved by using a longer focal length lens and moving the camera back. If this is not possible, a center filter would be necessary to compensate for this effect. The same problem applies to the enlarger/lens set up. Make sure your lens not only has enough coverage for the neg, but that the enlarger head is not too close to the baseboard causing the distance from lens to edge to be significatly greater than the lens to center distance. The same applies for the lens to negative distances. In general, use the longest focal length lens possible to minimize the fall off at the edges on both camera and enlarger. Also, be sure to check your enlarger light source to make sure you have even illumination of the negative. Condenser heads are notorious for having hot spots in the center if adjusted improperly, and even the best cold-light heads can be uneven, especially if the diffuser is close to the same size as the negative. Processing is also a consideration, especially if you tray process by hand. If you do, make sure that when you push a sheet down into the developer solution, you are giving the center of the sheet adequate agitation. Fingers can block the flow of developer across the center thus giving the edges of the film more agitation. Also, pushing down too fast or too slowly can change the amount of relative agitation at the edges of the film due to swirling of the solution at the edges which doesn't affect the center of the film. Hope this helps, ;^D)

-- Doremus Scudder (ScudderLandreth@compuserve.com), March 04, 2000.


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