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Process Panel
Process Panel
(C) Phil Bard
Published by Barry
22nd December 2009
Default Process Panel

This article is reproduced by kind permission of Phil Bard

Make Your Own Processing Panel

If you have a few simple hand tools, you can make this great little darkroom accessory. Used properly, it will enable you to process 4x5 sheet film without scratches or detectable mottling. I swear by mine.

For years I have developed TMax emulsions by interleaving them by hand in trays, finding it to be the only way to avoid the mottling caused by using film hangers. Then I came across the idea for this ingenious device, which I call the Processing Panel. Assembly took just a couple of hours and it only required a few quick tests to determine development time and agitation patterns. Since then I have used it to produce flawless negatives with great success.

By the way, here's a procedure you can use to find out if your current processing method is causing mottling:

  • Set your camera up facing a piece of white or gray poster board
  • Light the board evenly, best done with two equally bright light sources on opposite sides at 45 degree angles. Alternatively set up in either full sun or shade.
  • FILL THE CAMERA FRAME (important) with the card and rack the lens slightly OUT of focus.
  • Expose the board on Zone V (point a reflected light meter at the board and use the exact reading off it).
  • Process the film in your usual manner.
  • If you own a condenser enlarger, make sure the condenser is clean. If you print with a diffusion head, check the surface of the light source for dust or smudges.
  • Make a print with no negative in your enlarger, but leave the negative carrier in place. Focus properly (on the edge of the carrier). The overall print value should be a medium gray. This will test the evenness of your light source.
  • Make a print of the negative you just processed, also to a medium gray.

Evaluation: Any irregularities in the density of the gray in the first print are due to unevenness in the enlarger's light source. Check again for dirt on the optics. Otherwise think seriously about upgrading your enlarger. You will never be able to get open skies even in prints with this type of problem, no matter how good your processing technique. Unevenness in the second negative is mottling caused by your agitation pattern or development hardware. Do yourself a big favor: get out the tools, get down to Home Depot and make yourself up a Processing Panel BEFORE YOU PROCESS ANOTHER NEGATIVE. You will thank yourself later...

How To Make the Panel

Buy the following materials:
  • Enough 1/8" Plexiglas to make at least one panel 85/8" x 11" It's cheap so buying enough for an extra won't hurt in case you make a mistake on the first piece.
  • 18 nylon screws and 36 nuts for them. Use size 6-32, 1/2" long, or similar, but keep them small.
  • If you don't own one, a tap for making threaded holes for the screws, same thread size as the screws. Or you can get a machine shop to do the threading for you.

This is what the panel looks like:

Here's how to assemble it:
  • Cut the plex to the above size. If you're not using a table saw be careful to cut it square.
  • Measure a sheet of your film stock. The spacing on the screws needs to be such that a sheet of film fits firmly but without buckling between the screws on the panel, as shown in the detail. Leave the paper coating on the plex for the moment.
  • Lay out for screws in pencil. These distances are from CENTER TO CENTER of the screw holes:
    Distance "A" = width of film+thickness of screw shaft ("C" in detail).
    Distance "B" =length of film+thickness of screw shaft.
  • Check layout by placing a sheet of film down over the pencil marks. It should just fit between, adjust marks if necessary.
  • Drill holes with proper size bit for the tap you bought for the screw threading procedure. Use a drill press if available, otherwise be sure to hold drill perpendicular to panel.
  • Thread the holes with the tap, then remove the paper backing from the plexiglas. Insert screws and nuts as shown, leaving enough room for the film under the head. Tighten nuts snugly but DO NOT OVER TIGHTEN.
  • Drill four 5/8" holes, one in the center of each film holding area. A drill press and plastic cutting bit MUST be used for this or you will crack the panel. A machine shop will do this for a nominal fee. These holes allow circulating developer to remove the antihalation layer on the back side of the film.
  • That's it!

You can use this panel in an 8x10"; tray provided it's one that's wide enough to get your finger around the panel when submerged. I discard my developer after one use so I avoid 11x14" trays as it wastes too much chemistry (actually I get two runs out of one batch of solution). I've found that a CESCO tray works fine, PATERSON trays are too small. The presoak, stop and fixer trays can be 11x14" as these chemicals are reusable. You need to fill the developer tray almost full so that when the panel is lifted for agitation it DOES NOT come out of the solution. This will cause mottling. 64 ounces of developer works fine for me.

Placing the undeveloped film in the panel takes some practice. Make sure that the emulsion side is up when doing so, and handle it by the edges. I find that buckling it SLIGHTLY will allow it to slip under the screw heads. Practice on scrap sheets.

You should do your own tests for agitation and development times. What works for me is this:

  • Presoak for 2 minutes in plain water. This allows development to begin more evenly across the sheet.
  • Agitate continuously for the first 15 seconds in the developer. Lift the panel GENTLY by the right and then the left side, then by the sides closest to and furthest away from you (top and bottom).
  • After the first 30 seconds, lift the panel by the top edge once, then by the bottom edge once.
  • After the next 30 seconds, lift the panel by the right edge once, then by the left edge once.
  • Repeat this cycle throughout the development time.
  • Remember not to allow the film to come above the surface of the developer

Handling film is quite easy with the Processing Panel, you can even wash it this way if you want. Dry the panel thoroughly between sessions, water tends to accumulate under the screw heads, making it difficult to get dry film in place.

Let me know how it works for you. And congratulations! You're on the way to the perfect negative. Now all you have to do is shoot them...

(C)Phil Bard
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By Dave miller on 22nd December 2009, 09:54 AM

It seems to me that this design has a great deal of merit. It may even be possible to lean the unit on edge to allow the film to dry in-situ.
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By Dave miller on 22nd December 2009, 01:18 PM

Presumably if the base sheet was threaded then the back nuts could be dispensed with and the bolts could be trimmed off flush thereby reducing the amount of fluid required in the tray.
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