I recently obtained a used Beseler 23C series II enlarger with dga color head. My reason for getting this enlarger was to get the diffused light inherent with the color head. There is a noticeable light falloff at the edges of the negative. The effect is pronounced enough that I can see it when exposing the print. I have to add burning around all of the edges to even out this effect in my prints. This isn't horrible but not exactly optimal. The negative carrier is fairly thick above the negative -- from memory I would say it is somewhere between 0.060 and .080 inch thick. I have begun to suspect that there is a shadowing effect around the edges of the negative opening due to the thickness of the negative carrier. One remedy that comes to mind would be to file a bevel around the opening on the upper half of the carrier. So before I make scrap out of my negative carrier I thought I would get a second opinion. Could this issue be related to the diffused light source where a condenser light source might not? Anyone have any experience/advice?

-- Marc McCloud (marc.mccloud@hs.utc.com), April 09, 2001

Answers

Marc,

What you're describing can be caused by a couple things I can think of unrelated to your negative carrier. First, what lens are you printing with? Are you printing 35mm, 6x6, 6x7? You may also check that the light source is the proper distance from the neg to make an image (too close may cause shadowing).

I guess what I'm saying is, we need more information... Jon Osing

-- Jon Osing (josing@bcr.com), April 09, 2001.

Carriers will often produce a narrow area of "strangeness" around the frame, but it's very localized. I've seen other complaints about uneven illumination with these heads in another forum (defunct), so it may be the head. The condenser version is pretty good, but not perfect either. Is the falloff gradual or very strong right near the edge?

-- Conrad Hoffman (choffman@rpa.net), April 09, 2001.

The light source is not the correct distance from the negative stage. James

-- james (james_mickelson@hotmail.com), April 09, 2001.

Please excuse the slow response -- my home internet access is temporarily out of commision. OK, perhaps I need an owner's manual. Anyway, I'll try to fill in some apparently missing information. I am enlarging 35 mm negatives using a new 50 mm Rodenstock Rodagon lens. The light falloff around the edge of the frame is localized and is fairly gradual. By that I mean there is not a sharp step change in illumination. The diffusion element, the piece that replaces the condenser, is in place. I have the upper stage, I think that's what you would call the adjustment involving the upper bellows, all the way down (upper bellows fully compressed). Judging by several of your comments my light source is probably not set at the proper distance from the negative. Is there a procedure for this or is trial and error the best method? thanks, Marc McCloud

-- Marc McCloud (marc.mccloud@hs.utc.com), April 10, 2001.

I can't believe that your lens will not cover the 35mm frame. Although I am not familier with the DGA head, I would raise the upper element and see if that eliminates your problem. Also, does this happen if the lens is stopped down two stops?

-- Ed Farmer (photography2k@hotmail.com), April 11, 2001.

I think there is good coverage from the lens. The falloff is parallel to the edges of the negative carrier opening, as opposed to being circular which is what I would expect from inadequate lens coverage. I have adjusted the height of the light source however some of the effect remains. I think some further experimenting with the height will help. Thanks to all.

-- Marc McCloud (marc.mccloud@hs.utc.com), April 12, 2001.

I took my own advice and I modified the negative carrier by filing a bevel around the opening of the negative carrier. The negative carrier is made from a soft alumunium and using a new file it was very easy to file the shape I was looking for. I started by enlarging the opening to fit the image area on my negatives. (I don't know why but these openings are not full size.) I then carefully filed a 45 degree bevel on the top and bottom sides of the negative carrier leaving about .020 to .030 inch of the vertical wall. When I was all done, the negative carrier surfaces immediately adjacent to the negative (top and bottom) were the same size as the image area. The bevels open away from the negative thereby eliminating the shadowing effect. When I was satisfied with the result, I painted the resulting shiney surfaces with a flat black spray paint. The method was not real high tech but the light falloff was corrected.

-- Marc McCloud (marc.mccloud@hs.utc.com), December 09, 2001.