Light circle not covering on Beseler 45M. Helpgreenspun.com : LUSENET : Large format photography : One Thread
Here I am again. More trouble. I just got a Beseler 45M enlarger. The light circle doesn't cover the negative (print). The edges are just outside the bright circle. This shouldn't be. The entire negative area projected onto the print should be the same intensity. The enlarger came with a 35mm carrier. Does something in the housing need to be changed to support 4x5 negative printing? Again, thanks for saving me. By the way I just did my first Pyro negative developing and wow. Just wish I could print it. Doug
-- Doug Theall (email@example.com), February 19, 2001
Are you using the condenser lamp housing? If so, the problem could be that the condensers need to be adjusted. The knob on the top right rear of the lamp stage is used to make this adjustment. For 4x5 the condensers are positioned as close to the negative plane as possible. There should be a scale back there to show the appropriate positioning of the condensers for other formats.
If you have a Dichro 45S color head, the problem is probably that the incorrect mixing chamber is installed.
-- Ken Burns (firstname.lastname@example.org), February 19, 2001.
You didn't say what kind of light source you are using. If you are using the condenser head, you need to alter it's height above the negative holder depending on what size negative you're printing. There should be a scale near the upper bellows that reads "4x5","35mm", etc. I forget exactly what it looks like because the scale on mine is long gone. Adjust the span of the upper bellows to match your format. There is also a lock (on the left, I think) to hold it where you put it. Hope this helps.
-- Kevin Bourque (email@example.com), February 19, 2001.
I echo the other postings. For either cold light or condenser heads, the light source must be brought as close as possible to the negative stage for it to cover a 4x5 negative. Even after you do this, however, you still might notice that a condenser head has a very noticeable falloff. Using an incident light meter, and no negative carrier in the enlarger, I measured up to 1/2 stop difference in light intensity from center to edge of the circle of illumination (lens wide open). You might want to get around this falloff by using some sort of very thin diffusing material and gluing it to the edges of the bottom condenser.
-- Rico Obusan (firstname.lastname@example.org), February 20, 2001.
Rico. That 1/2 stop fall off is normal, and common to all enlargers and light sources. It's called the cos^4 law, and is due to the unavoidable fact that light has further to travel from the lens to the corners of the format, than to the middle. It's also the reason why a centre filter is sometimes necessary for very wide angle lenses.
-- Pete Andrews (email@example.com), February 20, 2001.
If your enlarger doesn't have the scale and you want one, you should be able to obtain one from Beseler. I got one from them a few years ago for about $5.
-- Brian Ellis (firstname.lastname@example.org), February 20, 2001.