Negative stage guide vignetting on Beseler 45?

[1kgcoffee]

Question is why?

I've been printing color with a Beseler 45mx condenser head and LIFX color LED bulb. One user here noted on some of my scans that there seems to be differing color casts on different parts of the print. After some examination I found color vignetting, the color and brightness on the outside of the light circle is different from that within. This can only be solved by lifting the negative stage guide higher than the Lens. Keeping the negative as far away from the condenser as possible gives a uniform light, but makes a smaller image circle.

I have tried two different enlarging lenses. With an 80mm Schneider lens, the stage guide has to be set at 35mm to accommodate both 35mm and 6x6. Set at 2 1/4 on 6x6 yields color vignetting. On my 50mm industar 50u with recessed lensboard, the bellows need to be overextended beyond 35mm at the stage guide and even then there is vignetting.

If I'm not mistaken, it should work perfectly without vignetting at stage guide 2 1/4 with an 80mm lens, and 35mm with a 50mm lens. Why is it doing this? If it makes any difference, the lifx bulb is flat shaped at the bottom.

Would very much appreciate some help as I am very close to getting nice prints. Also worried that the vignetting is present on graded B&W prints.

-1kgcoffee

 

[glbeas]

I would look at changing the distance between the bulb and the condensor. The settings you are changing now is to match the light coverage to the film format which shouldnt be messed with. It looks like the bulb your are using is longer than a standard enlarger bulb. Have you checked to ensure the bulb itself is not causing the color variations? It may not have enough diffusion over the led elements.

 

[M Carter]

Another though would be trying a sheet of diffusion material between the bulb and condenser - this could potentially even out the color projection of the bulb. A scrap of Dura-lar would be a quick and cheap test; you could also test between the condensers (filter slot on the mXT?) or under them.

 

[David Brown]

If it makes any difference, the lifx bulb is flat shaped at the bottom.

I would suspect that this is not helping. Have you considered getting the proper bulb for this enlarger head? They are neither rare or expensive.

 

[glbeas]

I would suspect that this is not helping. Have you considered getting the proper bulb for this enlarger head? They are neither rare or expensive.

I suspect this is one of those bulbs with programmable color, hence the reason for using it. Unfortunately it wasnt really designed for this application and hes just now finding the weak points.

 

[David Brown]

I suspect this is one of those bulbs with programmable color, hence the reason for using it. Unfortunately it wasnt really designed for this application and hes just now finding the weak points.

I agree.