Filing out negative masks with diffusion light source (Durst L1200 and CLS500)

I've filed out a lot of 35mm negative carriers in my day. Heck, I even filed out the negative strip holder for my Coolscan 5000! But the enlarger ones have always been with condenser light sources.

Now I'm trying to file out a spare Femomask 35 set for a Durst L1200 with the CLS500 head. The top mask has a straight hole that is seemingly the perfect size - leaves just enough of the rebate showing all around the image. The lower mask has a smaller hole that crops the image, but the edges are beveled at 45 degrees, so that the bottom side (away from the negative) is a much bigger hole. About exactly the same size as the top one, in fact! So I started by filing off those chamfers until the hole was the bigger size, with straight edges, then painted the filed parts flat black. Perfect! Until I tried to use it.

I'm used to the effects you get with weird reflections off of the filed edges, etc. but this was just downright bizarre. I was getting *shadows* around the edges, but away from the edge a bit (like the light was being canceled out due to interference patterns), in addition to just all kinds of softness and weirdness. I didn't even make a print as an example because it was so awful. I'm guessing this is due to the difference of the diffuse (scattered) light source instead of the straight beam of light from a condenser. I ended up printing the negs on a glass carrier and moving the built in masks in, but those are so far below the negative that they give really fuzzy edges; I couldn't move them as close to the image area as I wanted or they'd fuzz off the edge of the image.

So my question is, how do you properly file out masks for diffusion enlargers? Is it just a matter of chamfering off the new edges on the lower mask at 45 degrees again? The upper mask sides are straight, why the difference? And do I also need to file out the upper mask; is that opening being larger than the lower one actually an important part of the design? I'm kind of hoping to hear from someone who has done this and figured it out, rather than just blindly attacking the mask with a file again, since these masks aren't cheap to replace if I end up taking away metal I need back...

Thanks,
Duncan

On Meopta and Durst enlargers I always used AN glass on the top and filed out bottom negative mask. The bottom was always made with beveled edges+black paint and never seen problem with diffusion or condenser heads.

I'm trying to avoid glass, and I'm mostly shooting Double-X these days, which is the flattest film I have ever seen, so flatness won't be an issue. So it sounds like beveling the bottom mask edges is critical. And I probably have to make the upper mask hole larger too (which you have simulated by making it infinitely large, by using glass!) I guess I'll look at my other mask sets and see if the upper mask always has a larger hole.

Thanks,
Duncan

Fear of AN glass on the top of negative is most likely one of the biggest mistakes in photography, but of course, you are free to do what ever you think is right! )

Heh - I don't fear it (I used it to make the prints once my filed out carrier failed so spectacularly!), it's just two more surfaces to clean, and the 5222 just completely doesn't need it. That film is just scary flat. Why can't all film be that flat?

Duncan

I don't blame you for avoiding the glass. I loved my Beseler enlargers because they had glassless carriers. Now I'm using a Durst 606, and the glass is driving me crazy. Counting the negative, that's four surfaces to catch dust instead of just two. You can buy a glassless one for my enlarger, and I'm going to get one, or modify the one I have to make it glassless. Looking at prints from the Durst and the old Beseler w/ a glassless carrier, there is no difference in sharpness. But there is a difference in the time I am spending spotting prints!

You covered the cut edges of your carrier w/ flat black paint, right? All I can think of is to make a carrier, if possible, from mat board and see what happens w/ that one.

momus said:

You covered the cut edges of your carrier w/ flat black paint, right? All I can think of is to make a carrier, if possible, from mat board and see what happens w/ that one.

Click to expand...

I did, but the edges were now straight, not beveled away from the negative like they were originally. This was a quick job as a test, and I expected some stray reflections from the straight edges despite the paint, but not the mess I got!

Looks like beveling the edges is the first thing, and filing out the top mask to make it bigger than the bottom hole like before would be the next step.

Duncan

I filed my Omega 35mm carrier to look sort of like this from a side view

Top of neg carrier
V
======>---------<=======
^ ^
neg bottom of neg carrier. Both beveled edged painted black. Zone VI cold lamp, no probs.

Bout that glass carrier. With a diffuse light source any dust on top or bottom of the glass are out of focus. Even on the glass in contact with the neg, effects from dust are mitigated. I can see how with a condensed source this could be a problem.

Oops. the neg is that single line in the middle.