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Laser Cut Masks for my Durst 54 Enlarger (The Beast)

Two years ago I picked up 'The Beast' a Durst Laborator 54 Universal Camera 4x5 enlarger at the very satisfying price of free. I have installed it up in the top floor and have gotten some good use out of it but not often. I don't shoot a lot of 4x5 and print it less frequently. Recently however I have printed my 4x5 Gladiolas negative on it.

I have also had my Fuji GSW 690 camera whose 6x9 negative does not fit my original Meopta enlarger as it can only handle up to 6x6 negatives and an old MPP 6x9 rollfilm holder for my Intrepid 4x5 MkIII. This experience has reminded me that I am missing some key components from the enlarger. Namely I need a 4x5 and a 6x9 mask. I have a 6x8, 35mm masks that came with it. Previously I found I could suspend a 4x5 negative in the negative holder but it is rather tenuous and difficult to place it in the right position. I also learned in my last round of printing that light leaks around the negative and can produce noticeable glare on the print. This situation could not persist. To no avail could I find the requisite masks online.

Fortunately  I had recently been experimenting with a new online service I discovered called RazorLab. They will laser cut from different material any design you submit. I opted to see if this could help me here.

I chose as a material black mount board as this is cheap and is the right thickness. The challenge with this service is to find ways of solve problems in material that is essentially 2 dimensional. Here is what I ended up with.

First let's see what I am imitating. This is an example of the factory Durst mask for a 6x8 negative. It consists of 2 aluminium plates with locating studs on one side and matching holes on the other. Note the inset for a single negative to sit. I cannot make this in RazorLab so I ignored this. Also in general I do not separate negatives as they are difficult to manage in sleeves. The locating studs also serve to align the negative.

Original 6x8 masks
Assembled masks
I got the outside dimensions from carefully measuring my existing masks and got 154 x 123 mm. I used Inkscape which is a free drawing program that is one that RazorLab can accept vector files from (svg format). The drawing of the top and bottom masks are formed as below. In Razorlab cut lines are pure blue with a thickness of .010 mm. Anything in blue the laser  will cut through the material. Etching is indicated with other colors. Since these lines are so thin I thickened them to show below.

6x9 mask outline
Within the overall shape is the 6x9 window. In the process of doing this I discovered that I have 2 different sized 6x9 negatives. One is from my Fuji GSW 690 camera and the other from an MPP rollfilm back for my Intrepid MkIII camera. The roll film holder is about 5 mm longer. This surprised me as I made my first set of masks and then grabbed a 6x9 negative to check the fit and found the window much too long. So I made a new set assuming I had made a mistake (I also improved the 4x5 design in the same batch). This time I found the window too small. What the H???? While putting this post together it dawned on me that I might have used negatives from the two different cameras. Carefully checking I saw my first set were of the correct dimension for my MPP 6x9 rollfilm holder while the second one was good for my Fuji. Good luck after all and I had not lost my mind.

Outside the window I placed some alignment slots. The idea behind these is two-fold. These slot widths are same as the thickness of the card (about 1.4 mm). I cut two thin strips from the card of the same length and wide enough for the thickness of two card thicknesses. (about 3 mm). These I glue into one mask that is the base so the strips stick up. Then when I take another identical mask and place it on top the strip inserts in the slot of the top mask and helps align the whole thing. I space these slots so that they also help align the film strip image edge to the edge of the window. This should make it easier to keep the negative aligned while loading it all in the enlarger. 

Finished Cut Parts
Here are the parts as they arrive from RazorLab. This is black mountboard with 2 masks shown. On the back side one can easily see the burn marks from the laser cuts; there is a small of burnt paper and the soot should be cleaned off as well. Note also the two small black strips mentioned above that fit into the slots on one of the masks. The view below I try to show the glued in strips protruding.

Glued-in strips
This allows for alignment of the tops and bottoms as well as the film strip.

Negative in mask

As mentioned I also made a 4x5 version of the mask. Again I used the same outline but of course a larger window (119 x 95 mm) made by careful measurement of the image area of negatives. The window needs to be slightly smaller than the negative of course to keep it from falling through.

I also changed the alignment strategy as I am dealing with sheet film. This allows me to use a corner location strategy for alignment in both dimensions. The Inkscape drawing follows...

4x5 mask drawing
Here I re-use the same slot  (and alignment strip) dimensions from the 6x9 version. I merely place the alignment slot where it will ensure the image portion of the negative will appear at the edge of the window. The assembled pieces appear as follows...

Finished 4x5 masks
The next photo shows the negative snugged up against the alignment strips.
Alignment strips in action
And finally the top is placed  on the bottom mask completing the negative sandwich.

Negative Sandwich
This works quite well and avoids the problems of having glass in the mask such as newton rings and extra surfaces to collect dust.

Here is a video explaining and showing the finished pieces.

Finally I want to comment on further improvements. 1) The 6x9 alignment strips are too close together for some films. Indeed on reflection there is no real need to have them match the exact width of the film as you only needs one strip to align the image properly in the mask. The other is useful to keep the two masks aligned. 2) It may be useful to have the top mask slightly wider than the image as this may make it easier to see how the image is adjusted (left/right) with respect to the top mask. 3) The base mask alignment slots could be narrower to make for a tighter fit for the strip. The top mask should remain somewhat wider to make the whole thing easier to assemble.

My final design file will include both widths of 6x9 negative for my two cameras. It will also have the one alignment strip further away from the window to make it accommodate more variation in film width. Finally I will make the bottom mask slot narrower.

Finally some links...