DIY unsharp rig for 35mm/120
I recently took a stab at unshap work, on medium format and 35m work, and here how I attacked it:
I made a u channel about 8" long using foam core board strips about 2" wide glued to another piece of foam core. They are placed the width of 120 film wide. In the bottom of the channel I glued a piece of matte black paper in place to prevent reflections from mucking up the exposure the bottom peice of film gets. There are also 2 pieces of 1/8" glass that is the width of 120 film, and a bit longer than one exposure that sits on top of the film sandwich to hold the films together during exposure, and a piece of frosted mylar (ala back when drafting people used ink) taped between the two pieces of the glass to act as the diffuser. I sanded the glass to make sure no sharp edges exist to scratch the original negative.
With the lights on, I take the negative of choice, and pierce the film between exposures at at least two locations, by pressing through the film while it rests against a claen scrap piece of foam core. Piercing an exposure one or two away from the negative area of interest makes it easier to place the glass block.
On the channel I temporarily lay the film in and add extra push pins on the edge channels to denote where to place the glass and diffussion.
Under safelight, I work with ortho lith film as my masking film. I take 8x10" sheets and trim them 120 format wide by 5" long in my paper cutter, while wearing cotton gloves. Cutting 4x5 down could work as well. By making them 5" long, the handling while processing gives you somewhere to hold onto with tongs, etc, while procesing without having to touch the mask of interest area.
Under safelight illumination the lith film is placed emulsion down in the foamcore channel, lined up so it fits between the pine denoting the area of interest, and also so that it gets stabbed by the two pins. The film is then placed on the channel, (in my case, emulsion side up, but I have seen it as going down as well). Under safelight I am able to see the existing pin holes, and place the pins now through the film, lith film, and into the foamcore channel bottom.
The diffusion glass block goes on, and the assembly is placed generaly under the centre of the enlarger lens. I have previously set the enlarger to a standard height, aperture, and make sure that there are no filters dialled in, and lens is focussed on an empty carrier (about 40cm, F11 for me). I find that 120 carrier requires that I give a 10 second exposure to the lith film, and 35mm requires that I give a 20 second exposure.
The lith film gets extracted from the carrier and is put into a 5x7" white plastic tray. About 100ml of low contrast developer is poured into the tray (enough so that the neg can slosh about, and not sit stuck over a tray rib, or a bromide streak will result) For lith, I have successfully used T/O XDR-4 to get continous tone out of this film; there are likely other developers used very diluted that work fine as well.
The tray is continuously agitated. At about 2 minutes the negative usually 'looks' to me to be about a .35 density; develop longer if you need a denser mask. I pull the mask film, rinse it vigourously in a water bath, and then dunk it in a TF-3 rapid fixer for about twice the time it takes to clear ( under two minutes minutes), and wash it for a minute or two more. I squeege it between my fingers, shake it dry, and hair dryer it the rest of the way to dry if I am impatient at the moment.
The dry mask goes back on the pins, and then bits of tape are used to hold the sandwich in registration when the pins are pulled, and the sandwich positioned into the negative carrier. I find sprocket holes (in 35mm) and film edge markings are good to get close, but look very carefully to make sure all is lined up, particularly with 35mm with its film curve.
Using this proceedure I make masks 'on the fly' during black and white printing sessions. I find by pre-pinning the neg I can hold the channel at an angle to the safelight and see the pin holes under OC amber safelight levels. If I am doing a lot of masks I might go and change to 1A red filters, to brighten the scene up while working only with the lith film.
To date I have not attempted to use pan film, to do unsharp masking with colour negatives. Howard bond has developed curves in his article in last years sept/oct and nov/dec Photo techniques, but I have not yet fully deciphierd his techniques on using them. I use my colourstar analyser in denisty measurement mode to get the denisty of the negative while it is projected onto the baseboard, and it be zeroed to automaticaly subtract film base plus fog, so that helps to speed the math along.
