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Improving the SP-445 film holder.

Tim Gilbert

A brief history:

Let me try and make a really long story, somewhat shorter.

The first prototypes were completely flat, had a solid groove on each edge to hold the film and did not have the finger at the bottom edge. They were also 3D printed and felt flimsy.

The first change was to add the ridges: these reduced surface tension when removing the film and increased the flow behind the film. They also added stiffness.

We then chopped up the solid grooves into "fingers". This improved flow but also made the mold much easier to manufacture. Last, we added the finger on the bottom edge to keep the film from sliding out.

So far, so good. Great even. People find them intuitive to load and we've gotten rave reviews.

However, a few users, (about 3%), have reported issues. The good news is that none of these seem to affect the actual image quality but they're still annoying.

Fingerprints: These are solid bars in the margins of the film and match up with the fingers on the film holder. Fortunately, they're outside the image area (for the most part.) They're very sporadic; you'll see them on a sheet or two and then not see them for several tank loads.

Note that the film holder fingers have .025" of clearance. (This is 3 times the thickness of most film.) You can use fine sandpaper to increase the clearance. Just slide the sandpaper in place, rough side up, and remove enough material that your film slides in/out easily.

Also, make sure your film holder is flat. Though the fingerprints may be more related to the curliness of the film than to any aspect of the holder.

Blue or Green Bars on the back: Several people have reported that the anti-halation coating didn't completely wash off the back of the negative. (This coating keeps light from reflecting off the back of the film holder and blurring the highlights.)

While we've seen this occasionally, we don't have a sample to show you; we just rewashed the negative. Problem solved. To keep it from occurring, make sure the film isn't pressed tight against the film holder before washing.

Streaking: Several have reported numerous lines or streaks on the back of the film. You may have noticed these in the previous image.

At first glance, these seem to line up with the ridges in the film holder. However, when viewed under the microscope, you realize that something else is going on.

After consulting with industry experts, we believe that the issue is "differential drying". This is a result of using too much wetting agent. (In fact, one chemist told us that it is almost impossible to use too little wetting agent.)  A rough analogy: using so much soap to wash your hands that you can't get the soap off. Anyway, it can cause the film to dry unevenly. It is probably amplified by the ridges "protecting" part of the film.

The good news is that none of the lines show up in scans or prints but they're still disconcerting. We've sent S-445s off to Ilford's lab for review and will let you know what they find.

Now what?

We've learned a lot about film holders over the last year and we realized that they don't need to be as heavy as we first thought. (Our original opinion might have been influenced by the flimsiness of the first 3D printed prototype.)

We've tried a lot of different modifications. Here's a photo of our latest and simplest:

This takes about 5 minutes with an X-Acto knife and sandpaper. (Assuming you know how to handle a knife.) You might find that it helps to drill a small hole in each corner before starting.

4x5 film is stiff enough that it stays on it's own side the holder. So far, everyone who has tried it, has reported success.

Our next production run will probably incorporate some version of this mod.

Comments and suggestions are always welcome.


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