SP-445 Film system
We were frustrated by the lack of an easy to use, affordable film processing system for large format sheet film. After several prototypes and lots of experimenting, we're ready to launch the SP-445 processing system. It will process up to four sheets of 4x5 film in only 16 oz (475 ml) of solution.
(NOTE: we've updated our Project Description to reflect the latest changes but feel we should leave the original video in place. Please check the updates for the latest details.)
1. Easy to load: Remember, you have to do this in the dark!
2. Compact and efficient: Some processing tanks require 55 oz of processing chemicals! We set a "max liquid volume" limit of 16 oz (475 ml).
3. Simple and reliable: We wanted to avoid complicated seals or a hard to remove lid.
4. Easy to fill/easy to empty - and make it fast. We hate having to slowly trickle solution into a tiny fill port, waiting impatiently for the bubbles to clear so we can add more solution.
5. Excellent agitation: Inversion systems are prone to leaking; rocking/sloshing/tilting systems give marginal performance and rotary systems get complicated.
6. Inexpensive: It's just a plastic tank, it shouldn't cost more than your camera.
7. Observable: Can you tell that you've got the right amount of solution at the right temperature?
Meeting the Goals
1 - Easy to load
After a lot of experimenting, (including some wacky ideas), we realized that the perfect solution was right in front of us: the standard 4x5 film holder. Everyone already knows how to load it and you don't have to count grooves, (with your fingers in the dark) to make sure you're sliding the film into the right slots. Just like your standard film holder, each holds two sheets and the tank will hold two film holders. Here a picture of our 3D model: It should look familiar, it has the same two slots on the edges that all 4x5 film holders have. Note all the grooves on center plate, these are to help reduce surface tension when removing a wet sheet of film. Also, we've added a tab on the top to help you pull it out of the tank.
2,3,and 4 - Compact and efficient; Simple and reliable; Easy to fill/easy to empty
These goals are at odds with each other, so we had to think outside the box (or tank). Take a look at the cutaway rendering below, notice that we've moved the fill/drain port from top (its tradition location) to the end.
In fact, the entire end of the tank is the light baffle/fill port. You can see the baffle plates (with all the slots) and the frame rack that holds the film holders (orange).
You fill and drain the tank using the "spout" on the end. By redesigning the fill port and putting two sheets of film back-to-back, we significantly reduced the width of the tank. The new prototype will require about 475ml (16 oz) of solution but will accomidate up to 500ml.
Don't let the efficiency worry you. Remember, four sheets of 4x5 film have roughly the same surface area as a roll of 120. People have been processing 120 rolls in 400ml tanks for decades.
5 – Excellent agitation
So how do you agitate? Our original idea was to introduce the "turbulator" as described in the into video. This was the plunger shown in the first video. By pumping the plunder up and down, the piston action creates turbulence in the main chamber.
However, after further testing, we found it was probably too effective and we were getting uneven results with some black and what films.
Note: the reward description still lists a 'turbulator' as part of the package but we will not be shipping one at this time. (Kickstarter won't let us edit the reward text.)
So we're dropping back to the old stand-by: inversion. As detailed in the updates, we're developing a water-tight lid. The basic form of the SP-445 isn't changing, it will still have the light baffles on one end, hold two film holders, fill/empty with the spout.
6 - Inexpensive
This one was trickier. By the time you add up molding costs, shipping, development effort and leave some margins for distributors, it's hard to keep it under $100. But we did. We expect the "suggested retail" will be around $80-$90. However, we're running a special price for Kickstarter supporters: $47/system (plus shipping).
7 – Observable
I like to know what's going on inside the tank. By moving the fill/drain port to the edge, you can easily insert a thermometer during processing. You can also check that you've added the correct amount of solution by just looking at the level in the fill chamber.
A $27,700 funding goal?
It may sound like a lot of money but there are three major expenses to consider:
First, with the prototype is finished, it's time to start optimization. This will require several more sessions at the 3D print shop and/or at the machine shop. In addition, we'll actually have to shoot film for test processing.
Second, and most significantly, injection molds aren't cheap! And we'll need at least four, possibility seven:
- Main tank: pretty straightforward but deep with lots of grooves.
- Lid/top: Very straightforward. Shouldn't be a challenge.
- Lid lock: very simple part but if we decide to shoot it in a different color (black gets boring and we feel that the lock should be more noticeable), it would require its own mold.
- Film Holder Rack: supports the film holders and forms part of the light trap.
- Baffles: These are the two inserts that form the light-tight fill port. We hope to be able to fit both pieces in one mold with the Film Holder Rack.
- Film holders: Now things get tricky. Since we'll need two film holders per system, this should be a multi-cavity mold. That means a larger press and a more complicated mold. There are also some thin features that could be challenging.
- Tubulator rod - another mold. Might be able to combine with the baffle plates and rack.
Third, minimum production runs can be a real gotcha. We don't know exactly what the minimum production run will be, since it depends on a lot of factors but we expect it to be well over a 1000 complete sets. By having backers pre-committed to at least half the run, the risk becomes acceptable.
Fourth, (turns out there's a fourth), Kickstarter and your credit card company want their cut too. We don't blame them but we need to account for the 8-10% they'll take off the top.
Risks and challenges
This isn't our first injection mold! In fact, compared to some of our other projects, it's pretty tame. We don't see any major surprises but you never know. Stuff happens.
The biggest challenge will probably be the film holders.
First, the grooves that actually hold the film are pretty narrow and we're going to make them a bit wider. In theory, this could allow the film to float up. We'll need to do some testing but the easiest solution might be to just rotate the holder 90 degrees (hold the film on the top and bottom edges, then it can't float.)
Second, because the film holders are so thin, they could be a challenge to mold as one piece. Worst case, we'd have to mold it as three pieces (two outside rails and the center) and glue them together. (This is how we built the 3D printed prototypes.) While it isn't ideal, it could still be done in one mold but at the cost of a longer cycle time.Learn about accountability on Kickstarter
- (34 days)