One of the basic concepts of the Pinhole Lab Camera is that the negatives are even divisions of the most common photographic paper, 8x10 inches. That also means you have to cut the paper - accurately - under safelight.
Original description link Construction post link Link to Templates
A paper cutter is a common thing to find in a darkroom, but not always, and it's a bit of an expensive thing to get. I cut paper by putting stripes of light colored tape on a cheap cutting mat at the distances from the edge I want to make cuts, in this case 2½, 4, and 6 inches, and cutting with a steel rule and a craft knife. Your risk management officer wants me to remind you that this could be dangerous. Put the knife inside some kind of box with a white interior so it doesn't roll around and you can see it under safelight. If you haven't done this much before, practice a little outside the darkroom. Safelights can be pretty dim so wait till you're dark adapted and make sure you can actually see what you're doing. Put the cut pieces of paper in a light tight container.
I may have given the impression with the slots and ridges that you just have to place the paper in, close the camera and it'll stay put. A moving camera gets jostled about quite a bit, and if the paper doesn't stay in place - no picture.
The solution, as my young students would tell you, is more tape. Wrap a loop with the adhesive side out, and place it in the middle of the paper.
Then place it and press it down where appropriate for that format and give the camera a little shake to make sure that bit of tape keeps your negative in place.
These bits of tape should be considered consumables. They get misplaced in the darkroom easily and they don't last forever. I don't think they harm the chemistry much if forgotten during development, but you sure wouldn't want to use them with unexposed paper afterward.
For the 2½ inch distance, for both the square and rectangular formats, place the paper down toward the rectangular end of the camera and adhere it to the square side opposite the pinholes.
For the four inch distance, the paper goes in the Back. The Back is slightly larger than the paper, so try to get it square when you place it there. You might notice that the paper isn't perfectly flat. The pinhole doesn't care, and that's all part of the fun, eh pinholers? If that's a problem, the solution is, of course, more tape.
The curved formats are also attached with tape, again adhered at the center of the paper. Try to get the ends of the curves equal distance from the front of the camera.
I'm going to try to get the template so those ridges are a little closer to where they should be, but I wouldn't trust them to hold the paper in place while transporting the camera if they were the exact right size.
For the curve at the four inch distance, it's a slightly different process. Again, put the tape in the center of the paper and adhere it down with equal ends of the paper sticking out of the Back.
Then squeeze the sides inward a bit, insert them into the box, and place the Back of the camera on. (This really does look like I'm feeding it.)
Before closing the camera, check that the Pinhole Mount is still under the Pinhole Mount Lock. If you had some black or red tape, it wouldn't hurt to tape it in place. It has a tendency to get popped out from under the Lock during particularly excitable closing of the shutter and rubbing it to make sure it adheres.
The tape for the shutters should also be considered a consumable, and as noted in the construction post, you should carry spares.
I've recently found a couple rolls of 3M plastic tapes that you might find available: Black Colored Plastic Tape (the people who named that must not have grown up in the South) and Decorator and Repair Tape. They are lower tack than I remember but these rolls could be 10 years old. I'm kind of liking them for shutters because the handle flaps tend to lie flat against the camera and out of the way. The classic, of course, is opaque black photographic tape which is still available in a few brands. If you want to splurge for this and get noticeably higher quality, you can get 3M #235, which is a truly iconic material, but it's going to cost you as much as all the other materials. n.b. I also found a couple old rolls of electrical tape that wouldn't stick to the cardboard at all.
One problem with using tape as a shutter is it's tendency to pull off fibers from the card stock both damaging the camera and reducing the adhesiveness of the piece of tape. The solution to this is, of course, more tape. By placing a layer of your cheap masking tape around the pinhole, you create a surface that is more forgiving of adhering and removing tape. You might even be able to use black duct or gaffers tape for shutters after making this modification if you could tear it accurately in these small pieces.
Viewfinding is done with the aid of our first accessory, a cardboard straight edge. Because card stock has the tendency to curl, fold a piece the long way and clamp and glue to counteract that. It's not steel, but if you're careful, you can keep it straight.
The idea is to align the straight edge with the mark you made of the location of the pinhole on the sides of the camera in the front and where the edge of the paper is in the camera at the back. With some of the formats that's the corner of the box. For the 2½ x 4 inch format at the 2½ inch distance, as illustrated below, it's the front side of the Light Trap. You could also place marks where the curves intersect the side of the camera.
If you sight down the straight edge so it looks just like a line, you can see where the limits of the image will be. Previsualizing where you want those edges to be is part of the zen of pinhole thing. I think most photographers have some idea before they put the camera up to their eyeball, but it can be an odd thing for some people. (Pro tip: they're usually not as close as they should be.)
Of course since even the shortest of exposures is going to be fifteen seconds, the camera needs to be supported absolutely motionless. The iconic place for this is on the ground, but I find it tiresome that this often fills half the frame with a featureless foreground of the pavement of the school parking lot. That rising front pinhole should help a little with that.
The ultimate support is a tripod, and we'll get to that eventually, but the rising and falling front give you a some pointing flexibility if you have a level place to set the camera.
You'd be surprised how many benches, tables, chairs, trees, information kiosks, refuse and recycling bins, planters and walls that are nice and level that you can support a camera on that gets the point of view off the ground. Place the camera right on the edge so you're not just substituting the featureless top of your support for the pavement.
Note you have to hold the camera down when you take the tape off and you're liable to move the camera a bit when you remove your hand. With long exposures on a cloudy day that's not going to make much difference as long as you don't actually change where it's pointing. For shorter exposures of fifteen to thirty seconds on sunny day, you can probably hold the camera down with your hand.
The camera is very light and susceptible to being blown away by the wind. For longer exposures, unless you plan for a place to sit and rest your arm, most people can't keep from involuntarily wiggling and moving the camera if they try to hold it down for more than a minute. In that case you could find something you had around that you didn't use very often and had a little heft to it that you could set on the Pinhole Lab Camera to hold it down.