To make an exposure- after you have composed and focused the image, and while still under the dark cloth, you disengage the focusing screen and move it back and away from the focal plane. The focusing screen and film holders run in the same roller bearing track, and the focusing screen needs to be displaced only a few millimeters. It locates easily into its displaced position.
You emerge from the integrated dark cloth and drop down the lid, which seats itself magnetically against the camera back and forms a light trap, blocking all light to the inside of the camera. You already know the aperture, having measured the focus spread while still under the dark cloth, so you need to meter for shutter speed and add any adjustments- then set the lens and shutter. You disengage the preview, or whatever you have to do to your lens; and only then do you insert the film holder into the slot in the back.
To load a holder into the camera, you position the holder parallel to the camera with the flap near the opening, then rotate the flap 90º and insert it into the slot in the back. You rotate the film holder inline with the back, and push it into the slot. As soon as the holder is inserted, and pushed all the way in, you're ready to make a picture. While the film is inside the camera it cannot be inadvertently removed, since the film packet is locked inside. To remove the film holder, you locate the handle on the outer end, and withdraw it back into its sleeve. When the holder is completely inside the sleeve, let's call it a Darksleeve, you rotate the film holder on its hinge another 90º, meaning the film on the other side of the holder is ready for insertion in exactly the same way as the first. It takes a little while to get used to the new sequence of operating the camera, but it would be foolish to complain about a new trick if the problem turns out to be the old dog ...
The Film Holders are contained within reusable packets, like a bag mag, but containing two sheets of film. The target weight for the next batch of (11x17) holders is around 400g complete, using composite materials. The target price for the Darksleeves will be similar to a good used film holder, in sizes 11x14 and up.
The film holder is loaded in a similar manner to a traditional holder, in grooved slots on either side of a septum, and the film trapped using a magnetic composite clip. The light trap to the holder is based on a simple hinged flap, and the ends of the flap are held closed by magnetically assisted intermeshing fabric. The same magnets locate the film holder flap inside the camera. While the film holder is inside the camera, the packet cannot be inadvertently removed, it is locked into position.
As each holder is loaded with film, a pre-printed label can be attached. After the exposure is made, the shooting data is recorded, and the label removed, indicating that that side contains exposed film. A label still attached to the Darksleeve indicates that the film is loaded and unexposed.
The label goes into a notebook. I've never been good about recording shooting data, but since I've started this system, I've been very good...
One other thing- on my travels, I've been using a changing tent, a Harrison Standard 35mm, or 8x10 size. It's a tight fit, but possible, at least until a Jumbo sized one turns up. The film holders are much more compact to load, due to the fabric outer layer- standard holders double in size with the dark slide withdrawn.
So that describes the novel operation of the film holders, but there's more- The back on this camera, like many other large format cameras, is made of wood- American Black walnut in this case. It's a beautiful material to work with, and in use, but there is always the risk of warping, swelling, shrinking, moving- all of the things that wood does. A properly constructed camera made from carefully selected sections should never do any of the things I've described- and the camera should be carefully stored in controlled conditions too. However, you never know where your camera will be used, and climate and humidity will affect the properties of the wood.
A couple of years ago I bought an old Burke and James Mahogany 5x7 back from a well known retailer in the USA and it was so warped as to be completely unusable. A salutary experience…
The camera back and film holder system have been designed to be unaffected by any movement inherent in the material. The film holders run in spring loaded ball raced channels, and can easily accommodate dimensional changes brought about by the widest climatic fluctuations. Unlike conventional holders, they are not required to seat against the outside of the camera, and I don't have to worry about the possibility of a film holder developing a warp either.
Of course, most large format photographers will never have any of those problems, but they're not completely unknown. A completely new design gives the opportunity to eliminate the possibility of poor performance due to the dimensional instability of the materials.