I drum scan a lot of film and the majority of it is pretty close to 96mm x 120mm (exactly so for modern fidelity's that I own)
The 1951 ASA minimum diminsions are 3.636 x 4.686 inches with no maximum specified, but that proves nothing about what our holder diminsions are.
Of more concern to me than exactly where the film sits in relation to the ground glass is the fact that the glass-type Omega negative holder that I use is slightly smaller than the exposed area of film. I have had to learn to compose a bit less tightly to accomodate.
My Grafmatic septums give me 3.75 inches x 4.75 image area and I use a filed negative carrier that gives me all of that on my prints. (But if you consider the frame number wheel encroaches some of the image the usable long dimension is close to 4.686 inches).
To me, that means you may have to pick a film holder of one type, and duplicate it brand for brand, and vintage for vintage. The best way to do that would be to pick a desired holder and stick to it for all your shooting. For instance pick on brand and buy ten boxes of pairs up front.
Secondly insert them in the camera. I don't think they slide around as much as you've been advised here. The ridge for locating/registering the holders in position will be consistent on the camera and consistent on the holders because of the matching of type, brand and purchase date of the holders.
You should then end up with 20 DDS holders, unless you go to another holder system, that are identical in size of area of film exposed, and location in the back of the camera.
Then take a sheet of film (exposed, or negative shot) and slide it into one side of one of the holders. Then take a sharpie (fine point) and run it around the inside of the holder opening. Before you do this, slide the sheet of film to one side and one end, scribe a line, then move the film to the other end and other side of the holder, and scribe another line. Frankly, I don't think there is as much movement within the holder as has been mentioned here, but at least you will have a tolerance measurement. In fact, if you do this first on one holder and find there is much tolerance, then your expectation for this type of system is unrealistic. You should just drop the idea, load film, go ahead and use a grid, but go shooting and enjoy yourself.
If the tolerance is livable, the go ahead and create your grid on the ground glass, or on a thin sheet of overlay behind the ground glass.
Just remember, you will be limited to the holder system you design the system around. If you change to other types of holders, repeat this exercise again with the change, but if you go to multiple holders, you will need to match the holders for type, brand and consistently same purchase date.
Waste of time in my book. This is the kind of exercise I would dream up if I were afraid to load up some film and go shooting.
Not the grid.. the grid is a good idea. Exacting placement and the limitations already listed is where the waste of time comes in. Placement of the grid and not worrying about exact duplicate position will not negatively affect your images.
Guys, Thank you very much for all the wonderful information. I am indeed creating a gridded pattern on which I just wanted to have a rough idea what I should be composing to.. the whole glass or a rectangle within it... I have marked up a 94x120mm square as a guide to this and printed it out on a sheet of transparency. So this should be attached on the back of the ground glass? Not sandwiched in between the fresnel and gg?
Do you think this is going to improve your work?
Sounds like a pain in the ass, especially adding another layer of material between you and the image on the ground glass.
If you add a grid to a properly functioning ground glass and fresnel, it should be closest to the eye, not in the optical path between lens and focusing surface. I prefer lightly scribing a grid on the ground glass with something like a steel needle. This is less obtrusive than most printed grids.
I have heard the term "pin-regestration" in the past used in the context of overlaying negs in printing or in animation. ArePin-Regestratinn film holders what the OP should be looking for?
Am I confusing the term with something else?