Tweaking frame registration of Nikon FM series cameras

Discussion in 'Nikon' started by arnabdas, Apr 27, 2009.

  1. Not sure if at all possible but had to ask -- does anyone know if it is possible to tweak frame registration of Nikon FM series (FM2 or FM3A) cameras to space them a bit more apart?
    Essentially, I'm trying to put a gap of about 4-5mm between each frame and it's ok if I get 34 or so exposures per 35mm cartridge.
    Possible to do without much risk of ruining the camera?
  2. Arnab, I don't know for sure. Usually there is a gear that can be tweaked with a different ratio, but don't ask me which one<g>. But the reason I jumped in is to let you know a half-frame FM was made at one time, so it makes me think it is possible. Maybe talk with a good repair shop who knows mechanical cameras and see if they can help. SK Grimes comes to mind because they do machining.
  3. Hi, Arnab,
    Good to read your post here again. I'm not sure of your intention, but I'm afraid modifying the camera that way should be impractical or would at least require a redesign of the (part of the) film transport mechanism.
    How about just making dark frames (shot with a cap on the lens) alternating with the normally exposed frames? You will lose about as much as 18 frames but you can have more spaces between the frames.
    Or, do you want one complete film roll (or each pair of frames for stereo) with specifically 4-5mm spacing?
  4. What the F for? Just buy another film. Its not like they are expensive.
  5. The standard is that there are exactly eight sprocket holes per frame. Because of the way the perforations are spaced, there will be exactly 38mm between the start of one frame and the start of the next frame. If the film gate is 36mm wide, that leaves 2mm between frames. The film sprocket to the right of the film rails is what meters the film through and counts off the perforations. I don't know of a way of making the sprocket move more than eight perforations per frame, but I don't know much about the underlying mechanism.
    Would your needs be satisfied by blocking off a bit of the film gate, so that your images end up being 34mm wide? That would leave 4mm between frames.
  6. I think it could be done, if you have the machining capability to reproduce 2 gears in the advance train such that one is a tooth or two larger, and the other a tooth or two smaller than the originals ... but you will be restricted by the fact that you can't change the center-to-center distance between them so you may have to cut your new gears to a different tooth pitch from the originals in order to make it all fit. The amount of spacing you end up with may be whatever is the closest you can get to what you want. I don't know if you could get a machine shop to do this for anything like the cost of several Nikon FM3As, and of course the equipment to do it yourself, assuming you have the skills to use it, would cost much more than that. But if you were, for instance, Nikon, I think it's doable.
  7. Richard Cochran: Interesting, if you measure the projected image with different focal length lenses, you'll find the image size changes. Telephoto lenses will be approximately 24x26 but wide angle lenses will be somewhat larger. Actual measurements (all prime lenses on a Nikon F2): Nikkor 105mm, 24.01x36.03; Nikkor 20mm, 24.41x36.21; Heliar 12mm, 24.56x36.81
  8. Thanks guys for the insights. I was thinking perhaps there is a way to increase the "throw" of the film advance lever but looks like it's not simple.
    I forgot to mention that I need to achieve this for a modified film holder I am having made for my scanner -- this holder could hold film flatter compared to the unmodified OEM holders only if I could leave a bit more room to the sides of the frame.
    Thanks again,
  9. Hi Paul: This is because of the different angle at which the rays of light pass through the negative opening toward the film: the cone of light from a short lens will be broader than that from a telephoto, so the illuminated rectangle on the film is slightly larger. The hole in the aluminum chassis obviously has not changed, nor has the 8-sprocket-hole registration distance from each frame to the next.

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