Nikon F2 Large Format Backs
In general, the Speed Magny system is designed for use with Polaroid instant-development film. This is most useful for checking lighting and for very fast reportage. Later on, third parties (generally Marty Forscher) would produce special backs for Nikon's F series which allowed direct (i.e. not through the complicated optical gyrations that the Speed Magnys provided) taking of instant pictures. Note that the Speed Magny 100-2 and 45-2 are F2-mounting versions of the SM 100 and 45; the RF never was adapted to the F2. Because the tripod socket location and back-mounting apparatus of the F and F2 are different, the Speed Magnys are not interchangeable.
When the light leaves the rear of the lens, it would normally strike the film residing at the film plane. With a Speed Magny back attached, the light strikes a condenser field lens, reflects off a first-surface mirror set at 45 degrees to the light's path, is sent through an EL-Nikkor relay lens to magnify the image, and reflects off another first-surface mirror at 45 degrees, finally striking the large-format film. In order to make the Speed Magny attachments somewhat compact, Nikon chose to make the two mirrors perpendicular to each other, rather than parallel (as in a periscope), so the film chamber resides under the lens, with the emulsion side facing away from the subject.
Mounting a Speed Magny is fairly easy, since it replaces the current back completely:
Note that because 3.25 x 4.25 and 4x5 have different aspect ratios than a standard 35mm frame, the viewfinder shows slightly more area than will be captured on film. The actual area is approximately 95% of the vertical and 74% of the horizontal; perhaps the T screen would be somewhat useful in outlining this area. This is independent of the vignetting caused by different lens's focal lengths (which in turn is governed more by the location of the lens's exit pupil). These are tabulated below.
Speed Magny 100-2
This Speed Magny is supplied with a relay lens cap, which caps the EL-Nikkor and allows the Speed Magny to be removed without fogging the remaining film. Rotate the knob clockwise so that the "C" mark lines up with the white dot on the body of the Speed Magny. Earlier models do not have this capping feature.
Those of you with Crown Graphics will be pleased to note that you can use 3.25 x 4.25in. film with this Speed Magny, too, although you can't remove the film holder, so you're stuck with what Polaroid chooses to supply, although they do have quite a range of films to choose from.
Speed Magny 45-2
This is the most versatile of all the Speed Magnys, as it allows the film holder to be swapped between the standard Polaroid 4x5 sheet film holder (familiar to most of us who've done microscope photography) and the even more familiar 4x5 cut-film holders (e.g. those from Speed Graphics -- but I'm not sure if it will accept a Grafmatic holder).
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