Got my first M2 and I have no idea what frame I'm on!

[Richard G]

Meanwhile, back to the original problem: learn to see how much the rewind knob roatates with advancing the film. I've had reason to be watching this on my III recently. At first it rotates only a certain number of degrees for 36mm of film dispensed but towards the end of the roll the roatation is nearly 270 degrees as I recall. For a standard 36 frame roll it should be possible to work out with some accuracy where in the roll you are after watching one frame advance and watching the amount of rotation of that rewind knob.

 

[Richard G]

A roll of 36 Ilford FP4 has a central shaft diameter of about 10.5mm and the full wound film diameter could not be much more than 20mm in diameter.

As the circumference of the wound film is about 63mm (п x 20), the M2 rewind knob should rotate 38/63 = 6 tenths of a rotation (217 degrees) when advancing 38mm of film (a 36mm frame and a 2mm gap say). Towards the end of the roll the film is closer to the spool and for the last frame the rewind knob should rotate more than 360 degrees - 38/31.4 = 1.2 rotations.