Originally Posted by jamie young
Yep it's the distance between h and d as drawn
Thanks Jamie, thanks Len, thanks Clayton!
Now, it seems a clear and univocal description of the "variables" involved in the formula .
The "variables" are (in summary):
1. - the actual focal lenght;
2. - the "large gear radius" ;
3. - the "Diameter of film drum with average amount of film";
4. - the "Perpendicular distance from center of small gear to the LENS AXIS": as made clear by Jamie, is the distance between H and D in the previous drawing;
5. - the "Perpendicular distance from center of small gear to the FILM PLANE" (NEGATIVE IF FILM PLANE IS BEHIND GEAR: this happens, as clarifyed by Jamie, in #5, #6, #10 and #16 cameras);
6. - the "Slit width";
7. - the "Gear pitch" , with the meaning "diametral pitch" (rounded value of "number of teeth/outer diameter of the large gear, measured in inches").

So, after you give, in the formula (in http://digilander.libero.it/foto_ras/Cirkut_gears.zip) the correct "starting parameters" (or, as an alternative, fill with those values the file gearsInput.txt), you are prompted to type (I'm guessing from my trials of the program) the values (or - it should be the same - the number of teeth) of your smallest and of your largest "removable gear" available to you (the "small gear" above); finally, the program will determine the distance (from FP or lens rear nodal point) of the subject for which is necessary to use a "complete seat of gears" in a 1-1 step, from the highest to the lowest valued typed; the distance is expressed in inches or in millimeters, according to the initial choice.
In case the resulting distance is negative, that means that the gear is not appropriate.
This is what I've undestood: hope it's right ...

BUT (sorry, don't kill me ) a final question (really: no more questions!) is still alive. In theory of panoramic photography (as I can see from the articles in "Panorama"-IAPP Magazine, from 1999, downloaded completely: thanks to IAPP!) the rotation axis should be on the vertical of the real nodal point of the lens, otherwise some adverse effects could occur (blurring, I suppose). But in Cirkut it never happens! The pivoting axis is alwais between the lens and the film plane. In theory, the pivot should be in B, but in Cirkut cameras the pivot is in A .

What does it mean ? What does it implies ? No bad consequences, it seems, because none of panoramic photographers using Cirkut cameras reports them. So: 1) is the theory wrong? 2) are those possible bad effects obviated by some special feature in Cirkut cameras ? or is due to a systematic presence of Saint Veronica on the side of the photographers ?

Tahnks a lot !
Roberto.