Mathematics Applied To Holga Cameras
Mathematics applied to HOLGA cameras by stouf (via Lomography Blog)
“I ‘m going to make underwater shots with my HOLGA. I’ll put it inside an ewa-marine housing. Problem is that I won’t be able to see the shot number from the back…
So I though to make an external shot-counter. When you roll your film, you turn the wheel of a certain angle to fall on a correct shot position. This angle reduces as the diameter of the roll is increasing. Here, I used an empirical analysis (empirical means by experiment) to determine the good angles needed to turn the wheel in order to make 12 separated shots on a 120 film.
To make measurements of the wheel angles, I placed a sticker on the wheel, used my HOLGA normally (by watching shot numbers in the little red magic window) and noted every position of every shot on the sticker. I did this for four films (Provia, Sensia, Velvia and a strange one I forgot the little name). Then, I calculated a mean rotation angle over all films to obtain a mean measurement applicable to all films (I hope) by applying a third order polynomial regression. Finally, I produced a very sexy external shot counter with photoshop, printed it, and sticked it on the HOLGA wheel. I tried it recently… I don’t know yet if it works and if I deserve a Nobel… We’ll see… I’ll tell you soon how practical testing of my hypothesis went.
And as science is about sharing information, I put here a copy of the counter. Print it with the good size, stick it on your wheel and shoot. Oh, by the way, this is also useful when you do 70 mm and you can’t open the red window (‘cause 35 mm are transparent, you know…).
Oh yes, finally note that before shots N° 10 and 11, you must turn the wheel more than 360°… And after, less…
(via Lomography Blog)