This application will help you to find the correct exposure time for shooting macro photos using extension rings or bellows.
Extension bellows in most cases dont allow automatic exposures.
So, you have to select Manual Exposition in your reflex camera.
The best thing in this case is to measure the amount of light reflected by the subject, using an external exposure meter: this will indicate an exposition value (EV) normally ranging from 1 to 22.
Then, you should make a number of computations to find the correct exposure time, taking into account several parameters:
Exposition Value,
Lens focal length,
Bellows extension,
Sensitivity (ISO),
Diaphragm aperture.
Using this application, you only have to enter the above parameters, hit the Done button on the virtual keyboard, and the optimal exposure time will be quickly computed and shown, avoiding complex calculations.
Beware that the result can be computed only if all the required data have been entered with likely values.
Then, if you want to take more shots, changing one of the parameters, you only have to re-enter just that one, and the new exposure time will be computed and shown. Changing the diaphragm aperture, you will find more equivalent diaphragm-time couples.