newbie question on Extension Tube / Bronica ETRSi

[raytoei@gmail.com]

hi,

this is a newbie question.

i have an extension tube e-28 (e-14, and e-42 are the others) for my 75mm lens.

how do i calculate the exposure compensation factor for this tube ? I do have the AE II but since I am using external flash, I think the exposure compensation will have to be done manually.

from what I have read,
since i will be using f11 for the shoot,
75mm / f11 = 6.81818
75+28 = 103 and so the new relative aperture will be 103 / 6.81818 or f15.1 which is approximately one stop from f11.

so this means I have to increase EV +1 or open up one stop to f8 if I am using extension tube ?

is this correct ?

thanks

raytoei

 

[pvdhaar]

That's correct and corresponds to what you get when you start from magnification: in this case 28mm extension / 75mm focal length= 0.373. Then using the correction tables from e.g. Kodak: http://wwwca.kodak.com/CA/en/consumer/guideToBetterPictures/extensionChart.jhtml
this works out to be just a bit under a stop.