johnielvis

24-Sep-2011, 17:46

sick of seeing people being confused.

since I've been a working with the 1100 xxl a LOT lately on the studio cam in the apartment, i've needed to do some lens calculations....a LOT of lens calculations...tiring of that, I derived some formulas....HERE's what I've derived that are VERY useful for limited space...

first off--everyone knows--exposure "bellows" factor = (1 + M)^2

where M is magnification.

Second--bellows DRAW--total s' distance from lens aperture to ground glass is:

s' = (1 + M)*f

where M is magnification and f is focal length

so the 180mm lens at 2:1...bellows would be 180*(1+2) = 540mm

THIRD...important for close quarters is

TOTAL distance from subject to ground glass= d

d = f*(2 + M + 1/M)

that means at .5 magnification total distance from subject to gg = (2 + .5 + 1/.5)*f = 4.5*f

so the 180mm lens at 2:1 would be 4.5*180 = 810mm total distance.

now for the fun stuff...say you have a lens of focal length f and want to know the magnification possible for a distance d (the above total distance you have from camera back to subject front)...this is:

M = (d/2f - 1) - sqrt( (d/2f - 1)^2 - 1 )

this comes in handy when determining what lens you can use in what room depending on how big a field you want....

I LoVE this stuff....

since I've been a working with the 1100 xxl a LOT lately on the studio cam in the apartment, i've needed to do some lens calculations....a LOT of lens calculations...tiring of that, I derived some formulas....HERE's what I've derived that are VERY useful for limited space...

first off--everyone knows--exposure "bellows" factor = (1 + M)^2

where M is magnification.

Second--bellows DRAW--total s' distance from lens aperture to ground glass is:

s' = (1 + M)*f

where M is magnification and f is focal length

so the 180mm lens at 2:1...bellows would be 180*(1+2) = 540mm

THIRD...important for close quarters is

TOTAL distance from subject to ground glass= d

d = f*(2 + M + 1/M)

that means at .5 magnification total distance from subject to gg = (2 + .5 + 1/.5)*f = 4.5*f

so the 180mm lens at 2:1 would be 4.5*180 = 810mm total distance.

now for the fun stuff...say you have a lens of focal length f and want to know the magnification possible for a distance d (the above total distance you have from camera back to subject front)...this is:

M = (d/2f - 1) - sqrt( (d/2f - 1)^2 - 1 )

this comes in handy when determining what lens you can use in what room depending on how big a field you want....

I LoVE this stuff....