FFD Question (Flange Focal Distance)

[calebarchie]

Hi guys,

This might be a weird or silly question but in the sense of adapting a lens and the FFD is out by exactly 2.5mm (longer) are you able to calculate where the lens is actually going to be focusing?

Will it turn into some kind of macro? I suspect it will act much like an extension tube..
It is a 50mm focal length with an unknown magnification factor.

Thanks for the help.
Caleb

 

[bernard_L]

I suspect it will act much like an extension tube.

Correct. And, assuming it is indeed this way around (lens too far from film, not too close) your farthest focusing distance will be 50²/2.5=1000mm.

 

[calebarchie]

Correct. And, assuming it is indeed this way around (lens too far from film, not too close) your farthest focusing distance will be 50²/2.5=1000mm.

Hi Thanks for the clarification. I also figured the MFD would be around something like 36cm.
Although can you provide the explanation behind that formula? Because if it really is around a meter focused at infinity then this plan of mine might actually work!

 

[ic-racer]

1/p + 1/q = 1/f