joe mama ha scritto:
> hi,
>
> just as is the case with digital, i am trying to work with a crop
factor,
> but can't figure the math. i have a 4x5 camera that has a 6x9 reducing
back.
> my lenses are 203mm, 127mm and 90mm. what i am trying to fiure out is
what
> "effectice" focal length they become when using the 6x9 back. i'm
guessing
> somewhere around 1.5, but i don't know what to divide, or multiply. i'm
> assuming you take the overall square footage, teh divide the 4x5 into
6x9
> and get the CF. does that make snse???
>
> any help would be great.
Hi from Italy.
Before all sorry for my poor english!
I think you are used to 4x5 format and you are figuring how your lens
will "behave" using them on 6x9 format, compared to 4x5 behaviour
naturally!
Well, the crop factor is a linear expression and not a square
expresion. The simplest way, though a bit rough, is to compare the
normal lenses in both formats (105mm for 6x9 and 150mm for 4x5) and
divide the larger by the smaller.
In this case is 150/105=1.43 which we can consider 1.5.
The lens behaviour on 6x9 will be the same of 1.5 longer lens on 4x5.
For your lens:
- the 203mm will behave on 6x9 like a 303mm on 4x5
- the 127mm will behave on 6x9 like a 190mm on 4x5
- the 90mm will behave on 6x9 like a 135mm on 4x5
As usual in such cases you will gain in long focal and you will loose
wide angle.
Gully
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