Re: Focal lengths

----- Original Message -----
From: "Andrew Amundsen" <andy@tcinternet.net>

> Can someone tell me what the 12mm lens (in 35mm format) equivalent would
> be in 4x5" format?
>
> I'm using a dual focal length 4x5" pinhole camera which only gives it's
> focal lengths in 35mm format terms (12mm/24mm,super wide/wide). I have a
> chart down to 20mm from my Calumet Catalog, so I know my wide position
> is a 75mm in 4x5". I just need to know the 12mm!

Andrew:

If you believe that 24mm is equivalent to 75mm, then that means each millimeter
of focal length in 35mm format is equivalent to 3.125 millimeters in the 4x5
format ( 75 / 24 = 3.125 ). You can use this constant to find equivalences,
just multiply by the constant when going from 35mm to 4x5 and divide by the
constant when going from 4x5 to 35mm . In the case of 12mm, that would be
equivalent to 12 x 3.125 = 37.50mm in 4x5

I believe the constant Calumet uses is incorrect, it should be about 3.75,
making your 24mm and 12mm equivalents to 90mm and 45mm, respectively, in 4x5
format.

24mm x 3.75 = 90mm
12mm x 3.75 = 45mm

BTW, if you had a 4x5 lens 300mm FL and you wanted to know its equivalence in
35mm format, you'd divide 300 by the constant, like this:

300 / 3.125 = 96mm (using Calumet constant)
300 / 3.75 = 80mm (using the correct constant, IMO)

Guillermo
"If you give a man a fish he will have a single meal. If you teach him how to
fish, he will eat all his life.-- Kuan-tzu (Chinese Philosopher)"
Received on Tue Jun 11 20:23:52 2002