Why are lenses never measured in square format ?

[alex from holland]

I am just wondering
Why are lenses never mesured in quare formats.
We always talk about lenses suitable for 4 x 5, 8 x 10, etc.
But they actually cover 5 x 5 or 10 x 10.


Alex

[Leigh]

First...
Because they're defined in terms of common film formats... 4x5 is... 5x5 is not.

Second...
A lens that covers 4x5 might not cover 5x5, since the diagonal of 5x5 is larger than that of 4x5.

Lenses for some medium format cameras, particularly Hasselblad, are measured for square format (6x6).

- Leigh

[sanking]

I am just wondering
Why are lenses never mesured in quare formats.
We always talk about lenses suitable for 4 x 5, 8 x 10, etc.
But they actually cover 5 x 5 or 10 x 10.


Alex

Actually, lens cover a circle, not a square format.

Sandy

[sully75]

Actually, lens cover a circle, not a square format.

Sandy

snap!

[Vaughn]

Just for fun, I drew it out. A circle for 5x5 is about 7" and for 4x5 is about 6 3/8" in diameter.

Film dimensions are a bit smaller than stated size, but close enough.

[Leigh]

Just for fun, I drew it out. A circle for 5x5 is about 7" and for 4x5 is about 6 3/8" in diameter.

How about basic trigonometry?

Diagonal = sqrt( a^2 + b^2 )

5^2 + 5^2 = 25 + 25 = 50; sqrt( 50 ) = 7.071

4^2 + 5^2 = 16 + 25 = 41; sqrt( 41 ) = 6.403

- Leigh

[Vaughn]

Because "sqrt" looks too much like "squirt" and sounds a bit rude (like Giclee).

Also I was wrapping my head around the image circle needed for 4x5 rotated for both horizontal and vertical orientation and the visual helped. Of course it is the same, but seeing it helped.

vaughn

[Leigh]

Hi Vaughn,

I wasn't being critical. I was just playing, and pointing out how close your measurements actually were.

- Leigh

[Vaughn]

All in fun...

Plus I was up at the darkroom until 4am or so and got to bed at 5am -- then up at 9am. My brain won't do "higher" math right now. LOL!

Vaughn

[Dan Fromm]

They used to be offered with coverage defined by format. Rectangles, usually. Look at the older B&L catalogs on www.cameraeccentric.com