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View Full Version : Why are lenses never measured in square format ?

alex from holland
2-Mar-2012, 16:14
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
2-Mar-2012, 16:16
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
2-Mar-2012, 16:56
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
2-Mar-2012, 17:05
Actually, lens cover a circle, not a square format.

Sandy

snap!

Vaughn
2-Mar-2012, 17:07
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
2-Mar-2012, 17:11
Just for fun, I drew it out. A circle for 5x5 is about 7" and for 4x5 is about 6 3/8" in diameter.

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
2-Mar-2012, 17:16
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
2-Mar-2012, 17:19
Hi Vaughn,

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

- Leigh

Vaughn
2-Mar-2012, 17:20
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
2-Mar-2012, 17:26
They used to be offered with coverage defined by format. Rectangles, usually. Look at the older B&L catalogs on www.cameraeccentric.com

ic-racer
2-Mar-2012, 21:53
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
Square format film, film holders and camera backs are not common. Why fit a lens to a format that does not exist.

E. von Hoegh
3-Mar-2012, 08:06

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

How about just multiplying the length of a side of a square by 1.414 (sqrt2) ? (Winking smiley)

Gem Singer
3-Mar-2012, 08:19
ic-racer,

They are 6x6 square formats.

ic-racer
3-Mar-2012, 09:36
ic-racer,

They are 6x6 square formats.
This is the Large Format Forum :)

Non-Large Format lenses are usually not listed with any coverage specification. Exceptions I know are some shift lenses and the Zeiss Luminars (which give a non-format-specified angle of view for each lens)

OT: Another good reason why the Horseman 6x9 is a Large Format Camera: Not only do the lenses all have a published "coverage" specification, they display the image circle right on the lens barrel of each lens!

Leigh
3-Mar-2012, 11:59
How about just multiplying the length of a side of a square by 1.414 (sqrt2) ? (Winking smiley)
That works for a square (a = b), but not for a rectangle (a <> b).

I used the formula appropriate for the general case. (frownie)

- Leigh