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

[E. von Hoegh]

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

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

[Gem Singer]

ic-racer,

How about Hasselblads and Rollie TLR's?

They are 6x6 square formats.

[ic-racer]

ic-racer,

How about Hasselblads and Rollie TLR's?

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]

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