# lens – Hasselblad 250mm mounted on my Nikon full frame camera … what is its effective focal length?

The Hasselblad lens (250mm) was designed for 120 or 220 roll film … if I successfully mount it on a 35mm full-frame camera, how long does the lens last?

250mm.

What is the effective focal length?

250mm.

Indeed, the "Effective Focal Length" is based on the viewing angle achieved by a particular focal length when used with full-frame 36 x 24 mm cameras (a / k / a format). 35mm "135).

It is used on a medium format camera using a frame size of 6 x 4.5 (a / k / a "645") with exposed dimensions of 56 x 41.5 mm, a lens of 250 mm would have an "effective focal length" of about 155 mm. would give the same diagonal angle of view as a 155mm lens on a 36 x 24 millimeter FF camera.

When used on a medium-format camera that uses a 6 x 6 frame size with apparent dimensions of 56 x 56 mm, a 250 mm lens would have an "effective focal length" of about 135 mm because it would give the same angle diagonal lens 135 mm lens on a 36 x 24 mm FF camera.

6 x 4.5 (a / k / a "645") is probably the most common image size for 120/220 movies. With the other formats, the width of 56 mm remains constant (because it is the maximum usable width of the short side of the film strip), but the length lengthens progressively in the direction of the length of the film.

80mm = 80mm on the FF camera, "effective focal length" of 50mm on a 645 format camera.
100mm = 100mm on the FF camera, "effective focal length" of 65mm on a 645 format camera.
250mm = 250mm on the FF camera, "effective focal length" of 155mm on a 645 format camera.

Hasselblad's most popular devices used 120 exposed films with a 6 x 6 (56 x 56 mm) frame. Since the diagonal of a 6 x 6 frame is longer, the conversion factor changes.

80mm = 80mm on the FF camera, "effective focal length" of 44mm on a 6 x 6 format camera.
100mm = 100mm on the FF camera, "effective focal length" of 55mm on a 6 x 6 format camera.
250mm = 250mm on the FF camera, "effective focal length" of 135mm on a 6 x 6 format camera.