# Is there a formula to convert digital lens focal length to 35mm focal length ?

Discussion in '35mm Cameras' started by narke, Feb 28, 2005.

1. ### narkeGuest

Does it relative to CCD size?

narke, Feb 28, 2005

2. ### Justin ThymeGuest

Yes it is entirely dependent on CCD size. For DSLR's, most are close enough
to 1.5x. The Olympus E1/E300 are the only lowish-priced SLR's that are
significantly different, with a 2x equivalence factor.

Justin Thyme, Feb 28, 2005

3. ### Chris BrownGuest

Yes. To a first approximation, divide 43 by the diagonal of the sensor in
millimetres. This will give you the multiplication factor for field of
view/focal length (differing aspect rations will make this something of an
inexact sicence, but it should be close).

(43mm is the diagonal of a 35mm frame).

Chris Brown, Feb 28, 2005
4. ### Alan BrowneGuest

The focal length does not change at all.

The 'cropping' factor gives a final image similar to the effect of using a
longer lens of FL * cropfactor.

So, a camera with a 50mm lens and a 1.5 cropped sensor is said to be equivalent
to a 75mm lens. (But the focal length does not change, the sensor is just smaller.)

Cheers,
Alan

Alan Browne, Feb 28, 2005
5. ### Alan BrowneGuest

Just divide 36 by the width of the sensor. eg: the Canon 20D at 22.5 mm (x):

36 / 22.5 = 1.6

(Quicker than (36^2+24^2)^0.5 / (22.5^2+15^2)^0.5 and same result).

Cheers,
Alan.

Alan Browne, Feb 28, 2005
6. ### narkeGuest

understand. Thank You All

narke, Mar 1, 2005