On Jul 13, 2005, at 6:56 PM, William Robb wrote:
An 18mm lens on a Pentax DSLR should yield, within a very small
degree, the
identical result as a 28mm on a 35mm film camera. Two pics taken
of the
same subject from precisely the same location should be virtually
indistinguishable wrt image size and FOV Is this correct? What, if
anything, should be different between the two pics? I ask this
because
something tells me that they will not be the same in some respects.
Depth of field will differ, with the smaller format generating more
DOF at any given aperture.
Not sure by how much exactly, I expect you will probably open up a
full stop to get similar DOF from APS C sized digital as compared
to 35mm.
The 1.5x factor is a simple approximation to allow those familar with
35mm film cameras to know what focal lengths will give known field of
view values on the D/DS bodies. For example: a 50mm lens fitted to
the DS will render a field of view equivalent to a 75mm lens fitted
to a Pentax 35mm SLR.
For a lens which provides the same field of view on the *ist DS'
16x24mm format, you will gain approximately 1.5 stops of DoF compared
to the same field of view on 35mm 24x36mm format.
For more in-depth information about field of view and depth of field,
I use these calculators available on line:
Rui Salgueiro's field-of-view calculator
http://www.mat.uc.pt/~rps/photos/angles.html
DOFMaster
http://www.dofmaster.com/dofjs.html
Get to know the D/DS in terms of their format: a 35mm is a normal
lens, a 24mm is a wide lens, a 16mm lens or shorter is an ultrawide,
a 50mm lens is a portrait tele, a 135 is a telephoto, anything longer
than that is a long telephoto.
Godfrey
