William Robb wrote:
----- Original Message ----- From: "Shel Belinkoff"
Subject: Theory of Equivalency
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.
Exactly. The 18mm lens focused at 7 feet will have substantially more
depth of field than the 28mm lens focused at 7 feet if the aperture is
the same.
I suspect that the perspective would be different too. I think a cropped
18mm image will still show the exaggerated perspective of that lens.
The background will appear to be much further behind the subject than it
will in the image taken with the 28mm lens. That's my theory anyway.
Tom Reese
