"Mr. Bill" wrote:
>
> Right, but for the wrong reason.
>
> The depth of field would be the same as for the 50mm because the subject
> to sensor image magnification is the same as for a 50mm (because it IS
> what you are using). You are just cropping an 80mm view out of the
> image produced by the 50mm lens.
>
> Mr. Bill
>
> "M.J.Shupe" wrote:
> >
> > The pics would look like the same as if they were shot with an 80mm on
> > film, except the depth of field would be like a 50mm on film, or close
> > to it, depending on how you determine depth of field. Greater than the
> > 80mm on the 35mm camera, anyway.
Actually, I am right for the right reason(s). I realize that equal
magnifications at the sensor/film is what is happening, leading to the
*same* depth of field at the image sensor, but I was also considering
the size of the print, which is traditionally part of the DOF
calculation.
The depth of field would be the same as a 50mm lens on film image if
they were printed at different sizes. Because of the "cropping" that
you talk about, a print from the D30 at 8x10 would have the same depth
of field as the print from the 35mm film at 12.8"x16" (1.6 times
magnification factor). However, if you were to magnify the D30 shot so
that the images were the same size, your depth of field would be
lessened for the D30 shot because you would also be magnifying the sizes
of the circles of confusion and things toward the edges of the DOF in
the film image that *appear* sharp would be less sharp, again, by a
factor of 1.6, and may no longer be interpreted by the eye as being
within the DOF. This consideration is especially important because with
digital, there is no original to compare to the film chip, so you have
to consider the print (or scan of 35mm film) as the final product.
Still, if you didn't make both prints the same size, viewing distances
for 8x10 shots are closer than 12x16.8, giving the film image a greater
depth of field. These are the reasons that I said DOF on the D30 was
the same or less than the 50mm on film depending on how you define your
terms and what factors you choose to consider.
If you want to get even more complex, you can consider that the D30 has
limited resolution, and that for images larger than a certain threshold
size, depending on the veiwer and printing method, there would appear to
be less visible detail and less overall sharpness, which would also
affect how the viewer interpreted depth of field. This lessened overall
sharpness would cause the viewer to consider depth of field extended a
bit beyond what they would consider "in focus" in a sharper shot. As I
said, this is only for larger prints. Of course the resolution of the
film that is being used in the 35mm camera also causes a limit of
overall sharpness in some ways similar to the D30 resolution limit.
All in all, you are correct. If the film image were cropped to the same
size as the D30 image, you would have exactly the same depth of field.
However, that is not what the original poster was asking.
Mike
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