Hmm. I thought the two JPEG filenames, one "18mm.jpg" and the other
"28mm.jpg" were clear indicators of which camera took what image. But
I checked anyway...
Given the fact that the EXIF info on the 18mm.jpg image clearly
states that it was made with a Pentax *ist DS set to Manual exposure
mode, CW Averaging meter, ISO 400 @ 1/4 second, and no aperture or
lens information listed, I think it's a reasonable deduction that
this image is the DS and the one labeled "28mm.jpg" which contains no
EXIF information is the film camera.
Since there is no aperture information provided with the DS EXIF info
and the focus distance is not provided, any accurate calculation of
DoF for either image is impossible. I cannot by eye see any
significant difference in DoF ... neither image seems particularly
sharp, and both captures' post-processing to this size display reduce
image quality to the point where it is impossible to judge. Plus
there are differences in response curve between film and sensor, how
the capture was rendered, and quality of the two lenses to confuse
the DoF issue.
---
However, the purpose of the example was to demonstrate differences in
field of view and that is clearly seen. Two results:
- The two images were taken from two slightly different positions.
- The *ist DS sensor format has slightly different proportions
compared to the 35mm film format.
Thus the field of view of the two images is *slightly* different.
However, perspective is identical and overall field of view differs
by only an insignificant increment.
This can be seen clearly in the following composite image:
http://homepage.mac.com/godders/shel-fov-example.jpg
I took both images and reduced them to grayscale, the exchanged pixel
color on the 18mm.jpg image for Red and on the 28mm.jpg image for
Green. I then expanded the image canvas, duplicated the Green image
and pasted the Red image in twice as well. Aligning two layers at a
time (upper aligned on the foreground chair, lower aligned on the
background display case), we see how the format proportions differ,
how the eyepoint was slightly different, and how the perspective is
identical.
It would take a more rigorously defined test setup to evaluate DoF
differences properly.
Thanks for posting the examples, Shel!
Godfrey
