Mr. Emery & Orchid Table Top Photography Community,
In my previous posts on this thread I made the following statements:
Point and shoot cameras have great depth of field because thy use
such wide angle lenses.
This is only true if comparing two differing focal lengths from the
same subject to camera distance. If you move the longer lens back to
accomodate an identical field of view for both lenses DOP (depth of
field) will be more or less the same. While Mr. Emery has the
relationship between DOP and camera position reversed he is correct
that both wide and long lenses can achieve the same amount of DOP.
The close up feature (in point & shoot cameras) uses the widest
lens angle which produces a greater depth of field than the
Same correction as above. And since one would, of course, adjust the
subject to camera distance for identical framing this was pretty much
a non sequitur. Apologies.
The smaller the actual aperture (and the larger the f/number) the
greater the depth of field the lens is capable of. So to get the
greatest depth of field set your lens to the largest f/number it
offers, such as f/16, f/22, or f/32.
Mr. Emery has taken me to task on the above in terms of resulting
image quality. He is correct that diffraction (the bending and
blurring of the incoming light rays that pass within a certain
distance of the physical aperture) creates a softer image through a
lens set at its smallest aperture than at mid-range. And his
assertion that you will get a substantially poorer image at the
smallest aperture may be true for cameras with very short focal
lengths such as all point & shoots have. It is not a problem for the
the DSLR style cameras.
Here’s why: An f/32 aperture in a 100mm lens (such as you would use
on a DSLR) has an opening with an area of roughly 5.0 sq mm. A
similar aperture on a 4.3mm lens (which is the focal length at the
wide end of the Nikon Coolpix P300) would have an area of approx 0.21
sq mm. While the amount of diffraction will change with the area it
does not change proportionally and actually increases in distortion
as the aperture diameter decreases. While no point & shoots have an
f/32, whatever the smallest aperture is could possibly create
unacceptable image qualilty. In fact, on the P300 mentioned above the
widest aperture of the lens (at the wide end) has a square millimeter
area of only 4.17 - smaller than the 100mm lens at full stop down.
And likewise, the reason you get a sharper image at f/16 as opposed
to f/32 (in a given lens) is that the F/16 aperture is so much
larger than the F/32 reducing the effects of diffraction.
Despite that, if you’re using a DSLR style camera with a "macro"
lens in the 50mm to 105mm range, I stand by my statement to use the
smallest possible aperture for any close up work of three dimensional
subjects. Again, check out the photos on my website. The great
majority were taken at F/32 on a Nikon D40. Yes, if I blow the images
up to 100% on my computer I can see a subtle loss in sharpness. By
the time I’ve sharpened them in software they are quite acceptable.
More acceptable than similar photos at wider apertures in which much
of the subject fore and aft of the focus point will be truly out of
focus. If I want very large images- poster size say - I use software
which gives me the larger image with, again, acceptable sharpness for
the viewing distance of such a large photo.
For those of you using point & shoot cameras I’d say do a few tests
and find out where the acceptable range is between blurriness fore
and aft of the focus point and unacceptablly soft images overall.
Finally, in reference to Mr. Emery’s statement that
The reason point and shoot cameras offer increased depth of field
compared to most DSLR's is because of their smaller sensor size
he is incorrect. An image focused on a film/sensor plane will exhibit
the same depth of field regardless of the size of that film/sensor
plane. What changes, however, is the apparent magnifying power of the
lens when compared to the traditional 35mm format.
Often point & shoot focal lengths are given in “equivalent” figures
to full frame 35mm lenses - the current benchmark standard.
Consequently the Nikon P300 is marketed as having a focal length
range of 24mm - 100mm when in fact the actual focal lengths range
from 4.3mm to 17.9mm. The size of image, at 4.3mm say, in relation to
the sensor size of the P300, however, mimics the same ratio in image
size to format that one achieve in using a 24mm lens on 35mm film.
For people not wishing an education in optical science but wanting
to take the best possible photos of their work I would recommend the
short and concise explanation of depth of field found about half down
on this webpage:
Sorry for all the distraction from jewelry discussions,