Re: comparing depth of field

On Fri, 6 Jun 2008 17:46:19 +0200, "ben brugman" <ben@xxxxxxxxxxx>
wrote:


"bucky3" <bucky3@xxxxxxxx> schreef in bericht
news:2822c4c2-8d27-415a-be6c-713a087141ec@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Is there an objective spec that can be used to compare depth of field
for different cameras/lenses? Would hyperfocal distance be able to
serve this purpose?

I'm not an expert on photography. I would like to get a non-SLR camera
that can produce good bokeh (shallow depth of field), but I would like
to be able to compare specs.

To compare depth of field, you need to determine how to compare.
On way of doing is, is using a DOF calculator. And use a circle of
not determined by the format, but fixed as compared to the diagonal.
For example 1/1500 of the diagonal. This makes comparing of different
formats with different aperature settings possible.

But a ROUGH way is:
If the size of a sensor is X times the size of another sensor the aperature
number should be divided with the same number X.

Examples:
1 Sensor 1/6 in size of 35 mm format, aperature should be 1/6 of the number
in 35 mm format. 35 mm f 4.0 would be in 1/6 sensor size f 0.666666

Or the other way around 1/6 sensor size with 2.8 as largest aperature. Would
be for 35 mm format 6 times 2.8 is f 16.8

(The calculation is bases on the same angle of view, de same subject
distance
and the same coc where coc is a set fraction of the diagonal)

ben

(The rough method is not totaly accurate, but works for all subject
distances and
for all angles of view and is precise enough in all but the most critical
situations).

I agree with this approach... works surprisingly well for normal
shooting situations.

Note that focal length plays NO ROLE contrary to what many think,
provided the framing of the image is the same.

I also agree that rough methods are eminently useful for DOF
calculations. That's all most of need to know. Furthermore, hardly
anybody can actually compute accurate DOFs because the formulas depend
on the exit pupil magnification, which usually is unknown.

Archibald
.

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