Re: PHOTO-3D digest 2061

[P3D John Ohrt <johrt@xxxxxxx>]

P3D wrote:

> Another reason I think many have accused the Kodak of not focusing
> properly, particularly at infinity, is that their DOF scale is not as
> conservative as say, the Realist. On the Kodak, using the hyperfocal
> distance, it says you're in focus from 5 1/3 feet to infinity at f8.
> But if you set the Realist to the hyperfocal distance at f8, it says
> you/re in focus from 10 feet to infinity. So the Kodak is allowing a
> bigger "circle fo confusion" using their DOF scale, which might have
> been acceptable to most in the 50's, but is not for most on this list.


I think there is an issue being overlooked, literally.  As a general
rule, we have finer grained film today speed for speed than was
available in the fifties.  That means that a c of c barely detectable in
50's technology would more readily observed as degradation today.

Really, since you can't determine the hyperfocal distance without
specifying the c of c, the whole concept of accuracy of hyperfocal
settings on a lens barrel is suspect.  At best they give you a feel for
the degree of dependency on aperture.

Finally, control of the hyperfocal distance can be an important element
of the composition.  If you use it, you simply have to know your camera
and your film.

Don't look to me for advise, I have no artistic talent.


WRT to small apertures, I believe it was John B. who explained earlier
that if you encounter a loss of resolution as you decrease the aperture,
then you may be experiencing refraction effects which are dependent on
the physical size of the aperture, not the f/ number.  Thus a wide
angle, normal view, and telephoto all of the same quality would tend to
degrade when the aperture has a certain diameter, not a certain
f/number, hence each lens would degrade at different f/numbers, the wide
angle degrading at a lower f/ number than the normal and telephoto.

Did I get that right?

Anyway, we are discussing an area where workmanship and quality control
are very important.  The rule of thumb is if you are worried about it,
measure it.

Regards,
John
--
John Ohrt,  Regina, SK, Canada
johrt@xxxxxxx


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