P3D Re: Nimslo and Closup lenses

[erker@xxxxxxxxxxxxxx (Greg Erker)]

>I was at the 99 cent store the other day and noticed that they have plenty
>of reading
>glasses of all powers for, you guessed it, 99 cents each.  I want to use
>the lenses
>for taking close ups with the nimslo and wondered if the power (+1.00,
>+2.50,+3.25,
>etc.) were the same diopters as the Kodak close up lenses mentioned in the
>Kodak Photo
>guide.  Does any body have a list of the focus distance and depth of field
>for these
>type lenses used with the nimslo?

  Yes reading glasses are marked in diopters
just like closeup lenses. I don't know if
99cent glasses are as accurately measure/manufactured
as a camera closeup lens.

  For a lens focused at infinity you can
figure out the point of best focus. It is
1 divided by the CU lens diopter amount.
This gives you a distance in metres. If you
use 1000/diopters you get mm.

  The Nimslo lenses aren't focused at infinity.
I recall someone saying that they are focused
at 12 feet. This is approximately 4 metres. So
we can consider the camera to be focused at infinity
with a 1/4 diopter lens in front of it.

  And you can add diopters, so just add the 1/4
to the +2.5 or whatever strength you are using.
So, in this example you get 2.75 diopters, putting
the best focus at 364mm (about 14").

  Regarding DOF: wide open the lenses are f5.6
and at minimum aperture (bright sun or light
bulb shining on the sensor) you get f16. The
lens focal length is 30mm.

  Someone has a DOF calculator on a their
web page (somewhere). Using the above numbers
you can calculate what will be in focus for
various reading glasses.

Good luck - Greg

Medium format stereo and more:
http://www.angelfire.com/ca/erker



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