Nishika Camera Modification

[T3D <vidi@xxxxxxxxxxxxx>]

I said,

> But now it seems that there  is no combination of lenses that will 
> allow me to do what I want.

   Then John B. said,

"Could you restate precisely what you want?  I'm not quite following
what you want to do.  Sorry to be so slow..."

   I wanted to figure out what supplementary lens to add to the 34mm 
Nishika lens to allow the camera to focus at 18" without the ability
to adjust the lens to film plane distance s'.  But actually I'm the 
one who was slow the other day.  I completely overlooked how the new
object distance would change where the image would end up relative 
to this new combined focal length.  I've got it all now!

   I brought this little exercise to the attention of a colleague of 
mine and as soon as I posed the question he had the answer, "a 2 diopter"
he said!  I thought for a millisecond or to as I converted my 500mm FL
supplementary lens to diopters.  I said "now wait a minute... how did 
you get that so fast?"  He gave a very simple explanation.  The fixed 
focus camera lens of the Nishika is essentially taking collimated 
light and focusing it at the film plane.  Now, if your object is not 
at infinity (or far away) but is 18" instead, then you put the focal
point of a lens at that object and it will collimate the light as 
if it were at infinity!  So, in this example I just so happened to pick 
a distance which was 18" or 457mm (.5m), which just so happens to be
2 diopters.  So the 2 diopter (500mm) lens takes the diverging light 
of this "up-close" object, collimates it, shoves it into the 34mm lens 
of the Nishika which takes any collimated light no matter where it 
comes from and focuses it at the film plane as if nothing happened.  Now
why didn't I think of that?  Optics can be so simple.....

   Anyway, I've got it now and I'm going to go off and find someone who can
core drill a few 500mm Meniscus lenses from the Edmund catalog to a size 
I can fit in front of the Nishika lenses.  I'm still concerned about what 
the images will look like in those half-frame size mounts.  Should I not 
bother?  I'm so used to full frame I have a feeling I'll be dissapointed
when I view these because they wont be taking up so much field of view.
Any comments?


John V.






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