Hello!
For the past few days I have been thinking of optics and cameras. I have some
questions and I would be happy if you could help me with those:
1) If lens has a focal length of for example 21 mm (like my zuiko 21/3,5) it
means that the lens collects all rays of light into one point that is located
21 mm behind the lens. But is this measured from the surface of the rear
element or from somewhere else?
2) And a very off topic question:
I heard that you could build a telescope using two lenses: one with long and on
with short focal lengths. Then you just line up those lenses so that their
focal points coincide. I tried this with two of my zuiko lenses and it really
works as a short telescope. But how could I take photos with that kind of set
up? The problem is that I can look through that "telescope" and see the image
sharp at a great range of distances between my eye and the eyepiece (that is
the shorter ie. aft lens). This is due to my eye that has a built in focusing
mechanism. But when I tried to connetct that telescope to the camera I couldn't
see a sharp image through my cameras viewfinder. So, how could I connect that
self made telescope to my OM4Ti THEORETICALLY? (If we consider mathematical
lens formulas.) What about in REALITY? And is it possible that the image fills
only part of the film (makes a black barrell around a circle shaped image) or
should it fill the whole image?
Thanks allready in advance,
Olli (who is in need for a long zuiko and tries to replace it with cheaper
options that are never gonna work ;-)
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