[LRflex] Converters
- From: KEITH LONGMORE <keith@xxxxxxxxxxxxxxxx>
- To: leicareflex@xxxxxxxxxxxxx
- Date: Fri, 27 Jul 2007 13:05:33 +0100
Xavier, et al
Converters only work with telephoto lenses! If you fit a lens less than
100mm with a 2 or 3x converter, the angle of incidence of the light rays
near the edges is simply too great for the converter to cope with. My
Adaptall 2 Tamron is a set: the 135 and 2x converter work very well
together. About 45 years ago I had a a lens that was, I think, about 75
or 80 mm, with matching 2 x converter, and it was awful! In those days,
though, the converter was just a couplet; later ones are either 4 or 7
element, and work far, far better.
The posts about the other lens (24mm, I think?) and not working well on
a digital sensor is exactly the same problem! The angle of incidence to
the corners of film is far less than to the edges of a sensor, because
the lens is mounted so much closer to the sensor. With most digital
cameras, if you want the best performance, you really need a lens
designed for the closer distance. Because of the large angle of
incidence, too, you get much more chromatic aberration than you would
using the same lens with a 35 mm film camera. Another related point is
that the sensor is not a planar device; the light must travel down short
'tubes' to the actual sensor material, and these vary in length
depending on whether they are green, red, or blue elements.
Consequently, the sensitivity changes towards the edges with an
unsuitable lens, by an amount depending on the colour.
Hope this clarifies.
Regards
Keith Longmore
PS - got my Novoflex lens now. I haven't recovered yet from the shock
of seeing how big it is!! :-)
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