[APML] comments & image comparison for Nikon TC14

["Bobby Middleton" <bobm@koyote.com>]

We've talked about tele-extenders a few times and their use. I believe
most of those who had used them had used then with refractors. I did
some shots last night with my 12.5" f/7 newt and a Nikon TC14 (1.4X)
It gave a focal length of 3080mm and f/ratio of f/9.8. The middle 1/2 of the
35mm negs are good. Small stars without noticeable color. But the outer half
did have some elongated stars (is the correct term here coma or spherical
aberration?). It also introduced a bit of color. These deficiencies were
minimal but they got more noticeable at the edge of the frame.
I also had more vignetting than I would have had w/o the TC.
Will I use it again? You bet! Since it is needed for small targets the edge
degradation
really isn't an issue. Any target that covers more than half the 35mm frame
at 3080mm will do OK shooting at 2200mm w/o the TC.

I thought it might be interesting to post this image with my best composite
I made
last year with the 10" Meade SCT at 2800mm and f/11. This was my best pair
of
several attempts but in all fairness I had pretty good seeing last night
too. You will notice
better resolution and smaller stars with the TC shot than with the LX200
shot. Of course
that might not surprise anybody! <g> The pair is at:
http://www.koyote.com/users/bobm/comparison.htm

You will note some differences in exposure times and film types between the
2 pics
but I don't think these will apply to the differences of resolution of the 2
pics.

Thanks to Michael Stecker who suggested the simple fix for my loose fitting
TC
connection. It made the loose fit solid as a rock.
Bobby Middleton


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