RE: [APML] Suggested Astrophoto Accessories for Vixen VC200L

[Alen Koebel <alen_koebel@yahoo.ca>]

Thom Iwancio <tiwancio@sc.rr.com> wrote:

> When I got my NEG the t-ring that came with it 
> for an OM was what Lumicon called a "wide t-ring". 
> The inner part protruded from the camera adapter
> part. 

Would I be correct in assuming the inner part is
what John called the flange (which I think is a 
good name for it)?

> When I switched to a Pentax screw mount system I 
> was able to use this inner part with the outer part
> that mated to the Pentax (it was flush).  When I
> again tried this with a Pentax-K ring I found the
> diameters of the inner rings were different.
> Apparently not all brands / models of t-rings have
> the same dimensions of the components.  I was able
> to loosen the 3 set screws however and pull enough
> of the inner ring out to barely make purchase on
> the NEG. Barely!

Good thing. I also got lucky with my Pentax T-ring
(outer part, just to clarify). The "flange" on my
other NEG is longer, extending much farther into the
NEG's body. There is no question of getting a grip
with that one but, as I said in my reply to John, 
the extra length does require more care when
tightening everything up prior to the exposure.
Perhaps this longer flange is actually the more 
recent version, to correct the very problem you
described (I originally thought it might be an 
earlier version).

What seems clear is that everyone here is aware that
you can easily (depending on which model of T-ring 
you buy) change the NEG over for use with different
cameras. That was the whole point of my (disasterous)
reply to William. I thought he wasn't aware of that,
but it turns out he was. I don't know what Lumicon's
position on this is now, but they used to want you 
to send the NEG (or at least the rotating part) 
back to them for modification. But the modification 
is trivial - anyone can do it, assuming you have
a compatible T-ring. 

[PS. Another reason I don't myself think of the
rotating part as a modified T-ring is that, with 
the threaded insert gone it is no longer part of 
the T system - the T-thread is missing. It is just
a ring with a bayonet mount, "conveniently" sized 
for clamping to the NEG's flange (by design of the
NEG, of course).]    




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