Re: [APML] Epsilon 160 and 210 informations.

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

All faster newts (faster than f/6) are going to have some degree of uneven
illumination; getting worse as the f/ ratio gets lower. My 130 Epsilon
(f/3.3) certainly had some and it was quite difficult to hit critical focus.
Collimation was no easy matter either. Its new owner Mike Haldeman has been
doing well with it for CCD........ccd will allow one to get critical focus
conformation by checking diffraction spike sharpness.
The Tak BRC 250 I have also has uneven illumination issues. (It's f/5) But
so far I have been able to completely counter this with Photoshop
anti-vignetting techniques. It also has some difficulty for collimation and
getting critical focus reuqires photographic testing. The nice thing about
that is that with the carbon fiber tube focus is pretty much maintained once
set.
Advantages of fast newts: more apreture per $ spent, faster speed, and no
color issues. I think some have used the Ep 210 for medium format but I'm
not sure how bad the light cut-off was.
Bobby Middleton

,-:'~*~':-,-:'~*~':-,-:'~*~':-,-:'~*~':-,-:'~*~':-,-:'~*~':-,
"For we did not follow cleverly devised tales when
we made known to you the power and coming of
our Lord Jesus Christ,  but we were eyewitnesses
of His majesty."                                  II Peter 1:16

----- Original Message -----
From: "Chuck Vaughn" <aa6g@aa6g.org>

> The tradeoff is you get full illumination and simple collimation but
> you sacrifice photographic speed.

> > Jim and Chuck,
> > thank you for your help.
> > For you, a good apochromatic 100-130mm refractor will be better in use
> > and results??
> > teiva
> > http://www.astrosurf.com/leroi
>
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