Re: ATM Barlow Question

[Suzanne Sarlette/Gerald Pearson <suegerry@mut1.muscanet.com>]

Hi Matt,

Matt Devine wrote:
> 
> For my 6" F/8, I have considered using a 25 and a 16mm eyepiece.  
> ... either a Meade 2X shorty or Celestron Ultima 2X Barlow to obtain two
> additional magnifications.

I have both a Celestron Ultima 2x and a Klee 2.8x, and both work great
for me.  In particular, they work well with my 28mm & 7mm Pentax SMC
eyepieces, 25mm & 10mm Vixen Lanthanums, and a 6.7mm Meade Ultrawide.  I
think it's significant that both barlows are apochromatic and fully
multicoated.  Is the Meade 2x shorty apochromatic?  If it's only an
achromat, then I myself would avoid it.  IMHO, trying to save money on a
barlow is a false economy.


> I was told that Barlows in general add to a dimmer image, (light traveling
> through more glass) ...

That's _negligibly_ true (essentially false) for _fully_ _multicoated_
barlows.  Remember that many Nagler, Pentax, and Vixen eyepieces have
built-in barlows (that's how they get the short focal length), and I
don't hear too many people complaining about dim images in these premium
eyepieces.

BTW, I now use my 28 mm and 7 mm Pentax SMC (super multicoated)
eyepieces almost exclusively -- both with & without the barlows.  They
give great images, a 65 degree apparent fov, and 20 mm of eye relief. 
This gives me effective focal lengths of 28mm, 14mm, 10mm, 7mm, 3.5mm,
and 2.5mm.  (The Klee does give a little vignetting at the edge of the
field with longer-focal-length eyepieces.)  Since I purchased these
Pentax eyepieces, I haven't bothered with using my other eyepieces -- 35
mm Orion Ultrascopic, 2.5mm, 4mm, 10mm, & 25mm Vixen Lanthanum's, and
6.7mm Meade Ultrawide.
  

Hope this helps a little.

        -- Gerry