Craig Levine wrote:
The remaining choices a Cornado SM40/10, and the Coronado Maxscope
40mm.
I have a 4" f8 (~800mm focal length) refractor. The SM40/10 at first
blush is slightly less expensive than the Maxscope, but with the
addition of an adapter plate to mount it on the objective of the
refractor, the cost works out to be +/- the same. The maxscope is
smaller than my 4" scope, so there is the portability factor.
Does one of these options have any other benefits over the other? Can
the Maxscope be "de-tuned" i.e. is there a mechanism to change the
filter's angle to move the band-pass away from the H-alpha line to
observe fast moving (doppler shifted) events? Anyone know what the
lead-time is on the Maxscope? The SM40/10 is in stock at a couple of
places, but I haven't seen the Maxscope in stock.
Thanks for any input!
I have the SM40/10, which I use with my Tele Vue Ranger. I have not
tried the MS40, and I don't know where it might be in stock.
My understanding is that the doublet in the MS40 is optimized for H-alpha
observing. Since longitudinal chromatic aberration is out of play, I
take that to mean that the issue is spherical aberration. Ordinary
refractors are probably corrected for a shorter wavelength than H-alpha,
which sits at 656.3 nm. I'm not sure exactly how much difference this
makes with a 40 mm aperture, where the Airy disc size is already about
3 arcseconds full-width half-maximum (I think that's about right). It
might depend on the effective focal ratio, which is f/12 for the Ranger
stopped down to 40 mm, but is f/20 for your refractor. However, I really
don't know.
As far as I know, the MS40 and the SM40/10 (as currently packaged) both
come with the T-Max tuner, so that Doppler-shifted events can be viewed.
I like my SM40/10 quite a bit. It's the chief use for my Ranger now.
I put it on the photo bracket of my C5+ for tracking. It looks a bit
ungainly but works fine. I do hanker for a bit more aperture, but I'm
certainly happy with the purchase.
Brian Tung
The Astronomy Corner at
http://astro.isi.edu/
Unofficial C5+ Home Page at
http://astro.isi.edu/c5plus/
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http://astro.isi.edu/pleiadatlas/
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http://astro.isi.edu/reference/faq.txt