Re: [ATM] Mike Lockwood's Planetary

[Mike Lockwood <melockwo@uiuc.edu>]

Jay,

Jay Kirkland wrote:
> Since I first saw it on his site, I thought Mike Lockwood's 
> planetary was a bit of brilliance in both design and execution, and
> it has just furthered my desire to grind a long focus mirror.

Thanks very much!  It was built out of necessity - it had to be
compact and work well.  While my 16" F/4 can provide planetary images 
with better resolution on a good night (due to more aperture), the 10" 
has better contrast due to less obstruction, a wire spider (16" F/4 
does not yet have one of those) and more baffling.  The lack of coma 
is a real eye-opener.  The 10" cools off faster, weighs less, and 
assembles more quickly than my 16".

> But 2 thoughts came to me when I read the S&T article. 1) Many
> years ago, Richard Berry in Deep Sky Mag said that no matter how
> well baffled a scope, a full-length shroud might still give you
> that critical extra few tenths of a magnification in seeing. If you
> can possibly just glimpse the central star in the Ring with this
> scope as is, then that would make this scope a perfect test bed for
> the shroud/tenths of a mag theory. (Dobson's fav shroud was the
> weightless mylar space blanket.)

I think the shroud around the secondary cage is by far the most 
important.  Think of it this way - the closer the object to the 
eyepiece, the more scattered light it will contribute due to 
illumination of the inside of the cage, scattered light off the dirt 
on the secondary or its edges, or light straight into the eyepiece.

So, first priority is the secondary mirror itself, the edges of which 
should be blackened.  Don't overlook that small sliver exposed by the 
seam in the secondary holder, especially if it has some coating on 
it!.  Next is the spider, and the inside of the secondary cage.  So, I 
work hard to keep it dark in there.  The most important baffle seems 
to be the baffle below the cage on the side of the focuser, where 
light can easily hit the reflective side of the secondary and get 
scattered.  I extend that baffle down the truss at least a foot, 
preferably more.

Don't get me wrong - full length shrouds are good too.  Ever notice 
that many of the scopes containing mirrors that are reputed to have 
"superior contrast" are also wearing full-length shrouds?  I have.

> But what I'm most interested in is
> my biggest high power stumbling block: 2)What do you do to your
> bearings to make a scope track smoothly by hand at 500X? What are
> you using for bearings, if teflon are they ArmorAll'ed, how much
> force does it take to move the scope in alt and az? Great job! Hope
> you're enjoying Saturn.

As Bob N. later explained, I observe with the scope on an equatorial 
platform most of the time.  But hand guiding at 450X has been done on 
many occasions, and it works fine.  Not perfect due to some slight 
flexure in the rocker, but tracking is no problem after you get used 
to it.

Bearings are aluminum on Teflon (altitude) and glassboard on Teflon 
(azimuth).

	Mike Lockwood


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