Re: [ATM] Breathe through lightpath

[Dave Smith <smithersscope@yahoo.com>]

Thanks Gary,
I was about to comment likewise.

With regard to currents, I've noted similar effects on
my tridob. My focuser is mounted askew of the truss
tubes such that breath or heat only minimally traverse
the light path. Of course at or near zenith it is much
less of an issue. My son and I have played with this
effect to a large degree...backing out of focus to
generate the "washer" described earlier (a defocused
bright star). It's amazing to see something as simple
as a fresh eyepiece out of the toolbox demonstrate
*significant* currents.  I, personally, haven't had
much success eliminating these currents. The fans on
the primary work exceptionally well to scrub heated
air fronts generated there, but obviously have no
significant impact on currents more than 8 or 10
inches above the mirror in the light path. A light
breeze or fan, blowing "into the face" of the observer
may be a solution, but it's certainly going to be
cumbersome and annoying. In my light polluted
neighborhood I've learned to use a dark bath towel to
cover my head and shroud my eyesight at the eyepiece.
I haven't looked to see if this eliminates the
currents mentioned, but I can tell you it gets
suffocatingly warm after a few minutes (well, unless
it's 40F outside--then it's kind of nice).

To sum it up? Repositioning the focuser may be an
option. A shroud is also an option. I'm surprised no
one has offered that yet. I've never used one, so I
can't comment.
FWIW,
Dave


--- GARY FUCHS <gary@rcn.com> wrote:

> Hello,
> 
> I find it odd that erudite respected folks can study
> and describe at length - and that work will, and
> should be read and taken seriously -  details of
> tube currents, boundary layers, and all sorts of
> things that happen on or about the primary mirror
> and OTA and have an impact on observing, but this
> question, that seems no less important, is treated
> as less than worthy of serious consideration. 
> 
> Anyway, wouldn't a simple lightweight shield prevent
> the problem? 
> 
> Gary Fuchs
> 
> 
> 
> ---- Original message ----
> >Date: Thu, 28 Feb 2008 20:15:09 +0000
> >From: fundo@bellsouth.net  
> >Subject: Re: [ATM] Breathe through lightpath  
> >To: Don R Surles
> <Don.R.Surles-1@usa.dupont.com>,lopez@mv.mv.com
> >Cc: Arjan te Marvelde
>
<Arjan.te.Marvelde@hetnet.nl>,atm@atmlist.net,atm-bounces@atmlist.net
> >
> >You can try keeping your head above the optical
> path! <G>
> >
> >From: Don R Surles <Don.R.Surles-1@usa.dupont.com>
> >
> >> mother nature puts all sorts of obstacles in our
> astronomical viewing 
> >> paths...fog, dew, heat, cold, atmosphere, layers
> of air currents moving in 
> >> all directions, daily temp changes as day moves
> to night to day...and here 
> >> on the east coast we even have a few critters
> named mosquitoes who like to 
> >> crowd around the eyepiece.
> >
> >Hey...come down here to Memphis if you want
> mosquitoes.  They ain't big but they're numerous. 
> Even worse is Florida where they have multiple
> insecti to bother you...all night long.  Its so bad
> you have to keep a screen on the front of your car
> to keep the bugs from clogging the radiator.
> >
> >*****-----
> >Dan F.
> >Memphis, TN
> >_______________________________________________
> >ATM mailing list http://www.atmlist.net/
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 



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