Thanks very much folks!
For a long time I've thought a 10" f/5 Dob would be a great quick setup
all around scope. Now I tend to find it not so easy to use a Telrad type finder
on a Dob so low to the ground. Guess I could set it on a box.
Since I seem to have my AP900 mount with me much of the time, if I wanted
more aperture than my refractors will give me I could pop on something like
a C11 OTA. I would love to pop on an AP 10" MC but I don't think Roland
is likely to make more any time soon.
A C11 on the 900 would give me tracking and let me use my favorite finders
and be relatively comfortable. Heck, I could even learn how to use the GOTO
on the 900. This wouldn't be a quick setup scope but once together it would be
nice to use.
Rich
> Thanks Phil. You know what I think that it really boils down to for the
> manufacturers? They are thinking "cool factor". "What feature can we throw
> in there to get one over on the competition?" Since there's not too many
> things that can easily be changed, a CF tube is a quick shot. Potential
> customers drool at the mouth with new technology whether it makes a whole
> lot of sense... right? ;) Maybe, maybe not. I'm not hooked on the pitch.
>
> Michelle
>
> > -----Original Message-----
> > From: sf-bay-tac-bounces@No-Spam
> > [mailto:sf-bay-tac-bounces@No-Spam] On Behalf Of P T Chambers
> > Sent: Monday, March 14, 2005 12:35 PM
> > To: The Astronomy Connection
> > Subject: Re: [TAC] SCT OTAs
> >
> > Hi Rich
> >
> > I think this is going to be the subject of debate for quite a
> > while. I know of no "real" science that has been used here.
> > Probably because it takes two identical scopes with the exact
> > same exposure and measuring instruments like thermocouples
> > inside and out of each to do it right.
> >
> > However, the differences are slight if any IMO. The aluminum
> > casting on the front and rear and the corrector area are
> > pretty large by weight and area and they did not change.
> >
> > The benefit of the composite tube is that it does not change
> > its length with temperature so the focus is more stable over time.
> >
> > The overall weight might be slightly different but again,
> > this is overwhelmed by all the stuff that didnt change such
> > as the primary and the rear casting.
> >
> > There is another interesting thing to be noted. SCTs are
> > notorious dew
> > collectors on the corrector plate. Of course, as we all
> > know, dew collects because the temp of the object goes lower
> > than the surrounding air and the air against the surface gets
> > colder. Colder air cannot hold
> > as much moisture so dew forms. One of the ways to counteract dew
> > formation is the "dew shield". That prevents the corrector
> > from "seeing"
> > so much sky which, because of the black body phenom, keeps
> > the corrector from cooling off so quickly.
> >
> > In any case, insulating the case has the same effect. Black
> > or dark blue
> > radiates heat moreso than a light color and aluminum more
> > than graphite
> > composite. So the composite case, once reaching ambient,
> > wont cool off
> > the air as fast inside which should help prevent dew formation.
> >
> > The effect should not be great but should be more than the
> > cool down time issue since keeping the air warmer inside is a
> > lot easier than the amount of heat required for cool down.
> > (one has the thermal content of the primary and one doesnt
> > and also, the thermal differential (the driving
> > pressure) is greater for the cool down issue).
> >
> > This could easily be the subject of a doctorial thesis on
> > thermodynamics.
> > All we need is a Phd interested in thermodynamics and needing
> > a subject.
> >
> > LOL
> >
> > There are several folks convinced that the graphite case
> > cools down slower
> > but in general, I dont believe you can tell the difference.
> > There is
> > more variation caused by where you set the scope up (which
> > side of the MB parking lot, for instance) than there is in
> > the case material.
> >
> > It is not worthy of consideration in buying a scope. The
> > graphite ones should be more dimensionally stable.
> >
> > One thing I have wondered about is the length change with
> > temp. In terms of - ok, you put a losmandy aluminum track on
> > the top and bottom (top for a refractor guide scope, bottom
> > for a weight set) -. Now you have a situation where the case
> > doesnt want to expand and contract much with temp
> > differential but the tracks expand and contract a whole
> > bunch. There are some stresses that have to go somewhere.
> > With the aluminium case, since thermal expansion is two
> > dimensional, the expansion is the same for the tracks and the
> > case and the only stress is longitudinal in the bolts that
> > hold it together.
> >
> >
> >
> > ---------
> > Phil Chambers [ptchamb@No-Spam] (S.F. Bay Area - Calif. USA)
> >
> > On Mon, 14 Mar 2005, rnapo wrote:
> >
> > > Hi folks,
> > >
> > > Celestron makes SCT OTAs with aluminum tubes and carbon fiber tubes.
> > > The carbon fiber tubes look great. I've heard cool down times are
> > > better with the aluminum tubes.
> > >
> > > What do you folks think? What are the pros and cons of the
> > aluminum vs.
> > > carbon fiber tubes?
> > >
> > > Thanks very much,
> > > Rich
> > >
> > >
> > >
> > >
> > >
> >
>
Received on Mon Mar 14 20:05:04 2005