Re: ATM cost/benefit rationale for atm

[Bill McHale <wmchal1@umbc.edu>]

On Tue, 19 Jan 1999 santore@ibm.net wrote:

> 
> I am new to this list and after a week or so of lurking, I have a question
> to pose to the group.  
> 
> I am interested in getting a first scope and was weighing options of
> making or buying something like an 8" dobsonian.  Personally, I'd like to
> make one because (1) I enjoy building things (2) usually feel that I enjoy
> things I make more, understand them better, and generally prefer them to
> commercial products, (3) get the impression that hand made scopes can be
> superior.
>

These are all good reasons to make a scope.  If you were only planning on
making one because it would save you money then it might not be worth your
effort, however, since you have other reasons, you will probably find it
an enjoyable and worthwhile experience.
 
> However, for a variety of reasons I do not want to grind a mirror.  So I
> wonder how much truth is left in (3) if you start with a commercial
> mirror.  As a way of getting some idea of what a fixed dollar amount can
> get you if you make rather than buy I've been trying to put together a
> list of parts and prices for a home assembled scope that would roughly
> equate to one of the big three 8" f/6 dobs. (the "basic" model in the list
> below).  To get a sense for what I can do with a similar dollar amount
> I've upgraded some components until the cost works out about the same as a
> commerical 8 (the "improved" model).  Then, what if the budget creeped
> upward a little, could I put together something far superior to a
> commercial scope for anything close to the price?  Here is my list for
> comments:

Well I would not worry too much about the mirror; when looking objectively
at the commercial scopes, often the mirror is the best part of the scope.
And if you buy from a place that hand figures the mirrors, you should at
least match if not exceed the Quality of the big three.  Where the real
advantages lie is in the ability to make the whole Telescope work better.
Make sure your bearing surfaces are covered in Ebony Star Formica, that
the Rocker is make of high qualtiy plywood, that the spider, focuser and
finder are all high quality.

> 
> Item            Basic       Improved           Superior?      
> ---------------------------------------------------------------------
> Primary       8" pl 190   8" pyr  250  8" pyrex enh. 280 - 300 
> Secondary       30            35      enhanced   35 - 40
> Spider/Holder   50            50                 50 - 70 
> Focuser         30            30                 70
> EP (25mm)    Expl II 28   Sir. Pl. 50   Ultrascopic   80
> Finder       5x      17   6x30     40   telr or 8x50  50 - 75 
> Base/OTA        50            50                 50 - 80
> ---------------------------------------------------------------------
>                    $395          $505               $615 - 715
> 
> 
> I don't know if these are reasonable price estimates for components (or if
> it's a complete list).  Mainly this is a just a starting point to help me
> get a sense of what is possible.  Again, I am just trying to get an idea
> what benifit there is (in terms of overall quality and choice of
> components) to making versus buying, given that I am pretty well convinced
> not to grind a mirror.  The low price for the base/OTA assumes a trip to
> the hardware store  (and includes misc. such as mirror cell, fasteners,
> paint, hardware, etc.) and not buying a $90 sonotube from Orion or some
> such!  Still, is it reasonable?

Well alot depends on your ability to scrounge.  Your best bet to finding
out how much the individual component will cost you is to get an issue of
Astronomy or Sky and Telescope and see how the components cost.

In any case, much of the mounting can be made from a single sheet of 3/4"
plywood, so it can be low cost.  Heck if you want to go real bare bones,
you can make many of the other components yourself; amateurs have come up
with many ingenious methods for making focusers, spiders, tubes etc.

> 
> If the above is reasonable, would this 'improved' model be significantly
> better than a stock dobs?  Would another $100-200 really produce a
> superior scope?  Superior even than a commerical costing $600-700 (any
> examples)?
>

It all depends on how good you are able to make it.  In real terms, when
one factors the time spent, few people really save anything on the scopes
they build; however the scope rewards them in a way that a commercial
scope never can.
 
> Maybe someone that knows has already done this sort of cost comparison.
> 
> Comments are greatly appreciated!
> 
> -- Bob Santore
>    santore@ibm.net 
> 

Bill

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