[ATM] Hello list, some basic question for a new Dobsonian builder

[Mike Shuken <mikeshuken@value.net>]

Hello Everyone,

First I would like to say that I have no idea how this space bug suddenly 
bit me, but it did and I'm, well, not *obsessed* but it is becoming 
somewhat consuming!  My wife thinks I'm nuts.

Nothing like jumping in with both feet, I'd like to switch from my Nikon 
binoculars to a 10" Dobson Tube Telescope that I plan on building in the 
next month.  I've done a ton of research on the Internet and directly 
communicated with several amateur astronomers but I'm still stuck with a 
few questions.  I'm hoping this highly intelligent group will indulge a 
newcomer with what must seem like some very elementary questions!  Well, I 
guess we all have to start somewhere...

I will be using the basic plans from this web site: 
http://members.aol.com/sfsidewalk/tenin.htm - ahh, they make it look so easy!

Questions:

1) This primary mirror purchase is driving me crazy.  The real thrill for 
me is deep space, but I want to be able to do some "sidewalk" observing of 
the moon and planets to share with my friends and neighbors.  I thought 
that a 10" f/6 would be perfect - and I had just seen a kit with a primary 
and secondary for $399.00.  Problem is now I can't buy that kit, the 
company only sells a 10" f/5 ($400 for the set).  I found some very cool 
10" f/6 elsewhere but they range from $600 to $800 - and that's what I had 
in mind for the total budget of the telescope.  Should I continue to search 
for a less expensive 10" f/6?  Go with the 10" f/5 for $400?  Or not eat 
for two months and go for the $600 10" f/6?  (comparing apples to apples, 
let's say all of these mirrors are from 1/6 wave to 1/10 wave...).

2) Should my mirror be American made?  I like the idea of buying American, 
but how about Russian and Chinese mirrors?  All things being equal, I would 
pay a little more for a mirror if it was made in the USA, but that being 
said, I still have a limited budget  :-(

3) The spider in the plans is made from three cedar shingles and a piece of 
wood dowel.  It does not appear to be adjustable *at all* except by tapping 
it back and forth in the tube.  Is buying a commercial spider worth the $50 
or so?  How hard will is be to adjust my secondary mirror with a shingle 
spider?

4) I like the idea of having several different eye-pieces.  I was thinking 
of buying a set with a 25mm, 12.5mm and maybe 8mm Plossl eyepieces.  The 
instructions are not clear, is there a threaded piece that I attach to the 
tube and the eyepieces just screw in and out?

5) More on eyepieces, I though I had it figured out, but then I read this 
on a web site:

"Here is what happened to me. I talked to lots of people and decided to go 
for 0.75 inches of in-travel. My mirror arrived marked as 59.0 inch focus. 
I measured everything four times, cut the holes and found that I had lost 
about 0.3 inches of in-travel! I figured I might be off by maybe 0.1 
inches. I now suspect that the mirror was not what it claimed in this 
regard. My advice is to not take any claim about the mirror for 
granted...measure it! How, I am not sure, but it can be done. Better yet, 
figure out a way to temporarily mount the mirror in a way that you can 
adjust it. Find the focus of choice and then commit to boring holes.  And 
make sure you understand in-travel vs. out-travel...these relative terms 
can drive you crazy. "

(me again) I understand how to find the true focus length of the mirror, 
but the "in-travel vs. out-travel" I don't understand.  Does each eye piece 
have a specific "distance" it goes in and out, allowing you to slightly 
miscalculate the focus length you need to mount your mirrors at?

6)  Supporting the main mirror: this web page gives you two different ways 
http://www.glpbooks.com/oyb/roscope/pri_cell.html does it really matter 
which one I choose?


And I would just like to add:

1) Yes, I am trying to meet someone local or hook up with a club so that I 
can possibly have a mentor while I'm doing this.

2) But I want to start now, and I am thinking that the best way to figure 
some of these things out is to JUST BUILD IT!

3) I'm a little nervous, but then I remember, some guys were building these 
things centuries ago, so how hard can it be??  :-)

4) How can any curious person of moderate intelligence not be COMPLETELY 
overwhelmed with how awesome and how awe inspiring the heavens can 
be?  Well, it only took 35 years for it to happen to me, and I'm glad it did...

Thanks in advance for your advice and indulgence.

Mike



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