Another DOB question...

Greetings...

Well, I'm struggling through the vast mine fields of Dob purchasing...I'm
starting to think it's not worth it...The big Dobs are very, very cumbersome
and quality is very, very expensive...

Here's the question. I have 2 Orion 8" reflectors. One is F/5 the other is
F/4.5 I rarely use the 4.5--- So, how much better would THAT scope be if
I put a GREAT new mirror in it? I can get a new mirror---1/12th or better
at around $300. Would that make a huge difference? What about getting a
cheap 10" Dob and replacing the mirror?

What's gained?

Doink

Greetings...

Well, I'm struggling through the vast mine fields of Dob purchasing...I'm
starting to think it's not worth it...The big Dobs are very, very cumbersome
and quality is very, very expensive...

If I remember correctly, the last scope you were looking at was an 16 inch F5.8
DOB. At first that seemed ideal but now it appears you have come to realize
that a scope that is 8 feet long has some disadvantages.

This does not mean that all scopes larger than 8inches are so cumbersome as to
be unuseable, it just means you need to be careful in choosing.

Putting a nice mirror in that Orion scope is not going buy you the advantages
of 4 inches of added aperture. That factor of 2.25 in light gathering is way
too big to overcome.

My suggestion is to take it easy and check out some different scopes in person
and see what you think. A fast 12.5 inch scope can be quite portable, mine
fits in my '92 Escort and I can say that it out performs my XT-8 in just about
every way imagineable.

jon

Jon,

Thanks for the reply. I don't live where there is an abundance of test
scopes. I have to rely on information here---as a start. Then I do further
research online. It's hard to get straight answers...Of course another 4"
of aperture would be advantageous. BUT, I was trying to find out how much
difference a good mirror would make.

Initally I was moving toward Discovery Dobs...then I saw the 16" f/5.85 dob
on astromart and was able to learn a lot from the owner. I don't want to
use a ladder. So, Tscope at 14"???? I'm not sure the really fast scopes
give good views....do they? Would a 14" f/4.5 be comma crazy? I don't
know...seems there isn't much Dob experience on this board either....

So, I'll keep looking....probably stay with the known....Orions 12.5 is a
winner....
"Jon Isaacs" wrote in message
...
Greetings...

Well, I'm struggling through the vast mine fields of Dob purchasing...I'm
starting to think it's not worth it...The big Dobs are very, very
cumbersome
and quality is very, very expensive...

If I remember correctly, the last scope you were looking at was an 16 inch
F5.8
DOB. At first that seemed ideal but now it appears you have come to
realize
that a scope that is 8 feet long has some disadvantages.

This does not mean that all scopes larger than 8inches are so cumbersome
as to
be unuseable, it just means you need to be careful in choosing.

Putting a nice mirror in that Orion scope is not going buy you the
advantages
of 4 inches of added aperture. That factor of 2.25 in light gathering is
way
too big to overcome.

My suggestion is to take it easy and check out some different scopes in
person
and see what you think. A fast 12.5 inch scope can be quite portable,
mine
fits in my '92 Escort and I can say that it out performs my XT-8 in just
about
every way imagineable.

jon

So, Tscope at 14"???? I'm not sure the really fast scopes
give good views....do they? Would a 14" f/4.5 be comma crazy? I don't
know...seems there isn't much Dob experience on this board either....

The problem is not lack of experience, ChasP for example has plenty of
experience. Del Johnson has plenty of experience. Shneor Sherman has plenty
of experience. I have some experience...

The problem is that coma is a highly subjective issue and no one can make that
decision for you. The aberrations one sees are not only a function of the focal
ratio of the scope but they are also a function of the eyepiece you are using.

And then there is the issue of how much you are willing to trade in terms of
portability and useablity for a longer focal length.

And then of course there is the issue of whether you are going to buy a
Paracorr...

In the end, this is not something where there is a cut and dry answer, each
observer needs to decide for themselves.

My subjective views:

Fast scopes can obviously provide good views if the mirror is good and the
scope is collimation. I believe Todd Gross's all time planetary scope is a
fast Newt. Coma and Astigmatism in the eyepiece is a bigger issue than coma in
the scope. I chose a 12.5 inch F4.06 scope because I wanted something that was
easy to handle, fit in a small car. It works for me and with a Paracorr I
think it provides great views.

Whether you will think it provides great views, well I don't know but a 12.5
inch or 14 inch will definitely light up the DSOs in a way that an 8 incher
cannot.

jon

"Doink" wrote in message ...
Jon,

Thanks for the reply. I don't live where there is an abundance of test
scopes. I have to rely on information here---as a start. Then I do further
research online. It's hard to get straight answers...Of course another 4"
of aperture would be advantageous. BUT, I was trying to find out how much
difference a good mirror would make.

Initally I was moving toward Discovery Dobs...then I saw the 16" f/5.85 dob
on astromart and was able to learn a lot from the owner. I don't want to
use a ladder. So, Tscope at 14"???? I'm not sure the really fast scopes
give good views....do they? Would a 14" f/4.5 be comma crazy? I don't
know...seems there isn't much Dob experience on this board either....


A good mirror can make a big difference in the experience, but there
are definite limits to what it can do; especially considering that the
optics that Discovery and the Chinese are putting in scopes these days
are often pretty good. I would say that it might be worth it to step
up to a Royce, Swayze, Spooner, etc if you are only giving up one size
increment (going with a 12.5" instead of a 14.5", 8" as opposed to
10", etc) but not more than that unless the choice is between a truely
awful large mirror and a good small one.

Ok, regarding fast scopes; of course they can give good views. A top
flight mirror properly aligned will give a great image on axis and
Coma while visible is often less of an issue for most people than
abberations brought into play by their eyepieces. If worst comes to
worse, Tele Vue makes a nifty Coma Corrector.

Don't get me wrong, I am a fan of longer focus mirrors; they are
easier to collimate, they have greater depth of focus, its easier to
find good ones at a reasonable price and I can use a smaller diagonal
with them. That being said, if you can afford a premium mirror and
don't mind taking efforts to make sure its collimation is spot on a
big fast mirror can provide truely breath-taking views of anything you
could care to look at.

--
Bill

Unless there is something remarkable about your scope, you probably
wouldn't want to buy a mirror simply to upgrade it, since that is the
usually by far the largest cost item. I would sell it and use the
money to upgrade to a larger scope, or purchase a smaller more
portable one. I can't think of a good reason to own two 8" reflectors
if they are mounted and perform similarly.

Mark Pippin


"Doink" wrote in message ...
Greetings...

Well, I'm struggling through the vast mine fields of Dob purchasing...I'm
starting to think it's not worth it...The big Dobs are very, very cumbersome
and quality is very, very expensive...

Here's the question. I have 2 Orion 8" reflectors. One is F/5 the other is
F/4.5 I rarely use the 4.5--- So, how much better would THAT scope be if
I put a GREAT new mirror in it? I can get a new mirror---1/12th or better
at around $300. Would that make a huge difference? What about getting a
cheap 10" Dob and replacing the mirror?

What's gained?

Doink

The advantage of premium optics lies mainly in the fact that a
smoother mirror will scatter less light. On deep sky objects this is
not a huge advantage. If you are an experienced planetary observer,
you might be better off popping for a premium mirror.

However - with the scopes you are considering, Jon's right - aperture
is the important thing here.

Personally, I'd take a long hard look and try to figure out:

1) how large of a scope you are physically willing to deal with (size,
weight, ladder, etc...)

2) what your budget is

For many, the ideal compromise is somewhere in the 14-18 inch range.

A 14" Tscope will show you more than the 12" Orion - although this
will probably be more due to increased aperture than the optical
figure.

Once you get above 12", high quality stuff gets expensive very fast.
Not only the scope, but the eyepieces and accessories you have to use
in the scope. For example: As per your coma question - at f4.5, a
paracorr combined with good eyepieces (pans and naglers for the most
part) will give you a very nice (very expensive) view.



"Doink" wrote in message ...
Jon,

Thanks for the reply. I don't live where there is an abundance of test
scopes. I have to rely on information here---as a start. Then I do further
research online. It's hard to get straight answers...Of course another 4"
of aperture would be advantageous. BUT, I was trying to find out how much
difference a good mirror would make.

Initally I was moving toward Discovery Dobs...then I saw the 16" f/5.85 dob
on astromart and was able to learn a lot from the owner. I don't want to
use a ladder. So, Tscope at 14"???? I'm not sure the really fast scopes
give good views....do they? Would a 14" f/4.5 be comma crazy? I don't
know...seems there isn't much Dob experience on this board either....

So, I'll keep looking....probably stay with the known....Orions 12.5 is a
winner....
"Jon Isaacs" wrote in message
...
Greetings...

Well, I'm struggling through the vast mine fields of Dob purchasing...I'm
starting to think it's not worth it...The big Dobs are very, very
cumbersome
and quality is very, very expensive...

If I remember correctly, the last scope you were looking at was an 16 inch
F5.8
DOB. At first that seemed ideal but now it appears you have come to
realize
that a scope that is 8 feet long has some disadvantages.

This does not mean that all scopes larger than 8inches are so cumbersome
as to
be unuseable, it just means you need to be careful in choosing.

Putting a nice mirror in that Orion scope is not going buy you the
advantages
of 4 inches of added aperture. That factor of 2.25 in light gathering is
way
too big to overcome.

My suggestion is to take it easy and check out some different scopes in
person
and see what you think. A fast 12.5 inch scope can be quite portable,
mine
fits in my '92 Escort and I can say that it out performs my XT-8 in just
about
every way imagineable.

jon

"Mark Pippin" wrote in message
om...

I can't think of a good reason to own two 8" reflectors
if they are mounted and perform similarly.

In fact, it makes little sense to own more than one scope of any aperture
unless maybe, you are into imaging, and good sense to own them in sizes that
are multiples of the smallest... like 5", 10" and 15", or 4", 8" and 12".

-Stephen

I have two scopes, a Stargazer Steve 4.25 and my Babylon 8. I use the B8
for my sidewalk astronomy, for fast looks I use the Stargazer dob. Some
nights I use the SG one for main viewing if I'm not up to staying up a long
time. If I feel like a major viewing night, then B8 goes out to the field.


--


The Forgotten
http://home.inreach.com/starlord/forgotten.htm


SIAR
http://starlords.netfirms.com
Telescope Buyers FAQ
http://home.inreach.com/starlord
Bishop's Car Fund
http://www.bishopcarfund.netfirms.com/

"Stephen Paul" wrote in message
...

"Mark Pippin" wrote in message
om...

I can't think of a good reason to own two 8" reflectors
if they are mounted and perform similarly.

In fact, it makes little sense to own more than one scope of any aperture
unless maybe, you are into imaging, and good sense to own them in sizes
that
are multiples of the smallest... like 5", 10" and 15", or 4", 8" and 12".

-Stephen




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Well, I have started an astronomy group here in the boonies. I bought one
of the reflectors....The other was so cheap it was nearly given to me...so I
keep it for group use. That's a great reason to have more than one 8"
reflector...and to sell it? For what? $250? Why? It's better off here
where I can let people get experience with a decent scope...
And I have 120mm achro, 80mm Apo, Coronado PST, Etx-125, Etx-90, Etx-60, And
MK-67! So why not get a damn dob???????????????

What I don't understand is that the "good" ones are $2000. What about
getting a 12" Orion, selling the mirror for $150 and putting a really good
mirror in it?
I like the 14" TScope but by the time time you add the little things it's
$2800....Is it THAT much better than a Discovery 12.5"?

That's what I'm trying to learn from your experience...


Doink


"starlord" wrote in message
...
I have two scopes, a Stargazer Steve 4.25 and my Babylon 8. I use the B8
for my sidewalk astronomy, for fast looks I use the Stargazer dob. Some
nights I use the SG one for main viewing if I'm not up to staying up a
long
time. If I feel like a major viewing night, then B8 goes out to the field.


--


The Forgotten
http://home.inreach.com/starlord/forgotten.htm


SIAR
http://starlords.netfirms.com
Telescope Buyers FAQ
http://home.inreach.com/starlord
Bishop's Car Fund
http://www.bishopcarfund.netfirms.com/

"Stephen Paul" wrote in message
...

"Mark Pippin" wrote in message
om...

I can't think of a good reason to own two 8" reflectors
if they are mounted and perform similarly.

In fact, it makes little sense to own more than one scope of any aperture
unless maybe, you are into imaging, and good sense to own them in sizes
that
are multiples of the smallest... like 5", 10" and 15", or 4", 8" and 12".

-Stephen




---
Outgoing mail is certified Virus Free.
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