More on Dobsonians...

I was just looking at the dobsonians again, and had another question.
Both the Celestron 10 inch and the Orion 10 inch both say that they
have a "maximum useful magnification" of 600. The Hardin 10 inch
Dob's "maximum useful magnification" is only 250. I know that
magnification isn't all that important, but that seems like a pretty
big jump, although I'm not sure 'cause I'm new to all this. Does
anyone have any thoughts on why the Hardin would be so much lower than
the other two?

I'm no expert; but I thought that the general rule of thumb was that
the maximum useful magnification of a given telescope was 50x per inch
of aperture. Given that the newt/dob's you are looking at are 10inch
"theoretically" you should be good for 500x.

I have a 10" f/5 Guan Sheng dob, and personally I hardly really ever
exceed 300x with mine (for planets I mainly use a 9mm plossl with 2x
barlow giving 277x). Anything more than that either gives average
images, or with the eye pieces I have are too annoying to use (FOV/eye
relief).

And as a side note (again I'm no expert); I wouldn't get too hooked up
with the claimed maximum magnification of the scopes, and be looking at
things like accessories, mirror quality differences (if any?) and..
price.

I'm sure theres corrections to be made by the others. I hope that helps
some what.

Clarky wrote:
I was just looking at the dobsonians again, and had another question.

Both the Celestron 10 inch and the Orion 10 inch both say that they
have a "maximum useful magnification" of 600. The Hardin 10 inch
Dob's "maximum useful magnification" is only 250. I know that
magnification isn't all that important, but that seems like a pretty
big jump, although I'm not sure 'cause I'm new to all this. Does
anyone have any thoughts on why the Hardin would be so much lower
than
the other two?

In article , aar4teen88
@fast.net says...
I was just looking at the dobsonians again, and had another question.
Both the Celestron 10 inch and the Orion 10 inch both say that they
have a "maximum useful magnification" of 600. The Hardin 10 inch
Dob's "maximum useful magnification" is only 250. I know that
magnification isn't all that important, but that seems like a pretty
big jump, although I'm not sure 'cause I'm new to all this. Does
anyone have any thoughts on why the Hardin would be so much lower than
the other two?

IMO, Celestron and Orion are being pretty doggone optimistic, while
Hardin is probably closer to the truth on many nights. However, I think
250x is probably a bit low. Years ago, 60 x aperture in inches was a
rule of thumb, but I'd personally put it more in the 35x to 40x range.

Orion has a bent toward excessive (IMO) hyperbole, reminiscent of Radio
Shack, but maybe that's just a byproduct of a highly competitive market.
--

-- Len Philpot - --
------ ----- http://philpot.org/ --

On 13 Apr 2005 18:01:38 -0700, Clarky wrote:

I was just looking at the dobsonians again, and had another question.
Both the Celestron 10 inch and the Orion 10 inch both say that they
have a "maximum useful magnification" of 600. The Hardin 10 inch
Dob's "maximum useful magnification" is only 250. I know that
magnification isn't all that important, but that seems like a pretty
big jump, although I'm not sure 'cause I'm new to all this. Does
anyone have any thoughts on why the Hardin would be so much lower than
the other two?


As a general rule, with really good optics, 50x per inch is max power
for extended objects (moon, planets) then image deteriorates rapidly.
60x per inch for stellar objects like really close double stars.

However, since dobsonians are hand-driven, it is hard to keep an object in
view for more than a few seconds at a time with any power over 300x. This
is a much more practical limit, especially when the atmosphere bounces the
image about. Much like trying to read the
date on a penny at the bottom of a swimming pool.

Cheers,
Larry G.

Sales gimmicks, that's all!
Tascos 60mm refractor was advertised for 600x magnification!!!! hahahahaha!
JS

"Clarky" wrote in message
om...
I was just looking at the dobsonians again, and had another question.
Both the Celestron 10 inch and the Orion 10 inch both say that they
have a "maximum useful magnification" of 600. The Hardin 10 inch
Dob's "maximum useful magnification" is only 250. I know that
magnification isn't all that important, but that seems like a pretty
big jump, although I'm not sure 'cause I'm new to all this. Does
anyone have any thoughts on why the Hardin would be so much lower than
the other two?

Clarky wrote:
I was just looking at the dobsonians again, and had another question.
Both the Celestron 10 inch and the Orion 10 inch both say that they
have a "maximum useful magnification" of 600. The Hardin 10 inch
Dob's "maximum useful magnification" is only 250. I know that
magnification isn't all that important, but that seems like a pretty
big jump, although I'm not sure 'cause I'm new to all this. Does
anyone have any thoughts on why the Hardin would be so much lower than
the other two?

Conflict between two rules of thumb. It is pretty unlikely that the
discrepancy indicates any real difference between the optics.

One rule of thumb says that the maximum useful magnification for a
scope of aperture N inches is equal to 50 or 60 times N (depending on
whom you ask). That is where Celestron and Orion get their figure.
The second rule of thumb says that the maximum useful magnification
for any scope of whatever aperture is bounded, because of atmospheric
turbulence, to 250x or 300x (again, depending on whom you ask). That
is where Hardin gets its figure.

Even under average seeing, however, I would expect that a large scope
would still be able to use a higher magnification than a small scope;
it's just that the margin would be smaller.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

I have a 10 inch Teleport and on rare nights it will do 600x on the planets.

Bubba DeBub

"Brian Tung" wrote in message
...
Clarky wrote:
I was just looking at the dobsonians again, and had another question.
Both the Celestron 10 inch and the Orion 10 inch both say that they
have a "maximum useful magnification" of 600. The Hardin 10 inch
Dob's "maximum useful magnification" is only 250. I know that
magnification isn't all that important, but that seems like a pretty
big jump, although I'm not sure 'cause I'm new to all this. Does
anyone have any thoughts on why the Hardin would be so much lower than
the other two?

Conflict between two rules of thumb. It is pretty unlikely that the
discrepancy indicates any real difference between the optics.

One rule of thumb says that the maximum useful magnification for a
scope of aperture N inches is equal to 50 or 60 times N (depending on
whom you ask). That is where Celestron and Orion get their figure.
The second rule of thumb says that the maximum useful magnification
for any scope of whatever aperture is bounded, because of atmospheric
turbulence, to 250x or 300x (again, depending on whom you ask). That
is where Hardin gets its figure.

Even under average seeing, however, I would expect that a large scope
would still be able to use a higher magnification than a small scope;
it's just that the margin would be smaller.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

My Babylon 8 8inch f8 I've pushed to 300, but that was for MARS in 03, and
the air had to be still but I did get good views. But if I pushed to 400 or
500, I'd lay odds the view would not be that good. Someday I'll have to try
it to see what happens.

"Bubba DeBub" wrote in message
news:gnn7e.9320$%c1.5210@fed1read05...
I have a 10 inch Teleport and on rare nights it will do 600x on the
planets.

Bubba DeBub

"Brian Tung" wrote in message
...
Clarky wrote:
I was just looking at the dobsonians again, and had another question.
Both the Celestron 10 inch and the Orion 10 inch both say that they
have a "maximum useful magnification" of 600. The Hardin 10 inch
Dob's "maximum useful magnification" is only 250. I know that
magnification isn't all that important, but that seems like a pretty
big jump, although I'm not sure 'cause I'm new to all this. Does
anyone have any thoughts on why the Hardin would be so much lower than
the other two?

Conflict between two rules of thumb. It is pretty unlikely that the
discrepancy indicates any real difference between the optics.

One rule of thumb says that the maximum useful magnification for a
scope of aperture N inches is equal to 50 or 60 times N (depending on
whom you ask). That is where Celestron and Orion get their figure.
The second rule of thumb says that the maximum useful magnification
for any scope of whatever aperture is bounded, because of atmospheric
turbulence, to 250x or 300x (again, depending on whom you ask). That
is where Hardin gets its figure.

Even under average seeing, however, I would expect that a large scope
would still be able to use a higher magnification than a small scope;
it's just that the margin would be smaller.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Bubba DeBub wrote:
I have a 10 inch Teleport and on rare nights it will do 600x on the
planets.

Yeah, I should have said that the atmospheric limitation varies from
night to night.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

X-No-Archive: Yes
"...dobs are hand-driven..." - NOT for many of us. I've been using an
equatorial platform for over 8 years, as have many others. Some folks
use a Bartels drive. And there are other systems in use to keep dobs
tracking accurately. I regularly view at 750X when conditions permit,
and the image will stay in the field for half an hour, if I have set up
accurately.

Shneor