Hardin DSH-10, part 3

I've had the Hardin out twice now, and am still having optical problems. I
spent about an hour today in sunlight working on the collimation to a point
I thought was pretty darn good, even though I don't yet have any optical
tools.

At night, scope is still showing a lot of flare on stars, and ghosting on
planets. Some of this may be my own eyes, but I've yet to see an airy disk,
despite numerous attempts to get one, and I was under fairly clear skies.

I'm not ready to fault the quality of the optics, but I'm quite convinced
that the scope was terribly out-of-alignment when I received it, despite
advertised promises from Hardin that it would be aligned. My own
inexperience with collimating a fast reflector is probably not helping,
although I've sure learned a lot in the past few days. I just wish I could
feel better about this scope. The moon looked nice. At this point I would
tell anyone out there shopping for a cheap 10-inch that you get what you pay
for, and to consider looking for a used scope with time-tested optics.

Next step: collimation tools. If that doesn't do the trick, I'll be calling
Hardin for a refund or a swap.

--Eric Martin

go to a camera shop, ask if they have any discarded 35mm film cans (plastic
ones), get one, drill small hole in top of can, cut out most of bottem of can.
Dot main mirror in center, replace EP with filmcan, aline scope. I did it that
way for years, still have my 1st such tool.


--
"In this universe the night was falling,the shadows were lengthening
towards an east that would not know another dawn.
But elsewhere the stars were still young and the light of morning
lingered: and along the path he once had followed, man would one day go
again."

Arthur C. Clarke, The City & The Stars

SIAR
www.starlords.org
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http://www.freelancewrittersshop.netfirms.com
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"Eric Martin" wrote in message
.com...
I've had the Hardin out twice now, and am still having optical problems. I
spent about an hour today in sunlight working on the collimation to a point
I thought was pretty darn good, even though I don't yet have any optical
tools.




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What? Don't pop $120 on Tectron tools? Don't buy the newest laser thingy?

Well, I did drop $40 on a combo tool from Orion. It's a bad habit that needs
feeding, ordering astronomy stuff. But I"ll try the film can while I wait.

Thanks, Eric


"Starlord" wrote in message
...
go to a camera shop, ask if they have any discarded 35mm film cans
(plastic
ones), get one, drill small hole in top of can, cut out most of bottem of
can.
Dot main mirror in center, replace EP with filmcan, aline scope. I did it
that
way for years, still have my 1st such tool.

On 12/01/03 14:58 +0900, Eric Martin wrote:

I've had the Hardin out twice now, and am still having optical problems. I
spent about an hour today in sunlight working on the collimation to a point
I thought was pretty darn good, even though I don't yet have any optical
tools.

Did you try the ol' 35-mm film canister tool? Drill a 2 mm hole
in the centre of the cap and a 3 mm hole in the centre of the
bottom. Centrally dotting both the secondary and primary should
let you get a pretty decent collimation with just the canister.
YMMV, but that has been my personal experience (which,
admittedly, much slower f/8 optics).

I first tried just eyeballing the secondary in the focuser, but I
found that this was not accurate enough. My focuser fully racked
in and the cap of the canister removed enabled me to get the
secondary centred in the focuser. Once that was accomplished,
subsequent collimation of the primary netted much, much better
results.

At night, scope is still showing a lot of flare on stars, and ghosting on
planets. Some of this may be my own eyes, but I've yet to see an airy disk,

Is it flare or diffraction spikes? As for the Airy disk, you'll
need pretty high magnification in a 10" scope to see that. It is
my understanding that you need about 50x or higher/inch of
aperture to see the Airy disk and diffraction rings on most
scopes. At 210x in my 4" scope, the Airy disk is pretty obvious.
At an approximately 500x-600x in your scope, you should be able
to see the Airy disk. Since you've got a Dobsonian, Polaris would
probably be the best test for you because it will move in the FOV
the least. It has been my experience that seeing will play a roll
in the appearance of the Airy disk and diffraction rings.

Best of luck with the scope, Eric.

trane
--
//------------------------------------------------------------
// Trane Francks Tokyo, Japan
// Practice random kindness and senseless acts of beauty.
// http://mp3.com/trane_francks/

I'm not ready to fault the quality of the optics, but I'm quite convinced
that the scope was terribly out-of-alignment when I received it, despite
advertised promises from Hardin that it would be aligned. My own
inexperience with collimating a fast reflector is probably not helping,
although I've sure learned a lot in the past few days.

Hardin could only ship the scope aligned, there is no way to know that it would
arrive aligned. The scope definitely sounds like it is out of collimation. At
F5, it will need to be in pretty decent collimation. Of course the other two
issues that will cause ghosting are a scope that has not cooled down and an
instable atmosphere, the well know "Bad Seeing."

The two pages I recommend:

http://gilstrap.home.texas.net/collimat/NoTools.html

Though it does not seem to be up at the moment.

http://w1.411.telia.com/~u41105032/kolli/kolli.html

This is a complete discussion, follow the links.

I just wish I could
feel better about this scope. The moon looked nice. At this point I would
tell anyone out there shopping for a cheap 10-inch that you get what you pay
for, and to consider looking for a used scope with time-tested optics.

In my experience, you certainly get what you pay for, the OPT Star Hunter 10 I
have does very well, sharp images even at high powers.

Next step: collimation tools. If that doesn't do the trick, I'll be calling
Hardin for a refund or a swap.

It is possible to collimate without tools but a good cheshire or sight tube and
a laser collimator make it easier. But more important is to understand exactly
what you are trying to do.

My suggestion would be to find someone locally who can help collimate your
scope and teach you how to do it.

Where are you located??

Jon Isaacs

Thanks for all the responses. I probably did not have enough mag to see the
airy disk (the scope was cooled...I'd left it out since noon).

I'll be getting a collimator from Orion in a few days, which I think will be
very helpful. Eye-ball collimation works on a f/8, but I'm learning that an
f/4.9 is a whole different world.

--Eric Martin

It was funny, I got those tools ( someone donated them ) and the book, so I set
out to aline my scope. After many hours and after getting stressed out a bit, I
reach the part of the book that says, all this work is for fast scopes, that for
f8 or above it didn't matter as much.

Babylon 8 8 inch F8 Dob.

The sound everyone heard was me cracking a 2x4 over my head. ;}


--
"In this universe the night was falling,the shadows were lengthening
towards an east that would not know another dawn.
But elsewhere the stars were still young and the light of morning
lingered: and along the path he once had followed, man would one day go
again."

Arthur C. Clarke, The City & The Stars

SIAR
www.starlords.org
Freelance Writers Shop
http://www.freelancewrittersshop.netfirms.com
Telescope Buyers FAQ
http://home.inreach.com/starlord
Ad World
http://adworld.netfirms.com

"Eric Martin" wrote in message
news
Thanks for all the responses. I probably did not have enough mag to see the
airy disk (the scope was cooled...I'd left it out since noon).

I'll be getting a collimator from Orion in a few days, which I think will be
very helpful. Eye-ball collimation works on a f/8, but I'm learning that an
f/4.9 is a whole different world.

--Eric Martin




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"Eric Martin" wrote in message y.com...
I've had the Hardin out twice now, and am still having optical problems. I
spent about an hour today in sunlight working on the collimation to a point
I thought was pretty darn good, even though I don't yet have any optical
tools.

At night, scope is still showing a lot of flare on stars, and ghosting on
planets. Some of this may be my own eyes, but I've yet to see an airy disk,
despite numerous attempts to get one, and I was under fairly clear skies.


Hi:

Good collimation is always a good thing. But the "flare", if it's
concentric, is probably an artifact of your own eyes. And the
"ghosting" a fact of life with bright targets and especially less
expensive eyepieces.

Peace,
Rod

It may not matter as much, but believe me, it will help and make the difference
between a so-so image and a knock your socks off image.
Clear, Dark, Steady Skies!
(And considerate neighbors!!!)