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View Full Version : Buying Vs. Building a 10" Dob



skrap1r0n
2004-Apr-29, 03:20 PM
I am currently looking at buyting the Orion 10" Dob. It's going to run around $800. I am wondering, would I be able to build a 10" Truss Dob any cheaper?

Also, I am pretty handy in the shop, however I am wondering...Grind or Buy a mirror?

mike alexander
2004-Apr-29, 04:00 PM
As someone who has ground his own mirror, I can only say it was a lot of fun (?) but very satisfying when it was done. On the other hand, figuring it properly is not the easiest thing on earth, especially if you are going for a deep, fast one (then you have to send it out for coating). What does a good mirror cost these days?

Also, the trusses look so Palomar-cool, but the Sonotube route is much easier.

One more thought. If you decide to make your own mirror, a 10" is a pretty big first step. I'd seriously think about trying a smaller one first (say 6") to see if you like it.

skrap1r0n
2004-Apr-29, 05:28 PM
As someone who has ground his own mirror, I can only say it was a lot of fun (?) but very satisfying when it was done. On the other hand, figuring it properly is not the easiest thing on earth, especially if you are going for a deep, fast one (then you have to send it out for coating). What does a good mirror cost these days?

Also, the trusses look so Palomar-cool, but the Sonotube route is much easier.

One more thought. If you decide to make your own mirror, a 10" is a pretty big first step. I'd seriously think about trying a smaller one first (say 6") to see if you like it.

The Trusses make ot more portable, thats why I was thinking of going that route. How long did it take you to grind your mirror?

ChesleyFan
2004-Apr-29, 08:17 PM
I am currently looking at buyting the Orion 10" Dob. It's going to run around $800.

Let time I checked an Orion 10" was about $600 including shipping. Use that extra $200 for a good Panoptic.

Grinding a 10" mirror would be a pain in the butt, especially for a fast f/5 model like the Orion. Either that, or make it a slower optical system, but then you'll have a huge focal length and a correspondingly very big tube (a f/6 system would be about a foot taller; a f/7 more than two).

If you're serious about the homebuilt truss dob, you can buy an already ground and coated mirror from a place like Discovery (http://www.discovery-telescopes.com/optics.html). I'm guessing the cost vs. buying an Orion scope is about the same, though.

skrap1r0n
2004-Apr-29, 09:24 PM
I am currently looking at buyting the Orion 10" Dob. It's going to run around $800.

Let time I checked an Orion 10" was about $600 including shipping. Use that extra $200 for a good Panoptic.

Grinding a 10" mirror would be a pain in the butt, especially for a fast f/5 model like the Orion. Either that, or make it a slower optical system, but then you'll have a huge focal length and a correspondingly very big tube (a f/6 system would be about a foot taller; a f/7 more than two).

If you're serious about the homebuilt truss dob, you can buy an already ground and coated mirror from a place like Discovery (http://www.discovery-telescopes.com/optics.html). I'm guessing the cost vs. buying an Orion scope is about the same, though.

Oh I was going to get the Intelliquest version already rigged for the Push to Computer. However, that is not a necessity. The more I am out with my binocs, the less I seem to feel the need for the 'puter.

Also, what do you mean by fast? Shorter scope with a lower f/#?

AstroSmurf
2004-Apr-30, 10:14 AM
Grinding a 10" mirror would be a pain in the butt, especially for a fast f/5 model like the Orion. Either that, or make it a slower optical system, but then you'll have a huge focal length and a correspondingly very big tube (a f/6 system would be about a foot taller; a f/7 more than two).
Or build something different than a normal Newtonian. f/5 or thereabouts is pretty nice as a general-purpose scope; takes a while to grind though. My enthusiasm seems to have infected my dad, who's grinding a f/5 12" mirror now. We'll see how it turns out - he's probably going for an equatorial mount though, since he's going to do some astrophotography.

It seems to me that the flat secondary is going to cost more than the primary. Anyone know how you can get a hold of those without having to spend a small fortune? My dad needs a normal elliptical one, but I need a round one.

(I'm trying out the folded Herschelian from the March 2004 issue of S&T. I like planets, and it doesn't take much work to make a f/23.3...)

ChesleyFan
2004-Apr-30, 01:56 PM
Oh I was going to get the Intelliquest version already rigged for the Push to Computer. However, that is not a necessity. The more I am out with my binocs, the less I seem to feel the need for the 'puter.

Also, what do you mean by fast? Shorter scope with a lower f/#?

I'd suggest to do without the computer; you'll either quickly outgrow any need for a computer as you gain experience, or you'll tend to rely on the computer too much and never actually learn the sky. If you're building the truss dob you're probably already considering a life without the computer, anyway.

"Fast" means short f/ratio (I'd say anything below f/6 is fast). It relates to how much time is needed to take an photographic exposure. Longer f/ratio require more time for light to built up on the film (or in these days, the CCDs). Fast scopes are obviously prized for astrophotography, but they're harder to built: in the case of Newtonians the primary mirror has to be ground to better precision, and for refractors it usually means exotic lens elements and coating to eliminate color.

Padawan
2004-Apr-30, 01:57 PM
I am currently looking at buyting the Orion 10" Dob. It's going to run around $800. I am wondering, would I be able to build a 10" Truss Dob any cheaper?

Also, I am pretty handy in the shop, however I am wondering...Grind or Buy a mirror?


*Slightly off-topic*: Ahhhh, you are so lucky to even get one! i wish i had one :'( i'm stuck with a Meade ETX 90mm...with a bad front lense

skrap1r0n
2004-Apr-30, 02:44 PM
I am currently looking at buyting the Orion 10" Dob. It's going to run around $800. I am wondering, would I be able to build a 10" Truss Dob any cheaper?

Also, I am pretty handy in the shop, however I am wondering...Grind or Buy a mirror?


*Slightly off-topic*: Ahhhh, you are so lucky to even get one! i wish i had one :'( i'm stuck with a Meade ETX 90mm...with a bad front lense

I don't have it yet... Its going to take me several months of saving to get it.

SiriMurthy
2004-Apr-30, 03:44 PM
*Slightly off-topic*: Ahhhh, you are so lucky to even get one! i wish i had one :'( i'm stuck with a Meade ETX 90mm...with a bad front lense

Aaargh!! Me too. That too, I have a ETX 90 manual. Does not have the motorized drives. It was a good deal (?? or so I thought) when I bought it, though, I regret it now. Don't get me wrong, it is still a good scope for the size (I could see the surface features on Mars at its closest encounter recently), but I could have gone for a better scope.

skrap1r0n
2004-Apr-30, 04:25 PM
*Slightly off-topic*: Ahhhh, you are so lucky to even get one! i wish i had one :'( i'm stuck with a Meade ETX 90mm...with a bad front lense

Aaargh!! Me too. That too, I have a ETX 90 manual. Does not have the motorized drives. It was a good deal (?? or so I thought) when I bought it, though, I regret it now. Don't get me wrong, it is still a good scope for the size (I could see the surface features on Mars at its closest encounter recently), but I could have gone for a better scope.

That is precisely why I started out with a pair of $60 16x50 binocs. I didn't want to spend an assload on a telescope only to find out that the scope I bought wouldn't suit my needs. I originally wanted to get the ETX90 then after toing a TON of research, I settled first on an 8" dob, then quickly chnaged to the 10". Now I am considering building one, but I do not think I could build one for what I could Buy one for.

That being said, I may build a small 4" or 6" with the kids just to say we built one.

ChesleyFan
2004-Apr-30, 06:21 PM
As long as we're off-topic:

Personally, I'm saving up for a small high-end refractor and some nice eyepieces. I already have the 8" dob, so I'm looking for something more portable this time around.

bearcub
2004-Apr-30, 06:51 PM
As long as we're off-topic:

Personally, I'm saving up for a small high-end refractor and some nice eyepieces. I already have the 8" dob, so I'm looking for something more portable this time around.

Have you looked at the Orion 80 ED APO? It's going for $499 (OTA only). The reviews I've seen on it have all been very positive. It's the one I'm thinking about, unfortunately it's on backorder until 5/13. :(

It can be found here (http://www.telescope.com/shopping/product/detailmain.jsp?itemID=6306&itemType=PRODUCT&iMainC at=4&iSubCat=13&iProductID=6306).

mike alexander
2004-Apr-30, 06:56 PM
To answer SkrapFe's question on the mirror.

Rough grinding-about a week of evenings.

Smoothing and final adjustment of the radius- about another week

Polishing- probably about two weeks

Figuring- well, you never really finish, you just quit. I quit after about a month. There is some fun in figuring out how to do the Foucalt testing. Takes patience-more than I had at the time.

Since I couldn't afford to send it out for aluminizing I silvered it myself, which is not hard to do.

I would add that even a fairly lousy mirror can do well if you are going for low-power, deep sky stuff. It's actually pretty hard to make a totally worthless mirror. Seeing Saturn for the first time through a scope you have built is quite the experience.

Truss vs. tube is a builder's call. The tubing is cheap and sturdy.

For scads of practical advice see if you can find copies of Amateur Telescope Making (Ingalls, ed) of How to Make a Telescope (Jean Texerau). I do not know if they are still in print.

SiriMurthy
2004-Apr-30, 07:03 PM
That is precisely why I started out with a pair of $60 16x50 binocs.
I have 10x50 and a 20x50 binocs, but the problem is the stability when viewing the sky. I cannot hold it steady at all. Both the models I have don't sit very well on a tripod. ](*,) So I don't use my binocs that often. I just use my ETX 90.


That being said, I may build a small 4" or 6" with the kids just to say we built one.
I have built a 4" Newtonian long time ago and it was all fun. We could not get the lens alignment worked out properly. It turned out pretty good considering the fact that we even built our own telescopic tubes!! :wink: It was all educational.

Padawan
2004-Apr-30, 08:18 PM
*Slightly off-topic*: Ahhhh, you are so lucky to even get one! i wish i had one :'( i'm stuck with a Meade ETX 90mm...with a bad front lense

Aaargh!! Me too. That too, I have a ETX 90 manual. Does not have the motorized drives. It was a good deal (?? or so I thought) when I bought it, though, I regret it now. Don't get me wrong, it is still a good scope for the size (I could see the surface features on Mars at its closest encounter recently), but I could have gone for a better scope.


Man, you know what i discovered after being into stress with studies the past few years (and not being able to use the telescope)? If you let the scope rest horisontally for a longer period, then the anti-reflection thingy glued on the secondary mirror will descend sloooooowwwwllllyyyyy in height, because of gravity...making your view more and more blurry. So now, i dont have a use for that dang ETX. Atleast Dobsonians won't have this sort of problem because of their construction.

Note: i agree with you it is a good telescope, it's only that it is so small.

ChesleyFan
2004-Apr-30, 08:27 PM
Have you looked at the Orion 80 ED APO? It's going for $499 (OTA only). The reviews I've seen on it have all been very positive. It's the one I'm thinking about, unfortunately it's on backorder until 5/13. :(

Actually, I've wanted one of Vic Maris' Stellarvue Nighthawks for years now. It's not an apo, but I've heard it's very well corrected for a fast achromat.

The ED80 is backordered already? It was in stock as of yesterday on their website! It's definitely one fine scope, from what I've heard. You can check Astromart (www.astromart.com) for a barely-used one... I've seen a couple in the past few weeks, but they don't stay posted for long!