Dobsonian Decision

Post by **Airconvent** » Mon Nov 08, 2004 10:37 pm

Stuck in a tight situation, it looks like I may not be able to get my Nexstar 8 after all. The other night, I was intrigued by the Dob and its ease of use, albeit its clumsy size. I'm thinking instead of an N8, I will have to satisfy my thirst for a larger aperture via a Dob instead. 8" seems too big, so my possible target is a 6".

After some "survey", I'm looking at the following :

1. Chris Yeo's short FL 6" truss dob, it certainly looks attractive. I noticed that most Dobs are in the range 1250mm FL but his is shorter, making it more portable. Short of him selling it, I'm looking at something similar. Are there such products? Will a shorter FL be a disadvantage ?

2. Orion's 6" certainly looks attractive. only US$239. It should cost less than S$500 inclusive of shipping? The DSC model "manual Goto" sells for US$359 excluding shipping!

http://www.telescope.com/shopping/produ ... es#tabLink

3. Celestron's 6" Dob.

http://www.celestron.com/prod_pgs/tel/starhopper6.htm

4. Discovery 6" Dob. (looks big)

http://www.discovery-telescopes.com/DHQ.html

So what are your opinions? Build myself? That would certainly allow me to control the size of the mount and make it smaller but I'm totally useless as far as ATM is concerned....sigh...

rich

harlequin2902 · Post by **harlequin2902** » Mon Nov 08, 2004 11:22 pm

Airconvent wrote:1. Chris Yeo's short FL 6" truss dob, it certainly looks attractive. I noticed that most Dobs are in the range 1250mm FL but his is shorter, making it more portable. Short of him selling it, I'm looking at something similar. Are there such products? Will a shorter FL be a disadvantage ?

Due to the parabolic shape of primary mirrors used in them, Newtonian-type scopes usually suffer from coma. Coma is an optical defect in which stars at the edge of the field of view appear 'triangular'. The faster the f-ratio of the scope, the greater the effect.

Hm, among the 3 ready made ones you listed above, I guess the Orion's 6" XT6 Intelliscope is top on your list, since some form of GOTO is usually one of your main considerations ? Note that the scope is "GOTO-ready" but you have to add an extra US$149 for the computerized object locator itself, bringing the price to ~ US$500.

Post by **Airconvent** » Mon Nov 08, 2004 11:56 pm

harlequin2902 wrote:Due to the parabolic shape of primary mirrors used in them, Newtonian-type scopes usually suffer from coma. Coma is an optical defect in which stars at the edge of the field of view appear 'triangular'. The faster the f-ratio of the scope, the greater the effect.

Hm, among the 3 ready made ones you listed above, I guess the Orion's 6" XT6 Intelliscope is top on your list, since some form of GOTO is usually one of your main considerations ? Note that the scope is "GOTO-ready" but you have to add an extra US$149 for the computerized object locator itself, bringing the price to ~ US$500.

thanks Sam..
I thought the US$300 already includes the Intellsync? That's US$200+ for the 6" Dob + US$149 for the DSC?

rich

ariefm71 · Post by **ariefm71** » Tue Nov 09, 2004 12:04 am

Why don't you ask Chee-Chien to buy you an XT10 when he comes back from US? :-)

Post by **Airconvent** » Tue Nov 09, 2004 12:07 am

ariefm71 wrote:Why don't you ask Chee-Chien to buy you an XT10 when he comes back from US? :-)

actually, I already did but then I remembered he would probably have his hands full at the US Custom explaining his new LX200 14" is not a rocket launcher....??

Seriously, the size of the scope would prevent me from burdening him to bring it back...

harlequin2902 · Post by **harlequin2902** » Tue Nov 09, 2004 12:24 am

thanks Sam..
I thought the US$300 already includes the Intellsync? That's US$200+ for the 6" Dob + US$149 for the DSC?

rich

I think they are following what Meade is doing with their ETXs. The scope is indeed GOTO-ready, but you need to buy the object locator to be able to use the GOTO system on the scope.

This quote from their Intelliscope FAQ furthur confirms this :

" Q). Can I use an IntelliScope Dob without the Computerized Object Locator?
A.) Sure! Without the Object Locator the IntelliScope Dobsonian performs like a standard Dobsonian—with a slew of great design and performance features not found on competing Dobsonians."

MooEy · Post by **MooEy** » Tue Nov 09, 2004 12:25 am

shipping is going to kill. gif u an idea, go astro scientific, grab one of those newt ota, build the dob mount urself. they seem to have extremely gd prices on the celestrons now.

also, the intelliscope is just built in encoders. seem to be following the trend of teleport and starmasters. i'm actually interested in finding out if the intelliscope can take a laptop or a pda as it's controller.

~MooEy~

Post by **weixing** » Tue Nov 09, 2004 12:40 am

Hi,
Another options... buy my 6" Newtonian OTA... Ha Ha Ha...

By the way, why don't you just get a Sky-Watcher 6" dob... got a 2" Crayford-style focuser and it just S$800 new. And yes, it is bulky, but there are only a few dob that is not bulky... anyway, you drive

It is also quite "fast". At F6.6, it focal length is short enough to give a wide view and not too "fast" to have a lots of coma.

Have a nice day.

ariefm71 · Post by **ariefm71** » Tue Nov 09, 2004 1:02 am

I second what Wee Heng said. Get Weixing's OTA and ask Chris to get his carpenter make two sets of 1stbase collapsible mount. Ask the carpenter to make the side bearings/ota rings as well.

Post by **VinSnr** » Tue Nov 09, 2004 1:33 am

Rich,

Forget about the 6". The 8" tube is not really that much longer. In fact, I think the are both same length because the 6" is mostly f/8 and the 8" is mainly f/6.

The main portability concern is length. If they are both the same length, with the 8" only slightly heavier, why get the 6"?

There is a big noticable jump at the eyepiece when you go 8" from 6". Get the 8" if not, you will get aperture fever again in no time. And don't worry....an 8" f/6 will not give you coma. I know because my previous Portaball is an 8" f/6.

Ok..assuming you must get the 6". Then choose one with a good focuser. Very very important. I don't really trust Syntha focuser. But then think you want the DSC. If that's the case, Orion is the only one for you. But Orion has a Chinese focuser, which is not really that good. So the solution is this....get the Orion 6", and if the focuser has a lot of slop which you can't get rid off, then purchase an Orion helical focuser. Rough focus you will use the Syntha focuser, fine focus you will use the helical. This way, you wun get image shift due to the slop.

But my advice is still this: Get the 8".