Total Newbie - Page 2

astro_south (Andrew) · #21 09-04-2005, 01:35 PM

The 10" and 12" refer to the aperture of the scope - diameter of the light gathering source - in the case of the Newt it is the diameter of the primary mirror (at the bottom of the tube). The bigger this number the more light gathering ability the optics have, and the brighter objects will appear, and hence the deeper into space you can see. The trade off (and there is always something) is that a 12" mirror is heavier than a 10" mirror and the tube of the 12" your looking at will be longer than the 10" and may not fit your transport to a darker site - something to consider!

slice of heaven · #22 09-04-2005, 02:30 PM

Bazooka there is 2 types of 12s. 1 has a cooling fan (for faster cooling of the main mirror) and a crayford type focuser. The other has no fan and a rack and pinion focuser. I think there is still an option on plate glass/BK7 for the main mirror.
Not sure about the 10s.
Bintel and Andrews dobs are both gs.
I have to add that there are issues with the gs mount. As the mount is flexy and the alt/az movement leaves alot to be desired.
They can be altered easily depending on what you can put up with.
I think bintel supply the scope with 2 gs eps. Andrews supply a lesser standard of eps. Bintel DO collimate the scope prior to delivery which I think is important for a noobie.
As for size, an 8" can be mounted on an eq mount easier than the 10 or 12. But the large ap of a 10 or 12 will give better views.
Keep thinking and keep asking

Slice

janoskiss (Steve H) · #23 09-04-2005, 02:31 PM

Bazooka, you're not the only one getting confused... Andrew, the two types of 12 and 10" Dobs Bazooka is asking about are pyrex vs non-pyrex mirror and Crayford vs rack-and-peanut focuser.

Pyrex mirror will distort less with changing temperatures and Crayford focuser is smoother, making fine adjustments easier and less likely to nudge the scope off target at high magnifications.

I'd be inclined to say that the 10" deluxe from Andrews for $699 with the Crayford is your best choice under $1000. And you'll have $300 left over to spend on accessories.

and BTW, the Bintel Dobs are GS Dobs with a Bintel sticker. Bintel customers will tell you they get better support, so you might want to talk to Bintel too, even if their advertised prices are a little higher than Andrews'.

slice of heaven · #24 09-04-2005, 02:34 PM

Janos
How long have gs supplied pyrex mirrors?

Slice

ballaratdragons (Ken) · #25 09-04-2005, 02:38 PM

They don't. GS only have Optical Grade Plate Glass and 'BK7' Glass. 'BK7' being superior to Optical Grade Plate Glass. There is nothing wrong with the 'Optical Grade'. It all to do with cooling and in Australia they both work as good as each other. We don't use our scopes in temeratures of minus 10.

Striker (Tony) · #26 09-04-2005, 02:41 PM

Andy,

Make sure what ever you decide......that the primary mirror has been center spotted......Being new to this I dont think you would like to attempt taking the primary out to DIY.

From my understanding.....all of Bintels are spotted but you pay extra for this and 1 of the larger aperture dob's from Andrews are spotted aswell...I think the 12".

ballaratdragons (Ken) · #27 09-04-2005, 02:43 PM

Yep, the GS 12" from Andrews is centre spotted.(well, the Deluxe is, I don't know about the standard model)

janoskiss (Steve H) · #28 09-04-2005, 02:47 PM

Sorry for the wrong info then. This is getting more and more confusing. When I got my 8" there were two models and the only difference between them was the glass the mirror was made out of. I thought we had a lengthy thread on this already, about whether a pyrex mirror is essential for a 12" or would the cheaper glass in the "limited" edition GSO Dobs be ok.

But maybe that explains why my mirror is all chipped and crappy looking around the edges. Its made from crappy glass.

Edit: had a quick search of the archives. Majority concensus says no pyrex in GSOs. It's just that my brain is too small to retain the amount of info on the forums without jumbling some of it up.

ballaratdragons (Ken) · #29 09-04-2005, 02:54 PM

Steve, the Plate glass in GS scopes is good quality. GS don't use Pyrex because it is too damn dear and it would defeat the idea of affordable scopes. The BK7 is almost as good as Pyrex. We don't necessarily need Pyrex in Oz anyway.

Bazooka · #30 09-04-2005, 06:12 PM

Wow that was a confusing read. So let me try to get this straight. The Bintel and Andrews are the same Guan Sheng items, right? The 2 different part numbers shown on the Andrews sight for both the 10" and 12" Dob scopes is one is a plate glass lens where as the other more expensive is for a BK7 lens? This would explain the 'BK7' in the part number. Obviously the BK7 is a better option so I suppose I should look more towards this.
Are the focusers different or not? Quite confused here. And is there an option of a cooling fan or not? So much conflicting information????

Also what is centre spotted?

mick pinner · #31 09-04-2005, 06:45 PM

Buy an SCT, you will get all you need without having to upgrade to this and that at a later stage, they might be more expensive to begin with but every time you sell something to upgrade you lose money. ln my opinion save your money and buy a scope that you will be happy with for a longer period of time, in the meantime a good pair of binoculars will allow you to see some interesting stuff and learn the night sky.

slice of heaven · #32 09-04-2005, 08:13 PM

Confusing? no , we haven't started yet.
The main difference in the type of glass used in the mirrors is how quickly the mirror cools and how much distortion of the mirror surface is created while it is cooling. Theres more than 3 types but we'll stick with these.
Plate glass,BK7 and pyrex.
Pyrex cools quicker and you have less distortion.
Plate glass cools slower and distorts the most while doing so.
BK7 is in between.
Once there cooled and if your not standing in a snowfield it doesn't matter.
A mirror made of BK7 with a fan to reduce cooling times means your mirror will reach equilibrium with the outside temp quicker and your viewing session starts sooner.
Or put your scope with aplate glass mirror outside earlier as it takes longer to cool.
The reflective coating is on the front of the mirror, not behind the glass ,as per a normal mirror. Light doesn't travel through the glass so there is no difference in reflective quality.
As for cooling fans, you can fit a cooling fan from a computer to cool your mirror if your handy enough.

Slice

slice of heaven · #33 09-04-2005, 08:26 PM

The 2 types of focusers available on the gs are either a rack and pinion or a crayford style focuser.
Of the 2 gs focusers the crayford is the better option.
The gs rack and pinion it seems is a poorly designed one.
I haven't seen one but consensus here is their not worthwhile.

Slice

slice of heaven · #34 09-04-2005, 08:41 PM

To collimate (line up your optics) a centre spotted mirror makes this task a lot easier. It's a spot fitted to the centre of the main mirror so you know for sure your main mirror is angled perfectly.
It can be done yourself but if it's done before hand thats one less worry for you.

Slice

slice of heaven · #35 09-04-2005, 09:00 PM

Mick Pinner has brought up the choice of scopes and it is a good idea to check them out at a local group to understand what each are capable of.
A basic dob is the cheapest (inch of aperture per $) and simplest to set up and use. They are a good starting point.

Slice

janoskiss (Steve H) · #36 09-04-2005, 09:21 PM

Quote:

Originally posted by Bazooka
Wow that was a confusing read.

Sorry about that. Largely my fault. Don't despair. In the past year or so, there has been an explosion in choice and affordability of good quality, medium-to-large aperture scopes, so this is a great time to join the hobby. There are some fantastic scopes out there to suit your budget. There are also some real duds to be found in some camera shops and "Australiana" type shops and elsewhere.

janoskiss (Steve H) · #37 09-04-2005, 09:30 PM

Quote:

Originally posted by slice of heaven
Mick Pinner has brought up the choice of scopes and it is a good idea to check them out at a local group ...

Staying within the Local Group is probably a good idea.

PS. Sorry, couldn't resist.

ballaratdragons (Ken) · #38 09-04-2005, 11:36 PM

Quote:

Originally posted by Bazooka
Wow that was a confusing read. So let me try to get this straight. The Bintel and Andrews are the same Guan Sheng items, right? The 2 different part numbers shown on the Andrews sight for both the 10" and 12" Dob scopes is one is a plate glass lens where as the other more expensive is for a BK7 lens? This would explain the 'BK7' in the part number. Obviously the BK7 is a better option so I suppose I should look more towards this.

Yes, the Bintel and Andrews scopes are the same scope. Unless you are in a cold location it won't really matter which glass you use.

Quote:

Originally posted by Bazooka
Are the focusers different or not? Quite confused here. And is there an option of a cooling fan or not? So much conflicting information????

Also what is centre spotted?

Yes, the Focusers are different. The rack and Pinion standard version is a simple design and is prone to wobbles etc. The Crayford has smoother action, a clutch type device, a lock to hold focus and is better quality.

The option of a cooling fan depends on the size scope you get. I don't think all the sizes have this option but you can make one if you want one. I think It only comes on the 12" Deluxe.

But, the 12" Deluxe has the works. BK7 glass, cooling fan, Crayford Focuser, centre spotted mirror and the inside of the tube is already painted Matt Black (important).

I cannot say for sure if the GS 10" Deluxe has ALL the features but you could ring them and ask. The price difference between the Standard and the BK7 CRF version is only $50 on the 10" so I would guess it doesn't have ALL the trimmings.(just a guess though).

If you get a mirror that is not centre spotted and you want to do it yourself 'BEWARE!!' The mirror surfaces cannot be touched. AT ALL! The Aluminium surface is only .003248mm (5 light-waves) thick and the protective coating on most mirrors is only .000162mm (1/4 light-wave) thick. If you touch it and leave a finger-print do not try to rub it off. The coating WILL get damaged. When the time comes to clean your mirrors (not often luckily) we can guide you through the process.

Now that I have cleared some of the confusion, I will confuse you more. Save up heaps and get an SCT with Go-To.

Bazooka · #39 10-04-2005, 07:54 AM

After my last post I found this page that explained everything.

http://www.bintel.com.au/BT302.html

Whats a SCT? They sound expensive.

ballaratdragons (Ken) · #40 10-04-2005, 05:12 PM

Yes they are!!! An SCT is a 'Shmitt-Cassegrain' telescope. Although working on a similar principal to a reflector it is different.

It would take me about 500 words to explain the difference. Maybe someone else may have a very simple explanation??