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[marscreeper]

I need some input from you guys. I am going to buy a new telescope within the next week. I am currently looking at a Celestron - Starhopper 8 Inch Dobsonian is this a good telescope ?? I thank you for your time and consideration on this matter. Also what is the average max magnitude you can see with an 8, 10 ,or 12 inch Dobsonian, provide the focal leghth is the same,and you are using a 25 mm eyepeice.

MC

[marscreeper]

Ok guys i really needed your input on this.....but i guess i will go ahead and buy it. Thanks anyway..........MC

[katodog]

Here's a site that will help with your questions on power.

www.scopesim.com/


Any Dobsonian is a good one, and the bigger the better. Whether you go with Celestron, Orion, or any other, they are super easy to use and transport. My personal preference would be the 12" XT Classic that Orion just came out with.

[Chicago Astronomer - Astro Joe]

The 8" is a good scope, but again bigger is better. If you can squeeze a few more dollars and get the 10"...do it! You won't be sorry. I forget the formula, but a 10" over a 8" is more than just twice the light gathering power.

In the 8", objects will appear brighter and you will be able to catch dimmer ones too. It's remarkable the difference between peering thru my 4.5" and that of a 8".

We have a 8" dob at the Adler, and it perfoms quite well. I think you'll have fun with it.

[Rocketman]

I don't get it... How does a 10" accumalate twice as much light as an 8"?

8 inch = $350 shipped
10 inch = $530 shipped

[Chicago Astronomer - Astro Joe]

Well, most lay people would think that a 2" lens would collect twice as much a 1" lens, but it exponentially more. I wish I could remember the forumla, but it's greater than twice. Someone out there knows, I'm sure.

Here is a link and table to the light grasp of a given scope: www.siriusstargazers.com/Sirius%20Aper%20vs%20Mag.htm

For the price quoted, I would stick with the 8" inch dob. Almost the same views, but the 10" would show the objects a bit brighter and bring out the dimmer objects better. But you can't go wrong with the 8".

[Rocketman]

Now that's a good link, thanks Joe.

No wonder I don't like a 4mm eyepiece! I wish I had a 7 or 8mm. Feel free to drop one in the mail for me

[jglover]

rocketman2 said:

I don't get it... How does a 10" accumalate twice as much light as an 8"?

8 inch = $350 shipped
10 inch = $530 shipped

It's a question of areas of the mirrors. An 8 inch scope has a surface area of about 50 square inches, while a 10 inch scope has an area of 78 square inches (A=pi*r^2). So, a 10 inch scope has about 78/50, or 1.6 time the light gathering power of an 8 incher.

[jglover]

admin said:

Well, most lay people would think that a 2" lens would collect twice as much a 1" lens, but it exponentially more. I wish I could remember the forumla, but it's greater than twice.

Doulbing the aperture quadruples the light gathering ability of a scope. So a 2 inch lens has four times the area of a one inch lens, and four time the light gathering power. The formula for area of a mirror or lens is the radius squared times pi.....pi*r^2

[Chicago Astronomer - Astro Joe]

I didn't want to say it early on and place undue pressure...but I had an inkling John would be the one to shed light on this matter.

Thanks John.

[marscreeper]

Thank you all for your reply ...this really helps me ...thanks again MC

[jglover]

admin said:

I didn't want to say it early on and place undue pressure...but I had an inkling John would be the one to shed light on this matter.

Thanks John.

No problem Joe!

[marscreeper]

Thanks guys and gals, i have ordered the 8 inch scope and cant wait till it gets here ....hopefully i can see a lot more with it . Thanks again for your help ......MC

[Chicago Astronomer - Astro Joe]

Excellent!

I anticipate your first views* through your scope, should be breathtaking, and I would like to hear about your impressions on seeing various targets from them darker skies of Texas.

Begining views are always memorable.

(*Personal note: I really despise the term "First Light", pertaining to a telescopes first practical observation viewing. Just me.

[marscreeper]

Yes I decided on the 8 inch , however Rocket was really wanting me to get the 10 ....perhaps i will get it later. We will both have a blast with this one though, thanks for all your input and all your help on this . Keep up the good work on this forum it is a fantastic place to come and learn .......getting late ...cya later Joe


MC