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Difference between 8" and 10"...?

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I am looking to either buy a Skywatcher Skyliner 8" or 10" Dobsonian.

Now they both have the same focal length, so that means if I were to use the same eyepiece in both, they would both give exactly the same magnification?

So basically, what would be the advantages of buying the 10"?


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The light grasp of the 10" will be far better than the 8" revealing fainter images and detail, at the sake of repeating the old adage, aperture rules. The downside, bit bigger and heavier to move about, but well worth it if you can manage.

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Think of light as a vehicle for information. The more you can collect and bring to focus, the more information or resolution you will see. I would always recommend that you try before you buy - namely to go along to an observation evening (there are even some groups on here) to see for yourself the difference that aperture can make. It will also give you a chance to get up close to understand the weight and size of this kit should you need to transport it.


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Think pi r squared ( пr²)

To make it easy say pi = 3 r = radius

I know it's all Greek to some people ;-)

8" = 4" radius 4x4 (r squared) = 16 x 3 (pi) = 48

so an 8" scope has a light catching area of about 48 sq in

10" = radius 5 5x5 = 25 x pi (3) = 75 sq in

So the 10" has about 27 sq in more light gathering capacity.

More than 50% extra

It will also be heavier by a similar amount. Probably more because I'd guess the Primary and everyting else will be bigger and thicker too.


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I made the 8 to 10 step in SCTs a good few years ago and found the difference pretty impressive. More resolution on the planets, notably in picking out Cassini's on Saturn, and significantly brighter nebulae. But Gaz is right as the maths demonstrates. 6 to 8 is a bigger upgrade than 8 to 10. They are big things and Ken's right, know what you are taking on! That said, I'd go for the 16 inch!!! (Someone had to say it...)


Edit, I have just seen that Sarah is selling a ten inch on the For Sale board.

Edited by ollypenrice
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Something else to consider is that the 8" is f6 and the 10" is f5. So the 8" will be easier on "budget" eyepieces and easier to collimate. Not massively important reasons to choose one over the other but I just thought I'd mention it....

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IMHO the jump from 8" to 10" isn't as noticeable as the jump from 6" to 8".

I'd go along with that. I did have all three briefly at one point and ended up with the 8" as taking everything into consideration (including portablility) it was the one that offered the most at the time.


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I currently own 6" & 10" scopes, and had an 8" for 3 years. I would agree that

the jump from 6 to 8 is more noticable visually than 8 to 10.

It's tough advising whats best for someone else, so many variables to consider,

cost, portability, how hard is it to collimate, eyepiece considerations etc.

If you can get to a club, or retailer with a showroom, thats a big help.

All the best in your choice, Ed.

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Thanks for all of the advice guys

I guess magnification isn't everything then :D

It certainly isn't. One of my catchphrases when working with beginners is to say that we think of telescopes as being there to make small things bigger. But in astronomy they are even more useful for making faint things brighter.


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