Which telescope to get for a surprise birthday present!

[AstralTraveller (David)]

Originally Posted by mental4astro

You might like to see how it fits in your car too.

Originally Posted by Scorpius51

Check to see whether it will fit in your car across the back seat.

The 8 and the 10 are pretty much the same length but the 10 is fatter. The 8 will be a f/6 so 200mm x 6 = 1200mm focal length and the 10 will be f/5 so 250 x 5 = 1250mm focal length. The shorter ratio will make collimation more critical and increase off-axis coma but these disadvantages are more than offset but the increased light gathering ability, which is proportional to the ratio of the square of the apertures. So 8^2=64 and 10^2=100 so the 10 gathers 100/64 = 1.56 times more light than an 8 - a substantial increase. [If this makes the 10 more attractive you already have aperture fever .]

One thing which may be on the primary mirror, and should be there, is a centre mark, which aids collimation. It is normally a re-enforcing ring, the things you stick on pieces of paper when putting them into a ring binder so the hole doesn't tear. It doesn't affect the operation of the scope because it is in the shadow of the secondary.

[knightrider]

If it were me,

I'd go for a 6" newtonian on an EQ mount. Something like the following:
http://www.ozscopes.com.au/skywatche...telescope.html

It would serve you for years to come.

A 6" aperture is still a decent size scope and it will show you plenty the night sky has to offer. Realistically also you won't be getting any extra usable magnification out of a bigger scope, just makes the dimmer objects easier to see just that bit more.

It would be very easy to carry to and from the house, or if you wanted to transport it also.

The deal breaker for me would be the slow motion control knobs on the EQ mount as opposed to having to manually nudge and push the dobsonian mounted scope. Especially if you're using higher magnifications on the planets the nudging and pushing would become quite average as opposed to having slow motion knobs to finely track the object in the eyepiece.

And if he decided to upgrade later, he can buy that large aperture scope, say 10" or 12" to dedicate to it more, and still keep the 6" as a second scope. But I'd suggest to get the GoTo tracking on a later upgrade to get rid of the manual movement on the scope to keep things centered so you spend more time viewing than moving.

But as for getting the most aperture for your money, you can't beat the dobsonians.

[pw (Peter)]

I'm new to astronomy and recently bought my first telescope. I got a Bintel 8" Dobsonian and it has been great. Stars, planets, nebulas and so on are all clearly visible and exciting to find and observe. Get that Astronomy Australia 2013 book too, it has great ideas for what to look out for each month and charts to help you find the objects. Well worth the $25 or $35 that it costs.

[RobF (Rob)]

You could be quite surprised how big a 10" dob looks in the flesh first time. Quite a difference in weight and convenience lugging outside or fitting in a small car. The best telescope is necessarily the biggest if you can't be bothered setting it up....