[bkm2304 (Richard Brown)]

Originally Posted by BigJ

Hi,

I'm new to this group and considering my first real 'scope (my 30 year old 600mm Tasco with table-top- tripod doesn't count!).

I have been doing a lot of reading, and seem to have come to the conclusion that for general planetary, lunar and DSO work, an 8" Dob is ideal, especially considering the price. I'm considering a Celestron 8" Star Hopper. But some Celestron Schmidt-Cassegrains caught my eye

Now, here's what I don't quite understand: I have seen a lot of smaller Schmidt-Cassegrain's for sale, which are quite small (eg Celestron Nexstar 4 or 5), but inordinately expensive compared to the Dobs. Granted, some of the expense is because they tend to have fancy go-to mounts. Bus aside from that, if you were so into astronomy that you were prepared to spend $1,500 on a scope, why would you choose a 4" or 5" SCT over the light gathering power that an 8" Dob would give you?

Surely, optically speaking (and also since aperture wins), the view of distant nebulae, galaxies and star clusters would be inferior...?

Hi BigJ

As the proud owner of an SCT (Meade 10" LX200R) and a Meade 16" Lightbridge Dob, I can give you my experiences. The SCT is an F10 which is known to be superior to the shorter focal ratio scopes as far as planetary and lunar, high magnification viewing go. Comparing the F10 10" with the 16" F4.5 as i have done by literally running between the two scopes with the same eyepiece, this is true. But where the F4.5 16" comes into its own is in the deep sky object work. Using a 17mm eyepiece and looking at the same deep sky object - in this case it was eta carinae, there was no contest - the 16" F4.5 showed richer, more detailed view than the F10 SCT. Not that the F10 was poor, it was great, but the 16" had it for breakfast. On the other hand I look at planets through the F10 because of the crystal clarity I get compared with the 16".

The SCT I have is indeed a go to and when you master its foibles it is an amazing thing. I am not a "starhoppr" but like to get to the object and look at it rather than slowly work my way to it. The Dob on the other hand requires an addition of digital Setting circles which will cost another $1,000 minimum.

So cost of a 10 or 11" goto SCT from either Meade or Celestron will set you back between $5,000 and $7,000 depending on the extras you get. Yes this is due to the goto but also due to the increased number of surfaces in the light path that have to be configured. The cost of a 12" Dob ranges from $1,000 to $2,000 with serious scopes of the same apeture costing even more.

Then there are the refractor people. Small apetures (relatively speaking) are compensated for by incredible clarity and crispness of image to say the least. But the law is the law and a 100mm refractor worth $4,000 will never ever resolve more than a 10" Dob worth $800.

So your choice of scope depends on what you are into. For Generalist stuff you can't go past a 10" or 12" Dob or a 100mm refractor. But if you want to see faint things without the challenge of the hunt, then a goto is a worthy investment.



Richard