Advice on the New GS-650 carbon fibre OTA vs GSO-800 10" f4

[Nisch (Nischit)]

Hi guys,

Just wanted to know your views on which one of the above mentioned scope do you think is better as an astrograph for DSOs?
Any feed back is appreciated as i can't decide on which one to get.
Thanks

[glend (Glen)]

I had to make a similiar decision last week. It's going to depend in part on your mount capacity. I really don't think that there is much stiffness difference in the respective tubes in this size range (a usual selling point of carbon fibre) but the GSO newts in that range use good steel tubes and not aluminium so flex is not (IMHO) going to be an issue in that size scope. The 10" will be heavier for sure.

In my case I went for the GS-630 which is also 8" but it's an f5 (at 1000mm fl) steel tube which I prefer because it makes dealing with coma easier. You will need absolutely to get a coma corrector for that f4 for imaging. I have one on my f5 and I can see the difference - nice flat field and no coma in my images. The GSO Coma Corrector will be enough but you will need to watch the spacing to your camera sensor. The GSO Coma Corrector may need a spacer put in after the lense element, mine didn't for my DSLR. The GSO Coma Corrector spot range from the last lense element is 65-80mm to the sensor. The top portion of the Coma Corrector is 48mm deep, so check the distance to your sensor from there.

I'll also mention at this point that the mirror is a real gem, and almost has as much reach and resolution as my old 12".

The other thing in the 630s favour is its much cheaper than the CF GS-650, so much cheaper that you could buy a Moonlight focuser for it with the difference which is what I plan to do.

You need to watch out for the dovetail that is supplied with these scopes, it's a GSO version of the standard short Vixen bar, but if you have a newer NEQ6Pro mount it will not fit onto the newer dual mount head due to the length of the head being longer than the short bar slant portion. Its frankly dangerous as the scope can seem to be secured but the scope can fall out when you try to align. Luke is aware of the problem because I brought to his attention. Get him to send you a long bar (like the 13" one) it should be free as well. The longer bar will allow you to spread the rings farther apart and this helps with stability and controls any flex by reinforcing the structure.

So that's how I saw it.