GSO 8" F4 CF specs?

[garymck]

Hi does anyone know what the secondary mirror diameter is in the new GSO 8" F4 CF newts at Andrews? or alternatively the soon to arrive Skywatcher F4 newts? This vital spec seems not to be found anywhere I've googled. Thinking about one of these versus a Vixen R200SS. I'll probably go for the Vixen, but saving $600 seems attractive....

cheers
Gary

[bmitchell82]

... ide go the vixen every time! personal preference! either or your still going to need to purchase a decent focuser aaaaand a coma corrector! so be aware you need to factor these things in

[gbeal]

I thought the Vixen came with the coma corrector?
Gary

[bmitchell82]

Not that i was aware of though i have been known on a fair few occasions to be incorrect :)

[gbeal]

LOL, you Brendan? Never. I might the one being incorrect, but I was sure that they made one, and that it was matched for the Vixen newt. Many have used the MPCC though, and it seems to work universally.
Gary

[Visionoz]

Yep, they make one and I believe it is an "optional extra" = you have to buy it!!

HTH
Cheers
Bill

[bmitchell82]

:) there you go! :D I know you where looking at the Vixen at one point in time Bill. :) In any case the optics are decent.

Yes gary I am not all knowing :P maybe vocal but not all knowing! hehehe

[netwolf]

I have looked at the Vixen R200SS also, they come up time to time on the used market. But I always wonder how much better it would be than the GSO/Skywatcher ones 8" f4's.
Some time ago i saw this comparison between a TEC140 and GSO 8" F4, and it was impressive what the GSO achieved.
http://msfastro.net/articles/gso_tec/gso_tec_compare.html

$600 could get you a Moonlite focuser and quite possibly a nice Coma corrector. But that price difference if buiying used reduces a bit and often you can also get a nice focuser and coma corrector in the package with a used Vixen.

[Shiraz]

Hi Gary

From memory, Craig Starke did a relevant GSO/Vixen f4 comparo (on CN?) a while back - should be easy to find - think he concluded that there wasn't much in it for imaging, since both scopes were optically much better than the atmosphere. edit - here http://www.cloudynights.com/ubbarchive/showflat.php/Cat/0/Number/1415200/page/2/view/collapsed/sb/7/o/all/fpart/1

Whatever you get though, you will probably (almost certainly) need to replace the focuser, as Brendan pointed out.

FWIW, the 62mm secondary fitted to my older f4 GSO (steel tube) produces acceptable vignetting on a QHY8. There are also "astrograph" versions (eg the AT) with 70mm secondary - but I don't know which is fitted to the GSO CF (so can't answer your basic question...). However, fitting a different secondary is not difficult and the extra ~10% sensitivity you get from a high reflectivity secondary might be worth having anyway.

The steel tube on mine changes length with temp and messes up focus since the f4 sweet spot is so small. Suggest that CF would be much preferable to Aluminium if the local temp varies a lot. f4 scopes are also PITA to keep aligned, but that is another issue.

Regards Ray