8"SCT Vs 10" Dob your views

scarper (Mart) · #1 03-08-2009, 03:33 PM

hi all I just wanted to ask the question about this.
I have an 8"sct and got to thinking would a 10" dob be better for imaging, if so how??

Thanks in advance
Mart

netwolf · #2 03-08-2009, 03:53 PM

The biggest factor in all imaging is the Quality and performance of the Mount. Spend more on the mount and start with small wide field Refractors and move up to Long Focal Imaging with a 8" SCT. Thats the standrd advise. But very rarely can people afford or do they even if they can spend more on mounting than optics.

Not sure that is a fair comparission, the Dob is not really a Imaging platform. That is without any modification Imaging is very challenging. Planet imaging can be done, but requires a great deal of paitience to hand track.
Eqatorial Tables/Platforms can be uses to give tracking, which would defineltly improve Planet imaging performance, but DSO imaging would still be a challenge. Alt/AZ motorisation for tracking and or Goto would further improve Planet imagin performance, and you could do limited short exposure DSO work before field roation gets you.

The 8" SCT in Alt/Az mode is a very portable setup for Visual and Planetary imaging. Limited DSO imaging as field rotation will hinder you in Alt/Az mode. But then you could ad a EQ Wedge and do DSO that way. Generally speaking the Alt/Az mounts have very poor Periodic Error performance and will require Guiding for DSO imaging. Further even with guiding there is a upper limti to what you can do with these. But many users with lot of love and care and fine tuning have produced stunning results. The best upgrade if your serious for DSO on this type of setup would be a camer with adaptive optics setup. I have seen some awesome shots from such setups.

8" on a EQ mount, is perhaps the best of the lot. As with the Alt/Az to really to long exposure DSO work you need a Wedge, that turns that into a EQ mount. So this is perhaps the best you coudl go with. But when you start dealing with Wedges and EQ mounts you loose some of the portability factor fo this type of setup over a Dob.

renormalised (Carl) · #3 03-08-2009, 03:57 PM

No, you have no ability to track an object using a dob...even if you added an Argo Navis to your dob, you still can't track anything with it. All it allows you to do is find an object as you slew the dob by hand towards where it is. The SCT has the RA and Dec drives to slew the scope and goto capability to track an object whilst being guided.

renormalised (Carl) · #4 03-08-2009, 04:02 PM

Quote:

The best upgrade if your serious for DSO on this type of setup would be a camer with adaptive optics setup. I have seen some awesome shots from such setups.

Plus a field derotator wouldn't go astray, either.

scarper (Mart) · #5 03-08-2009, 07:57 PM

thanks for the replies guys.
I think I may have left out a vital bit of info.....I do have an eq6 pro mount, but was wondering if the dob would perform better then the sct on this mount. ie the 10"s extra light gathering against the zoom factor of the sct. make sense????

sorry for the confusion

cheers
Mart

netwolf · #6 03-08-2009, 09:07 PM

Carl,
JMI now offer a Tracking addon for the Lighbridge Dob's. Also Skywatcher is bringing out Goto dobs. While the standard dob may not have tracking many users have succesfully added tracking and gooto to there dobs.

Mart,
On a EQ6 you would be better of a with the Equatorial version of the Newtoniian OTA. The Dob version tends to be a bit longer and heavier than the EQ version. But i am guessing you want to use at as a Dob and also now and then on the EQ6. Eric (Ezystyles) had this very setup using the Skywatcher/Celestron CN10 ota.

An 8" SCT would be better from a Weight and length perspective. A 10 OTA is more of a challenge to balance and would cause more of a turning moement than a 8" SCT. There is however the issue of FL. An 8" SCT native FL is F10 ~2m while a 10" F5 dob has a FL of 1.25m. The EQ6 is a good mount, but at longer FL's its Perodice Error will become more of a challenge. So both scopes have there plus and minus points, you need to find the balance.

What kindof imaging do you intend to do and what kind of camera do you intend to use?

renormalised (Carl) · #7 03-08-2009, 09:32 PM

Quote:

Carl,
JMI now offer a Tracking addon for the Lighbridge Dob's. Also Skywatcher is bringing out Goto dobs. While the standard dob may not have tracking many users have succesfully added tracking and gooto to there dobs.

Good to know...if I decide to fork out for a dob. There's been tracking platforms out for dobs for years now, but I wouldn't use them for anything other than lunar pics, and the bright planets at a pinch.

Yeah....a dob OTA could fit to the EQ6 but it's going to be a bit of a handful. If you wanted to, you could fork out for a "normal" 10" OTA and fit that to the EQ6, but you still have the issues with portability and setting up. Now, if you were considering a permanent mount, with pier, EQ6 head and observatory, then the 10" would be stellar (pardon the pun

). In that situation, the 10" would clearly out perform the 8" SCT for the most part. But then it depends on what you want to get out of your scope...as Fahim has mentioned.

netwolf · #8 03-08-2009, 10:58 PM

Sadly i heard on the CN forums that Brian Reed who makes the Roud Table Platforms is not going to make any more. On the upside i have been following the progress of a localy made platform. Telescope and Astronomy's last newsletter mentions that they now have a working platform available for customers. http://www.telescopes-astronomy.com.au/

But as Carl has noted these are not really suitable for long exposure DSO Work. But Mike (iceman) did do quiet a bit of his initial Planet work hand guided then on a Brian Reed Platform.