What do you recommend 8 inch or 10 inch Newtonian
Posted 18 September 2013 - 03:57 AM
I am looking to buy a Newtonian for Astrophotography but I between the 8 inch or 10 inch, What do you recommend ???, about the Newtonian fast a F/4 OR F/5 .
Posted 18 September 2013 - 04:11 AM
the 8" is always going to be better than the 10" unless you have a capable mount ( = AP900 or comparable).
i have a Mach1 and I got an 8" for it. I don't like over-stressing the mount.
Posted 18 September 2013 - 04:42 AM
Posted 18 September 2013 - 05:11 AM
personally, for an NEQ6 i would stay with the 8". some people put 10" or even 12" on the NEQ6 but i guess they like losing their hair...
Posted 18 September 2013 - 08:44 AM
Posted 18 September 2013 - 08:59 AM
And I also got a Keller reducer which brings it down to f/2.9 - there is no APO out there that can do f/2.9 (the fastest are the Borg 125SD with super reducer, and Tak FSQ-106 with reducer, both for $$$$$ lots of money $$$$$)
Posted 18 September 2013 - 09:06 AM
Posted 18 September 2013 - 09:12 AM
The 8" is about 22lb and is about 30" long, making it roughly the same footprint as an Orion 100ED. I'm pretty sure an Atlas could carry it competently.
Now the 10" is a totally different story...
Posted 18 September 2013 - 10:16 AM
Collimation is easy. It really isn’t as hard as everyone makes it sound.
The Carbon Fiber Newts are also a lot lighter so that can make a big difference. There is an 8 inch Carbon Fiber Newt under $900 right now.
Posted 18 September 2013 - 11:43 PM
Posted 19 September 2013 - 12:51 AM
There's someone in the local club with an AP 130 that he used for many years. But these days he's using a Tak Epsilon...
Posted 19 September 2013 - 05:30 AM
Posted 19 September 2013 - 10:05 AM
Posted 19 September 2013 - 10:18 AM
Posted 19 September 2013 - 01:32 PM
As far as collimating the scope goes, it isn't any harder than any other Newt to collimate, just slightly more important. I think this issue gets a little overblown. I think this comes more into play for visual work. For visual, if you are using an f/5 newt, you don't have to be exactly spot-on, but at f/4 it becomes more important. But anytime I image, I want to be spot-on regardless if I am f/5 or f/4, so there was really no change for me going from f/5 to f/4 as far as collimation goes.
Posted 19 September 2013 - 01:55 PM
Posted 19 September 2013 - 01:58 PM
1. The RC would require subs that are 4 times longer to get the same level of exposure than the Newt.
2. The image scale would be different for the two scopes with the RC being better suited for smaller targets. I think galaxies and planetary nebula, whereas the Newt can handle larger objects.
3. Matching the focal length to the pixel size comes into play here as well. The RC matches better with cameras with bigger pixels, and the Newt mathces better with smaller. I usually want about 1-2 arc.sec./pixel.
4. The newt is a little trickier to balance the scope with due to the focuser sticking out of the side of the tube rather than the back. I turn the scope in the rings so the focuser is pointing down towards the mount to help with balance.
5. The Newt definately needs a coma corrector for nice round stars in the corners of the image. I use the MPCC with great results. The RC benifits from a field flattener from what I understand, but I have no experience in this area. The Newt has a nice flat field already, so no field flattener is necessary.
6. The RC would require more accurate tracking due to the longer focal length and longer exposures.
So, it really comes down to what kind of targets the OP is interested in, what kind of camera (and pixel size) will the OP use, and how much effort does the OP want to put into accurate tracking (will the OP be autoguiding, manual guiding, unguided).
Either scope would work very well, just a matter of preference.
Posted 19 September 2013 - 02:46 PM
Or you can use a barlow on the Newt to get you up to F/8 for galaxies, though I have not heard of people doing so.
Posted 19 September 2013 - 06:39 PM
Posted 19 September 2013 - 09:05 PM
Now that I'm waiting for my AT8IN, I am slightly concerned about losing long focal length for those pesky little PNs.
While I wish a barlow would work, since I have a 2" lying around, I suspect it doesn't. Otherwise ASA wouldn't be selling this super-pricey 1.8X barlow corrector -
(I already have the 0.73X reducer, which I thought was pretty expensive, but the barlow corrector costs nearly double!)
I guess the bottom line is you really have to keep a separate OTA around for those tiny planetaries.
As for the R200SS - yes it's a nice f/4 newtonian, but it is rather expensive ($1500+) compared to the Orion, Astro-Tech, etc. versions.
Posted 20 September 2013 - 12:23 AM
Posted 20 September 2013 - 12:35 PM
But I have been wanting to pick up a 2" 2x Televue Powermate because I think that would work well, but funds are tight right now. Has anyone tried one of these on a newt for imaging?
Posted 20 September 2013 - 01:31 PM
The CA becomes much less of an issue closer to the focal plane.
Posted 20 September 2013 - 01:53 PM
Posted 20 September 2013 - 02:23 PM