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What do you recommend 8 inch or 10 inch Newtonian

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#26 Zad

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Posted 20 September 2013 - 02:25 PM

Flateners usually decrease the scopes focal length or are neutral, but barlows increase the focal length (by a factor of 2x or more most often). So CA is more prevelent in a barlow.

#27 bandazar

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Posted 20 September 2013 - 04:56 PM

If I was really into deep sky, my personal favorite apertures would be 5" and 14". I wouldn't necessarily compare 2 adjoining apertures if I had the chance to go to a star party and see what a telescope of a specific aperture can do for me.
14" because I really enjoy m13, and it is probably the largest "easily" transportable scope. And 5" as the quick look scope (I'd actually stick with a cass in this range though, or maybe a good wide field refactor).

#28 Kendahl

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Posted 24 September 2013 - 12:07 AM

Otherwise ASA wouldn't be selling this super-pricey 1.8X barlow corrector

$1,500. Ouch! That makes the Feather Touch with the integrated Paracorr a bargain at $860.


As for the R200SS, ......it is rather expensive ($1500+) compared to the Orion, Astro-Tech, etc. versions.

Several months ago, I questioned the price difference between the Vixen and the others. A guy familiar with both replied that the Vixen was significantly better.

#29 orlyandico

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Posted 24 September 2013 - 08:40 AM

Kendahl, the $1,500 barlow corrector is a tele-extender.

ASA also makes a reducer/coma corrector for about $1,000 - I think it's harder to make a good extender than a reducer.

#30 andysea

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Posted 24 September 2013 - 11:54 PM

Fast scopes are obviously the best for AP. However people seem to forget how difficult it is to get perfect focus on an f/4 system. The CFZ in the blue wavelength at F/4 is 37microns.
I think it would be pretty hard to nail perfect focus by focusing manually. I found a focus mask only useful to get in the ballpark.

#31 Zad

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Posted 26 September 2013 - 10:15 AM

I use a focus mask on my 8" f/4 with LiveView on my DSLR, and have never had any trouble reaching foucus. Takes all of 30 seconds.

Here is a sample:

www.astrophotogallery.org/showfull.php?photo=10324

#32 andysea

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Posted 26 September 2013 - 12:58 PM

Interesting. I haven't had much luck with the focus mask. I use it to get close enough but then I let the Sequence Generator Pro take over and dial in on perfect focus for the entire frame. I refocus every 1c of temp shift.
I feel that the focus mask leaves too much guesswork to the user. This is probably not a huge issue with slower systems. F/4 is however pretty fast.
That's just my experience tho.

Andy

#33 Zad

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Posted 26 September 2013 - 02:00 PM

Using the Live View feature of my Canon 450D has increased the accuracy of my focus a great deal (not to mention the process is a great deal faster). So, I don't really have any issues finding a great focus, but f/4 is more sensitive to temperature changes then a slower scope in theory. So far, I haven't really run into too much temperature change issues so far as far as focus goes.

My issue is where I live (mid-atlantic) there are not very many good nights for imaging. So, I have chosen to go with one shot color camera, and a fast scope (to get as much data as I can on the rare good nights). For most targets so far, I have only needed about 3min. subs max. So in about 1 hour and 15 minutes, I can get 25 subs. The temperature usually doen't change that much for me in that time period, so I just take my darks and move on. I really need to do an experiment to see how much each degree of temperature change effects my focus. So far, I really haven't noticed much. But with f/4 I don't have to take subs for very long. Once I start imaging dimmer objects, I may run into this issue more. But I will cross that bridge when I get to it.

#34 nighthound

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Posted 26 September 2013 - 03:19 PM

I use the Vixen R200SS, it's very light and a good match for my Losmandy G-11. I added a low profile Moonlite focuser to the Vixen, makes fine focus no problem. I would recommend a high quality collimation kit. I use the Cat's Eye Infinity XL system, very accurate. Once you get the hang of them you can make minor tweaks quickly, even in the dark.

#35 andysea

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Posted 27 September 2013 - 12:52 PM

Steve
I've been thinking about taking a plunge back to the dark side of reflectors for a while and the VIxen R200SS looks like a great candidate.
Do you think that the stock focuser with a robofocus would be adequate for AP? Does it have a threaded draw tube? I want all threaded connections.
Thanks
Andy

#36 nighthound

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Posted 30 September 2013 - 02:45 PM

Andy, to be honest I removed the stock focuser so many years(5-6) ago I forgot the build type. I do remember it being high profile and that was a problem for acquiring focus with a DSLR. It also felt a bit crude in movement for my taste. The Moonlite fixed that and with the dual focus adjustment, fine focus is very easy. Sorry I can't give you a more definitive answer on your robofocus matchup, if you already have it there's no harm in trying it to see how it works out provided the stock focuser's higher profile isn't an issue. There may be a more refined stock focuser on the new R200SS, not sure.

Here's what mine looks like:
http://i3.photobucke...stro Equipme...
http://i3.photobucke...stro Equipme...

#37 andysea

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Posted 30 September 2013 - 08:24 PM

Thank you so much Steve! The photos really help.That is a beautiful telescope.
One more question. What is the drawtube length of the focuser?
Thanks
Andy

#38 nighthound

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Posted 30 September 2013 - 09:19 PM

You're welcome Andy. I have the 2 inch travel with the three screw, brass compression ring and 1.25 inch eyepiece adapter. The 2 inch travel tube has a physical length of about 3 3/8 inches total. The area at the top where the three compression screws is 3/8 of that. Mine has the Dual Rate Tri-knob adjustment with Shaft Lock. Shaft lock is great to prevent focus shift from camera weight. See link below to read more (scroll down):

http://www.focuser.c...ugin=dstore....

Steve

#39 andysea

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Posted 30 September 2013 - 09:54 PM

Awesome thanks again Steve. I am familiar with the moonlite focusers. I used to own a 10"RC with the moonlite on it and it had the shaft lock, it was definitely rock solid.

Andy

#40 orlyandico

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Posted 30 September 2013 - 10:53 PM

I just had the AT8IN out a couple times with the ASA reducer. Collimation is a pig. The AT8 definitely needs reinforcement of the tube under the focuser.

So far I'm using the stock focuser and manually focusing. I'm only getting 4" stars. My pixel scale is 2.68". But then I have to image through haze and clouds.

As an aside, the 8" is the most I want to manhandle. It takes 2 x 9 lb and 1 x 6 lb counterweights to balance on the Mach1.

#41 andysea

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Posted 01 October 2013 - 12:12 AM

I think the Vixen r200ss is lighter than the At8in. Another option would be the Officina Stellare 200mm RH but the price point is way higher.

#42 orlyandico

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Posted 01 October 2013 - 02:18 AM

Yup the RH seems to be the Ferrari in this range... Too rich for my blood.

#43 Zad

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Posted 01 October 2013 - 11:36 AM

I just had the AT8IN out a couple times with the ASA reducer. Collimation is a pig. The AT8 definitely needs reinforcement of the tube under the focuser.

So far I'm using the stock focuser and manually focusing. I'm only getting 4" stars. My pixel scale is 2.68". But then I have to image through haze and clouds.

As an aside, the 8" is the most I want to manhandle. It takes 2 x 9 lb and 1 x 6 lb counterweights to balance on the Mach1.


Orion updated their version of this scope (it is now listed as an f/3.9, and the older version was listed as f/4) to include a steel reinforcement plate under the focuser. I got mine right after the update (thankfully), and I haven't had any issues with the focuser sagging. I use a 450D and an MPCC. I am not sure how much more the focuser can handle because I haven't tried. Perhaps others can chime inn...

#44 mpgxsvcd

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Posted 01 October 2013 - 11:54 AM

well of course collimation of the f/4 will be harder. but it's almost 1 stop faster for photography (1.56X so a 10-minute sub on the f/4 would be equivalent to a 16-minute sub on the f/5). Both will need a coma corrector for astrophotography.


The procedure for collimating an F5.0 scope is identical to that of an F4.0 scope. So why would one be any harder?

#45 mpgxsvcd

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Posted 01 October 2013 - 12:10 PM

Yea, but you've been at this awhile....Be truthful now, would you really recommend a 10" newt for AP to a person with no astronomy or photography experience?????? Now, if I already had some experience and was looking to "upgrade"....


Absolutely I would recommend a Newt on a CG-5 even as a beginner scope as long as the person can lift the Newt up onto the mount. For most Newts that is 15-30 pounds. The weight may be an issue for some. However, a decent refractor or SCT still weighs more than some people want to lift. If you can pick up 30 pounds to chest level I would say that there is no reason not to get a Newt.

I started with an 8 inch Newt on my CG-5 and it couldn't be simpler with the cameras that I have.


The Fast Newts just make aligning and centering so much easier with the right cameras. That is the biggest frustration for most beginners. The collimation concerns are simply a myth. It is easy to do with a laser collimator. It takes about 1.5 minutes with some Bob's Knobs.

I think too many people have become afraid of Newts too actually find out if they work or not. Each type of scope has its benefits and drawbacks. However, if you want to do anything but widefield, you don't want to spend a lot of money, and you want good fast results you are going to end up with a Newt.

Pretty much every beginner is looking for exactly that.

#46 Zad

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Posted 01 October 2013 - 12:37 PM

Absolutely I would recommend a Newt on a CG-5 even as a beginner scope as long as the person can lift the Newt up onto the mount. For most Newts that is 15-30 pounds. The weight may be an issue for some. However, a decent refractor or SCT still weighs more than some people want to lift. If you can pick up 30 pounds to chest level I would say that there is no reason not to get a Newt.

I started with an 8 inch Newt on my CG-5 and it couldn't be simpler with the cameras that I have.


The Fast Newts just make aligning and centering so much easier with the right cameras. That is the biggest frustration for most beginners. The collimation concerns are simply a myth. It is easy to do with a laser collimator. It takes about 1.5 minutes with some Bob's Knobs.

I think too many people have become afraid of Newts too actually find out if they work or not. Each type of scope has its benefits and drawbacks. However, if you want to do anything but widefield, you don't want to spend a lot of money, and you want good fast results you are going to end up with a Newt.

Pretty much every beginner is looking for exactly that.


I agree that there seems to be a lot of misconception about a fast Newt for imaging in regards to collimation. I think they got this reputation from the visual world. If you are not spot-on with a slow Newt, it's not a big deal as far as visual goes, but as you get faster, you want to be spot-on. But if you are imaging, you are going to want spot-on no matter what. So for me, it makes no difference at all. In fact, it is easier for me to collimate my 8" f/3.9 than my 10" f/4.9 because of the shorter focal length. I use a cheshire with a built in sight tube. The 10" f/4.9 has a 1200mm focal length, so the mark on the mirror appears very tiny, and I have to stop looking through the collimator to adjust the primary becuase I can't reach while looking. But on my 8" f/3.9, the spot appears bigger in the collimator, and I can reach all adjustment knobs while looking through the collimator simultaneously. Never takes more than a minute or two to achieve pretty darn perfect collimation. I am thinking of upgrading to a more fancy schmancy laser, but if it aint broke....

#47 orlyandico

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Posted 01 October 2013 - 02:07 PM

Well..........

I've been playing with the AT8IN for the past few nights. And tonight after looking at my streaked stars I decided to mount the AT90EDT again.

Man it's much easier to use. The focuser is great, you can live without a Feathertouch with the AT90's stock focuser. The stars are round and small. No irregular shapes from mis-collimation. No changing star shapes from different scope positions (I think my focuser still sags in spite of the reinforcing plate I put in).

I almost considered giving up on the AT8IN.. but that f/3.0 is too tempting. It's like a GM truck. It catches light very fast, but is rough around the edges.

I hope the stars will get round when I get my laser collimator. Or I'll lose all my hair.

#48 andysea

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Posted 01 October 2013 - 03:54 PM

I wonder if the carbon fiber tube version would work better.

#49 orlyandico

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Posted 01 October 2013 - 06:31 PM

I have no idea... there are a lot of things that can stand improvement on the AT8IN.. the tube that flexes is one.. a better focuser.. better mirror support. Well it is a $500 tube. Even the AT90EDT from the same company (which is almost 3 stops slower) costs nearly 3 times more.

A friend characterizes the AT8IN as having "lots of potential." I guess when looked at that way...

#50 Zad

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Posted 02 October 2013 - 08:05 AM

I was hoping that AT would update this scope after Orion updated their version to address these shortcomings. I think a few tweeks from the factory is all it needs. The Orion version has the reinforcement plate, and a collimitable focuser. Plus it's a little lighter as well (less tube in front of the focuser, which may help reinforce the focuser as well).

Have you tried sliding the tube rings closer to the focuser (and sliding the plate in the saddle the opposite way to maintain balance)? That may help reinforce the tube near the focuser. I am also wondering if you can tighten the friction in the focuser. Perhaps the focuser drawtube itself is flexing.






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