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Equipment Discussions >> Reflectors

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gdd
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Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: orlyandico]
      #6090975 - 09/20/13 01:23 AM

I did find a case where a person used a cheaper barlow with a at8in and was satisfied with results for m51. Maybe not quite as good as the ASA, but worth trying since you already have one.

Gale


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Zad
super member


Reged: 01/05/08

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: gdd]
      #6091825 - 09/20/13 01:35 PM

I have been wanting to try out a 1.5x 2" barlow that I have on my Orion 8" f/3.9 Newt, but I haven't gotten around to it. My main concern is CA, since it was not designed for AP, and it was relatively inexpensive.

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?


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: Zad]
      #6091918 - 09/20/13 02:31 PM

not sure if CA is an issue. The usual refractor flatteners are just achromatic doublets.

The CA becomes much less of an issue closer to the focal plane.


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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: orlyandico]
      #6091947 - 09/20/13 02:53 PM

It's a newt, newt's shouldn't have CA....that's a refractor abberation....newts have coma instead......

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Zad
super member


Reged: 01/05/08

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: csrlice12]
      #6091980 - 09/20/13 03:23 PM

Barlows can produce CA. In fact some barlows are advertiezed as "ED" or "Apochromatic". Astro Tech has a " 2X achromatic Barlow" AND a "2X apochromatic ED Barlow" on their site right now.

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Zad
super member


Reged: 01/05/08

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: Zad]
      #6091989 - 09/20/13 03:25 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.

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bandazar
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Reged: 10/19/05

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: Zad]
      #6092224 - 09/20/13 05:56 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).


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Kendahl
member


Reged: 02/02/13

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: orlyandico]
      #6097768 - 09/24/13 01:07 AM

Quote:

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.


Quote:

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.


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: Kendahl]
      #6098075 - 09/24/13 09:40 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.


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andysea
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Reged: 09/03/10

Loc: Seattle, WA
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: orlyandico]
      #6099650 - 09/25/13 12:54 AM

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.


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Zad
super member


Reged: 01/05/08

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: andysea]
      #6102134 - 09/26/13 11:15 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

Edited by Zad (09/26/13 11:19 AM)


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andysea
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Reged: 09/03/10

Loc: Seattle, WA
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: Zad]
      #6102422 - 09/26/13 01:58 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


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Zad
super member


Reged: 01/05/08

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: andysea]
      #6102512 - 09/26/13 03:00 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.


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nighthound
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Reged: 08/30/06

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: Zad]
      #6102616 - 09/26/13 04:19 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.

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andysea
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Reged: 09/03/10

Loc: Seattle, WA
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: nighthound]
      #6104297 - 09/27/13 01:52 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


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nighthound
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Reged: 08/30/06

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: andysea]
      #6109497 - 09/30/13 03:45 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.photobucket.com/albums/y67/Nighthd/Astrophotography/Astro%20Equipme...
http://i3.photobucket.com/albums/y67/Nighthd/Astrophotography/Astro%20Equipme...


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andysea
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Reged: 09/03/10

Loc: Seattle, WA
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: nighthound]
      #6110065 - 09/30/13 09:24 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


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nighthound
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Reged: 08/30/06

Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: andysea]
      #6110173 - 09/30/13 10:19 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.com/cgi-bin/dman.cgi?page=productdetail&plugin=dstore....

Steve


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andysea
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Reged: 09/03/10

Loc: Seattle, WA
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: nighthound]
      #6110252 - 09/30/13 10:54 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


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: What do you recommend 8 inch or 10 inch Newtonian new [Re: andysea]
      #6110377 - 09/30/13 11:53 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.


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