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choosing my birthday gift! your ideas

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#1 Hilmi

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Posted 24 March 2013 - 12:46 PM

I am buying myself a new scope to replace my Meade LX200r which heavily vignets once I add my Moonlite focuser and once I add my reducer it gives me only f8 even though the spacing is correct.

So I am now considering 1 of 2 scopes. With sale at OPT there is only $20 difference in price. To start with. Lets get one thing clear. I have no interest in Hyperstar, my camera is way too big and I am not planing to change cameras.

OPT version of AT8RC currently on 15% sale.
Pluses
10 inches back focus.
Natively f8
Ships internationally without any use if intermediatary


negatives
No reducer available
Distraction spike (I'm not really partial to diffraction spikes, the distract from the image)

Celestron 8" Edge HD
Pluses
Native reducer
Option to run at f10 if I want narrower field of view

negatives
Moving mirror
International shipping complications

Any advice would be appreciated. Especialy if you happen to have owned both.

#2 Hilmi

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Posted 24 March 2013 - 12:50 PM

I'm also open to other scope suggestions, but due to the investment I made on the moonlite focuser, I am reluctant to go for a non casagrain design

#3 CounterWeight

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Posted 24 March 2013 - 01:26 PM

I haven't used either of them but those two are different enough -will look forward to hear what others think. My only thoughts are that if you don't like spikes (I know I don't) that just leaves the one, I'd say go for something I wanted to start with. The HD has mirror lock from what I'd read - is there still some shift with that?

#4 Hilmi

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Posted 24 March 2013 - 01:36 PM

The thing is, I'm under time restrictions to choose. The OPT branded AT8RC carbon fiber is on sale for a limited time.

If it helps, I am considering adding a rotator in the future to further improve my automation.

#5 Hilmi

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Posted 25 March 2013 - 12:17 AM

Will I get more responses in the cats and cases forum? I can ask the moderator to move the topic. Thought I would post it here since my primary use is imaging

#6 guyroch

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Posted 25 March 2013 - 12:42 AM

OPT version of AT8RC currently on 15% sale.
Pluses
10 inches back focus.
Natively f8
Ships internationally without any use if intermediatary


negatives
No reducer available
Distraction spike (I'm not really partial to diffraction spikes, the distract from the image)



The AT8RC certainly has an excellent FR/FF.

I use the Astro-Physics Telecompressor CCDT67 on both the AT6RC and AT8RC. It's a reducer but works darn well as a flatner too.
http://www.optcorp.c...8-telescopes...

I suggest you get the Astro-Physics Part #AP16T to pair with the CCDT67 to ensure you have the proper spacing.
http://www.optcorp.c...-t2-threads....

Guylain

#7 korborh

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Posted 25 March 2013 - 12:44 AM

The RC8 is PITA to collimate. Having owned the AT8RC and the Edge (11), I would recommend the Edge8 scope. You can easily work around the moving mirror but beware the RC's finicky collimation.

#8 guyroch

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Posted 25 March 2013 - 12:58 AM

The RC8 is PITA to collimate. Having owned the AT8RC and the Edge (11), I would recommend the Edge8 scope. You can easily work around the moving mirror but beware the RC's finicky collimation.


Please do tell. I have no issues collimating my AT6RC and/or my AT8RC.

Guylain

#9 Hilmi

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Posted 25 March 2013 - 01:44 AM

Guylain,

From your experience does the scope work without a field flatner when working at f8? Also how tight are the stars? My LX200R almost always gave me bloated soft stars when compared to my televue 60is which gives sharp tight stars.

Korboh, about the collimation difficulty could you please elaborate?

#10 korborh

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Posted 25 March 2013 - 01:59 AM

If you are lucky to not need more than minor collimation adjustments then RC8 fine. But if you ever have to adjust the primary and go a bit too far off then the RC is very unforgiving. Especially these cheap RC scopes don't have good and repeatable mechanics. You will also have to invest in high-quality collimation tools (expensive ones). There are other design issues with RC8 that can potentially give you headaches like the primary connected to the focuser and resultant flexure issue.
In contrast EdgeHD is so much more robust and simple proven design. Great for imaging and visual. I dont see *any* advantage of RC8 over Edge8. The mirror of RC8 is *not* fixed as you will realize when you start seeing flexure in imaging.

#11 Hilmi

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Posted 25 March 2013 - 02:24 AM

What about back focus? That is the main reason I am moving away from the LX200R. Once my moonlight focuser is in there, I cant use the reducer since it vignets and it also brings the focal length to F8 instead of F6. The reason being that there is not enough back focus to accommodate the focuser and the reducer.

So I figured the real advantage of the AT8RC is that I can accomodate the moonlite focuser, the STT8300 with self guiding filter wheel and potentially a rotator in the future in order to aid in the process of finding guide stars. Since it is natively F8 I dont need the reducer any more.

How much back focus does the EdgeHD provide?

Thanks

Hilmi

#12 Mike7Mak

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Posted 25 March 2013 - 03:06 AM

I use the Astro-Physics Telecompressor CCDT67 on both the AT6RC and AT8RC. It's a reducer but works darn well as a flatner too.
http://www.optcorp.c...8-telescopes...

I suggest you get the Astro-Physics Part #AP16T to pair with the CCDT67 to ensure you have the proper spacing.
http://www.optcorp.c...-t2-threads....

I would suggest trying the above on the LX200R. It puts the reducer inside the Moonlight and closer to the visual back opening. I had vignetting problems with reducers mounted after the focuser but not with the CCDT67 inserted into the focuser on a 2" nosepiece.

#13 Hilmi

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Posted 25 March 2013 - 03:19 AM

Mike

I feel like the LX200 has been a money black hole. One fix after another. I am reluctant to put anymore money into it. First it was the focuser then the microfocuser, then the mirror lock then the reducer needed an upgrade then now another reducer upgrade.

#14 guyroch

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Posted 25 March 2013 - 07:37 AM

Guylain,

From your experience does the scope work without a field flatner when working at f8? Also how tight are the stars? My LX200R almost always gave me bloated soft stars when compared to my televue 60is which gives sharp tight stars.

Korboh, about the collimation difficulty could you please elaborate?


You need a field flatner with the AT8RC. The AT2FF works well too.

Guylain

#15 guyroch

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Posted 25 March 2013 - 07:58 AM

If you are lucky to not need more than minor collimation adjustments then RC8 fine. But if you ever have to adjust the primary and go a bit too far off then the RC is very unforgiving. Especially these cheap RC scopes don't have good and repeatable mechanics. You will also have to invest in high-quality collimation tools (expensive ones). There are other design issues with RC8 that can potentially give you headaches like the primary connected to the focuser and resultant flexure issue.
In contrast EdgeHD is so much more robust and simple proven design. Great for imaging and visual. I dont see *any* advantage of RC8 over Edge8. The mirror of RC8 is *not* fixed as you will realize when you start seeing flexure in imaging.


Now that you mention it... my primary mirror is a tab bit off on the AT8RC... but the AT6RC is perfect. Instead of toying with the primary I decided to buy a tilt adjuster. I Haven't used it yet so I can't comment on it.

http://www.optcorp.c...t-adjuster.html

I'll have to change my statement now... my primary mirror is off and so collimation could be a pain :(

Guylain

#16 Hilmi

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Posted 25 March 2013 - 08:00 AM

What level of pain are we talking about here? Pain as in it takes 3 hours then it stays put for the next 6 months or pain as in every time you set up the scope you have lost collimation and have to spend an hour or two to get it back into alignment?

#17 guyroch

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Posted 25 March 2013 - 08:34 AM

For me it's "Pain as in it takes 3 hours then it stays put for the next 6 months"

Guylain

#18 korborh

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Posted 25 March 2013 - 10:07 AM

Hilmi, the Edge8 does not have a lot of backfocus to allow a separate crayford focuser. With the new upcoming reduccer, backfocus is even less. So if you really need an external focuser then Edge8 will be an issue. That being said, you can use the primary mirror knob for focusing and it works quite well for imaging (automated with Fmax). The RC8 has generous backfocus but you will have to limit the weight on the focuser tube otherwise its going to cause flexure and collimation issues. Hanging a moonlite +5lbs of imaging gear will not be possible without significant flexure and mechanical issues.

As for pain, I had to get mine professionally collimated after unsuccessfully working on it for a week (~12+hrs.). If you get the RC8 you may want to invest in high quality collimation tools like Howie laser and/or Tak collimation scope. These are very pricey accessories.

#19 cherokawa

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Posted 25 March 2013 - 01:39 PM

Just my 2 cents - you could also consider the Vixen VC200L. Fixed primary, 42mm image circle, f/6.4 reducer is available, collimation is not a major pain. I don't own one, but would like to, someday.

Downside - some people don't like the square stars caused by the thick secondary vanes. I think this effect is apparent only on bright stars, but not sure if this is important to you.

#20 Hilmi

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Posted 25 March 2013 - 01:55 PM

I like my stars nice, round and tight :) That's one of the other reasons I am trying to move away from my current scope. It gives me bloated stars, I don't have enough knowledge to know why. All I know is that my refractor gives me nice tight stars, but my refractor is only 360 mm focal length, so it's not a fair comparison.

#21 Hilmi

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Posted 26 March 2013 - 01:52 AM

Seems that the freight forwarders are not gentle with things like scopes. I found a video on youtube of a person in the UAE who ordered an Edge HD and it came with a smashed corrector plate. Cant order directly from USA since Celestron wont let them sell it that way and the local dealer doesnt sell the HD scopes, especially as OTA only.

So if the RCs have flexture, the HDs have shipping complications, whats an imager to do? Any other suggested imaging scope to complement my 360mm f6 refractor?

#22 wolfman_4_ever

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Posted 26 March 2013 - 02:00 AM

Your not going to get those nice tight stars in the edge comparing to a refractor.. at f10 they will bloat... At f7 they bloat... Jedi Patiwan must learn processing skills. This is the way of the astrophotagraphy force. :p

#23 Hilmi

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Posted 26 March 2013 - 06:30 AM

But I want the cake and I want to eat it too!

#24 saadabbasi

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Posted 26 March 2013 - 03:59 PM

Hilmi, when I was considering buying a 2nd OTA for longer focal length work I had the choice of going with the ATRC or Edge HD - which had just come on the market.

I was reluctant regarding the Edge HD because they had no reducer at the time and Celestron was taking it's sweet time so I went with the ATRC8.

The ATRC8 is a fine scope but for a beginner like me it is too difficult to collimate. I have read threads upon threads and I still have trouble thinking about the process. I have never touched the primary and I'm still not sure if I should. My collimation isn't way out - it's alright, I can see the bands on Jupiter and but it is somewhat off and I'm just not sure how I'm going to nail it - you can see what it looks like here: http://i.imgur.com/4seBDFH.jpg You can see that the outer gray circle is not concentric. I have no idea how to interpret this.

Furthermore, the primary of this scope is attached to the focuser - so if you adjust the primary, you tilt the focuser.

If you have a heavy imaging train, you will have to upgrade the stock focuser. I use a Moonlite focuser.

In retrospect, I feel I shoud have gone with a Edge HD scope. The flat field means I don't have to worry about buying a flattener. Sure, native f-stop is F10 but I honestly don't think it's that big of a deal. Yes, the mirror isn't fixed but just buy a OAG and you will be happier for it. I use an OAG with a 85mm refractor too - I can do 30 minute sub-exposures with my FSQ on a G11.

Due to my location, I don't think it will be easy to sell the ATRC8 otherwise I would have switched to the Edge HD already.

#25 Hilmi

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Posted 26 March 2013 - 04:38 PM

Saad,

Thank you for your feedback.

-Do you feel the flex is from the focuser? I own a Moonlite focuser if the focuser is the case, I'm not too concerned. --Tilt of focuser can be adjusted as it contains collimation capability built into the flange
-If you move to EdgeHD, you loose your investment in the moonlite focuser due to lack of back focus. With the mount you recently purchased, you would be more and more interested in automation, just as I am.

For me, I have been considering this for a few days now since I before posted this question. Now I have come to the decision that the loss of auto-focus should I go to the EdgeHD is something I am not willing to accept. I spend too much time on the roof imaging as it is and the more I automate, the more time I can leave the scope un-attended and be with my family.


Therefore, I have decided to go for the RC and live with the collimation challenge till I figure it out. The way I see it, once you have learned to do it properly, you should not suffer too much. I can even ask the vendor to collimate it for me before delivery. I heard that once collimated, they hold collimation very well.






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