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  #61  
Old 18-09-2017, 11:26 PM
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Andy01 (Andy)
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Fyi, I'm following this with great interest and appreciation for all the thoughtful input from you all.
I'm learning heaps from your combined contributions.
As you know, I'm more creative than technical, so I'm all ears to your input.

My experience and results with refractors appears to have been satisfyingly simple in hindsight, by comparison with say Paul H & Lee's experience with bedding down their fast newts and the issues they have had to patiently work through!

Probably worth mentioning that in my very hands on, manual workflow I use a mac, focus manually (once only, at the start of an imaging run, just set & forget, with parfocal Astrodons that don't seem to shift) spend ages framing my targets for aesthetic reasons, and shoot mainly NB from my suburban Melbourne backyard - with occasional trips to my mate's country property for LRGB stuff.

So I'm kinda hoping for a solution that just works out of the box!

My pimped out hypertuned, belt modded EQ6 was aquired from a fellow iis member who used it to do amazingly sharp 1hr subs with a homemade a 10" f4 CF newt riding on top.

So as I have a young family with 3 lots of school fees, I've no plans to upgrade the mount (or my camera) yet, and that's going to have a significant bearing on the max weight of any proposed ota.

I've also considered & been researching longer refractors, Mak-Newts, CF Newts, Truss Newts, SCT's, hyperstar etc - seems that there are a great many options out there.

So please keep the discussion going- I'm sure that not only myself but many others are benefiting from your combined wisdom

Cheers
Andy

Last edited by Andy01; 18-09-2017 at 11:39 PM. Reason: Typos
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  #62  
Old 18-09-2017, 11:29 PM
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alocky (Andrew lockwood)
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The impact of aperture on resolution is pretty old news, the size of the airy disc is determined solely by the aperture of the telescope. This is because the hole in the end of the tube is a boxcar window filtering the wavefront coming towards us. Even if you don't know what a Bessel function is, the fact is, an infinitely wider aperture gives you a perfect spike response to a star, and a small aperture gives you a sort of ringing peak with sidelobes that would be a lot easier to draw than describe.
This leads to another of the frustrating myths - my 4" APO is better than a 25" dob because I can see the airy discs on a good night. The fact is, those discs are more than 6 times bigger in the 4"!
Now of course then you have the impact of central obstruction and all the other fun and games but these are secondary (excuse the pun).
Unfortunately, galaxies are small and faint.
And apart from Mike, we really aren't getting much out of the planetary nebulae yet! That's next challenge.
cheers,
Andrew.
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  #63  
Old 19-09-2017, 12:03 PM
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Merlin66 (Ken)
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Andy,
Yes, but....
""the size of the airy disc is determined solely by the aperture of the telescope""

you should say "the angular size...." the seeing disk still dominates.
If you have say, excellent seeing conditions of 2 arc sec.
The seeing disk (FWHM) would be:
400 fl = 3.9 micron
1250 fl = 12.1 micron
2500 fl = 24.2 micron

Lucky fast frame imaging (ie solar etc.) can effectively freeze the seeing and give much better results.
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  #64  
Old 19-09-2017, 04:49 PM
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Andy01 (Andy)
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Just doing more research, any thoughts on RC's like this?

From Andrew's website...



RC-10" f/8 Carbon fibre astrograph w/M-LRC F/L 2000mm
Newest model with Carbon fibre tube, Super-flat field
Now A$2299


RC-10 10" carbon fibre has TWO Losmandy "D" style 3" wide dovetail
plates fitted, 40cm long each; one on top and one underneath.
Includes one 50mm and two 25mm focal extender rings!
Resolution of 0.46 arc-sec. Weighs about 16kg.

We recommend Skywatcher EQ6PRO, EQ6R, AZ-EQ6 or
Celestron CGEM, CGEM-DX & up computerised
equatorial mounts for use with C.F. RC-10".
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  #65  
Old 19-09-2017, 06:18 PM
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peter_4059 (Peter)
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That's a good choice. Definitely get the 10" though.
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  #66  
Old 19-09-2017, 06:30 PM
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Andy01 (Andy)
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Quote:
Originally Posted by peter_4059 View Post
That's a good choice. Definitely get the 10" though.
Maybe so, but further research suggests that a decent focusser upgrade & reducer/flattener are required as well as a fancy Tak collimator, heaters & dewshield, which I'd guess brings it up well past $3k. Hmmm
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  #67  
Old 19-09-2017, 06:33 PM
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Atmos (Colin)
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You will definitely want both a flattener and a better focuser otherwise you won't be happy with the results.
The Tak collimating scope may help but you can get along without it.
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  #68  
Old 19-09-2017, 06:45 PM
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rustigsmed (Russell)
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Perhaps a 10" cf newt instead, investigate using it with a Barlow and a focuser upgrade will be cheaper and probably easier than the rc
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  #69  
Old 19-09-2017, 06:53 PM
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peter_4059 (Peter)
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Quote:
Originally Posted by Andy01 View Post
Maybe so, but further research suggests that a decent focusser upgrade & reducer/flattener are required as well as a fancy Tak collimator, heaters & dewshield, which I'd guess brings it up well past $3k. Hmmm
Maybe true but you avoid the-ho hum 1000mm focal length and once you get the collimation dialed in and CALIBRATED you will be set for any galaxy you like to point it at.
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  #70  
Old 19-09-2017, 07:01 PM
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Quote:
Originally Posted by peter_4059 View Post
That's a good choice. Definitely get the 10" though.
I was pretty happy with mine but I did put an Atlas focuser on it.

CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED
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  #71  
Old 19-09-2017, 08:33 PM
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Andy01 (Andy)
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Quote:
Originally Posted by peter_4059 View Post
That's a good choice. Definitely get the 10" though.
Out of curiosity, what's the advantage of the 10" vs. the 8" other than 2000mm vs 1600mm?
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  #72  
Old 19-09-2017, 08:36 PM
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Quote:
Originally Posted by Andy01 View Post
Out of curiosity, what's the advantage of the 10" vs. the 8" other than 2000mm vs 1600mm?
100/64 times the light gathering ability for a start. And big scopes are cool
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  #73  
Old 19-09-2017, 08:44 PM
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Quote:
Originally Posted by RickS View Post
100/64 times the light gathering ability for a start. And big scopes are cool
Ok, notwithstanding size does matter lol if they're both f8 how is it different? (or am I missing something basic here?)
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  #74  
Old 19-09-2017, 09:09 PM
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Octane (Humayun)
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Bigger mirror = more light.

H
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  #75  
Old 19-09-2017, 09:09 PM
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rustigsmed (Russell)
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Quote:
Originally Posted by RickS View Post
I was pretty happy with mine but I did put an Atlas focuser on it.

CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED CALIBRATED
Very subtle Rick
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  #76  
Old 19-09-2017, 09:33 PM
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Quote:
Originally Posted by peter_4059 View Post
Andy, this might help....
The exchange rate on photons has been very favourable lately.

Quote:
Originally Posted by rustigsmed View Post
Very subtle Rick
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  #77  
Old 19-09-2017, 10:08 PM
DJT (David)
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Hi Andy

Currently chasing ARP galaxies with an RC8 and an ST2000 from Sydney close to CBD. Saw your image on AB and hope I can get somewhere close to that!

Yes, get a better focuser, yes, get the Tak collimator, you shouldn't need a dew shield and I rarely put my dew heaters on. You should get Bobs knobs and a tilt plate and also you would probably need counter weights as it's ar.! Heavy.

On point of principle I havnt put a reducer on, I would just lose the focal length I am after and I image " naked", ie, no flattener as for this specific small ccd sensor /scope combination, you dont need it. Even with a larger CCD I just Crop though I do have a flattener that does work well when I get round to setting it up. ( very amused with the constant underlining of the phrase super flat field on the ad.....)

Slow bugger though but a larger mirror like a 10 or 12 is very tempting and am not in a rush.

Even with the upgrades though you are getting good bang for buck over the more expensive RC's without over capitalising. Holds Collimation very well and barely needs refocusing during the night.

If you get hacked off with LRGB, do what SteveC does and chase NB PN's

Gawn, you know you want one


Quote:
Originally Posted by Andy01 View Post
Maybe so, but further research suggests that a decent focusser upgrade & reducer/flattener are required as well as a fancy Tak collimator, heaters & dewshield, which I'd guess brings it up well past $3k. Hmmm
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