#81  
Old 01-01-2014, 09:37 PM
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Logieberra (Logan)
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FYI - there is also talk of a GSO 20" RC truss. 13K USD. See here (no pic available at this time): https://www.astronomics.com/astro-te...scopes_c6.aspx
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  #82  
Old 02-01-2014, 09:08 AM
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This is great news. It seems like large aperture imaging is becoming way more affordable. A 20 inch RC would be awesome with even a decent figured mirror. No wonder RCOS shut down. That sort of competition would make it impossible to compete.

Even if the focuser etc is poor it would be worth while to get one and add the high quality extras like FLI Atlas focuser, solid tube adapters, and perhaps replace the secondary spider if needed and perhaps add some baffles and flock it.

Do they sell flatteners/correctors? Then again I bet a Tak flattener would work anyway and an APM reducer would also probably work.

Greg.
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  #83  
Old 02-01-2014, 05:01 PM
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Re flatteners, I read this on cloudynights:

"Astronomics says yes flatteners are being designed for each size scope, to be threaded to the rear cell".

I'm not sure of the relationship between Astrotech (aka USA rebadged GSOs) and Astronomics. Anyone know?

Last edited by Logieberra; 02-01-2014 at 06:09 PM.
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  #84  
Old 02-01-2014, 06:20 PM
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Something else that I came across---

Astronomics sells a dedicated Focuser collimating ring for 10" and 12" Astro-Tech Ritchey-Chrétiens.

Details here: https://www.astronomics.com/focuser-...ns_p20076.aspx

My question is, I wonder if this will be needed for the 12", 16" and 20" truss line? Or has the 'fix' been incorporated? If not, I dare say that this is an essential upgrade - regardless of the focuser you intend on using.

Here's their blurb:

This Astro-Tech FCR1012 focuser collimation ring is an economical and very useful addition to the imaging train of Astro-Tech 10" and 12" Ritchey-Chrétien astrographs to improve your image sharpness when imaging with DSLRs and CCDs that use large format 35mm-class CCD sensors.

The focuser on 10” and 12” Astro-Tech Ritchey-Chrétien astrographs threads directly onto the rear cell of the central baffle tube/primary mirror assembly. Machining tolerances in the various components can sometimes lead to a very minor tilt in the alignment of the focuser and camera in relation to the scope’s optical path. This is rarely visible in images taken with an APS-C size imaging sensor (up to an approximately 23mm diagonal).

However, with large format 35mm-class DSLR and CCD sensors, image sharpness in the corners of your images will be improved if your camera is precisely aligned with the scope’s optical path.

This focuser collimation ring allows you to do just such a precise alignment, by letting you separately align your focuser/camera combination to the scope’s optical path completely independently of the baffle tube/primary mirror alignment.

The focuser collimation ring consists of two spring-loaded rings with push/pull collimating screws that let you tilt the rings slightly in relation to each other and then lock them firmly in place. The collimation ring fits between your scope’s rear cell and your focuser/camera combination. Once installed, you can then adjust the tilt of the collimation ring to zero out any tilt in your focuser during final scope collimation.

The telescope side of the collimation ring has M117 x 1 female threads that connect to the rear cell of your scope (or to any 117mm extension rings you have attached to the rear cell to provide the proper scope to camera spacing). The camera side of the collimation ring has M117 x 1 male threads for attaching your focuser. The collimation ring takes up only 15mm of back focus.
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  #85  
Old 03-01-2014, 06:04 PM
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This is the same product from Teleskop Express. I have been using one of these on my RC10 for over a year now.

http://www.teleskop-express.de/shop/...efractors.html

It does help a lot if you have any problems.

all the best

Paul
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  #86  
Old 06-01-2014, 10:06 PM
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Quote:
Originally Posted by Logieberra View Post
FYI - there is also talk of a GSO 20" RC truss. 13K USD. See here (no pic available at this time): https://www.astronomics.com/astro-te...scopes_c6.aspx
I really wish manufacturers would stand on their (legitimate) merits and refrain from marketing BS such as this:
large R-Cs need carbon fiber tubes, quartz mirrors, and cooling fans

Oh really....? How many professional institutions (that collectively) spend millions of dollars analysing mechanical merit functions opt for RC's which are constructed using quartz mirrors and something other than a welded steel truss?

Cue; tumble weed emoticon.

Some suggested further reading:

http://www.amazon.com/Construction-O.../dp/1441930329

Last edited by clive milne; 06-01-2014 at 10:34 PM.
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  #87  
Old 06-01-2014, 10:44 PM
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Clive
The quote you give is actually from Astronomics talking about the RC astrographs from Astro-Tech. They are not a manufacturer but a reseller.
I cannot find anywhere that GSO makes such a statement.
Cue: emoticon of person with their pants down
Allan
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Old 06-01-2014, 11:02 PM
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Allan... to my understanding Astro tech have suggested they intend to manufacture telescopes around GSO optics (which makes them the manufacturer and GSO the subcontract component supplier) ... in any case, you seem to have missed the point with with respect to the merit function of quartz optics installed in carbon fibre tubes.

Can you show me an example of a large ground based telescope that bothers with the expense of carbon fibre truss tubes and quartz optics that isn't designed for launch in to space?

Last edited by clive milne; 06-01-2014 at 11:17 PM.
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  #89  
Old 06-01-2014, 11:19 PM
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Clive
Your first statement is totally incorrect
And your second statement doesn't make sense as I read it.
But what ever you want
Allan
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Old 06-01-2014, 11:24 PM
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Quote:
Originally Posted by allan gould View Post
Clive
Your first statement is totally incorrect
And your second statement doesn't make sense as I read it.
But what ever you want
Allan
So can you explain to me why professional telescopes like the VLT, Keck etc don't require a carbon fibre truss for starters...?
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Old 06-01-2014, 11:38 PM
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I'm trying to understand... is your point that the claim:large R-Cs need carbon fiber tubes, quartz mirrors, and cooling fans
is actually not specious... or are you just nit picking who is making it?
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  #92  
Old 06-01-2014, 11:44 PM
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I'm not talking about large ground based or space based scopes. Where did you get that from?
Your original statement said manufacturers claimed certain things and you were blatantly wrong. A rebadger/reseller made that statement NOT GSO the manufacturer, that's all I stated.
Allan
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  #93  
Old 07-01-2014, 07:04 AM
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Quote:
Originally Posted by clive milne View Post
So can you explain to me why professional telescopes like the VLT, Keck etc don't require a carbon fibre truss for starters...?
One reason is because they temperature control the entire observatory contents as much as possible....Wish I had enough solar panels to run AC in my obs...

EB
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  #94  
Old 07-01-2014, 07:45 AM
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Originally Posted by clive milne View Post
So can you explain to me why professional telescopes like the VLT, Keck etc don't require a carbon fibre truss for starters...?
The amateur tends to operate smaller mounts, no? The thermal properties of CF aside (a subject best left for the science types on here), if a truss tube shaves even a few KG off the end weight, great!

Below - the same 12" RC mirrors - truss vs. closed tube.
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Old 12-01-2014, 08:14 AM
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And it looks like the 10" GSO RC will go truss down the track-

http://www.webastro.net/forum/showthread.php?t=86847
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Old 12-01-2014, 02:50 PM
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Originally Posted by Logieberra View Post
The amateur tends to operate smaller mounts, no? The thermal properties of CF aside (a subject best left for the science types on here), if a truss tube shaves even a few KG off the end weight, great!

Below - the same 12" RC mirrors - truss vs. closed tube.
Im using a 10" GSO RC at the moment and it has an aluminium tube. To be honest I dont think that a CF tube would offer any advantage to me as the fans equilibrate the scope to ambient temp quickly and since Im running SG Pro to refocus the scope at every 1 degree C in temperature change what would be the point except in weight saving.
But looking at the image of the 10" truss scope, there is some seriously thick Al plates there that I would be surprised if there was a real weight advantage. Even the weight of the 12' scope in tube or truss form is the same. And since there is no CF tube for the 12' it would be a toss up between the two and depend on what characteristics you are after in an OTA.
Interesting times ATM.
Allan
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Old 12-01-2014, 03:36 PM
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Quote:
Originally Posted by allan gould View Post
Im using a 10" GSO RC at the moment and it has an aluminium tube. To be honest I dont think that a CF tube would offer any advantage to me as the fans equilibrate the scope to ambient temp quickly and since Im running SG Pro to refocus the scope at every 1 degree C in temperature change what would be the point except in weight saving.
The CF tube offers no improvement in focus stability anyway, Allan. I have one and the primary mirror cell and the spider assembly are bolted to each end of the full length metal dovetails. I think the CF tube is mostly there to look cool

Cheers,
Rick.
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Old 12-01-2014, 03:51 PM
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The CF tube offers no improvement in focus stability anyway, Allan. I have one and the primary mirror cell and the spider assembly are bolted to each end of the full length metal dovetails. I think the CF tube is mostly there to look cool

Cheers,
Rick.
I wouuld have to agree Rick. So far as I have been able to assertain the weight difference between the 12" aluminium tube and the CF tube is between 1-2 Kg. Worthwhile but not extreme.
Allan
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  #99  
Old 12-01-2014, 04:18 PM
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Quote:
Originally Posted by RickS View Post
The CF tube offers no improvement in focus stability anyway, Allan. I have one and the primary mirror cell and the spider assembly are bolted to each end of the full length metal dovetails. I think the CF tube is mostly there to look cool

Cheers,
Rick.
Ive wondered why some manuf do that, primary mirror cell assy bolted with metal dovetails to spider assy and a CF tube. seems so daft to me..... There just has to be a reason for that contradiction.....
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Old 12-01-2014, 04:23 PM
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Ive wondered why some manuf do that, primary mirror cell assy bolted with metal dovetails to spider assy and a CF tube. seems so daft to me..... There just has to be a reason for that contradiction.....
Because doing it properly is a bit more difficult and expensive and maybe nobody will notice?
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