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Old 19-12-2014, 11:48 PM
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12" f/3 Newtonian - any reviews?

I found an interesting Newtonian -
TS 12" f/3 ONTC Newtonian 1/6 Lambda - Carbon Tube - tailor made.

http://www.teleskop-express.de/shop/...ilor-made.html

It only weighs 17Kgs & is not as long as my 14Kg 8" f/6 Newt. with it's heavy tube rings
so I reckon I would get away with using it on my modified NEQ6 pro mount.

F3 sounds really interesting.
It will collect 9 times more light per square unit than my 8" f6 Newt.
That would get me 9 x faster results.

I am wondering about diffraction spikes.
I bet Alnitak would go right across the frame of the horse head nebula?
Maybe it would need a curved spider?

I also wonder about focusing at f3?
Maybe it just wouldn't work without an electric focuser?

Can anyone find any pictures taken with one or any review?
Does anyone know anything about this scope?

Note:
there is also a 10" version:
http://www.teleskop-express.de/shop/...ilor-made.html

cheers
Allan
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Old 20-12-2014, 05:14 AM
glend (Glen)
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Allan I reckon that the coma would drive most imagers crazy at F/3 regardless of the benefits, and collimation would also be a constant headache. As to the weight, there are much lighter alternatives if you have some ATM skills - my 10" f/5 imaging newt OTA only weighs 12.6kg, uses carbon fibre struts. There are a fair number of exotic designs emerging in the market but you have to consider the night to night use and management of the setup. The quest for ultra low F numbers is nuts in my opinion, and not worth the alledged benefits in exposure time savings. For imagers who are setup to guide their mounts the potential of shorter subs is not that great an attraction to justify the probems you would buy into at F/3.
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Old 20-12-2014, 08:27 AM
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Quote:
Originally Posted by glend View Post
Allan I reckon that the coma would drive most imagers crazy at F/3 regardless of the benefits, and collimation would also be a constant headache. As to the weight, there are much lighter alternatives if you have some ATM skills - my 10" f/5 imaging newt OTA only weighs 12.6kg, uses carbon fiber struts. There are a fair number of exotic designs emerging in the market but you have to consider the night to night use and management of the setup. The quest for ultra low F numbers is nuts in my opinion, and not worth the alleged benefits in exposure time savings. For imagers who are setup to guide their mounts the potential of shorter subs is not that great an attraction to justify the problems you would buy into at F/3.

Hi Glen,
thanks for your reply.
I don't agree that it is nuts to consider f/3.
That scope is a carbon fiber tube which should give high stability
for collimation - it's not a cheap scope.
The bad weather & lack of time means only fast instruments
can collect enough data in the short time windows opened.

I wrote to TS & they have no pictures taken with this f/3 scope.
I have written again as I don't want to be a guinea pig.

One problem is my RCC1 coma corrector which is designed for f/4 to f/7.
Even the ASA 2" Coma Corrector Quattro 1.175x they recommend
says it works only from from f/4 to f/6.
My KAF8300 chip has a diagonal of only 22.5 mm - not too large.
I think the RCC1 would still work -
see mine here:
https://www.flickr.com/photos/247194...in/photostream


I'd love to see some result pics.

cheers
Allan
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Old 20-12-2014, 10:07 AM
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I had to guess a few figures but I still processed the design with
Newt for windows 3.1 by Dave Keller.
The results are in the attached pic.
It looks like the 2" focuser they supply is too narrow.
Any ideas?

Also - just out of interest:
Contrast factor = CF = 5.25 - 5.1x - 34.1x²+ 51.1x³

where x is the obstruction ratio = 3.94/12 = 0.328 = 32.8%

therefore:
Contrast factor = 1.71.
Unobstructed = 5.25.



cheers
Allan
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  #5  
Old 20-12-2014, 11:08 AM
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OzEclipse (Joe Cali)
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Power Newts & Philipp Keller Corrector

Check out the Newton Corrector on Philipp Keller's site
http://www.astrooptik.com/

I believe this corrector or something very similar is used for the Boren Simon Powernewt scopes.

http://www.teleskop-service.de/astro...astrofotos.htm

Joe
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  #6  
Old 20-12-2014, 11:26 AM
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Quote:
Originally Posted by OzEclipse View Post
Check out the Newton Corrector on Philipp Keller's site
http://www.astrooptik.com/

I believe this corrector or something very similar is used for the Boren Simon Powernewt scopes.

http://www.teleskop-service.de/astro...astrofotos.htm

Joe

Thanks Joe,
none of those correctors are recommended for f3.
I think they would all give eggy stars at the corners.

cheers
Allan
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Old 20-12-2014, 04:37 PM
clive milne
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If I had a microline camera I would go for a Rowe Ackerman astrograph instead.
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  #8  
Old 20-12-2014, 05:27 PM
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rmuhlack (Richard)
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how about the Televue Paracorr? Looks like it works down to f3
http://www.televue.com/engine/TV3b_p...ot#.VJUkcDAMCw
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  #9  
Old 20-12-2014, 05:35 PM
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strongmanmike (Michael)
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Mirror Optics are same as for my scope and ASA's N series in fact (except mine are 1/10 Lambda )

Good luck taming it properly though, probably need to be a handy tinkerer

Mike
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  #10  
Old 20-12-2014, 10:48 PM
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Quote:
Originally Posted by rmuhlack View Post
how about the Televue Paracorr? Looks like it works down to f3
http://www.televue.com/engine/TV3b_p...ot#.VJUkcDAMCw

Maybe but I forgot one thing till now:
My QHY9 camera requires 70 mm of back focus when used with a TS9 OAG.
An OAG is essential with my NEQ6 pro modified mount.

My project with my 8" Newt. was only saved by the extra long back focus RCC1.
It has 91.5 mm of back focus.
see here:
https://www.flickr.com/photos/247194...in/photostream

All the ASA correctors & the Televue Paracorr have too little back focus.
It worked out well for me with the RCC1 as it also screwed into
a Varilock spacer which allowed me infinite adjustment of the spacing.

The QHY9 camera has a long nose piece which makes it waste back focus to the camera chip.

It means that none of the ASA Newts. or these other Newts will be suitable for me.
They need 3" focusers with expensive correctors that don't have enough back focus.

Does anyone have some ideas?


cheers
Allan
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  #11  
Old 20-12-2014, 10:49 PM
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Quote:
Originally Posted by strongmanmike View Post
Mirror Optics are same as for my scope and ASA's N series in fact (except mine are 1/10 Lambda )

Good luck taming it properly though, probably need to be a handy tinkerer

Mike

Yes Mike - I have a feeling that only microns of movement would put the collimation out at f3.
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  #12  
Old 20-12-2014, 11:03 PM
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You'd be better off getting an Orion Optics UK AG scope like Mike's. Is there much of a price difference by the time you add in a proper corrector, 1/10th wave mirror, extra rings for the focuser?

You can make adapters to get rid of the nose piece on your camera.

Greg.
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  #13  
Old 20-12-2014, 11:11 PM
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Quote:
Originally Posted by gregbradley View Post
You'd be better off getting an Orion Optics UK AG scope like Mike's. Is there much of a price difference by the time you add in a proper corrector, 1/10th wave mirror, extra rings for the focuser?

You can make adapters to get rid of the nose piece on your camera.

Greg.

Hi Greg,
would such an adaptor still include the optical window?
I wouldn't want to run the camera without that.

My mount is not good enough to hold an OTA like Mike's.
This is starting to get too expensive -
new mounts, new correctors etc.


cheers
Allan
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Old 20-12-2014, 11:17 PM
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Hi Greg,
I'd probably be better off with something like this which would work
with all the equipment I have now:

http://www.teleskop-express.de/shop/...rbon-tube.html



TS UNC 10" f/4 Newtonian telescope with German made carbon tube and 2" ACUN focuser
... Aperture 250mm - Focal length 1000mm - with optimized focus position for maximum illumination
... 94% reflection high quality diffraction limited optic - each telescope is tested on our optical bench
... only ca. 11kg weight with cradle rings!


I could always upgrade the mirrors & other parts at a later date for more performance.
At least it's light too!


cheers
Allan
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Old 21-12-2014, 07:16 PM
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I just checked out the TS UNC 10" f/4 Newtonian.
using Dave Keller's Newt for windows 3.1.

(Luckily I have a Win XP laptop to use the program because it won't run on a modern 64 bit operating system.)

I found that even that needs a larger focuser than a 2'"
There was 75% vignetting of the rays at the front aperture & the focuser.
I also notice that other 10" f4 systems use a 3" or larger focuser.

My 2" RCC1 coma corrector goes deep inside the focuser so even that would cause vignetting.
I need to use that RCC1 so that I can use my QHY9 + filter wheel + OAG = 70mm of back focus.

What is going on?

cheers
Allan
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Old 21-12-2014, 07:49 PM
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Quote:
Originally Posted by alpal View Post
I just checked out the TS UNC 10" f/4 Newtonian.
using Dave Keller's Newt for windows 3.1.

(Luckily I have a Win XP laptop to use the program because it won't run on a modern 64 bit operating system.)

I found that even that needs a larger focuser than a 2'"
There was 75% vignetting of the rays at the front aperture & the focuser.
I also notice that other 10" f4 systems use a 3" or larger focuser.

My 2" RCC1 coma corrector goes deep inside the focuser so even that would cause vignetting.
I need to use that RCC1 so that I can use my QHY9 + filter wheel + OAG = 70mm of back focus.

What is going on?

cheers
Allan
Dont worry so much about the 75% rays, what you want to do is get the 100% rays covering your chip. Also you need to set your focuser camera travel to the backfocus of the camera outside of the focuser. Here is a 12 inch f3 design from newt for the web (which means you dont need to use the software you can just run the webpage version) using 55mm camera backfocus you will need a 3 inch focuser and a 120mm secondary.

Why not look at reducing a more modest scope with the ASA reducer corrector?

Here is the website btw
http://stellafane.org/tm/newt-web/newt-web.html
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Last edited by Peter.M; 21-12-2014 at 08:00 PM.
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Old 21-12-2014, 09:43 PM
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Peter,
Quote:
Why not look at reducing a more modest scope with the ASA reducer corrector?
Hi Peter,
thanks for all the work you did there.
It proves the 12" f/3 can't work with a 2" focuser as I thought -
& neither can the 10" f/4.

Notice TS sells Newts. with the bigger focusers:
http://www.teleskop-express.de/shop/...fertigung.html

It doesn't matter what option I choose I am still
unable to use my QHY9 camera because of the back focus problem.
No 1:1 corrector has 70mm of back focus.

I don't think I can upgrade.

By the way I checked my 8" f/6 Newt. om Dave Keller's program
& it comes up as a perfect system.

cheers
Allan
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Old 22-12-2014, 07:08 AM
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This is very strange:
http://www.optcorp.com/qhy-9-mono-wi...heel-qhy9.html

If you look at the QHY9 camera there is no nose piece in the optical train.
They say that it has a back focus of 35mm.

Quote:
This QHY 9M comes with a five-position filter wheel for 36mm filters, and has a total backfocus of 35 mm.
Then they show a picture of the camera with a nose piece.

My back focus with my QHY9 is about 70mm with
the nose piece, filter wheel & OAG.
This means that I can't use it with the available 3" coma correctors.

Can anyone explain this?

( PS - I wrote to OPT to ask them )

cheers
Allan
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  #19  
Old 22-12-2014, 08:01 AM
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hi allan,

not sure if this will help you out? did you have a moonlite focuser?

http://www.teleskop-express.de/shop/...ous-point.html


cheers,

rusty
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  #20  
Old 22-12-2014, 08:15 AM
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Quote:
Originally Posted by rustigsmed View Post
hi allan,

not sure if this will help you out? did you have a moonlite focuser?

http://www.teleskop-express.de/shop/...ous-point.html


cheers,

rusty

Thanks Rusty,
once again 66.6mm of back focus.

The nose piece on the QHY9 is too long to allow for that.
I need 70mm.

cheers
Allan

I have written to a guy called Bern who may have shorter nose pieces available.

see this thread:
http://stargazerslounge.com/topic/12...ictures/page-2

QUOTE:
I just got off the phone to Bern at Modern Astronomy and he has a batch of short nose pieces which were made especially for this scenario, i.e:

QHY9 / Protective glass chamber / QHY filter wheel / Nosepiece / Skywatcher reducer.


Maybe he can help?

cheers
Allan

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