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 Post subject: Canon EOS adapter
PostPosted: Sat Dec 15, 2012 9:11 pm 
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I expected the EOS adapter I've bought to be complete, however it seems to need a 45mm threaded tube as well to fit my 2" eye piece. I can't find one on the web without knowing what it's described as. Anyone help? Thanks Bill C


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 Post subject: Re: Canon EOS adapter
PostPosted: Sat Dec 15, 2012 9:26 pm 
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Is it a "T Mount" you mean ?

the link above is for a 2" one but they also sell an 1.25" T Mount Adaptor

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Phil
Skywatcher Explorer 200P & EQ5


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 Post subject: Re: Canon EOS adapter
PostPosted: Sun Dec 16, 2012 7:32 am 
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What 'scope are you using Bill?
Many refractors and Newtonians already have a T-thread on the back of their eyepiece-holders, but for Maksutovs and SCTs you'll need an extra adaptor from the threads on their backs.


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 Post subject: Re: Canon EOS adapter
PostPosted: Sun Dec 16, 2012 2:31 pm 
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Thanks for that. T mount is the name I needed. I have a 200 mm Skywatcher Newtonian reflector on a EQ5 mount. There's no sign of a thread on the 2" focus tube.


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 Post subject: Re: Canon EOS adapter
PostPosted: Sun Dec 16, 2012 2:54 pm 
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Well the thread may be concealed underneath the eyepiece-holder? Bring it along on Tuesday and we'll have a look.
My old Helios 200P had a 1.25" eyepiece-holder which unscrewed to reveal a T-thread beneath.
But often Newtonians don't have much range on their focussers, and so it can be difficult to get the camera close enough to the focal-plane to achieve focus - and any added length from adaptors just makes this worse. I remember that Carl had to move the primary mirror up the tube of his 130P slightly in order for his camera to reach the focal-plane.

But it looks like someone has managed it:
http://www.flickr.com/photos/rborges/3501808581/

There are 2" to T-thread adaptors available from several sources:
http://www.harrisontelescopes.co.uk/acatalog/T_Adaptor_2_.html
http://www.rothervalleyoptics.co.uk/revelation-2-quot-t-adaptor_d5542.html
http://www.iankingimaging.com/show_products.php?category=19
http://www.scopesnskies.com/prod/GSO/revelation/accessories/t-thread/eyepiece-adaptor.html
but note the previous comments about needing low-profile adaptors to achieve focus, so choose one with the shortest possible "shoulder" protruding out from your eyepiece-tube.


Last edited by rwilkinson on Sun Dec 16, 2012 5:02 pm, edited 2 times in total.

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 Post subject: Re: Canon EOS adapter
PostPosted: Sun Dec 16, 2012 4:16 pm 
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Thanks Ros. I've unscrewed the eyepiece holder and there's no male thread either end of the tube. I've read about the possible focus problem but maybe with the slightly larger diameter of the telescope tube I may avoid Carl's problem.


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 Post subject: Re: Canon EOS adapter
PostPosted: Sun Dec 16, 2012 5:08 pm 
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I've just spotted that there's also a coma-corrector (to improve the shape of the stars around the edges of your images) available for your 'scope:
http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Telescopes-Skywatcher.asp?p=0_10_5_1_3_140
But this uses a wider bore than the 42mm T-thread, so you'd also need a new M48 adaptor for your EOS:
http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Telescopes-Skywatcher.asp?p=0_10_5_1_3_32


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 Post subject: Re: Canon EOS adapter
PostPosted: Sun Dec 16, 2012 8:27 pm 
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Hi Ross. Over the nine months or so that I've had the scope, I've gradually acquired accessories.
It came with a 2" 28 mm eyepiece and since then I've bought (all 2") a 2 x barlow, coma corrector, 0111 nebula filter & pollution filter. A 1.25" reducer to fit a 8 mm - 24 mm zoom eyepiece & 1.25 mm moon filter.
I've just checked the EOS adapter and it's 48 mm. I'm not sure now whether that's going to fit the t mount I ordered this afternoon on e bay.


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 Post subject: Re: Canon EOS adapter
PostPosted: Sun Dec 16, 2012 9:02 pm 
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Bill,
You can never have too many adapters!
T-threads are 42mm.
48mm is the standard eyepiece thread - the ID thread on 2-inch barrels.
I would guess you want the camera adapter to screw into the coma corrector? Does that have a thread? The coma corrector to chip distance is critical.
As Ross had warned getting enough out-focus for a camera with a Newtonian is usually a problem. It often needs the main mirror moving forward or a low profile focuser. I once mounted the focuser base inside the tube.


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 Post subject: Re: Canon EOS adapter
PostPosted: Sun Dec 16, 2012 10:05 pm 
Another option is to use an "extension tube" such a this one:-
http://www.firstlightoptics.com/baader-planetarium/baader-hyperion-finetuning-ring.html

When i fitted a dual speed focuser to my 6" Newt I has to attach a 28mm tuning ring to the base of the 1.25" adaptor to enable me to achieve focus with EPs

When it came to AP I was not able achieve focus with my Canon DSLR and standard T-ring adaptor, so I purchase one of these:-

http://www.pulsar-optical.co.uk/prod/astro-engineering/astro-camera-adaptor/AC696-2inch%20to%20camera/DSLR.html

It had a much lower profile than fitting the T-adaptor to the threads on the end of the EP holder and also allowed me to slide it into the 2" EP holder, thereby giving me slightly larger apperture.

As David R says "you can never have enough adaptors".

Well - you do not really want that many adaptors, but unfortunately this hobby dictates that you DO need this many adaptors to enable you to gain focus for visual or AP

Ian


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