Astro-Tech AT8RC availability in the UK

[Gib007]

Hello, anyone know if one can source an Astro-Tech AT8RC telescope in the UK? They are looking mighty attractive over a Skywatcher Explorer 200PDS for narrowfield DSO imaging but I have yet to see it available. Thanks!

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[Oddsocks]

The Astro-Tech AT8RC is a trade name used in the States.

The scope is made by the GSO company of China and re-badged for several different importers around the world under different brand names.

The identical scope is sold in the UK under the Altair Astro brand and can be found at several uk retailers with just a few minor differences in the accesories supplied.

http://www.altairastro.com/product.php?productid=16346&cat=268&page=1

http://www.opticstar.com/Run/Astronomy/Astro-Telescopes-Altair.asp?p=0_10_1_9_50

http://www.iankingimaging.com/show_product.php?id=1141

William.

[r3i]

It's also available from Telescope House under the Revelation brand name: http://www.telescopehouse.com/acatalog/Revelation-Ritchey-Chretiens.html

As William said, they're all the same scope underneath the different badges. The main differences between them are basically: the tube material (carbon fibre or metal - think it's steel but not 100% sure on that); the types of dovetails fitted; and the types of focuser options available.

[kirkster501]

..and very good scopes they are too!

[Gib007]

Excellent, thank you all very much. Now I have the dilemma of having to spend considerably more money to get this rather than Skywatcher's. Such is life in astronomy I guess.

Would you say f/8 is good for astrophotography though? Seems a little slow. Perhaps a focal reducer would come in handy but would that act as field flatenner or would that be needed extra? Thank you again!

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[johnrt]

Excellent, thank you all very much. Now I have the dilemma of having to spend considerably more money to get this rather than Skywatcher's. Such is life in astronomy I guess.

Would you say f/8 is good for astrophotography though? Seems a little slow. Perhaps a focal reducer would come in handy but would that act as field flatenner or would that be needed extra? Thank you again!

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Yes f/8 is too slow for DSO work, have a look at the Astro Physics CCDT67 telecompressor it works very will with the 8" & 6" RC's and would bring the 8" down to a speedy f/5.3.

[pete_l]

Would you say f/8 is good for astrophotography though? Seems a little slow. Perhaps a focal reducer would come in handy but would that act as field flatenner or would that be needed extra? Thank you again!

Have you considered just binning¹ your CCD?

That would give you pixels 4 times the size, which sounds to me just like working with half the focal length (and therefore a lower F ratio).

[1] I don't mean to suggest throwing it away, but combining the pixels

[Gib007]

Yes f/8 is too slow for DSO work, have a look at the Astro Physics CCDT67 telecompressor it works very will with the 8" & 6" RC's and would bring the 8" down to a speedy f/5.3.

Excellent, thanks for the suggestion. I will have a look at that!

Have you considered just binning¹ your CCD?

That would give you pixels 4 times the size, which sounds to me just like working with half the focal length (and therefore a lower F ratio).

[1] I don't mean to suggest throwing it away, but combining the pixels

Hehe no worries, I already do this with my RGB images but definitely not with my Luminance images!

[Gib007]

I have a quick question about the AT8RC and the Astro-Physics CCDT67 Telecompressor. In a PDF on Astro-Physics' website, it states the focal reduction factor is calculated by:

(305 - (16 + all_other_extensions)) / 305

By all_other_extensions, we include the CCD camera for example (17.5mm in my case) and any spacers. Anyway, if you look at the AT8RC available from Altair (http://www.altairastro.com/product.php?productid=16346&cat=268&page=1), it includes three extension tubes between the focuser and the actual telescope (100mm total).

My question is simple - is this 100mm also included in the focal reduction factor or do we only include distance AFTER the focal reducer in the optical train (after being toward the CCD sensor)?

Thanks!

[johnrt]

Yes the amount of reduction is decided by the distance from the reducer to camera chip.

[Gib007]

Yes the amount of reduction is decided by the distance from the reducer to camera chip.

Excellent, thank you, exactly what I had hoped. With the CCDT67, the spacers and adapter I currently use and my ATIK 383L+ CCD camera, that's 69.5mm, giving me 0.7721x focal reduction. Telescope would therefore be an f/6.2 system with 1255mm focal length. Sounds good to me and FOV is also excellent for small DSOs. I guess I'd need to have a Bahtinov mask custom-made for this configuration.

[dmahon]

Take a photo and upload it to astrometry.net - it will tell you the arcsec per pixel and you will be able to calculate the focal length.

[kirkster501]

The CCDT67 works very well indeed. Highly recommended for the RC scopes. Without it your exposures willl need to be very long, unfeasibly so....

[Gib007]

Take a photo and upload it to astrometry.net - it will tell you the arcsec per pixel and you will be able to calculate the focal length.

Is this how people do it? It's not a bad idea in order to get an accurately made Bahtinov mask but wouldn't seeing and focus (considering no Bahtinov mask is being used!) be a factor in these calculations? Thanks for the idea though!

The CCDT67 works very well indeed. Highly recommended for the RC scopes. Without it your exposures willl need to be very long, unfeasibly so....

Indeed, I will place an order for the CCDT67 ASAP, probably even before the telescope as the CCDT67 will have to ship from the USA. It's unfortunate Astro-Physics are so convoluted with international orders. I think I even have to fill out a form by hand...

[swag72]

I didn't get my CCDT87 from the US - TS have them in, that's where I got mine http://www.teleskop-...for-GSO-RC.html

[r3i]

I didn't get my CCDT87 from the US - TS have them in, that's where I got mine http://www.teleskop-...for-GSO-RC.html

Same here, that's where I got mine from. They also sell their own branded version of the GSO RCs if you wanted to buy everything from a single supplier. They also sell a tilt plate which goes between the scope and the focuser which is very handy to get everything lined up.

[Gib007]

Perfect yeah, just found that too. I'm really grateful as having to fill in a sheet of paper and post it to the USA sounded very 1970's to me. As for the tilt plate, I'm not entirely sure it's needed, no? As far as I've read, the focuser is completely fixed square-on on to the primary mirror so all you need to adjust is the primary mirror tilt and the focuser follows suit. That of course excludes the secondary mirror but last night I read on the collimation process using stars and there was no need to touch the focuser tilt relative to the primary mirror.

[r3i]

Perfect yeah, just found that too. I'm really grateful as having to fill in a sheet of paper and post it to the USA sounded very 1970's to me. As for the tilt plate, I'm not entirely sure it's needed, no? As far as I've read, the focuser is completely fixed square-on on to the primary mirror so all you need to adjust is the primary mirror tilt and the focuser follows suit. That of course excludes the secondary mirror but last night I read on the collimation process using stars and there was no need to touch the focuser tilt relative to the primary mirror.

What you say is true only if everything in the image train has been perfectly manufactured. In reality there are lots of possibilities where mechanical inaccuracies will introduce misalignment of the optical path, particularly within the focuser mechanism and the tilt plate provides a facility to compensate for this. The GSO RCs have a fundamental design flaw in that the rear cell is fixed to the primary mirror. The tilt plate provides the facility to de-couple the focuser from the primary mirror to enable complete alignment of the optical path.

[Gib007]

Ordered from TS!

Now all I need is the actual telescope. I think I'll wait another month or so. I have my new Peugeot RCZ coming soon and I don't want to live on £0 in my bank account, hahaha. This hobby is going to break me.

[Gib007]

I couldn't contain myself. My wife helped me out financially to be sure I'd be ok when the car arrives and here it comes, the AT8RC from Opticstar!

Now just need to sort out a Bahtinov Mask. With the CCDT67 Telecompressor and 62.5mm of spacers, I've calculated my focal length will be 1206.76mm, along with the telescope's 203.125mm of aperture, that's f/5.94. Would you say this Bahtinov Mask would cut it:

http://www.ebay.co.uk/itm/Bahtinov-Mask-for-8-Ritchey-Chretien-f8-scopes-/290949384705?pt=UK_Telescope_Eyepieces&hash=item43bdef4a01

Or do I need one custom-built because of the change in focal length and focal ratio?

Thank you!

[r3i]

That Bahtinov mask should be fine. I've recently been trying to find out if you need a precise match between the mask and the optical characteristics of your scope and from what I can gather you don't. From my own experiences that does seem to be the case as I use a mask on my 8"RC at both prime focus and with the reducer that was designed for my last scope, which was an 8" SCT with a 2000mm focal length.

[Gib007]

That Bahtinov mask should be fine. I've recently been trying to find out if you need a precise match between the mask and the optical characteristics of your scope and from what I can gather you don't. From my own experiences that does seem to be the case as I use a mask on my 8"RC at both prime focus and with the reducer that was designed for my last scope, which was an 8" SCT with a 2000mm focal length.

Excellent, thank you, just what I needed to know!

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[Gib007]

Quick question - looking at the telescope here:

http://www.opticstar.com/Run/Astronomy/Astro-Telescopes-Altair.asp?p=0_10_1_9_50

It has two Losmandy dovetail bars - one on the top, one on the bottom. Obviously the bottom bar attaches to the mount. I would however like to attach my Orion Mini 50mm Guidescope (for autoguiding) to the top dovetail bar, rather than the finderscope saddle on the rear near the focuser. This would balance weight a little better as well.

Is there an adapter for this? Basically a dovetail to finderscope saddle adapter. I've been looking and I found one from ADM but it costs like £300 and has lots of control for aiming angle. I don't need anything special - I quite literally need a finderscope saddle on top of a clamp.

[r3i]

I'd get one of these and drill & tap the appropriate bolt holes to allow one of these to be attached (the shoe can be bought from all over the place not just from the link I gave you).

[Gib007]

I'd get one of these and drill & tap the appropriate bolt holes to allow one of these to be attached (the shoe can be bought from all over the place not just from the link I gave you).

Thanks a lot for the idea. It turns out the Orion Mini 50mm Guidescope comes with one of those finderscope saddles and with a dovetail adapter for them. All I would need is a Losmandy clamp with a screw hole to accept this adapter and that's it - not even a need to drill. I will probably order that clamp you linked and use that to screw the adapter on to. Thanks again!