Bolton Astronomical Society

Less is more (use) - a compact 70ED refractor
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Author:  rwilkinson [ Wed May 20, 2015 7:48 am ]
Post subject:  Less is more (use) - a compact 70ED refractor

As I explained in last night's presentation, I think that perhaps the "best" telescope to have is one which is small and convienent enough to be used most often, particlarly in circumstances when you wouldn't have time to set up a larger instrument. Now both my Celestron C8 and StarWave 80ED work very well on a "German" equatorial mount (with counterbalance weight), but the kit takes up the entire boot of my car (and needs three trips from the back garden to carry it all down there), so I only make the effort to take it away with me to major star-parties, not on short business trips. However a smaller refractor would be portable enough to take with me any time, which is why I recently bought a TS Optics 70ED:

I was originally looking to get a StarWave 70ED (to match my '80), but these are no longer available as Optical Tube Assemblies, and I didn't want to pay an extra £100 to get it bundled with a superfluous eyepiece, star-diagonal and finder (which I already had), so I went for the Telescop Service version instead. In contrast to StarWave's white-painted metal, TS use carbon-fibre tubes, which look quite smart in the daylight (but are not as eye-catching at dimly-lit star-parties!). The back-end can be rotated relative to the main tube and features a 2" diameter draw-tube with a slow-motion control which makes focusing very smooth and easy.

The size and weight of this instrument are much more "in scale" with its 70mm aperture than the massive StarWave 80, so it can fit on a lightweight mount, even a photographic tripod - in fact it's supplied with a mounting-shoe with tapped with the standard 1/4" tripod-thread. This can be bolted straight onto a standard dovetail-bar, but I had a pair of old tube-rings left over from my 80mm achromat which (with a little padding and baize lining) give a more secure two-point mounting for the OTA. Mounted in this way, I can quickly attach this 'scope to my CG5 or a much lighter mount such as a Celestron NexStar or even an LCM:
File comment: Night and day - the TS 70ED on Celestron NexStar and LCM mounts in the Wye Valley and in Bolton
70ED_mounts.jpg [ 234.48 KiB | Viewed 4165 times ]
This whole kit is light enough to be carried around the garden fully-assembed, so that I can find the best viewing position to see between the surrounding trees and houses. The high-quality ED optics allow the use of a much higher magnification than could be expected - I've been viewing Jupiter and Venus at up to x133 (using my 6.3mm eyepiece and a Barlow-lens!). And as I recently demonstrated, this lightweight arrangement can even be used for imaging:

I've fitted my 'scope with a Rigel Quikfinder: a lightweight TelRad-type reflex-finder which superimposes a virtual pair of red cicles (of diameters 2 and 0.5 degrees) on the sky, to help with star-hopping to a target. And I'm also getting an erect-image 45-degree diagonal, which converts the 'scope into a terrestrial spotting-scope (with the image the right-way around and the right-way up).

Although the 'scope comes in a nicely-fitted well-padded travel-bag, I soon found that its zip-fastener wasn't really up to the job, so I've transplanted mine into a tough briefcase-like tool-case from TriFibre - I found one which was just the perfect size to take the exisiting foam inserts, with a little room left over for my solar filter and Bahtinov mask:
File comment: Just in case - snug in its original foam padding within the new TriFibre tool-case.
justincase.JPG [ 208.91 KiB | Viewed 4161 times ]

Author:  DRatledge [ Wed May 20, 2015 4:51 pm ]
Post subject:  Re: Less is more (use) - a compact 70ED refractor

wow - didn't realise it was the carbon fibre tube - pretty cool!
I think it is the same optics as the Starwave version - they say the supplied case is only fit for transit which confirms what you found.

Author:  rwilkinson [ Sat Aug 15, 2015 6:36 pm ]
Post subject:  Re: Less is more (use) - a compact 70ED refractor

As this 'scope is so lightweight, it even works on an old EQ1 mount which I've had in the back of my shed for years:
File comment: Solar observing with a (filtered) lightweight refractor on a small EQ1 mount
TS70 on EQ1.jpg
TS70 on EQ1.jpg [ 310.1 KiB | Viewed 3930 times ]
And with just a primitive DC motor-drive it tracked the Sun very well - keeping it in view for over half an hour at 42x magnification.

Author:  bbones [ Mon Aug 17, 2015 1:34 pm ]
Post subject:  Re: Less is more (use) - a compact 70ED refractor

Which method did you use to set up the mount to enable such good tracking?

Cheers Bill

Author:  rwilkinson [ Mon Aug 17, 2015 2:22 pm ]
Post subject:  Re: Less is more (use) - a compact 70ED refractor

bbones wrote:
Which method did you use to set up the mount to enable such good tracking

I just used a magnetic compass to aim the polar axis North, and its latitude scale to set the elevation.

Author:  bbones [ Mon Aug 17, 2015 2:39 pm ]
Post subject:  Re: Less is more (use) - a compact 70ED refractor


Author:  bbones [ Mon Aug 17, 2015 6:29 pm ]
Post subject:  Re: Less is more (use) - a compact 70ED refractor

Well I must have got something right. I have tracked the Sun for 4 hours 30 minutes without any manual intervention and it was still in the centre of the eyepiece when the Sun set behind the neighbours roof top

I will try again tomorrow to make sure I can remember the Handset Setup.


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