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An equipment question

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#1 MG1962


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Posted 22 December 2012 - 02:20 AM

I observe my variables exclusively with an Celestron SE8. To compliment the scope I was considering purchasing a wide field refractor and adapting it to my mount, so really only looking at an OTA

Anyway from a variable star point of view, does anyone think such a rig would have value, or better to stay with the 8inch

#2 Hubert


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Posted 22 December 2012 - 03:45 AM

I think this is a good investment. You can observe bright variables with it and and the fainter ones with your C8.


#3 Rich (RLTYS)

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Posted 22 December 2012 - 07:32 AM

A rich field type refractor is always useful for VSOing. Go for it.

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#4 RAKing


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Posted 24 December 2012 - 07:19 AM

I agree with everyone above. I used 80mm and 90mm refractors on my SE mount. They work great!



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#5 BrooksObs


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Posted 24 December 2012 - 05:25 PM

Speaking as someone with a very, very long record in the field of variable star observing, I would recommend sticking with the SE8. It has the ability to cover more worthwhile variables over a greater portion of their cycle's then will some much smaller aperture scope.

My personal recommendation would be that if you truly wish to have an instrument that compliments your SE8 in your variable star observing program and you a really familiar with the sky, that you purchase a pair of larger (say 9x63, 15x63 or 15x70) binoculars and use these to cover the brighter stars.


#6 brianb11213



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Posted 26 December 2012 - 09:49 AM

There is an excellent justification for a smaller instrument for VS work: if a star is too far above the threshold, visual estimates become unreliable (especially when the star has a deep colour). Also large aperture scopes have smaller true fields of view than smaller scopes, which makes comparisons more difficult ... a largish scope working at a highish focal ratio, like your 8" f/10 SCT, is fine for faintish stars but not for the brighter ones.

IMO a 8" scope is ideal for visual VS work on stars in the approximate range mag. 11.0 - 13.0. (You should be able to see fainter stars than that but errors accumulate close to the threshold!) A 80mm short focus refractor for stars in the approximate range 9.0-11.0 would complement it nicely. But I'd query whether it's a good idea to have it on the same mount: a good but easily portable altaz mount will allow you to move to a different observing place, so you can access the bits of sky that are hidden from your usual spot, without having to go through the tedious alignment procedure again ... and the SE mount is IMO compromised by relying on the motor drive.

One practical aspect of this ... if your scopes have the same type of finder then it is easier to locate an object in the scope on a "dumb" (push to) mount by comparing the field shown in the finder on the scope equipped with goto.

Personally I use several instruments for VS work: naked eye, 4x20 binoculars (hand held), 10x50 binoculars (on a camera tripod), 80mm f/6 doublet refractor & 6" SCT tube (on a Skytee 2 altaz mount) and a CPC 1100. That gives me a complete working range with "optimal efficiency" from about mag. 2 to mag 14 with a faintest object threshold (on a transparent dark night) of around mag. 16.

#7 MG1962


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Posted 26 December 2012 - 12:48 PM

Thanks everyone for the excellent input - Seems the refractor is a good option provided I can get enough value from my observing program to justify it.

I think the suggestion for a separate tripod makes good sense and I will ultimately go down that road. Many variable observers have suggested binoculars, but the times I have used binos I have never really enjoyed them....but who knows what the future may bring

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