Jump to content


Photo

Are setting circles needed

  • Please log in to reply
13 replies to this topic

#1 spacebloke

spacebloke

    Lift Off

  • -----
  • Posts: 20
  • Joined: 24 Feb 2011
  • Loc: Bridgnorth, England

Posted 21 March 2011 - 11:41 AM

Hello everyone,
I have just bought a Eq5 pro goto and the setting circles are rubbish and get stuck when turning the RA axis.
So, seeing as my mount is the goto version do I really need to use the setting circles? I've got a guider and off axis guider on the way so that will help with tracking.
In terms of alignment can I just align with polaris and do a two or three star alignment from there?
Any help would be welcome, I've never used an Eq mount before so I'm a little clueless :question:

#2 wbrogdo1

wbrogdo1

    Mariner 2

  • *****
  • Posts: 201
  • Joined: 21 May 2008
  • Loc: Lakeland, FL

Posted 21 March 2011 - 12:47 PM

if you have goto, the setting circles are not needed.

#3 AlBoning

AlBoning

    Viking 1

  • -----
  • Posts: 592
  • Joined: 06 Mar 2011

Posted 21 March 2011 - 01:22 PM

Quoting from "Amateur Astronomer's Handbook" by J. B. Sidgwick.

"...the usefulness of a telescope is increased 100% by mounting it equatorially...."

"The addition of circles to the equatorial increases the instrument's usefulness by perhaps a further 10%."

"Circles are a convenience, but by no means a necessity."

"Given a good star map, all the preliminary work of identifying the neighborhood of a faint object can be done during the day...."

Paraphrasing, "Given the presence of GOTO, all the work is done."

Somewhere in my astronomical library I read that most of today's EQ mounts have setting circles that are too small to be useful.

I like setting circles, I like having them, the idea of moving from the target observed to another nearby target by using them is appealing.

I have made several efforts to teach myself how to effectively use the setting circles of my EQ mount since it is not GOTO. The experience was frustrating as it was time consuming, clumsy, and cumbersome compared to just pointing with a Telrad. Because...

My EQ mount (a Vixen Polaris clone) has what I consider to be a design flaw which makes using either the slow motion controls or slewing, in conjunction with the circles impossible. One must unlock the axes and move the scope by hand. Considering that the dec circle is divided in 2 degree increments, that I have to hold the scope in position, tighten/loosen the axes locks and hold a flashlight just to read the circles, all at the same time and hit the desired coordinates accurately usually from a contorted position ... is way, way too much trouble.

I have noticed that Vixen does not include setting circles on their mounts, they are optional.

Having written this motivated me to take another look at my EQ head. It occurs to me that the placement of pointers on the opposite side of the circles from where they are now would allow one to make accurate small displacements in dec and RA by using the slow motion controls or slewing. That would be useful with a prepared observing list that included the displacement in dec and RA from a nearby and easily found target. So ... thanks for helping me think of a solution.

#4 dawziecat

dawziecat

    Vanguard

  • *****
  • Posts: 2425
  • Joined: 20 Oct 2010
  • Loc: Rural Nova Scotia

Posted 21 March 2011 - 01:50 PM

My setting circle story:

Flash back to 1986 . . . the year of Halley's return.

My 1984 vintage, fork mounted C-11 stayed at our country home which we went to on weekends.

We left the city and arrived in the dark. I set up the C11 while my wife cooked dinner.

Halley was not visible to the naked eye so I set the circles and dialed in its coordinates . . . peered through the 55mm Clavé . . . . and there it was.

Called the wife out and she answered, "Already?" It was pretty fast work for an object I couldn't even see with the naked eye.

Setting circles require a little knowledge but they work pretty well. Having an understanding of sidereal time helps.

#5 frolinmod

frolinmod

    Surveyor 1

  • -----
  • Posts: 1895
  • Joined: 06 Aug 2010
  • Loc: Southern California

Posted 21 March 2011 - 07:15 PM

The Amateur Astronomer's Handbook by J. B. Sidgwick must be like ancient Greek by now. I remember checking an old copy out from the library in the 1970s.

The last time I used setting circles was in the 1980s and even back then they were starting to go out of style. Setting circles are so retro.

#6 spacebloke

spacebloke

    Lift Off

  • -----
  • Posts: 20
  • Joined: 24 Feb 2011
  • Loc: Bridgnorth, England

Posted 22 March 2011 - 04:36 AM

Great stuff, so I don't need them then

#7 SkipW

SkipW

    Ranger 4

  • -----
  • Posts: 337
  • Joined: 03 Feb 2011
  • Loc: Oklahoma, USA

Posted 22 March 2011 - 09:05 PM

Another thing: the "RA" circle is usually Hour Angle, not RA.

To use the Hour circle you have to know the RA of your object and the local sidereal time, then subtract RA from time to get HA. If you have a good sidereal clock and a well-aligned mount with accurate circles that can be read precisely, it can be an interesting exercise.

GoTo is easier. So is star hopping (usually).

#8 eric_zeiner

eric_zeiner

    Phoenix's Dad

  • *****
  • Posts: 8040
  • Joined: 09 Dec 2006
  • Loc: Georgia USA 34 31'57.18N 83 53'26.30W

Posted 23 March 2011 - 04:09 AM

I have nice setting circles on my Sears, I just can't figure out how to use them :bawling:

#9 frolinmod

frolinmod

    Surveyor 1

  • -----
  • Posts: 1895
  • Joined: 06 Aug 2010
  • Loc: Southern California

Posted 23 March 2011 - 09:42 AM

One of the problems with setting circles is that some RA circles are driven and some are not. If they are driven, then you just need to set the RA circle to the RA of whatever you're observing and from then on it will accurately indicate RA all night. You're all set. Lucky you. But if the RA circle is not driven then every time you want to use it you have to first re-set it to the RA of whatever you're currently observing. And then some RA circles don't indicate RA at all. They're just hour circles. For those you have to subtract the RA of whatever you're observing now from the RA of wherever you're going to and move the scope by that many hours as indicated on the circle. And most circles are not very precise. You usually end up doing some hunting in the target area anyway. They're better than nothing, of course.

#10 Skylook123

Skylook123

    Fly Me to the Moon

  • *****
  • Posts: 7495
  • Joined: 30 Apr 2005
  • Loc: Tucson, AZ

Posted 23 March 2011 - 12:41 PM

One little issue with setting circles is that the usefulness can occasionally vary with the focal length and resulting field of view at the eyepiece. My first telescope was a 6" f/5 newtonian reflector on a tiny little GEM and tripod. But the small setting circles were great; the relatively low power/large FOV matched well with the limited precision of the setting circles. I spent a couple of years navigating around with a Sky Atlas 2000.0 and the setting circles.

Fast forward to nowadays, when I use an Atlas EQ-G. The setting circles, even if they worked the way one would think they should, are just to coarse to point closer than a box of several eyepiece fields on a side. But with GOTO and pointing information in the hand controller, the only thing I use the setting circles for is prior to power up, as an aid along with a bubble level in setting a good home position to start from.

I think early in our astronomical lives we've all used some flat sky projections that, by themselves, are not adequate in locating eye candy. The setting circles do help, with smaller instruments and no computer/electronic aid.

#11 JoseBorrero

JoseBorrero

    Gemini

  • *****
  • Posts: 3170
  • Joined: 04 Sep 2009
  • Loc: Puerto Rico Island

Posted 23 March 2011 - 12:59 PM

RA setting circle shouldn't be moving, only when putting the correct RA. AGAIN that's normal don't try to loose them.

#12 greju

greju

    Mercury-Atlas

  • *****
  • Posts: 2892
  • Joined: 13 Oct 2005

Posted 23 March 2011 - 05:47 PM

I have nice setting circles on my Sears, I just can't figure out how to use them :bawling:


You are a grown man and you are gonna admit to that? :roflmao:

#13 cheapersleeper

cheapersleeper

    Gemini

  • *****
  • Posts: 3354
  • Joined: 22 Jan 2010
  • Loc: Sachse TX

Posted 23 March 2011 - 06:12 PM

Setting circles are awesome...on Dobsonians.

#14 ColoHank

ColoHank

    Vanguard

  • *****
  • Posts: 2330
  • Joined: 07 Jun 2007
  • Loc: western Colorado

Posted 24 March 2011 - 11:28 AM

If setting circles are all you have, and if they're good ones, they work just great! Setting circles are bombproof, unfailingly reliable, quiet, quick and easy, they don't eat batteries, and they're accurate enough to put objects in the eyepiece. They're what everyone but star-hoppers used until just recently, remember?

Attached Files








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics