Setting Circles

[JimD]

Hello all,

I've been attempting to use my declination setting circle as an aid to finding things. My polar axis is only set approximately, but good enough so that I can visually track objects with the RA slow mo with very little drift in declination.

So I looked up the Dec of Saturn and Betelguese (using Stellarium which is set to my home location), as they are very easy to find from my back garden. These were: -

Jupiter +20 deg 45'

Betelguese +7 deg 24'

Now I'm not expecting to be able to set the tiny setting circles on my EQ3-2 to exactly those settings, but when I visually centred up to both objects, the readings on my Dec circle were: -

Jupiter about 10 deg

Betelgues about 0 deg.

Which is a tatie field out!

I even tried setting the dec circle to 20 and trying to alter the polar axis alignment & RA to centre Jupiter in the finder, but no amount of adjustment could bring it nearer to being in view.

Help! What am I doing wrong here?

[triton1]

have you calibrated the setting circles?Find a bright star.centre it check its co-ordinates with stellerium then set your setting circles to it.\in theory moving to new co-ordinates should be pretty close

[JimD]

Hi triton1. No I didn't calibrate the circles. The manual seems to be a bit misleading in this - in one section it says that the 'declination scale is factory set and does not need to be calibrated' but then later on tells you to adjust it by slackening the allen screw if it's reading the wrong value on a known object!

If it's clear tonight I'll give it a go. I just wanted to check on here that I wasn't doing something daft (a strong possibility with me) before I messed about with the setting.

[BargeGazer]

I find that the setting circles on my EQ3-2 are less than useless. Set it up and by the time I have swung the mount a bit they have stuck/come loose and are of no use whatsoever for finding things.

Why they even fit something so useless is beyond me - and that seems a fairly common response for this mount. Everything else o the mount seems pretty good though so best to be like everyone else and just pretend that they are not there!

David

[CSM]

To use the setting circles on my Skywatcher 130 you need at least 3 hands. Also placed most inconveniently so that you can't really see or align them properly. Best described as gimmicks.

[JimD]

Well, even though the setting circles are pretty poor by most standards, they will be of use to me. My problem is light pollution - I can only see the brightest stars, which makes it tricky to find anything that isn't very close to one of them.

My plan is to use the declination setting circle (the RA business is still in my 'too hard' box) to get me into the right ball park so at least I have a fighting chance of finding my target by scanning around from that point.

[DaveS]

It's not just the Eq3.2. The circles on my HEQ5 are little more than ornamental .

I guess they expect everyone to use GOTO. I think you may have to go a lot more up-market Lossmandy perhaps?

[Ulysses]

Hi, once you get the hang of using them, they can work very well. I use the setting circles to find all my targets to image as my mount is a non-GOTO. The trick is to start with a good polar alignment. To find an object, find the nearest bright star to it. Point the telescope at that star and centre it in the eyepiece. It should be easy to find through the finderscope. Now you will need to know the RA and Dec coordinates of both the star and the object of interest from a reference book etc. With the telescope pointing at the bright star, rotate the setting circles so that they line up to the star's coordinates. The circles are now calibrated. Now, manually move the mount in RA and Dec so that the circles line up with the coordinates of the object you wish to look at. Check that the circles are moving when you move the mount this way! Depending on the scope field of view, the accuracy of the circles and polar alignment, the object of interest should be in the field of view or very close. This does take practice, but I've become so used to using them now, I would not bother with a GOTO system. In fact, for me, a GOTO would not be a possibility as I wouldn't want to go slewing around for alignment stars with the mount loaded up for astrophotography. Good luck with it, Cheers, Paul

[JimD]

Well, I had a go with this last night; centred scope on Jupiter, got the Dec from Stellarium and set the dial to the correct value. By the time I went looking for a star to test it on (Rigel was handy) the clouds came over.

[midnight_sky_watcher]

Hi , Small circumference setting circles are really hard to read and set accurately due to the small setting lines within them. I have the eq 6 pro, the setting circles on that mount are easier to see and stand a better chance of actually hitting the object your looking for.

Grant....

[Neil_F]

I have found (and it may be just me being thick) that the setting circles are a) a waste of time, and only correct for one particular time? If you set the circles to say Polaris then try and find Jupiter, after 10 or 15 minutes your target object has moved by several degrees, and is no longer at the point you set on the circles. It's all Greek to me.........

[DaveS]

Probably the easiest way is to get the dec circle right, then just set the mount to the dec of the object sought and sweep in RA, otherwise I remember quite an involved procedure requireing a sidereal clock.

[JimD]

Probably the easiest way is to get the dec circle right, then just set the mount to the dec of the object sought and sweep in RA, otherwise I remember quite an involved procedure requireing a sidereal clock.

Yes, that's exactly my plan.

[dephelis]

I have found (and it may be just me being thick) that the setting circles are a) a waste of time, and only correct for one particular time? If you set the circles to say Polaris then try and find Jupiter, after 10 or 15 minutes your target object has moved by several degrees, and is no longer at the point you set on the circles. It's all Greek to me.........

Once the declination circle has been set, using a reference star, it does not need to be changed again. It will remain correct as long as you are polar aligned. The RA circle does need to set, again against a reference star, each time you want to use the setting circle to move to another object. This is because RA/Dec are coordinates on the celestial sphere and our view of the celestial sphere changes due to the Earth's rotation.

Altitude/Azimuth references your location at a specific time. So 45 degrees altitude and 0 degrees azimuth will always be halfway up to the zenith and due north.

Using RA/Dec will mean that you have a fixed coordinate value for any given object whereas the same object will have a different Alt/Az coordinate throughout a nights observation. To find objects in Alt/Az requires you to have planetarium software to give you the current position for any given object, with RA/Dec you can just use a list of coordinates.

[Neil_F]

Dephelis, what an excellent explanation, well done sir! I think for a relative newbie like me, starhopping is probably the easiest way to find something. My setting circles will just be something pretty to look at while my scope cools...lol.

[dephelis]

Dephelis, what an excellent explanation, well done sir! I think for a relative newbie like me, starhopping is probably the easiest way to find something. My setting circles will just be something pretty to look at while my scope cools...lol.

Thanks

I felt that way too, about 3 years ago when I got back into astronomy. It's well worth persevering with it though as it can come in useful for finding things when the star hop is long. Most setting circles are too small to be terribly useful most of the time, but they have their moments.

In my case they helped me find M81 from my light polluted skies in London. It took a few nights practising it, but once you've worked out what you're doing and you can do it fluidly, it will just click.

[Phil Fargaze]

If you are setting up every time as opposed to keeping the mount in an observatory it can help to mark the position of the tripod feet once that accurate polar alignment is achieved.

[JimD]

Great success with this last night - My brother in law was round last night (he's been gagging to have a look through my scope ever since he found out I'd bought one ), and we couldn't wait for dark, so were having a look at the moon.

I wondered if it might be possible to see Jupiter even though it wasn't visible to the naked eye (it was about 4.30 and about an hour from sunset). Bring on the setting circles - checked on Stellarium for the RA of the moon (about 4hrs) and Jupiter (about 2hrs) and set the RA setting circle accordingly. Diallied in the declination for Jupiter (about 20) and swung back through 2 hrs of RA - Jupiter appeared in the WA eyepiece with just a tiny bit of fiddling with RA.

I had a bit of problem with the RA circle sticking, so it took a couple of goes, but I did it!