HEQ5 Pro polarscope.

[wxsatuser]

Quick question about the HEQ5 polarscope.

Have had a go at centering the reticule.

I can get the circle to follow a point, the end of a TV aerial about 50 feet away, but

is it normal for the view to appear to rotate off centre?

[jambouk]

You want the aerial to be centred smack bang in the middle of the polar scope reticule, under the cross hairs at the very centre, and be there when the RA axis has been rotated through 180 degrees. You don't want to have the aerial centred on any bit of the circle, that is where you will place polaris eventually and the purpose is that polaris will then be off centre so it positions the true north celestial pole in the centre of the polar scope (under the cross hairs again).

I've noticed whatever i've centred in the polar scope often wobbles a bit as the RA turns even if it is bang on centre at 0 degrees and 180 degrees.

James

[brantuk]

Yes - the pole star isn't exactly in line with the Earths axis - it describes a very small orbit in the sky. So once you get the pole star to follow  around the line of the large circle in your retcule, then all the stars rotate about the center of the mount axis - as does the pole star which is slightly off center.

[wxsatuser]

Thanks guys.

I followed this video.....from about 4mins onwards.

Everything aligns as the video but just the view thru the scope moves off centre as RA is rotated.

[jambouk]

When you are centreing the polar scope reticule, centre the thing you are looking at (eg the aerial) where the point of the red arrow is.

Then when you go to polar align, the handset (or your tables) will give you a time once you know your location, time, date etc, and this is the time the small circle (blue arrow) needs to be positioned around the larger circle. So if the handset says polaris time 6 o'clock, then your little circle is in the right position in this image, if the handset says 12 o'clock, then you need to turn the RA axis 180 degrees to get the little circle in the 12 o'clock position. Then you will use just the alt and az adjusters to get Polaris to sit bang in the middle of the little (blue arrow) circle. At that point, the North Celestial Pole will be bang in the middle of the cross hairs (red arrow) and you will be polar aligned.

I hope that helps.

James

[wxsatuser]

Thats fine James, no problem with that.......when I get to that stage, next clear night.

I assume the wobble of the view is just the way the polarscopes are fitted to the mount, some better than others.

[jambouk]

I don't know what causes the wobble, I suspect it could arise from a number of places:

Inaccurate reticule (painted to etched or however they mark it).

Slightly offset reticule in one plane and not the other.

Polar scope not fitting the hole up the mount perfectly, or imperfectly manufactured polar scope.

Laxity in the RA axis of the mount....

But I've got it, and my mate has got it, so I don't think it is uncommon, and if you do your polar alignment carefully, you should be able to get reasonable polar alignment, certainly good enough for visual and good GOTO, and probably for some short exposure imaging (1-5 minutes depending on how good it is). I suspect if you are after imaging for 5 minutes or more, you will need to do much better polar alignment (drift aligning etc) but even then you will start to stray into the territory of periodic errors, which again one can reduce with the handset (I've not tried yet but want to). Alternatively you need to guide, but that still requires, I believe, reasonable polar alignment.

Oh how it would be nice to have an observatory and permanent set up

James

[wxsatuser]

Thanks James.

Just wanted to make sure there was no real problem, if others have it, then I will not worry.

Hopefully I will be guiding.

My obsy is nearly finished, just putting lining in, then the fun begins.