Simple Az Setting Circle and Wixey on a SkyTee2

[chiltonstar]

Posted by request!

After some rather annoying evenings using my normal star hopping method, frustrated because of the 70-80% cloud cover so I had very few reference points to start from, I decided to construct a simple Az setting circle, and add a Wixey inclinometer so that I could get accurate enough alt-az settings to get to the right part of the sky, even when partly clouded!

The az scale was an image of a 360 degree protractor (using macro lens to retain linearity) enlarged to ca. 200mm diameter, printed on thin card and then laminated onto 1mm high-density waxed card (aka pizza base) and covered with plastic stick-on film. To get it to be relatively stiff to turn, I added a disk of high density foam on it to grip the 100mm non-rotating base of the Skytee. The pointer is a miniature laser pointer, with a disc of blue acetate over it to reduce the intensity. It is mounted on a small aluminium bracket to avoid fouling the slomo knob, and the angle can be adjusted up or down to centre on a larger or smaller scale. It is fastened to the Skytee on a flat surface using velcro.

Alt uses a normal Wixey with a magnetic base, clamped in the top mounting position on a ferromagnetic plate.

Modus operandi: level base, find a star somewhere in the right area of sky and centre on it. Zero the Wixey on a level surface and clamp it in position. Using Skysafari (settings adjusted to horizon coordinates, ie alt-az) read the az value and set the scale to that by rotation. Loosen the mount clamp for the top mount and move the Wixey and clamp in the alt axis until it reads the right value for the star (again, from SkySafari) and clamp. Then just "push-to" the right coordinates for the target!

Accuracy and repeatability? I've managed to use it twice so far (alas, the climate), both times finding Neptune in a partly clouded sky, once using the Moon to set up and the second time using Vega. On both occasions, Neptune was in the finder view (9x50 RACI) about 0.5 degrees from the centre.

To increase the readability of the az scale, I'm working on printing out a large enough disc to lay on the ground, just outside the tripod legs.

Some pics below....

 

Edited August 18, 2019 by chiltonstar

[jock1958]

Thanks for that and an excellent idea for locating difficult to locate targets like Neptune. 

Like you I’ve wasted untold hours trying to find objects in the mixed weather we endure in the UK! 

[Mark at Beaufort]

That is really good. I tried to produce a similar arrangement for my Skywatcher Heritage 130P. Whereas the Alt scale works reasonable well the Azimuth scale is fixed so I only get a rough idea of the degree position before moving the scope.Photos attached.

[chiltonstar]

1 hour ago, Mark at Beaufort said:

That is really good. I tried to produce a similar arrangement for my Skywatcher Heritage 130P. Whereas the Alt scale works reasonable well the Azimuth scale is fixed so I only get a rough idea of the degree position before moving the scope.Photos attached.

A good arrangement - you're circle cutting skills are obviously better than mine!. I use the setting circles on my EQ mount (Vixen SP), but to be honest, it's not that convenient with the 180 Mak due to lack of rings - I tend to end up in some very odd positions trying to observe, and for this reason, an Alt Az arrangement is easier (on the neck!).

Once the az circle is set to true geographic north, it remains fixed and the calculation of current alt and az is done by Skysafari - so convenient, unlike EQ setting circles where the RA scale has to be adjusted all the time.

I wanted an accuracy of <1 degree because of the limited FoV of the Mak, and this seems to work.

Chris

[jock1958]

My version of @chiltonstarexcellent idea. Bullseye spirit level from Homebase £2.60, digital level from Axminster £19.00 ish, aluminium pointer and laminated paper scale free. To give me more room behind the scale pointer decided to remove the forward Az slo mo wheel and like you attached pointer with Velcro for easy removal when not required. 

Edited September 20, 2019 by jock1958

[jcj380]

Before I put encoders on my Twilight 1, I used the same set-up.  I purchased a printed round angle gauge for the AZ though and glued it onto a thin round piece of craftwood.  It worked pretty well as long as the mount was level and I zero adjusted the Wixey.  Much less expensive than encoders!