Dob setting circles

[Gazabone]

Just wondering if anyone else has tried the mod featured in the July Sky @ Night mag - adding altaz setting circles.

I completed mine today by eventually adding adjustable feet but did try it out several nights ago (levelling the mount by propping it up) but it wasn't terribly successful. I'm very at home with EQ setting circles (getting my targets in the ep first time at least 95% of the time with a 2038 focal length scope). I should say that on my Dob, I'm using a 24mm 68 deg ep with a 1200mm Dob so magnification is 50X so my field of view is 1.36 degrees.

I'll try again using the altaz coordinates from Stellarium now that I have it set not to skip to a time when it's dark but I think I had it set correctly the other night. I set the azimuth circle to Polaris using Stellarium but, to experiment I tried using the setting circle/inclinometer to find Albirio but was about 10-15 degrees out (the altitude was pretty good, the problem seems to be with azimuth).

On the upside I did find a non-battery inclinometer for under £5 on Amazon (might upgrade this though if I think I can get it all to work).

Anyway, the point of this post is to hear of anyone's experience of using altaz coordinates to find stuff.

Happy viewing all

[laudropb]

Hi. I was thinking of trying this myself. Can I ask, where did you get the adjustable feet ?

[happy-kat]

When I used mine if the base is absolutely not level then the altz was very messed up on accuracy

[Gazabone]

Hi. I was thinking of trying this myself. Can I ask, where did you get the adjustable feet ?

Hi laudropb, 

I got them from B&Q yesterday, about £7.50.  I'm sorry I don't have a product code but there were 2 possibilities in stock locally.  There are other versions available on Amazon; try searching (or asking shop staff) for either Plinth Feet or Adjustable Feet.  They are intended to support kitchen cabinets etc so reasonably robust as far as weight support is concerned but I don't want to test it out for heavy sideways knocks!.

[Gazabone]

Thanks happy-kay,

I suspected that might be a bit of a problem but I guess the higher the object is in the sky, the bigger the error.  I checked mine out yesterday and although I levelled the base well, as I rotated the base it went a bit off level (by about 1.5º to 2º) so that isn't going to help!  Still worth persevering with as I really struggle with star hopping!

[Lowjiber]

I have azimuth circles on every az/alt mount I own, and use them a lot.  Below are three that I've built.  The first is on a Twilight II dual az/alt mount.  Number two is one on a Twilight I az/alt mount, and the last is one on a new Dob mount that I just posted here...

http://stargazerslounge.com/topic/247660-diy-dob-mount-for-f5-150mm-newt/

Not bragging, but I'm pretty darn good with 'em.  Here are a couple of thoughts...

The mount has to be as level as possible for the circle to maintain accuracy throughout the entire range (360^o )

Stellarium is the key to success.  I always run the time ahead about two minutes to allow me time to place the Stellarium data on the circle and inclinometer and get my eyepiece/chair ready to observe.

The comments above are obvious, but here comes something that can really make your circle deadly...

As most know, Polaris is not the North Celestial Pole (NCP).  It describes a circumpolar route with a radius of 0.7,^o around the NGC.  So, depending upon where in that "orbit" Polaris is located on a given night your circle and inclinometer (I use a Wixey) data can be off as much as 0.7^o.

I'm not going into how to set-up and level the mount, but when you get ready to make the initial adjustment of your pointer... do the following....

Center Polaris in your eyepiece.  Get the current (plus the two minutes mentioned above) az/alt data from Stellarium.  Set the pointer to the exact azimuth that Stellarium gives for Polaris that night... it may be as much as +/- 0.7^o as mentioned above.

Next, check your inclinometer.  Since you stil have Polaris in the eyepiece, it should read the same as the current Stellarium reading.  If it does not, it likely didn't get zeroed properly during the set-up phase.  Not to worry.  Just make a mental note of the difference plus-or-minus between the Wixey and Stellarium, and apply that small difference to the target's altitude during the session.

Clear Skies 

[Gazabone]

I have azimuth circles on every az/alt mount I own, and use them a lot. Below are three that I've built. The first is on a Twilight II dual az/alt mount. Number two is one on a Twilight I az/alt mount, and the last is one on a new Dob mount that I just posted here...

http://stargazerslounge.com/topic/247660-diy-dob-mount-for-f5-150mm-newt/

Not bragging, but I'm pretty darn good with 'em. Here are a couple of thoughts...

The mount has to be as level as possible for the circle to maintain accuracy throughout the entire range (360^o )

Stellarium is the key to success. I always run the time ahead about two minutes to allow me time to place the Stellarium data on the circle and inclinometer and get my eyepiece/chair ready to observe.

The comments above are obvious, but here comes something that can really make your circle deadly...

As most know, Polaris is not the North Celestial Pole (NCP). It describes a circumpolar route with a radius of 0.7,^o around the NGC. So, depending upon where in that "orbit" Polaris is located on a given night your circle and inclinometer (I use a Wixey) data can be off as much as 0.7^o.

I'm not going into how to set-up and level the mount, but when you get ready to make the initial adjustment of your pointer... do the following....

Center Polaris in your eyepiece. Get the current (plus the two minutes mentioned above) az/alt data from Stellarium. Set the pointer to the exact azimuth that Stellarium gives for Polaris that night... it may be as much as +/- 0.7^o as mentioned above.

Next, check your inclinometer. Since you stil have Polaris in the eyepiece, it should read the same as the current Stellarium reading. If it does not, it likely didn't get zeroed properly during the set-up phase. Not to worry. Just make a mental note of the difference plus-or-minus between the Wixey and Stellarium, and apply that small difference to the target's altitude during the session.

Clear Skies

Many thanks for that, good idea to run Stellarium a couple of minutes fast. It's heartening to hear from someone that they work well so well worth persevering with.

Clear skies to you too.

[steppenwolf]

I am guilty of writing the article in S & N  I'm afraid :grin:  I bought the adjustable feet from  'The Tool Station'.

I find that mine works very well with my 10" Dob and 17mm eyepiece but please remember that the circles are designed to work with the original S & N project and the mounting of the circle assumes that the azimuth bearing is a fixed 'post' and that the rocker box revolves around it.

[jonnymac]

I have been looking at making a few upgrades to my dobsonion telescope and I was wondering if setting circules would still work with something like this  http://equatorial-platforms-uk.co.uk  .  I'd like to try a little astrophotography and some astro- sketching and this along with setting circles and a inclinometer would make evening much more enjoyable.

[Gazabone]

Many thanks for all the responses to this post, the mod was finished on Sunday and managed to get some clear skies tonight. The good news is, it works! I was finding targets I've only ever found before either with a goto scope or setting circles on an eq mount.

I found that I had to recalibrate the azimuth circle for different parts of the sky but that's no hardship as I have to do that using eq setting circles (and, as far as my Dob is concerned, probably an indication of how cackhanded I am with anything practical).

I think I might invest in a digital inclimoniter as the analogue version I got very cheaply takes a while to settle down after every move!

However, all in all, it's added a new dimension to my observing and I'm a happy boy again.

[Gazabone]

I am guilty of writing the article in S & N  I'm afraid :grin:  I bought the adjustable feet from  'The Tool Station'.

I find that mine works very well with my 10" Dob and 17mm eyepiece but please remember that the circles are designed to work with the original S & N project and the mounting of the circle assumes that the azimuth bearing is a fixed 'post' and that the rocker box revolves around it.

Don't be afraid of writing the article in S@N, if it was me, I would be immensely proud of it. If nobody else thanks you for doing it, please accept a big thanks from me. I had some fun doing the mod and even more fun using the scope. Happy viewing

[steppenwolf]

If nobody else thanks you for doing it, please accept a big thanks from me.

I'm really pleased that you have made good use of the article - I really enjoyed making mine and it certainly does make it much easier to find fainter objects. Mine remains pretty accurate providing I ensure that the rocker box is accurately level before and after calibration.