18 replies to this topic

[Orion68]

I did an experiment tonight - using the Questar tracking motor while the Q was mounted in Alt-Az orientation.The mount was an Losmandy AZ8 with a spare riser section attached to the tripod. Then, the scope was mounted with the base resting flat on the top of the riser. (no wedge).

 

My thought was that with the tracking motor running I would only need to adjust the altitude slow motion control to keep an object centered in the field of view. This would be better than having to constantly adjust two separate slow motion controls.

 

Did it work. Yes and no. It was much improved but I still had to adjust both azimuth and altitude slow motion controls somewhat. However, the adjustment needed was much less than what would have been needed without the tracking motor running. I tracked two objects: Mars and Jupiter.

 

Mars - was 20-30 degrees above the Eastern horizon. With the tracking motor on, I still needed to use both slow motion controls to keep the object centered. The adjustment needed in altitude was "more than" needed in azimuth. Also, the azimuth adjustment was to go backward, as if the motor was advancing the scope too quickly in azimuth. Even though adjustments were still needed, it was noticeably less than if the tracking motor had been off.

 

Jupiter - was approaching the Meridian. Again, I needed to adjust with the slow motion controls in both azimuth and altitude. But, in this case, more adjustment was needed in azimuth than in altitude - and the azimuth adjustments were needed in order to speed up the tracing - just the opposite of what I needed to do for Mars. I found this curious and the opposite of what I expected.

 

Overall, using the tracking motor made for a more enjoyable viewing session. However, my thought that the azimuth slow motion control could be ignored due to the tracking motor running was not correct and that was disappointing. I need to work out the Geometry to understand why azimuth adjustments were still needed.

 

Feel free to offer any thoughts about the mechanics involved.

 

Edited by Orion68, 11 February 2025 - 12:23 AM.

[Siderius]

If automatic tracking with an Alt-Az mount were easy, or even doable back in the day, Questar would have done it.

It takes a computerized controller to track a celestial target in Alt-Az, and the altitude and azimuth tracking commands are different for each celestial target. You *must* have a controller you can tell what you want to look at. It's not so much a matter of go-to as it is the rate of drive for each axis over time once you've centered the target.

Your experiment went about as expected: better than nothing, but still having to tweak both axes, lousy azimuth tracking on high altitude targets.

[Loren Gibson]

I had pondered doing a similar thing with my Questar Standard when mounted on the Tristand for low declination targets in the south. It would be easy to unclamp the altitude motion in the Tristand and tilt the polar axis high enough to view the low-declination object, then adjust the altitude of the mount head back to the normal position when finished. I never tried doing this.

 

Loren

[jack s]

If you used a vaiable speed drive correcter you could periodicaly adjust the drive speed to compensate. Speeding up slightly or slowing down slightly. It still would not be perfect but you would have to adjust RA less. I have never done this (yet) but I think pushing a button would be less annoying then reaching for a knob.

 

jack

Edited by jack s, 11 February 2025 - 12:04 PM.

[Orion68]

I had pondered doing a similar thing with my Questar Standard when mounted on the Tristand for low declination targets in the south. It would be easy to unclamp the altitude motion in the Tristand and tilt the polar axis high enough to view the low-declination object, then adjust the altitude of the mount head back to the normal position when finished. I never tried doing this.

 

Loren

I would encourage you to give it a try and see if it provides any benefit - I think it will.

 

With your Tri-Stand I am sure you will have no problem plugging in the power cord. I use my AZ8 tripod and a riser section to mount the scope and had to do some modifications to allow access to the power jack on the bottom of the scope. The acorn nuts in the picture can be screwed up or down to level the scope.

 

Envious of your Tri-Stand, I've wanted one for years.

 

[Orion68]

If you used a vaiable speed drive correcter you could periodicaly adjust the drive speed to compensate. Speeding up slightly or slowing down slightly. It still would not be perfect but you would have to adjust RA less. I have never done this (yet) but I think pushing a button would be less annoying then reaching for a knob.

 

jack

I totally agree with you - it is annoying having to reach around to the front of the Q to access the Azimuth slow motion control.

 

The drive corrector sounds very interesting. If you decide to work on it, good luck and I look forward to hearing about your results.

[NC Startrekker]

Somewhere among the many topics and threads on this forum are instructions for swapping the position of the azimuth slow motion control knob from its customary position in front of the forks to behind the forks below the control box. I will endeavor to dig them up but would welcome anyone who knows where they are off hand to chime in in the meantime. 

[jack s]

Just rotating the optical tube through the forks will do it. After removing the eyepice holder it will pass through the forks but it will be upside down so you then need to then rotate the optical tube on it own axis 180 degrees to put the eyepiece back on top.

The down side of this, is it reverses the position of the declination lock and adjuster  to opposite sides.

 

The other way is to unbolt both fork arms from the tuntable, lift arms and optical tube up, rotate the turntable 180 degrees and then reatatch the fork arms to the turntable, This retains the original positions of the declination controls.

With the right wrench this can be done while leaving the optical tube atached to the arms.

 

jack

Edited by jack s, 12 February 2025 - 02:04 AM.

[Retired Ipswich]

Could Orion68 tell us their latitude as I suspect this will go a long way to explaining the situation.

 

If you observe from either the North or South Pole on the Earth your drive would only need to be in azimuth (and the telescope sitting upright). Conversely if you observe from the Earth’s Equator your drive would only need to be in altitude (and the telescope sitting on its side).

 

The choice of object is also interesting. Jupiter hardly moves against the background taking 11.86 years to make a complete circuit of the sky. Whereas Mars takes 2.14 years and strongly retrogrades around the time of opposition (most recently 16 January 2025).

 

As far as swapping the position of the RA knob is concerned all that is required is a manoeuvre equivalent to a German Equatorial meridian flip (which I prefer to call a ‘double reversal’). This is a 180 degree reversal on both the R.A. and Dec axis. Unfortunately this leaves the telescope upside down (not noticeable with a refractor). With a Questar this is simply cured by turning the control box upside down (or downside up?).

Edited by Retired Ipswich, 12 February 2025 - 12:20 PM.

[Orion68]

I am at just over 44 degrees North. (Eugene, Oregon)

[Retired Ipswich]

I am at just over 44 degrees North. (Eugene, Oregon)

So the celestial equator intersects your horizon (due East or West) at about 45 degrees? Due South the sky will move parallel to your horizon.

[Orion68]

Ipswich, That sounds right. Out of curiosity, I'm going to try one more experiment as soon as the sky clears.

 

Since a star viewed near the Eastern horizon moved in azimuth slower than  the tracking and a star near the Meridian moved faster than the tracking - I'm going to track a star that is half way between the Eastern horizon and the Meridian to see if the tracking at that point in the sky is more accurate.

[Toddeo]

"Since a star viewed near the Eastern horizon moved in azimuth slower than  the tracking and a star near the Meridian moved faster than the tracking - I'm going to track a star that is half way between the Eastern horizon and the Meridian to see if the tracking at that point in the sky is more accurate."

 

               Why bother, what's the point? Are you only going to use the set up when viewing objects right in the middle?

[Orion68]

Of course, you are right. It's not practical to only view objects at 45 degree elevation, nor do I intend to. This is just to satisfy my curiosity and maybe learn a little more about the difference between the two coordinate systems. To me this is fun stuff and I have time to do it, but I can understand that it might not be worthwhile for everybody.

[Toddeo]

[Jim Curry]

I routinely observe the moon in aa, setting the scope base flat on a table. Because I'm scanning the terminator I'm using mostly altitude with occasional tweaking of AZ controls but I don't find it an issue.  

Edited by Jim Curry, 14 February 2025 - 08:24 PM.

[Spikey131]

If you have the right table, setting the Questar up on the legs is easy.  You don’t need very precise alignment to get decent tracking this way.

 

 

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[Orion68]

A table, even a picnic table, is a great way to view with the Questar. Maybe even the best way.

[Orion68]

I added an extra Azimuth setting circle, that will remain static with the tracking on. This will make it possible to use tracking in Alt-Az mode and still retain a usable Azimuth setting circle for finding objects.

 

Just need some decent weather to test everything out and see if it proves to be useful. If not, it was still fun experimenting with a new way to use the Q.