On Dec 27, 2024, at 8:01?AM, K9RX - Gary via groups.io <amateurK9RX@...> wrote:

?

Gabriel,

Good morning sir.?

Please keep in mind tracking is indeed updated continuously and very accurately. However the actual alignment accuracy is the overall determining factor of how well that tracking applies to the real sky! There are mount errors - and you will have errors in alignment... both of these will conspire to make tracking less than ideal.?

I've not heard of anyone reporting a temperature component to tracking accuracy and that is over 2+ decades and nearly 2400 systems world wide. My strong suspicion would be that indeed it is simply alignment and mount errors that you are seeing.?

I would say that I would not use any form of pseudo closed loop tracking. The ServoCAT combined with the Argo Navis have a full closed loop tracking system that is extremely accurate to the alignment. This means it can run all night long with zero accumulated error in the track positions. But as mentioned above the alignment results are the key - if they're not accurate then any closed loop system is going to track to THAT 'model' and not the actual sky motion. So one does not want to use AutoLOCK with ServoCAT/AN while doing imaging for this reason. It is wonderful for visual use? and it is highly recommended when doing so.?

There is no closed loop equivalent with the Nexus since the system is proprietary to the Argo Navis and ServoCAT per agreement at the time of development. So most definitely do not use it there as well. UNLESS Serge is closing the loop through platesolving ...?

Last you have mentioned long exposures multiple times... but field rotation is going to be your nemesis here... unless you get a rotator (the Wanderer looks good... ) I don't think longer exposures - unless well placed in the sky to reduce the impact of field rotation, is recommended.?

I'll repeat what I said earlier on. I'd use very short exposures and filter on FWHM (SharpCap will do this on the fly, a very nice feature). When I say short I mean really short. There's one imager that used a 12" and did 10's of thousands exposures of 0.1 seconds and had incredible results! I'd stick at no more than 2 seconds personally.?

Gary Myers

------ Original Message ------

From "Gabriel Wiklund via groups.io" <gabriel.wiklundholeshot@...>

To [email protected]

Date 12/27/2024 5:53:51 AM

Subject [ServoCAT] Interesting Alt/Az driver rate calculators

Hi all,

?

In the first calculator (from Mel Bartels who pherhaps many of you already are familiar with) this question is asked:

"How long can an altazimuth telescope track with constant rates of speed in the azimuth and altitude axis?

An altazimuth telescope's drive rates vary continuously, more so in certain parts of the sky. Further, the rate of change in the drive rates changes. If the drive rates are left unchanged, eventually the tracking error will build to an unacceptable level. This calculator illustrates tracking errors. The error threshold and the time of constant drive rates can be varied."

?

?

This may pherhaps explain why my tracking is not as accurate as in the beginning of an evening, since i so far have noticed this at high altitudes. (i have now noticed this in both azimuth and alititude axis). Correct me if i am wrong: Without Astrolock the calculated drive rate is accurate for the objects location in the sky at that very moment, which makes sense for a visual system not intended to track the same object within the same pixels for hours and hours. When looking at the screen the drive rates are fixed except when Astrolock is engaged do the numbers change. So in other words, a few hours later the calculated drive rate would be slightly different. Last night i switched of Nexus, pointed at Polaris and from there performed the 2-star alignment again. Slewed back to the object and now tracking was like in the begining of the evening again, i did after a while notice some altitude drift but I think I recentered without taking out the backlash properly or something. Highly unscientific test with too many variables pherhaps.??

?

Next calculator:?

?

?

"This calculator outputs the altazimuth coordinates along with the tracking rates and the change in the tracking rate. Use the change in tracking rates to determine when an update to the tracking rates is required. There are no corrections applied to the coordinates such as precession and refraction."

?

Interesting stuff! I am fascinated by alt/az tracking theory!

?

Gabriel?

?

?

?

?

?

On Dec 24, 2024, at 4:30?AM, Gabriel Wiklund via groups.io <gabriel.wiklundholeshot@...> wrote:

?

First night out yesterday through Infrastructure mode and the Meade generic driver.

?

Night and day difference. The 2-star align was done inside the house. Automatic slew and center worked, center after drift worked, and the speed of the manual slew is just right to center manually as well. Center after drift was set to 2.2 arcminutes if I remember correctly and that drift was detected after ~ 1 hour and 20 minutes. The object was centered well enough after a few tries without my intervention.

?

I have set Platesolving accuracy to 1.8 arcminutes and it worked quite well except a few times it took a while. 2.2 arc minutes would probably be just right to not get stuck on certain objects. I would probably increase center after drift to 3 arc minutes.

?

I could do all this by the fireplace inside (-15°C outside).

?

On to another topic:

Generally as a typical night goes by it seems that tracking accuracy decreases. I wonder if re-doing the 2-star alignment would solve this (adding sync points does not). Pointing accuracy does not decrease. Mickey have you experienced this and found a way to fix it?

?

Gabriel?