dseaman6745T Another question relates to the backlash settings in the mount (AVX).

That question should probably be directed to the mount manufacturer. With what I know, ASIAIR itself does not do any backlash compensation. It simply sends short and slow slew commands to the mount.

are the settings for RA and Dec duration important for maximizing efficiency?

Not especially. But if you are well polar aligned, you can reduce the max Declination pulse duration and avoid correcting wind gusts. A perfectly polar aligned mount should not need any declination adjustment -- other than that, the two things that cause a star to move in declination is an error in estimating the centroid of the star (i.e., error caused by "seeing") and something like a wind gust. Or a racoon nudging your tripod leg.

the calibration should be done with the scope pointed towards the meridian

Calibration should be done near the celestial equator. If you do it far away from the equator, you may find that the RA and Declination corrections (the red and blue vectors in the ASIAIR guide info window) are not orthogonal.

The only reason you do it near the Meridian is to avoid atmostpheric refraction and atmospheric turbulence (going through a thicker layer of air). Neither should be a big deal if you are within 40 or 50 degrees of the Meridian.

do you need to recalibrate since the guiding scope is now using different stars for guiding?

As long as there is no differential flexure between what the guide camera sees and what the main camera sees, a delta RA and delta declination should be the same.

Remember that field rotation will be referenced to the location of the guide star (or the weighted average of guide stars in the multi-centroid case). The field will not be rotating around the center of your main camera frame. But, if you keep exposures shorter than say 180 seconds, you should not encounter a problem.

Chen

galactique I calculate my RA and DEC durations need to be a little less than 600ms using 0.5 sidereal guide rate so I will
test that next time out, instead of currently 2000ms

The number that I gave earlier was for the Calibration steps, Mel.

I.e., it is based on finishing the 25 pixel movement that PHD2 wants in 12 or so steps. Very precise mounts will need fewer steps, so the Calibration pulses can be longer (i.e., finishes in 5 or 6 steps). Poor mounts may need even more steps (so even shorter Calibration pulse durations), so that the measurement errors are averaged out.

Calibration has to do with estimating how much the mount moves and in what direction. This produces the red and blue vectors that are drawn in the same Calibration Info window. The more steps it takes, the more point you can use to estimate the vector's direction and length.

I typically rotate my guide camera angle so that one of the sensor axes is parallel to the RA (or declination) axis. What this does is to make the red and blue vectors also line up with the two gray axis lines. This is not strictly needed, since PHD2 will figure out the rotation. But it does reduce the measurement noise a tad. I simply glue a small bubble level to all of my guide cameras -- just need to be within a degree or two for the sine and cosine values to be mostly decoupled.

The max RA and max declination pulse lengths as a whole different story. They are there primarily to limit the error in movement when there is a measurement error of where the centroids are (and also to avoid correcting for wind gusts and sudden large atmospheric turbulence, etc). If you want to be OCD about it, you need to know the first derivative of your periodic error curve. You want the max value to be at least long enough to correct for the worse case star movement in the time between frames of the guide cameras. I.e., you want the max pulse to be longer than the time a star along the periodic error curve has moved by 0.5 arc seconds (or whatever criteria you use) between the frame times. The derivative of the periodic error curve for some mounts like the one the original poster and I use are very sinusoidal, so you only need to know the peak periodic error and its period (in time) -- i.e., derivative of sin(kt) is equal to k.cos(kt). This is why you can pretty much also guess how the ZWO mount would need by just looking at the curve that ZWO had published. Any bumps in the curve will need a faster frame rate to correct.

Chen

galactique OAG guiding I get about 580ms: so this is the Calibration Step ?

Just calculate the Calibration Steps to get about 10 to 12 steps (in your case) for PHD2. Check the PHD2 log to see how many steps it took to get 25 pixels worth of movement. You can also just watch it while it is calibrating. Notice that it will move up to 25 pixels and then reverses direction.

BTW, this is why you also want to calibrate near the celestial equator. If you try to calibrate near the poles, it could take half a day's worth of steps to move a star by 25 pixels.

If you find that it takes more than 12 steps to complete 25 pixels, just increase the Calibration step. And vice versa.

Max RA and declination duration are exactly that, the maximum that PHD2 will correct per guide frame. If your camera's FPS is high, you can use a shorter max duration. If your FPS is low (like 0.5 frames per second), you will need to use a longer duration -- but ultimately, it depends on the first derivative of your periodic error curve.

The max durations simply limits how much PHD2 is permitted to apply per guide frame. If you set it too low to match your mount, you will not be able to keep up with the mount errors.

You can set the max pulse duration to 10 seconds, if you like -- this will handle even horrible periodiuc error curves. But with a max value that is unneccessarily large, something like a wind gust or centroid measurement error can cause auto guiding to make very wild back and forth swings, especially when you set a high feedback loop gain (shown as RA and declination "aggr" percentages).

You cannot use someone else's numbers. That is why I ROTFLMAO each time some idiot on Facebook (redundant phrase) asks for someone else's number. It depends on your guide pixel scale, your mount's periodic error and backlash, seeing conditions, etc.

Just remember that PHD2 goes by pixels units in the camera x- and y- directions, while the mount (and guide pulse) works in units of arc-seconds, not pixels, and in the Hour Angle and Declination directions, not camera x and y directions. Once you grok that, it will all come together.

Chen

dseaman6745T How do you calibrate with the scope in one position and then move the scope to the target and use a different area for guiding?

(1) Turn guiding off.

(2) Slew the mount to some location close to the Celestial Equator that is on the same pier side as your intended target. The closer you are to the meridian, the less influence you will get from atmospheric refraction. If the Celestial Equator is too low for you (e.g., you live in Anchorage), use somthing a bit higher in altitude.

(3) Calibrate the guiding.

(4) Turn guiding off.

(5) GOTO your target. The mount should not do a meridian flip; if it did, step (2) was not done correctly.

(6) Turn on guiding.

I am still needing 25-30 steps for calibrating the West/East component even when the calibration is done near the celestial equator.

As I posted earlier, if you want fewer calibration steps, increase the Calibration step size. They have a 1-1 inverse relationship. Too many steps is not really a problem; just a waste of time -- and not a horrible waste either since each of the shorter step takes a shorter time. 25 steps is perfecty fine. 12 steps is sufficient. 6 steps is probably a little too low unless you have a premium mount. 1 step is probably enough if you are calibrating the Hale Telescope.

Chen