Issues with Asiair Plus and NEQ6 mount.

philippe barraud

When I start a goto, the slew is perfect but the plate-solve always fails, although the object is perfectly centered. I use a newtonian telescope with a 800mm focale length.
Guiding is impossible because Asiair fails to calibrate the mount: it makes huge movements, and thus the star is lost.
In other words, with this mount connected with USB, imaging is impossible with Asiair, so I have to use a PC and MaximDL.
It is very strange and disappointing because with my Celestron CGEM, everithing works fine.
Philippe

w7ay

@philippe barraud#54569 the slew is perfect but the plate-solve always fails

Plate Solve is not related to your mount, but to your telescope and camera.

What plate solve does is to take an image of the sky. Before the film days, this is making a glass photographic plate at the focus of a telescope; so the name "plate" has stuck with astronomers).

Asterisms (pattern of stars) are then generated for the stars that are seen in the FOV of the plate. These asterisms are then compared against a database of thousands of asterisms. Once the asterims on the plate match the asterisms in the database, the plate solve process can then locate the center of the FOV of the plate.

Think of it as a smart pattern matching process.

To get an asterisms of stars, you need to make sure there are enough stars available. Depending on the region of the sky, 25 stars may be sufficient, but about 100 detectable stars are prefereable.

The stars also need to look like points of light. Very defocus stars will be rejected.

You will need to carefully focus the telescope. And then set the exposure time to get sufficient stars.

With the ASIAIR, there is a Detect Stars in the Tools Menu icon of the Preview window (right under the Plate Solve menu icon). Take a preview image. Then tap on Detect Stars. That will tell you how many stars are detected and what the star sizes are. If the average star size is greater than 4 or 5, you need to focus better (unless you are very over-sampled -- in which case, plate solve will not work anyway).

Once you have enough stars in your FOV, to match the database of asterisms, your plate scale is important (how many arc seconds per pixel, which depends on the camer and the focal length of the telescope). ASIAIR knows the pixel size of your camera, so you just need to give it an accurate focal length to use. If you are unsure of the actual focal length of your telescope, set it to zero (yes, zero), and ASIAIR will make a more exhaustive search. It will take longer to solve when focal length is set to zero.

If Detect Star tool can see many stars, then check the focal length that you give to ASIAIR. Set it to zero if this is the first time you use ASIAIR, and do a plate solve. ASIAIR will fill in the correct number after a successul plate solve.

The same holds for the focal length of your guide scope. That needs to be correct too, otherwise, the autoguide steps will be completely wrong.

Chen

philippe barraud

Thank you Chen for these quite clear explainations.
For the plate solve, it was my mistake: I forgot to change the focal length after changing the telescope. From 250mm to 800mm, it makes quite a difference ! Now it works in seconds.
Regarding guiding, I probably have the same issue, since the autoguiding steps are far too large. I had set the scope focal length at 180mm, or in reality it is 320mm. I will see tonight if it works.
Philippe

philippe barraud

Unfortunately, I could not solve the guiding problem. The focal length was right (240mm), but calibration failed. So I tried different focal lengths, and it did not change anything. Whatever be the focal lenght, the calibration steps are far too large, so that the guide star is inevitably lost out of the green square. Changing the other settings doesn't give any result either.
How can I do to force shorter calibration steps ?
I finally gave up guiding with ASIAR and used PHD2 on a computer, and it worked.

w7ay

@philippe barraud#54659 Whatever be the focal lenght, the calibration steps are far too large, so that the guide star is inevitably lost out of the green square.

Philippe,

With the RA direction (East and West calibrations), you can also lose a star if tracking is turned off. So, be sure to monitor that too while you are debugging. There have been reports of unexplainable loss of tracking with some mounts.

How can I do to force shorter calibration steps ?

Calibration Steps (pulse duration) is in the Guide Settings window. Or, you can also reduce the guide rate to reduce the movement. But, if your problem is caused by tracking being turned off, then neither of these will help.

I finally gave up guiding with ASIAR and used PHD2 on a computer, and it worked.

The full PHD2 is the best solution; you have fine controls that have been removed from ASIAIR's autoguiding, and the software is stable. You just need to remember to turn it off before issuing a GOTO from ASIAIR.

And if you are using a computer (assuming it is Windows) to run PHD2, you might as well switch to using N.I.N.A. for everything else too.

Chen