5 replies to this topic

[Ike582]

I'm imaging M33 tonight in the suburbs of Chicago.  I've got clear Bortle 6 skies, and M33 is very high in the sky at the moment.  I've been imaging for two hours, but my image timer shows only 33 minutes.  Every minute or so I get a "Stack Failed - star trails" alert.  Is this normal or am I doing something wrong?  Anything I can do to improve my hit rate?

 

Thanks

Edited by Ike582, 14 December 2023 - 10:54 PM.

[maniack]

Wait for the object to be further away from the zenith. The closer the object is to the zenith the harder it is to track on an alt-az system.

[Another_Dave]

Operating an alt-az mount near zenith means that a small azimuth movement causes a lot of field rotation. It's apparently too much per sub for the exposure length the Z50 is trying to use in the situation.

[jprideaux]

Yes, alt-az mounts have difficulty tracking right near zenith and the software will tend to reject stacking as the target passes too close to zenith.

Equatorial mounts don’t have a problem with zenith. They have a problem with tracking close to the celestial poles. All mount designs have problems tracking close to their axis of rotation.

It is good to use some software that will show where the target will go (relative to zenith) throughout the night and either pick targets that will not get too close to zenith or pick times in the night to image where the target does not get too close to zenith.

Edited by jprideaux, 15 December 2023 - 12:36 PM.

[Ike582]

Good info, thanks

[Special Ed]

Yes, alt-az mounts have difficulty tracking right near zenith and the software will tend to reject stacking as the target passes too close to zenith...

 

...It is good to use some software that will show where the target will go (relative to zenith) throughout the night and either pick targets that will not get too close to zenith or pick times in the night to image where the target does not get too close to zenith.

Actually, this info is right inside the Seestar app.  Go to the object catalog, click on the name of the target you want to image, and scroll down.  You will see a graph with a curve showing the altitude of the target for the entire time it is visible from your location, as well as the direction of the target in azimuth.  Then you can plan accordingly.  I think imaging while the target is below about 70 degrees altitude will minimize (but not eliminate) stack failure.