S30: higher rejection ratio for mosaic with 60sec EQ

francescoCh

Hello. Yesterday evening I took live pictures (stack) of the Pleiads in EQ mode using the 60secs exposure. In 60min I got 49 images (that would be around 18% rejection ratio),
Then I started a planned mosaic for the California nebula. Size was 1.2x and field was rotated in order to fit the whole thing. In 2H20min I got 79 images which would be a 43% rejection ratio, and mosaic was still incomplete.
AFAIK sky was clear the whole time, missing pictures where evenly distributed in the observation time (no big hole that is). Those I have do not show any issue (like clouds, trees, ufo's).

So I wonder if anyone had a similar experience and if there's a reason for that behavior.
It's also puzzling it couldn't complete the mosaic.
Thank you in advance.
francesco

Tech@ZWO

1.Equatorial Mount Switching：Equatorial mount switching must start from the device's initial position;，otherwise, it may affect calibration.
2.Polar Axis Calibration：Polar alignment must be performed first. Low precision during alignment may cause star trails and result in image loss
3.Equatorial Mount Mode and Exposure Time：In equatorial mount mode, using longer exposure times for individual shots can yield better results but also increases the likelihood of discarded frames.For example, during a 60-second exposure, any unexpected event causing star trails (star point dragging) will result in the image being discarded.
4.Check for Star Trails in Single Images：Check your individual images for star trails. If present, determine whether the trails existed from the beginning or occurred after running for some time.
5.Discarded Images During Stacking： Discarded images during stacking can also be influenced by environmental factors such as wind or ground vibrations.

francescoCh

Thank you for your answer.
I realize my question wasn't specific enough.
I was wondering why in mosaic mode the rejection ratio climbs to 50%, instead of being roughly the same as in non-mosaic mode.
This issue has been bugging me for a while and maybe there's a technical reason (mechanical stress induced by the extra movement?).
BTW, I'm aware of the points you made and I usually get a 10%-20% ratio for non mosaic 60sec EQ mode images, which i think is fine.

KatNRick

I would guess that non-mosaic EQ images should only require movement of a single motor (az) if perfectly polar aligned. Toss mosaic into the mix and both motors require movement which incorporates the likelihood of gear backlash entering more significantly into the equation.