ASI2224 images bad compared to SeeStar

KNicholas2

I am fairly new to this - but the images from my ZWO 224MC are awful when compared to those from my SeeStar.
Here is my setup: William Optics Gran Turismo GT71 mounted on an M5 mount, ZWO 224MC main camera, ASI120 guide camera.
The images I get are "very small" (thumbnail size), to see the image as a whole requires enlarging the image where the image is over-pixilated, almost no detail and noisy.
When I make the same target with my SeeStar, the image is larger with good detail.
What am I doing wrong? Am I expecting too much from this camera?

Thank You!
Kim N.

Astrop

The 224 is quite an old camera now in relative terms (maybe 4 years plus now which doesn't sound that old), it also has a tiny 5 x 4mm sensor, though it's a comparable size to the imx462 within the Seestar.

Your issue is your Seestar is 250mm focal length, your GT71 is 419mm, as a general rough scale nearly twice the focal length. So with the scope your images will be more "zoomed in", as a result you may find the signal weaker, when in fact it's spread out across more pixel area. So if you compare both, youll perceive to find the SS image brighter, but in AP if you scale comparison images to the same pixel scale you'll often find they look very similar.

You haven't mentioned how long you're imaging for. A SS I believe by default takes 10s images and continually stacks them until you stop it, for your scope how long per image and total time were you imaging for? Was it like for like time? How did you stack? Did you take and apply calibration frames?

Astrop

Also, the 224 isn't really suited for DSO imaging, some people have got excellent results from it, but because its a tiny sensor, and it has bad amp glow the amp glow pretty much covers the whole of the image, therefore you need to either cool it, or take very short exposure images (less than 10s), therefore need to take and stack a lot of them to reveal the faint objects in detail. More total imaging time will give better quality, stronger signal, and less LP or background noise once multiple images are stacked.

KNicholas2

Thanks for your input.
To address your questions, I was shooting for 20 second exposures, stacked approx. 30 images in Siril.
Maybe I'm asking too much for such a tiny sensor....
Also, the amount of backfocus extender needed to get focus seems excessive.
Maybe I don't fully understand back focus - but the specs say 12.5mm.
(I wanted to include a photo but I can't get that to work either!)

Astrop

KNicholas2 back focus

Are you using a field flattener? If so the backfocus spec of a lot of flatteners is typically 55mm from the bottom of the fixing thread (where any adaptor would screw on and come to a physical stop) to the sensor.

The 12.5mm you're referring to is the front of camera to sensor distance, if using a flattener with 55mm BF you need to add another 42.5mm of spacer rings/tubes.

A field flattener has a fixed BF distance as the back of the glass to camera doesn't move, it's the point where when in focus via your telescope focuser is where it's focus point is projected. If you're not using a flattener then you simply attach your camera to the rear of the focuser of the scope (either screwed on or with the 1.25 inch nosepiece adaptor) and rack your focuser until it reaches focus, ability to focus this way depends on the travel of your focuser.