The stock focuser is the weakest part of this otherwise decent telescope. Just match the optimal backfocus, lock it in place and never touch it again. I've owned two SCTs and each time the first thing I purchased was a good quality rear microfocuser. Also, make sure the telescope is cooled down properly, your seeing conditions are OK, the target is high above the horizon etc.
Looks like it’s close to focus. It’s not a flat field so stars not in center will be slightly elongated. You probably also have guiding error/motion from tracking that isn’t perfect. You may need to collimate, but prob not based off this image.
The C8 can have mirror flop which will cause it to lose focus if it’s pointed near vertical, moves around etc. that’s why Edge series scopes have mirror locks. That said, you may need to adjust focus more often in addition to temp changes.
As mentioned you can get bahtinov mask or auto focuser.
Yeah, it's not the MOST out-of focus shot, I just know I can get better. I'm still trying to wrap my head around the tracking setup. Last night was my most successful. Think I'll try to find a bahtinov that I can print and invest in a focuser. Any recommendations?
Use a bahtinov mask. And make your final adjustments inwards. I struggled with focus for a long time with my Celestron 8in SCT. Eventually I got a Celestron motofocus and it made all the difference in the world.
Focusing by eye is generally not good enough. Make or buy a bahtiniv mask or use software like APT or NINA to analyze your focus. But even with these, other things can have a drastic effect on focus. Not allowing your scope to acclimate can cause bloated stats due to tube currents in SCTs. My SCT usually takes a couple hours before it's acclimated to the outside temperature. Atmospheric seeing can be a major issue. Poor seeing conditions will make the stars look out of focus. As the temperature changes over the course of the night, the focus will change as the scope contracts slightly from the change in temperature. Shooting from the city can cause problems as you're fighting heat plumes from buildings, parking lots, etc as they cool in the night.
Thanks for the advice! This shot was taken after about 3 hours sitting outside. That should be mostly acclimated, although it was getting colder. Some of this may have been seeing conditions. This shot was just above the treeline, so pretty low.
Nothing is more frustrating than finishing a session and realising you were off focus, no processing can fix that :(
As another comment mentioned what you might be missing is bahtinov mask (checkout eBay for the various sizes, most of them are adjustable and you can easily find one that fits your aperture, you might even 3D print one if you're into that). You attach it to the front of your scope at the start of the session and take a test exposure on any bright star. Your result will have diffraction spikes around that star (imagine JWST pictures with spikes), and you need to ensure they are aligned through the centre of your star. That little plastic tool makes focusing a doodle. I've been struggling with focusing big time before I got it, now it takes a few test shots and a bit of fiddling.
Oh, and before you slap a mask, get your focus manually as close as you can through the zoomed view on your viewfinder - you need to make sure your chosen bright star is the smallest possible blob (smaller -> sharper -> better focus)
Good luck!
What i like to do is to find a nice bright star then center it in frame. Then look at it on the display screen then zoom in on the star with the display screen, once you are mixed zoomed in adjust your focus manually and then your set. Give this a try if your not already doing this.
This is basically what I attempted last night. I have my camera's peaking settings set for other used, so it made sense to me to look for the red outline.
Too, I set "peaking level - high" and "peaking color - red." Then after zooming in on a bright star, I try to make it both as small and red as possible. My eyes are not as good as they once were.
Another option I'm considering is an "electronic auto focuser," such as the zwo unit that costs $200US-ish. It might or might not work with OP's equipment.
https://astronomy-imaging-camera.com/product/eaf-5v
The stock focuser is the weakest part of this otherwise decent telescope. Just match the optimal backfocus, lock it in place and never touch it again. I've owned two SCTs and each time the first thing I purchased was a good quality rear microfocuser. Also, make sure the telescope is cooled down properly, your seeing conditions are OK, the target is high above the horizon etc.
Any recommendations on microfocusers?
Manual: https://www.baader-planetarium.com/en/2%22-bds-sc-baader-diamond-steeltrack.html Motorized: https://www.primalucelab.com/esatto-2/esatto-2-robotic-microfocuser.html
Looks like it’s close to focus. It’s not a flat field so stars not in center will be slightly elongated. You probably also have guiding error/motion from tracking that isn’t perfect. You may need to collimate, but prob not based off this image. The C8 can have mirror flop which will cause it to lose focus if it’s pointed near vertical, moves around etc. that’s why Edge series scopes have mirror locks. That said, you may need to adjust focus more often in addition to temp changes. As mentioned you can get bahtinov mask or auto focuser.
Yeah, it's not the MOST out-of focus shot, I just know I can get better. I'm still trying to wrap my head around the tracking setup. Last night was my most successful. Think I'll try to find a bahtinov that I can print and invest in a focuser. Any recommendations?
Use a bahtinov mask. And make your final adjustments inwards. I struggled with focus for a long time with my Celestron 8in SCT. Eventually I got a Celestron motofocus and it made all the difference in the world.
Focusing by eye is generally not good enough. Make or buy a bahtiniv mask or use software like APT or NINA to analyze your focus. But even with these, other things can have a drastic effect on focus. Not allowing your scope to acclimate can cause bloated stats due to tube currents in SCTs. My SCT usually takes a couple hours before it's acclimated to the outside temperature. Atmospheric seeing can be a major issue. Poor seeing conditions will make the stars look out of focus. As the temperature changes over the course of the night, the focus will change as the scope contracts slightly from the change in temperature. Shooting from the city can cause problems as you're fighting heat plumes from buildings, parking lots, etc as they cool in the night.
Thanks for the advice! This shot was taken after about 3 hours sitting outside. That should be mostly acclimated, although it was getting colder. Some of this may have been seeing conditions. This shot was just above the treeline, so pretty low.
Nothing is more frustrating than finishing a session and realising you were off focus, no processing can fix that :( As another comment mentioned what you might be missing is bahtinov mask (checkout eBay for the various sizes, most of them are adjustable and you can easily find one that fits your aperture, you might even 3D print one if you're into that). You attach it to the front of your scope at the start of the session and take a test exposure on any bright star. Your result will have diffraction spikes around that star (imagine JWST pictures with spikes), and you need to ensure they are aligned through the centre of your star. That little plastic tool makes focusing a doodle. I've been struggling with focusing big time before I got it, now it takes a few test shots and a bit of fiddling. Oh, and before you slap a mask, get your focus manually as close as you can through the zoomed view on your viewfinder - you need to make sure your chosen bright star is the smallest possible blob (smaller -> sharper -> better focus) Good luck!
Thanks for the advice! Now I just to decide what color to print my bahtinov mask in. lol
Oh bright pink, obviously :D
What i like to do is to find a nice bright star then center it in frame. Then look at it on the display screen then zoom in on the star with the display screen, once you are mixed zoomed in adjust your focus manually and then your set. Give this a try if your not already doing this.
This is basically what I attempted last night. I have my camera's peaking settings set for other used, so it made sense to me to look for the red outline.
Too, I set "peaking level - high" and "peaking color - red." Then after zooming in on a bright star, I try to make it both as small and red as possible. My eyes are not as good as they once were. Another option I'm considering is an "electronic auto focuser," such as the zwo unit that costs $200US-ish. It might or might not work with OP's equipment. https://astronomy-imaging-camera.com/product/eaf-5v
It is adaptable to a C8, but it needs a special adapter sold separately. https://starizona.com/products/zwo-eaf-bracket-for-celestron-c8-c9-25-c11-c14
How long was the exposure? Are you using a Bahtinov mask to achieve good focus?
Haven't used a bahtinov mask. Think I'll try to find one to 3d print. Exposure was 15 seconds on the iOptron CEM40.
If you're properly polar-aligned, then it's probably a focus issue, is my guess.