I use Nebulosity to stack the images and have just used rotational alignment. For giggles I just now tried rotate and translate and lo and behold I now have circular stars. My thought is that apparently the mount is just slightly out of level and PHD2 is correcting for it. It's not noticeable in my older images because they were of relatively short duration, but now I'm doing hours on the same object. Take this in the "For what it's worth" category.
Alignment trick
- Star Dad
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Alignment trick
Hi everyone - Maybe you all know this but I just discovered a "trick" in aligning. I'm now taking 2 minute exposures (optimal in Bortle 4.5 skies) over a long period of time. I stacked the latest images and noted that I had star trails... that is elongated stars. Not huge but enough that all the stars were elongated and the farther from the center the bigger the arc.
I use Nebulosity to stack the images and have just used rotational alignment. For giggles I just now tried rotate and translate and lo and behold I now have circular stars. My thought is that apparently the mount is just slightly out of level and PHD2 is correcting for it. It's not noticeable in my older images because they were of relatively short duration, but now I'm doing hours on the same object. Take this in the "For what it's worth" category.
I use Nebulosity to stack the images and have just used rotational alignment. For giggles I just now tried rotate and translate and lo and behold I now have circular stars. My thought is that apparently the mount is just slightly out of level and PHD2 is correcting for it. It's not noticeable in my older images because they were of relatively short duration, but now I'm doing hours on the same object. Take this in the "For what it's worth" category.
"To be good is not enough when you dream of being great"
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Re: Alignment trick
Nice tip... Thanks.
I like your signature. It's similar in nature to one of mine... "When you stop getting better, you quit being good."
Clear Skies & Stay Safe
I like your signature. It's similar in nature to one of mine... "When you stop getting better, you quit being good."
Clear Skies & Stay Safe
John (Urban Astronomer) Apertura AD10 Dob; XLT 150 Dob; XLT 120EQ; Lunt Solar 60 PT/B1200; ES AR102; SW Pro 100ED; 2 SW Pro 80ED's; 90mm Eq; WO Z-61; SW 90mm Virtuso Mak; 2 Orion ST-80's; Quark-C; Cams: Polemaster, ASI120MM-S, ASI174MM & ASI174MM-C
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Re: Alignment trick
I have Nebulosity 3 but never used it becauseStar Dad wrote: ↑Thu Nov 19, 2020 4:20 pm Hi everyone - Maybe you all know this but I just discovered a "trick" in aligning. I'm now taking 2 minute exposures (optimal in Bortle 4.5 skies) over a long period of time. I stacked the latest images and noted that I had star trails... that is elongated stars. Not huge but enough that all the stars were elongated and the farther from the center the bigger the arc.
I use Nebulosity to stack the images and have just used rotational alignment. For giggles I just now tried rotate and translate and lo and behold I now have circular stars. My thought is that apparently the mount is just slightly out of level and PHD2 is correcting for it. It's not noticeable in my older images because they were of relatively short duration, but now I'm doing hours on the same object. Take this in the "For what it's worth" category.
... Henk. Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: Alignment trick
Hi Star Dad - When you have rotation of your images it implies that your Polar Alignment is off. If the rotation isn't bad enough to cause star trails in any single image, then, the stacking should take care of it by rotating the individual images to all align. However, if you get star trails in your individual subs then you will need to improve your Polar Alignment.
Have fun.
Steve
Have fun.
Steve
Steve King: Light Pollution (Bortle 5)
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Re: Alignment trick
My polar alignment is spot on - I use Polemaster. I am going to have to use both rotation and translation on other images to be sure. Last night I did about 4.5 hours on the Crab Nebula (M1), so we'll see how that works out. My individual images are dots, no sign of trails. I do see a regular "heartbeat" in PHD2 indicating an adjustment signal being sent to the mount every 15 seconds or so. I'll have to keep an eye on that next session.
I use Nebulosity for image taking, preprocessing (darks, flats, etc), stacking. Last night I was having severe trouble trying to get my barlow in focus and discovered that I could stretch the image (in Nebulosity) which helped me get into focus a lot quicker. Almost all of my images in the past months have been 1-2 hours of data. My last two sessions I've upped the time to 3-4 hours, and this is the first I've really noticed the oval stars. When I useStarTools I always have to crop about 10 pixels or so on all sides. That has always been the case. So perhaps my bubble is off just a smidge.
I use Nebulosity for image taking, preprocessing (darks, flats, etc), stacking. Last night I was having severe trouble trying to get my barlow in focus and discovered that I could stretch the image (in Nebulosity) which helped me get into focus a lot quicker. Almost all of my images in the past months have been 1-2 hours of data. My last two sessions I've upped the time to 3-4 hours, and this is the first I've really noticed the oval stars. When I use
"To be good is not enough when you dream of being great"
Orion 203mm/f4.9/1000mm, converted TASCO 114mm/f9/1000mm to steam punk, Meade 114mm/f9/1000, Coronado PST, Orion EQ-G, Ioptron Mini-Tower and iEQ30, Canon 70D, ASI120MM,ASI294MC, Ioptron SkyHunter
Orion 203mm/f4.9/1000mm, converted TASCO 114mm/f9/1000mm to steam punk, Meade 114mm/f9/1000, Coronado PST, Orion EQ-G, Ioptron Mini-Tower and iEQ30, Canon 70D, ASI120MM,ASI294MC, Ioptron SkyHunter
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Re: Alignment trick
My thought is that apparently the mount is just slightly out of level and PHD2 is correcting for it.
- If the polar alignment is, as you state, "spot on," then it doesn't matter if the mount is level or not. This is not your problem.
- Your problem might be polar alignment, Pole Master is not infallible.
- It could also be flexure in the newt
OTA especially if you are using the newt with a separate guider.
Joe
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Re: Alignment trick
If the stars in the individual images are "sharp" than your Polar Alignment is good enough.
Getting Polar Alignment good enough to ensure images over 2,3, or 4 hours aren't slightly rotated is not necessary. Any good stacking program will take care of offsets (offsets occur for anyone using Dithering) as well as rotation. The rotation from image to image is likely unnoticeable. However, over the course of an evening of collecting images rotation is inevitable. That's why rotation is an integral part of stacking.
Just keep using the "rotate and translate" option and you should be fine.
Just FYI I know thatDSS uses "rotate and translate" as does PixInsight.
Cheers,
Steve
Getting Polar Alignment good enough to ensure images over 2,3, or 4 hours aren't slightly rotated is not necessary. Any good stacking program will take care of offsets (offsets occur for anyone using Dithering) as well as rotation. The rotation from image to image is likely unnoticeable. However, over the course of an evening of collecting images rotation is inevitable. That's why rotation is an integral part of stacking.
Just keep using the "rotate and translate" option and you should be fine.
Just FYI I know that
Cheers,
Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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