Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

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realflow100 United States of America
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Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#1

Post by realflow100 »


1.25" 4-inch 100mm reflector F/4 focal ratio

From what I can find the closest option available is to get a pair of lenses from edmund optics website and stick them into a lens holder of some kind (I have a few things that can hold the lenses and a way to space them out if I need to)

the ones i'm looking at are a -100mm plano concave and 100mm double convex (only available options) 25mm diameter total price under 70$ including tax and shipping. I dont see any 150mm ones available though so I hope 100mm ones arent too short of focal length.

I'm not sure on what kind of spacing I should use for the lenses. should I just try various things and see what works the best? or is there a good starting point to start from?
Im using it for astrophotography purposes with a crop sensor canon DSLR

I already modified the telescope for prime focus by spacing the mirror deeper into the telescope tube and have collimated the telescope.
my coma issue is extremely severe. everything looks crazily blurry and stretched out of focus toward the edges. most noticable to the left and right so this is why im attempting to make my own coma corrector.
I have come from the astronomy forum and posted here
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#2

Post by Sky Tinker »


The industry has forgotten those of us with fast-reflectors with 1.25" focussers. I have a 100mm f/4 myself...
mounted2b.jpg
mounted2b.jpg (23.45 KiB) Viewed 3688 times
I've taken afocal-shots through it, through this eyepiece and that. I also have a 127mm f/8 "Bird Jones", which is actually a 127mm f/4 Newtonian incognito, and exhibits an unhealthy dose of coma at the lower powers as well.

I came across these...

https://stargazerslounge.com/topic/2886 ... corrector/

That thread details a Ross-type coma-corrector, and perhaps what you're trying to achieve.

This vendor has produced 1.25" coma-correctors in the past, and by special-order... https://www.siebertoptics.com/

All I've see online over the years in so far as discussions are recommendations and suggestions to either fit a 2" focusser onto the telescope in question, or acquire one with a 2" focusser which would require going up to a 130mm at least. Of course, such does not console.
"Look, son! Up there!" His son shouted back, "I see it! What is it?" The father regaled, "The galaxy! Andromeda! Our origin, our destiny!" And so the boy was hooked, and for the rest of his natural life.

"Desserts tend to corrupt, and absolutely delicious desserts corrupt absolutely." - Chef Acton

Alan :Astronomer1:

Apochromat: Takahashi FS-102 4" f/8 - Achromats: Meade S102 102mm f/5.9, Antares 805 80mm f/6(flocked & blackened), Meade "Polaris" 70mm f/12.9, Sears(Towa) #4-6340 50mm f/12(flocked & blackened) - Newtonians: Orion 6" f/5(flocked & blackened) - Catadioptrics: Explore Scientific 127mm f/15 Maksutov-Cassegrain, Celestron "PowerSeeker" 127mm f/8 "Bird Jones" reflector(modified, flocked, blackened, and collimated!) - Mounts: Meade LX70(EQ-5), Astro-Tech Voyager I alt-azimuth
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#3

Post by realflow100 »


I just cant afford that kind of cost. if a a coma corrector costs more than my telescope might as well just buy a refractor instead that already has great image quality instead of buying a 2" focuser reflector then buying an even more expensive coma corrector for doing imaging with it.
Ive been looking at that post thats where I got the idea from and I want to replicate it. I already ordered the lenses because they were so cheap
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#4

Post by Sky Tinker »


realflow100 wrote: Wed Jan 22, 2020 6:09 pm I just cant afford that kind of cost. if a a coma corrector costs more than my telescope might as well just buy a refractor instead that already has great image quality instead of buying a 2" focuser reflector then buying an even more expensive coma corrector for doing imaging with it.
Ive been looking at that post thats where I got the idea from and I want to replicate it. I already ordered the lenses because they were so cheap

Ah, but a short, fast refractor, and an achromat I'm guessing, has its own problem: chromatic aberration; false-colour. Also, the stars would appear not as sharp points of light, but bloated, swelled. Although, the stars would be round nonetheless, for the most part. There may also be some distortion at the edges due to field-curvature, resembling coma, but perhaps not as bad as that of the 100mm f/4 Newtonian.

What sort of mount are you using, or are planning to use?

This refractor would be the equivalent to your 100mm f/4, an 80mm f/5 achromat...



If you were to consider that one, you'd be paying for the telescope. The manufacturer throws that tripod in essentially for free, and just to get the telescope up off of the ground.
"Look, son! Up there!" His son shouted back, "I see it! What is it?" The father regaled, "The galaxy! Andromeda! Our origin, our destiny!" And so the boy was hooked, and for the rest of his natural life.

"Desserts tend to corrupt, and absolutely delicious desserts corrupt absolutely." - Chef Acton

Alan :Astronomer1:

Apochromat: Takahashi FS-102 4" f/8 - Achromats: Meade S102 102mm f/5.9, Antares 805 80mm f/6(flocked & blackened), Meade "Polaris" 70mm f/12.9, Sears(Towa) #4-6340 50mm f/12(flocked & blackened) - Newtonians: Orion 6" f/5(flocked & blackened) - Catadioptrics: Explore Scientific 127mm f/15 Maksutov-Cassegrain, Celestron "PowerSeeker" 127mm f/8 "Bird Jones" reflector(modified, flocked, blackened, and collimated!) - Mounts: Meade LX70(EQ-5), Astro-Tech Voyager I alt-azimuth
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#5

Post by realflow100 »


I'm using a reflector telescope and DOB mount.
it is the 100mm aperture F/4 orion skyscanner telescope. mirror modified extended deeper into the tube to reach prime focus with a camera (was extremely difficult because it was stuck in with extremely strong double sided tape straight to plastic.
coma is extremely excessive toward the edges. and past about 50% away from the middle is where coma starts to be a problem already. and im not even using a full frame camera.
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#6

Post by realflow100 »


I just got the lenses but now I need to order some washers to space them out and have them work in my filter because the filter things i have are too small so the lenses just fall through them. i need 24 x 27mm washers but the closest I could find is 22 x 28 washers. what a pain!
hopefully I can get the lenses close enough to the camera that they won't vignette or cut the light path.
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#7

Post by realflow100 »


I actually found a way to mount the lenses in some filter housings! but now my struggle is HOW to space them out. I dont know how much space i need between the two lenses for them to be effective.
I tried many many different spacings and it just doesnt seem to work the way I want. they SEEM to give the best result if i have the positive lens on the INSIDE of the telescope adapter tube almost touching the cameras mirror and the other lens at the end of the telescope adapter.
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#8

Post by Sky Tinker »


realflow100 wrote: Thu Jan 23, 2020 8:02 pm I'm using a reflector telescope and DOB mount.
it is the 100mm aperture F/4 orion skyscanner telescope. mirror modified extended deeper into the tube to reach prime focus with a camera (was extremely difficult because it was stuck in with extremely strong double sided tape straight to plastic.
coma is extremely excessive toward the edges. and past about 50% away from the middle is where coma starts to be a problem already. and im not even using a full frame camera.

Yes, my Zhumell Z100 is essentially the same as the Orion "SkyScanner" 100mm, as is the Sky-Watcher "Heritage" 100P. I took the mirror out of my own, too. I made an opening on the back of the cell to allow the mirror to "breathe", to acclimate more easily. I then re-installed it with five points of aquarium-type silicone round, instead of the foam-tape that the factory had used...
primary cell14c.jpg
primary cell14c.jpg (27.47 KiB) Viewed 3606 times
Had I known that it was foam-tape, I would've poured charcoal-lighter fluid into the cell and let it sit for a day; or longer, depending.

Yes, those Chinese adhesives are particularly tenacious.
"Look, son! Up there!" His son shouted back, "I see it! What is it?" The father regaled, "The galaxy! Andromeda! Our origin, our destiny!" And so the boy was hooked, and for the rest of his natural life.

"Desserts tend to corrupt, and absolutely delicious desserts corrupt absolutely." - Chef Acton

Alan :Astronomer1:

Apochromat: Takahashi FS-102 4" f/8 - Achromats: Meade S102 102mm f/5.9, Antares 805 80mm f/6(flocked & blackened), Meade "Polaris" 70mm f/12.9, Sears(Towa) #4-6340 50mm f/12(flocked & blackened) - Newtonians: Orion 6" f/5(flocked & blackened) - Catadioptrics: Explore Scientific 127mm f/15 Maksutov-Cassegrain, Celestron "PowerSeeker" 127mm f/8 "Bird Jones" reflector(modified, flocked, blackened, and collimated!) - Mounts: Meade LX70(EQ-5), Astro-Tech Voyager I alt-azimuth
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#9

Post by realflow100 »


I still haven't figured out the right spacing for my lenses. I keep fiddling with them and nothing seems to be right. i tried spacing them out more and more. it doesnt really do much then starts to get worse so i tried having them practically touching and adjusting the distance from my camera lens with various filters to act as spacers and still cant get it perfect. maybe its just not quite the right focal length to work?


also for mine to get my telescope to work with prime focus I had to use an empty metal chicken can to act as a "spacer" to move the mirror quite a ways further up the telescope tube to get my camera to reach focus!
but ive been struggling with extremely bad coma for quite a while and trying to fix it with this lens thing but i dont know how to space them out.
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#10

Post by Sky Tinker »


realflow100 wrote: Sat Jan 25, 2020 2:18 am I still haven't figured out the right spacing for my lenses. I keep fiddling with them and nothing seems to be right. i tried spacing them out more and more. it doesnt really do much then starts to get worse so i tried having them practically touching and adjusting the distance from my camera lens with various filters to act as spacers and still cant get it perfect. maybe its just not quite the right focal length to work?


also for mine to get my telescope to work with prime focus I had to use an empty metal chicken can to act as a "spacer" to move the mirror quite a ways further up the telescope tube to get my camera to reach focus!
but ive been struggling with extremely bad coma for quite a while and trying to fix it with this lens thing but i dont know how to space them out.
According to that link within Stargazers Lounge...

https://stargazerslounge.com/uploads/mo ... a78a0f.JPG

The spacing of the lenses of the author's mod is accomplished by the two filter frames when screwed together. Then, the author used a filter extension-tube(s) to space those lenses about 80mm or so from the camera...

https://stargazerslounge.com/uploads/mo ... ae505e.jpg

1.25" extension tube for example...

https://www.ebay.com/itm/New-1-25-Filte ... .l4275.c10

Three of those would make for a 75mm length, similar to that specified within that diagram.
"Look, son! Up there!" His son shouted back, "I see it! What is it?" The father regaled, "The galaxy! Andromeda! Our origin, our destiny!" And so the boy was hooked, and for the rest of his natural life.

"Desserts tend to corrupt, and absolutely delicious desserts corrupt absolutely." - Chef Acton

Alan :Astronomer1:

Apochromat: Takahashi FS-102 4" f/8 - Achromats: Meade S102 102mm f/5.9, Antares 805 80mm f/6(flocked & blackened), Meade "Polaris" 70mm f/12.9, Sears(Towa) #4-6340 50mm f/12(flocked & blackened) - Newtonians: Orion 6" f/5(flocked & blackened) - Catadioptrics: Explore Scientific 127mm f/15 Maksutov-Cassegrain, Celestron "PowerSeeker" 127mm f/8 "Bird Jones" reflector(modified, flocked, blackened, and collimated!) - Mounts: Meade LX70(EQ-5), Astro-Tech Voyager I alt-azimuth
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#11

Post by realflow100 »


I'm using -100mm and 100mm focal length lenses though they didnt have any 150mm ones that I could find.
so that might not work unless its modified to account for the difference in focal length of my lenses
I tried putting them practically anywhere between 50mm and 120mm distances away and it doesnt quite work.
Is the 80mm from the sensor itself? or distance from the adapter? or what?
I tried to measure with a tape measure (measureing the distance roughly by using the sensor indicator symbol on the body) and its within range of that but my lenses being 100mm instead of 150mm might mean i need to put it closer or farther away.

The coma doesnt seem to go away really no matter how close or far away i put the lenses. theres no "good" spot. its either way too much making it worse. not enough. or doesnt seem to do much.

Could someone add me on discord and try to help me with live chat?

Squishy Fox#6932
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#12

Post by realflow100 »


Nevermind I gave up and threw the lenses in the trash cause they got scratched trying to re-arrange them the other way around in the filter housings so I can put them closer to the camera sensor.
I give up this is hopeless
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#13

Post by Sky Tinker »


My last reply was about as much as I could muster on the subject. It sounds like the lenses were of plastic, if they were that easy to scratch. I hope you find a solution nonetheless.
"Look, son! Up there!" His son shouted back, "I see it! What is it?" The father regaled, "The galaxy! Andromeda! Our origin, our destiny!" And so the boy was hooked, and for the rest of his natural life.

"Desserts tend to corrupt, and absolutely delicious desserts corrupt absolutely." - Chef Acton

Alan :Astronomer1:

Apochromat: Takahashi FS-102 4" f/8 - Achromats: Meade S102 102mm f/5.9, Antares 805 80mm f/6(flocked & blackened), Meade "Polaris" 70mm f/12.9, Sears(Towa) #4-6340 50mm f/12(flocked & blackened) - Newtonians: Orion 6" f/5(flocked & blackened) - Catadioptrics: Explore Scientific 127mm f/15 Maksutov-Cassegrain, Celestron "PowerSeeker" 127mm f/8 "Bird Jones" reflector(modified, flocked, blackened, and collimated!) - Mounts: Meade LX70(EQ-5), Astro-Tech Voyager I alt-azimuth
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#14

Post by ARock »


Not that I know much about coma correction, but have you looked at this?

https://www.cloudynights.com/topic/4741 ... corrector/
AR
Scopes: Zhumell Z8, Meade Adventure 80mm, Bushnell 1300x100 Goto Mak.
Mount: ES EXOS Nano EQ Mount, DIY Arduino+Stepper drives.
AP: 50mm guidescope, AR0130 based guidecam, Canon T3i, UHC filter.
EPs: ES82 18,11,6.7mm, Zhumell 30,9mm FJ Ortho 9mm, assorted plossls, Meade 2x S-F Barlow, DGM NPB filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#15

Post by realflow100 »


No there were definitely glass lenses I could easily tell. I scratched them cause the edges of one lens scraped against the surface of the other lens trying to cram them into the filter housing :(

I looked at that but i dont have a 3D printer or any way to do that.
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#16

Post by ARock »


realflow100 wrote: Sun Jan 26, 2020 9:37 pm I looked at that but i dont have a 3D printer or any way to do that.
These days getting things 3D printed is not very hard or expensive. Try treatstock.com
You need to design it though. :) Or you can ask someone who has already done it for the stl file.
If you want to design it, but not from scratch, you can search thingiverse.com for eyepiece adapters, you can get some designs which include the cad file along with the stl file. Then you modify the cad file, to your specification. I like scad files I can modify with openscad which is text based, and has tutorials on youtube.

https://www.thingiverse.com/thing:2015811
AR
Scopes: Zhumell Z8, Meade Adventure 80mm, Bushnell 1300x100 Goto Mak.
Mount: ES EXOS Nano EQ Mount, DIY Arduino+Stepper drives.
AP: 50mm guidescope, AR0130 based guidecam, Canon T3i, UHC filter.
EPs: ES82 18,11,6.7mm, Zhumell 30,9mm FJ Ortho 9mm, assorted plossls, Meade 2x S-F Barlow, DGM NPB filter.
Binos: Celestron Skymaster 15x70 (Albott tripod/monopod), Nikon Naturalist 7x35.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#17

Post by realflow100 »


Waaay out of my scope of DIY lol and I dont have any spare money right now so I will have to wait until next month before I can get anything. and I think i will just save up for a few months and get a high quality refractor telescope that doesnt need any correcting optics added so I can just stick my camera on it and use it.
Its a struggle to do untracked astrophotography. i just barely caught the faintest hint of nebula in pleiades with 35 frames stacked of 1 second exposures (big bloated blurry stars and tons of coma toward the edges im lucky it was even able to stack the frames)
orion nebula came out pretty decent though actually. even with the extreme coma issue. you can see some details in the nebula and colors.
https://cdn.discordapp.com/attachments/ ... -_Copy.png this is 40 frames of 0.6 second exposures at iso 1600 in roughly bortle 6 to 8 (crazy glare from street lights)
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#18

Post by ARock »


Quite good for 0.6 sec shots !!

What scope/mount do you have?

Use the free "crop a corrector" like me, crop the image and take only the central part. :)
AR
Scopes: Zhumell Z8, Meade Adventure 80mm, Bushnell 1300x100 Goto Mak.
Mount: ES EXOS Nano EQ Mount, DIY Arduino+Stepper drives.
AP: 50mm guidescope, AR0130 based guidecam, Canon T3i, UHC filter.
EPs: ES82 18,11,6.7mm, Zhumell 30,9mm FJ Ortho 9mm, assorted plossls, Meade 2x S-F Barlow, DGM NPB filter.
Binos: Celestron Skymaster 15x70 (Albott tripod/monopod), Nikon Naturalist 7x35.
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realflow100 United States of America
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Re: Attempting to make cheap simple coma corrector for 1.25" 4-inch 100mm reflector

#19

Post by realflow100 »


dob orion skyscanner 100mm F/4. dob mount. untracked (no tracking)

And cropping isnt even good enough. only the center like 35% of the image is usable. and past 50% it starts to get really bad. and past 75% its beyond horrible.
i'd have to have tracking and be aimed directly at orion nebula perfectly to be able to crop it to just the orion nebula to have anything usable come out of it.
and I cant track anything. cant afford.
Svbony SV503 70mm ED F6 420mm FL refractor telescope (New)
Canon EOS 100D/SL1
Tamron 18-200mm F3.5-F6.3 II VC lens
canon 50mm STM F1.8
svbony 8-24mm zoom eyepiece
svbony goldline 66 degree 9mm and 6mm + 40mm plossl + 2x barlow.
svbony UHC 1.25 filter + astromania 1.25" O-3 filter + also an svbony H-B filter.
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