weird ringed artifacts in my images

[wesdon1]

3 hours ago, labtech1122 said:

Hi, I'm wondering if any one can help me,

I've just started imaging through my telescope and keep getting a very strange set of rings on my images with bright stars, the rings move around and change position depending what angle the camera is at.

also the stars at the edges look like they are trailing or out of collimation or out of focus or something. 

im using a celestron nexstar 6slt with antares x0.63 focual reducer, sc -tpiece and canon 650D. 60mm guide scope with svbony sv305pro to guide

I've been racking my brain a lot about this and really need help. DSS wont stack them because it cant see stars and when I got it to stack a couple of images it didnt actually align the images it just put them one on top of the other.

blue ring (2).CR2 21.26 MB · 7 downloads blue ring (3).CR2 21.45 MB · 3 downloads blue ring (4).CR2 21.55 MB · 2 downloads blue ring.CR2 21.53 MB · 2 downloads

definitely out of focus, imo. Try getting your stars as tiny and "dense" as possible when focusing mate. There's tons of people on here who know the hobby inside out, who will give you amazing advice, so keep coming back here, and try YouTube vids aswell. In time, things you find difficult today, will feel second nature, you just have to stick with it mate. Best of luck!

[labtech1122]

4 minutes ago, wesdon1 said:

definitely out of focus, imo. Try getting your stars as tiny and "dense" as possible when focusing mate. There's tons of people on here who know the hobby inside out, who will give you amazing advice, so keep coming back here, and try YouTube vids aswell. In time, things you find difficult today, will feel second nature, you just have to stick with it mate. Best of luck!

thanks  ive been trying the same thing over and over for over a year now and am finding it really hard to get to grips with, ive got a pretty good understanding of a few things but since getting the FR i get the blue rings and the trail shapes in the corners. im agreeing with people its probably back focus but ive got the same things ive seen other people have but not getting any results

[labtech1122]

22 minutes ago, labtech1122 said:

 

does this set up look ok? telescope, FR screwed strait onto scope, t adapter, t ring then camera?

[wesdon1]

11 minutes ago, labtech1122 said:

does this set up look ok? telescope, FR screwed strait onto scope, t adapter, t ring then camera?

Although i don't own a SCT 'scope, I do know from my own personal experiences with using my DSLR camera on my Newtonian Reflector telescope, that you really benefit from having a selection of back focusing/spacer rings, to find the exact back focus/sweet spot, where the cameras sensor is perfectly focused, and you lose the image artefacts, like rings that you're seeing in images etc. Also, make sure that when you're imaging, your telescope isn't pointing closely at local street lights/garden flood lights etc, because some of those rings look like what I got when a street light was shining down my telescope OTA from an angle, causing ring like artefacts etc. I really hope you don't give in  and keep going, I promise you you'll feel awesome when you work this issue through! 

Wes.

[wesdon1]

34 minutes ago, labtech1122 said:

does this set up look ok? telescope, FR screwed strait onto scope, t adapter, t ring then camera?

@labtech1122 Yes the camera and FR etc all look to be properly connected, but that still doesn't necessarily mean it's in good focus. I would suggest, alongside my previous advice, that you find a very bright star, use Live-View on DSLR ( if you have it? ) and get the star perfectly focused, preferably with a Bhatinov mask. A Bhatinov Mask isn't a must, because you can get great focus without one, but they just make things a lot easier, in my experience. And if after great focusing, you're still seeing artifacts, then try imaging a target that doesn't have you telescope pointing anywhere near a street light, or garden flood light, etc ( maybe image something above 70+ degrees Altitude? ) Then again if you STILL have that ring/artefacts, maybe it's time to get that FR looked at? Ultimately it'll be a process of elimination, one after another, of all possible causes, until you find the cause. Just don't give up, you will find the cause and be that much the happier for persevering! ( I'm speaking from BITTER personal experiences!! LOL )

[labtech1122]

Do you think swapping to this (see image) would help, i would be able to move the back focus around on this set up (the celestron adapter is a fixed length) as you can see i can use a multitude or focal lengths with the 1 1/4" tpiece

The thing about it is this way will be 1 1/4" instead of the 2" that the celestron one is, will this make any negative or positive impact on the images taken, i may be wrong ut thought that the 2" would let more light in?

[labtech1122]

the thing i was worried aout with the 1 1/4" before when i was using it all the time was it once being screwed down with the two tightening screw that it wasnt properly central and you would a little bit of tilt

[newbie alert]

That T adapter would work with a Celestron reducer but it's a Antares one, which I'm sure that I've seen 85mm thrown about rather than the 105mm that Celestron spec... Have a little search on Mr google

[Elp]

I'm assuming your scope (SLT) is just a model number variation of the Celestron C6 SCT design (SE, nexstar, edge etc). Out of curiosity, are you using the supplied mount or an EQ one?

If the former, add in the reduced focal length you're trying to image at (1000mm+) that mount won't be sufficient to prevent star trailing. You ideally need equatorial for deep sky, more so for long exposure, even more so for long focal length.

Having tried imaging recently with my C6 SCT at F6.3, it isn't easy getting bang on focus, or getting good guiding. The bloated stars and confirmed by failure to stack is indicative of out of focus stars with poor FWHM values. The software doesn't see them as points of light so can't register the pictures. You can sometimes brute force the registration by choosing different registration algorithms (I use Siril more because of being able to customise such things), but usually any stacking program won't like the data.

You mentioned you're using a guidescope, unless it's a similar imaging scale to your SCT your guiding won't be good at all. Long focal length really needs a matching guidescope (usually an actual refractor telescope being used for guiding duties) or an off axis guider (what I use). Even then, any poor seeing may result in bad guiding which short focal length imaging can usually get away with.

With my F6.3 Celestron reducer I work to 105mm back focus from the rear of the reducer lens to the camera sensor, so maybe find out what your reducer BF distance is, it might be similar. You mentioned the visual back, you don't need this, the reducer screws directly to the back of the scope and then your spacers, adaptors etc follow. Work on this until you can get the stars round. Also confirm via visual observation with your diagonal and an eyepiece when you look at stars or planets, are they completely round with no edge shadowing, if not your scope collimation could be off.

The good thing about an SCT is backfocus isn't so critical as it is with a refractor due to how the scope is designed so a few mm off won't cause an issue. I think your edge stars will be a problem due to the sensor size, larger the sensor, the more precise to perfect your backfocus needs to be to get a completely flat field, in such instances its much less hassle to crop the final image.

As for the artifacts, if they're rotating when you're rotating the camera, the camera is the likely culprit as there's a lot of internal surfaces for light to reflect off unlike in an astro camera where the sensor is closer to the mounting face.

I wouldn't get discouraged, part of the "fun" in AP is problem solving and looking for ways to improve. If it were easy, more people would be doing it.

[labtech1122]

6 minutes ago, Elp said:

I'm assuming your scope (SLT) is just a model number variation of the Celestron C6 SCT design (SE, nexstar, edge etc). Out of curiosity, are you using the supplied mount or an EQ one?

If the former, add in the reduced focal length you're trying to image at (1000mm+) that mount won't be sufficient to prevent star trailing. You ideally need equatorial for deep sky, more so for long exposure, even more so for long focal length.

Having tried imaging recently with my C6 SCT at F6.3, it isn't easy getting bang on focus, or getting good guiding. The bloated stars and confirmed by failure to stack is indicative of out of focus stars with poor FWHM values. The software doesn't see them as points of light so can't register the pictures. You can sometimes brute force the registration by choosing different registration algorithms (I use Siril more because of being able to customise such things), but usually any stacking program won't like the data.

You mentioned you're using a guidescope, unless it's a similar imaging scale to your SCT your guiding won't be good at all. Long focal length really needs a matching guidescope (usually an actual refractor telescope being used for guiding duties) or an off axis guider (what I use). Even then, any poor seeing may result in bad guiding which short focal length imaging can usually get away with.

With my F6.3 Celestron reducer I work to 105mm back focus from the rear of the reducer lens to the camera sensor, so maybe find out what your reducer BF distance is, it might be similar. You mentioned the visual back, you don't need this, the reducer screws directly to the back of the scope and then your spacers, adaptors etc follow. Work on this until you can get the stars round. Also confirm via visual observation with your diagonal and an eyepiece when you look at stars or planets, are they completely round with no edge shadowing, if not your scope collimation could be off.

The good thing about an SCT is backfocus isn't so critical as it is with a refractor due to how the scope is designed so a few mm off won't cause an issue. I think your edge stars will be a problem due to the sensor size, larger the sensor, the more precise to perfect your backfocus needs to be to get a completely flat field, in such instances its much less hassle to crop the final image.

As for the artifacts, if they're rotating when you're rotating the camera, the camera is the likely culprit as there's a lot of internal surfaces for light to reflect off unlike in an astro camera where the sensor is closer to the mounting face.

I wouldn't get discouraged, part of the "fun" in AP is problem solving and looking for ways to improve. If it were easy, more people would be doing it.

hi yes its a celestron nexstar 6slt, the mount im using is a skywatcher eqm-35pro, guide scope is the svbony 60mm and guiding with PHD2. i have had a look around on loads of forums and some people say its 85mm but are then corrected by many others that its 105mm so not really sure what is correct

"You mentioned the visual back, you don't need this, the reducer screws directly to the back of the scope" i dont remeber mentioning that as i have got the reducer screwed directly to the back of the scope, i shared an image of it saying i could use this instead of the celestron adapter as i can put my 1 1/4" t piece into it and make the BF adjustable.

"are they completely round with no edge shadowing, if not your scope collimation could be off" yes i have done this and the collumation is just right

"part of the "fun" in AP is problem solving and looking for ways to improve" yes i do definately like the reserching and working out differnt things and how to fix the problems i just need to do a trail and error because a minority say 85mmBF and the others say 105mmBF so im going to try both

do you know of any adapters that i can use that come wiith differnt size spacers? the on i have is the celestron #93633-A and is a fixed length

[labtech1122]

1 hour ago, newbie alert said:

That T adapter would work with a Celestron reducer but it's a Antares one, which I'm sure that I've seen 85mm thrown about rather than the 105mm that Celestron spec... Have a little search on Mr google

would this one work better do you think?

[labtech1122]

or maybe this one? what is the correct thread and pitch of the back of the celestron 6" sct telescope

[Elp]

I THINK, its m48 on the back of the reducer but don't quote me on this because mine has reducer > OAG > filter drawer > camera rotator > 11mm spacer ring > astro cam which gets me near enough 105mm and the threads all miraculously match up.

If you place a ruler on the back it will give you a very rough indication of its metric diameter, if you've got some adaptors or dslr step up/down rings at hand that will help confirm.

The m42 rings are useful though and is what I mainly use when I need them, but I also have m48 to m42 step down rings and step up rings just incase I need to adjust things.

M42 and t ring are very close in thread pitch, you might find they're quite interchangeable depending on how well they've been machined but m42 is 1mm pitch, and t ring is also m42 but is 0.75mm pitch, not much in it at all but get whatever suits your setup to avoid any issues.

Edited February 19, 2023 by Elp

[labtech1122]

i was haing a look at what you said about the guide scope not being enough, i just read that for a focal length of 1500mm main scope a 150mm+ guide scope will be fine. so with the reducer i hae just under 1000mm FL and the guide scope is 240mm FL. in yoour opionion is 240mm enough?

[labtech1122]

"A small 150-200mm guide scope should work up to 1,500 to 2,000mm focal length telescopes" i quoted this from google, is that right?

[Elp]

I seriously doubt it, at bare minimum I work at 1/3 but it boils down to the imaging/resolving scale of the camera which is connected to the guidescope and whether it matches the imaging train.

In simple terms I think of it this way, if you're looking at something in the far far distance (say a person standing still and they take a sidestep), to your eyesight they might not have moved, but if you look through binoculars or something similar you'll likely see the movement, same principle with monitoring a starfield rotation.

You'll also see this visually when looking through a short focal length telescope and a long one like yours and you're not sidereal tracking, in the longer one stars will move more frequently and faster, so your guidescope needs to be able to pick up on this and send commands to your mount.

Edited February 19, 2023 by Elp

[labtech1122]

my The imaging / guiding ratio is 1:2.2

[labtech1122]

2 minutes ago, Elp said:

I seriously doubt it, at bare minimum I work at 1/3 but it boils down to the imaging/resolving scale of the camera which is connected to the guidescope and whether it matches the imaging train.

In simple terms I think of it this way, if you're looking at something in the far far distance (say a person standing still and they take a sidestep), to your eyesight they might not have moved, but if you look through binoculars or something similar you'll likely see the movement, same principle with monitoring a starfield rotation.

You'll also see this visually when looking through a short focal length telescope and a long one like yours and you're not sidereal tracking, in the longer one stars will move more frequently and faster, so your guidescope needs to be able to pick up on this and send commands to your mount.

ok fair enough, i think having a 500mmFL refractor on the side would look mental and put the mount well over its weight. i was looking at off axis guiding but this puts more weight on the back end of the image train and ive got the scope nearly as far as it goes on the dovtail to balance as it is, i dont think i would be able to balance it with added bits on the back

[labtech1122]

9 minutes ago, Elp said:

I seriously doubt it, at bare minimum I work at 1/3 but it boils down to the imaging/resolving scale of the camera which is connected to the guidescope and whether it matches the imaging train.

In simple terms I think of it this way, if you're looking at something in the far far distance (say a person standing still and they take a sidestep), to your eyesight they might not have moved, but if you look through binoculars or something similar you'll likely see the movement, same principle with monitoring a starfield rotation.

You'll also see this visually when looking through a short focal length telescope and a long one like yours and you're not sidereal tracking, in the longer one stars will move more frequently and faster, so your guidescope needs to be able to pick up on this and send commands to your mount.

would having a barlow on the guide scope work? just spitting ideas

[Elp]

You can try binning the guidecam X2, might help a little. Guiding also has a lot to do with your settings and the seeing on the night.

I've got the same Dec balancing issue but am working on a counterweight solution up front.

[labtech1122]

10 minutes ago, Elp said:

I seriously doubt it, at bare minimum I work at 1/3 but it boils down to the imaging/resolving scale of the camera which is connected to the guidescope and whether it matches the imaging train.

In simple terms I think of it this way, if you're looking at something in the far far distance (say a person standing still and they take a sidestep), to your eyesight they might not have moved, but if you look through binoculars or something similar you'll likely see the movement, same principle with monitoring a starfield rotation.

You'll also see this visually when looking through a short focal length telescope and a long one like yours and you're not sidereal tracking, in the longer one stars will move more frequently and faster, so your guidescope needs to be able to pick up on this and send commands to your mount.

"In the past, before the age of computers and digital cameras, astro images would use a guidescope that was about 1/3rd the focal length of a telescope for visual guiding with the human eye. So when talking to older Astro- imagers, you may still hear this recommendation. For example, if your telescope has a focal length of 1500mm, older astrophotographers may recommend guide scopes with a focal length of 500mm. However, digital cameras today are much more sensitive than the human eye and most guide cameras can detect apparent deviations in the guide star of about 0.1 pixels on average. So assuming that you want to detect a tracking error with a sensitivity up to1 pixel, a soft rule of thumb would be to select a guide scope with a focal length that is at least about 1/10th the size of your imaging scope"

[labtech1122]

1 minute ago, Elp said:

You can try binning the guidecam X2, might help a little. Guiding also has a lot to do with your settings and the seeing on the night.

I've got the same Dec balancing issue but am working on a counterweight solution up front.

i havent really had an issue with the guiding in all fairness, i will try binning at x2, how do i do that on phd2?

ah yes nice idea, i would do that but it would over weight the mount

[Elp]

I use an Asiair so sure someone with direct PHD2 use can advise on how to change bin.

Being better balanced will also help with the guiding, on my last test, I think it for me I only need around 500g up front to balance it, but it depends on the setup being used.

[labtech1122]

at the moment i have it pretty well balanced but have very little room to move further down. the only thing that does change the balance is the guide scop is in the 2 oclock posion on the telescope with refernce to where it attaches on the mount so its heavier one side than the other. not sure if thats a problem though or how to change it, i dont hae any other mounting points on the telescope

[labtech1122]

also you would happen to know the correct or where i cand the correct BF for the ntares x0.63 FR do you?