Unfortunately I am experiencing strong microlensing diffraction effects on bright stars with my camera.
Below are two images of the iris and ghost nebula with the bright star theta cepeus sitting in the middle to illustrate this issue.
I am observing this effect with different scopes paired with the qhy268mc so the telescope can be ruled out as a cause.
Interestingly, I have heard from others using a simillar camera, such as the ZWO 2600MC, who have not reported experiencing any of these effects.
The attempts to remove this artifact are never a real success. I initally try to mitigate it using pixelMath but in the end photoshop is my friend.
So my questions are:
- Is this effect common among other users of the same camera, or are there individuals who have not encountered it?
- Do other cameras produce it too?
- Would the use of a UV/IR-cut off filter make any difference in addressing this problem? In my understanding this is one of the main phyiscal differences of those two cameras with the ZWO having such a non-removable filter whereas the QHY doesn't.
- How do you deal with this artifact in post?
cs, michael
Single 3 minute sub:
Starless version (just for illustration) with > 50h of total exposure time:
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Have you tried a different UV/IR filter? I have never seen anything like this before with any of the IMX571's. Consider this post more or less me subscribing to find out exactly whats wrong here! That's really bad.
Are you sure the filter might not be in backwards? Looking at this photo: https://www.astrobin.com/sul3rw/B/ It almost feels like it's reflecting light back.
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In my understanding and as you stated, it's most probably light that is reflected from the sensor and diffracted by the microlenses back onto the sensor cover or the heating glass and from there, again back to the sensor.
The idea of the cover being installed backwards also crossed my mind, but why would such a glass only be coated on one side?
Nevertheless, I'm not the only one experiencing this issue, so maybe there are some faulty items. You can check out these links for more information:
- A discussion on Cloudy Nights: link
- There is also a video by the YouTuber Galactic Hunter addressing this effect: link
The probability that this effect will disappear with a UV/IR filter is shrinking, given that you found one of my images showing this artifact even with the use of the NB filter attached, but I'll give it a try anyway.
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Michael:
In my understanding and as you stated, it's most probably light that is reflected from the sensor and diffracted by the microlenses back onto the sensor cover or the heating glass and from there, again back to the sensor.
The idea of the cover being installed backwards also crossed my mind, but why would such a glass only be coated on one side?
Nevertheless, I'm not the only one experiencing this issue, so maybe there are some faulty items. You can check out these links for more information:
- A discussion on Cloudy Nights: link
- There is also a video by the YouTuber Galactic Hunter addressing this effect: link
The probability that this effect will disappear with a UV/IR filter is shrinking, given that you found one of my images showing this artifact even with the use of the NB filter attached, but I'll give it a try anyway.
I think these topics you're referring to are all referring to the 1600, which is known for microlensing. You shouldn't be having this issue with an IMX571. I'm gonna ask around see if anyone else has had this issue, point them here. It definitely looks like microlensing, but I just find it hard to believe.
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Michael:
Unfortunately I am experiencing strong microlensing diffraction effects on bright stars with my camera.
Below are two images of the iris and ghost nebula with the bright star theta cepeus sitting in the middle to illustrate this issue.
I am observing this effect with different scopes paired with the qhy268mc so the telescope can be ruled out as a cause.
Interestingly, I have heard from others using a simillar camera, such as the ZWO 2600MC, who have not reported experiencing any of these effects.
The attempts to remove this artifact are never a real success. I initally try to mitigate it using pixelMath but in the end photoshop is my friend.
So my questions are:
- Is this effect common among other users of the same camera, or are there individuals who have not encountered it?
- Do other cameras produce it too?
- Would the use of a UV/IR-cut off filter make any difference in addressing this problem? In my understanding this is one of the main phyiscal differences of those two cameras with the ZWO having such a non-removable filter whereas the QHY doesn't.
- How do you deal with this artifact in post?
cs, michael
Single 3 minute sub:
Starless version (just for illustration) with > 50h of total exposure time:
I think you just have a defective AR window. Sometimes the simplest answer is the correct one. If you REALLY want to rule out the telescope, use any other camera that you have just to be sure, even if its a planetary one. It might look a little weird but at least you'll know if its the AR window or not.
Just make sure that any other camera you use has the same set-up (same filters, imaging train, etc).
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Thanks Brian! Although I think I just figured it out and have the solution :-)
It's hard to believe but it seems like the UV/IR Filter (2" from Optolong) indeed did it's magic!
Have a look on these two cropped images I just shot as a quick test with my bigger sope (1800mm).
It's just one single sub of 60s each on Vega (a Lyr) stretched half way:
no Filter:
with UV/IR Filter: (diffraction pattern is completely gone)
I'm definitely going to try it also on Theta Cepheus with my smaller scope but I'm very positive that it will work out the same way.
Just have to figure out how to attach both filters when using the l-extreme one emission nebulae since the two filters cannot be screwed together.
But after all it makes me wonder why the QHY268 doesn't come with a pre-installed UV/IR filter then?
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Indeed, the AR Window could still be defective in my case even if I've found a solution to the problem.
I might contact QHYCCD to get their opinion on it.
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You do realize you can't image without at minimum a UV/IR filter in place right?
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Brian Puhl:
You do realize you can't image without at minimum a UV/IR filter in place right?
Well, it took me almost two years to realize but now I know  |
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You shouldn't need a UV/IR filter when using a dual NB filter. It already cuts out way more light than the UV/IR. I have 4 full spectrum cameras (including 2 QHY) and you only need the UV/IR when you are not using any other filter or if the filter you want to use lets light through from outside the 375-700nm window, usually this is only visual filters but some IDAS need a second filter.
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Joe Linington:
You shouldn't need a UV/IR filter when using a dual NB filter. It already cuts out way more light than the UV/IR. I have 4 full spectrum cameras (including 2 QHY) and you only need the UV/IR when you are not using any other filter or if the filter you want to use lets light through from outside the 375-700nm window, usually this is only visual filters but some IDAS need a second filter.
That was also my understanding, but at least the Optolon L-extreme proves otherwise as this images shows: https://www.astrobin.com/sul3rw/B/
As far as I can recall, no broadband subs were captured.
Will need to test that out on bright stars with the dualband alone and with both filters attached.
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Michael:
Joe Linington:
You shouldn't need a UV/IR filter when using a dual NB filter. It already cuts out way more light than the UV/IR. I have 4 full spectrum cameras (including 2 QHY) and you only need the UV/IR when you are not using any other filter or if the filter you want to use lets light through from outside the 375-700nm window, usually this is only visual filters but some IDAS need a second filter.
That was also my understanding, but at least the Optolon L-extreme proves otherwise as this images shows: https://www.astrobin.com/sul3rw/B/
As far as I can recall, no broadband subs were captured.
Will need to test that out on bright stars with the dualband alone and with both filters attached.
Well that is interesting but makes some sense, the L-Extreme is a well known halo offender. I wonder if you would see the same with an IDAS NBZ or Antlia ALP-T, both of which usually have much less halo than the L-Extreme. If you were local, I'd happily lend you mine to try. I had actually forgotten that halo's are the root cause of micro lensing.
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Joe Linington:
Michael:
Joe Linington:
You shouldn't need a UV/IR filter when using a dual NB filter. It already cuts out way more light than the UV/IR. I have 4 full spectrum cameras (including 2 QHY) and you only need the UV/IR when you are not using any other filter or if the filter you want to use lets light through from outside the 375-700nm window, usually this is only visual filters but some IDAS need a second filter.
That was also my understanding, but at least the Optolon L-extreme proves otherwise as this images shows: https://www.astrobin.com/sul3rw/B/
As far as I can recall, no broadband subs were captured.
Will need to test that out on bright stars with the dualband alone and with both filters attached.
Well that is interesting but makes some sense, the L-Extreme is a well known halo offender. I wonder if you would see the same with an IDAS NBZ or Antlia ALP-T, both of which usually have much less halo than the L-Extreme. If you were local, I'd happily lend you mine to try. I had actually forgotten that halo's are the root cause of micro lensing.
Thanks, well the L-Ultimate as an upgrade has crossed my mind and I might even borrow it from someone...
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Michael E.:
Thanks, well the L-Ultimate as an upgrade has crossed my mind and I might even borrow it from someone...
I've just had a look at my picture of the Jellyfish nebula with the very bright eta Gem. Picture taken with the L-Ultimate filter, the bright star also seems to have some strange diffraction pattern. I never thought about micro lensing, since I never had issues with the L-Ultimate like this before. Also pictures of bright stars taken with mu Optolong UV/IR-cut filter never had this issue. Filters are always in the same orientation in the filter holder, so that didn't change.
Optical train is a long FL refractor (975mm), L-Ultimate filter, Player One Poseidon-C camera (which is also an IMX571 sensor with standard AR window).
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Huib Wouters:
Michael E.:
Thanks, well the L-Ultimate as an upgrade has crossed my mind and I might even borrow it from someone...
I've just had a look at my picture of the Jellyfish nebula with the very bright eta Gem. Picture taken with the L-Ultimate filter, the bright star also seems to have some strange diffraction pattern. I never thought about micro lensing, since I never had issues with the L-Ultimate like this before. Also pictures of bright stars taken with mu Optolong UV/IR-cut filter never had this issue. Filters are always in the same orientation in the filter holder, so that didn't change.
Optical train is a long FL refractor (975mm), L-Ultimate filter, Player One Poseidon-C camera (which is also an IMX571 sensor with standard AR window).
Interesting to see that the L-Ultimate does that too.
Since your camera also doesn't come with a built-in IR/UV-Cut filter, have you tried combining the two?
I've never experienced any of those artifacts since using this IR/UV-Cut filter and I'm using it even in combination with an NB-filter.
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Michael E.:
Huib Wouters:
Optical train is a long FL refractor (975mm), L-Ultimate filter, Player One Poseidon-C camera (which is also an IMX571 sensor with standard AR window).
Interesting to see that the L-Ultimate does that too.
Since your camera also doesn't come with a built-in IR/UV-Cut filter, have you tried combining the two?
I've never experienced any of those artifacts since using this IR/UV-Cut filter and I'm using it even in combination with an NB-filter.
Haven´t tried that, the L-Ultimate shouldn´t need that because it also blocks UV/IR frequencies.
I could add another filter, but this would place it 45mm away from the other glass surfaces, which increases the chance of reflections. In my set-up, I have the L-Ultimate filter only 10mm in front of the camera's AR-window.
What's strange, is that I see this pattern in eta Gem, but not in the much brighter Alnitak, which I imaged with exactly the same settings the night after.
I will not investigate further for now, and return to the Jellyfish nebula (and eta Gem) when the skies are clear again.
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Huib Wouters:
Michael E.:
Huib Wouters:
Optical train is a long FL refractor (975mm), L-Ultimate filter, Player One Poseidon-C camera (which is also an IMX571 sensor with standard AR window).
Interesting to see that the L-Ultimate does that too.
Since your camera also doesn't come with a built-in IR/UV-Cut filter, have you tried combining the two?
I've never experienced any of those artifacts since using this IR/UV-Cut filter and I'm using it even in combination with an NB-filter.
Haven´t tried that, the L-Ultimate shouldn´t need that because it also blocks UV/IR frequencies.
I could add another filter, but this would place it 45mm away from the other glass surfaces, which increases the chance of reflections. In my set-up, I have the L-Ultimate filter only 10mm in front of the camera's AR-window.
What's strange, is that I see this pattern in eta Gem, but not in the much brighter Alnitak, which I imaged with exactly the same settings the night after.
I will not investigate further for now, and return to the Jellyfish nebula (and eta Gem) when the skies are clear again.
The combination of both filtes is indeed counterintuitive and yet it made a difference - at least for me.
My image train seems to work just fine with a distance of about 2 - 3cm between the two filters (can't measure it right now) and hasn't produced any reflections, even with two completely different scopes.
No artifacts on alnitak is strange. Might be too blurry perhaps...
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