Any one experiencing same halo issue when using L extreme? I also found bright star on the left always had this offcenter halo. There also a bunch of small orange star that had halo while other star around doesn’t had. Is this all normal? I attached stacked photo with only BGE and autostretch.
My setup is Skyrover 90SAP + Filter Wheel + QHY268C
📷 Orignal stack
📷 Abberation Inspector
📷 Offcenter Halo
It is normal for refractors and leaky cameras in the IR. L-Extreme also leaks in the IR so there you are, halos.
Firstly, the L-eXtreme filter is known for its halos:
https://www.cloudynights.com/forums/topic/745455-l-extreme-extreme-halos-help
Secondly, the halos from off-axis stars are offset because of the design of the Skyrover 90SAP optics.
That is why i didn’t buy L-Extreme or previously L-eNhance, i directly jumped with L-Ultimate, kind of better for halo even slight, i will test it one day i hope.
I hope the new Sky Rover 90mm won’t have this issue with optics, it is the only triplet of 90mm f/6 now i can find with good lower price, and i think it will do the job.
The point I was making about the optics is that with some optical designs the ray bundles forming the images of off-axis stars arrive at the sensor at an angle which means they also pass through the filter at an angle. So the double reflection within the filter substrate leading to the halo means that the halo will be offset. My Redcat51 does the same thing but my Tak Epsilon does not - it’s simply a question of how the optics were designed.
andrea tasselli · Jun 18, 2026, 07:53 AM
It is normal for refractors and leaky cameras in the IR. L-Extreme also leaks in the IR so there you are, halos.
So is it advisible to add a IR behind the narrowband filter? Won’t double filter introduce even more internal reflection?
sharkmelley · Jun 20, 2026, 07:21 AM
The point I was making about the optics is that with some optical designs the ray bundles forming the images of off-axis stars arrive at the sensor at an angle which means they also pass through the filter at an angle. So the double reflection within the filter substrate leading to the halo means that the halo will be offset. My Redcat51 does the same thing but my Tak Epsilon does not - it’s simply a question of how the optics were designed.
Thanks for the info, I thought I had a bad tilt that causing the halo off-axis. So there is no other way to correct this?
Swee Sin Eng · Jun 20, 2026, 12:05 PM
andrea tasselli · Jun 18, 2026, 07:53 AM
It is normal for refractors and leaky cameras in the IR. L-Extreme also leaks in the IR so there you are, halos.
So is it advisible to add a IR behind the narrowband filter? Won’t double filter introduce even more internal reflection?
Not if it is further away from the sensor.
sharkmelley · Jun 20, 2026, 07:21 AM
The point I was making about the optics is that with some optical designs the ray bundles forming the images of off-axis stars arrive at the sensor at an angle which means they also pass through the filter at an angle. So the double reflection within the filter substrate leading to the halo means that the halo will be offset. My Redcat51 does the same thing but my Tak Epsilon does not - it’s simply a question of how the optics were designed.
All optics have the off axis ray bundles arriving at an angle, that is not the reason. The reasons why refractors (but not the well colour-corrected ones) are more affected by this is that they have different path lengths and ray heights as functions of the wavelength, especially away from the RGB lines.
andrea tasselli · Jun 20, 2026, 12:49 PM
All optics have the off axis ray bundles arriving at an angle, that is not the reason. The reasons why refractors (but not the well colour-corrected ones) are more affected by this is that they have different path lengths and ray heights as functions of the wavelength, especially away from the RGB lines.
I’ve no idea what you mean by “different path lengths and ray heights” and I don’t know what are “RGB lines”
But you think this explains the sharply defined offcenter halo in the original post. Is that right?
I have the L-Extreme on a redcat51 and have included an original stack and an inspector panel set for comparison. I have never seen an offset with this filter like your zoom. My nemesis for halos was the Celestron-branded Ha-Hb-OIII triband for the RASA, which seemed inclined to halo just about any bright star… Haven’t seen anything like that with the L-Extreme. Maybe there’s a quality issue?
📷 stacked.jpg
📷 inspect.jpg
sharkmelley · Jun 20, 2026, 10:29 PM
andrea tasselli · Jun 20, 2026, 12:49 PM
All optics have the off axis ray bundles arriving at an angle, that is not the reason. The reasons why refractors (but not the well colour-corrected ones) are more affected by this is that they have different path lengths and ray heights as functions of the wavelength, especially away from the RGB lines.
I’ve no idea what you mean by “different path lengths and ray heights” and I don’t know what are “RGB lines”
But you think this explains the sharply defined offcenter halo in the original post. Is that right?
That’s right.
We can easily do some quick calculations to tell if the halos might be caused by a double internal reflection within the filter glass, which is the typical cause of sharply defined filter halos.
The larger halos in the image (whether offset or not) appear to be around 0.5mm diameter.
The formula for the diameter of a halo caused by internal reflection is:
halo_diameter = 2 * filter_glass_thickness / filter_refractive_index / focal_ratio
We know that the l-extreme is 1.85mm thick. The Skyrover 90SAP has an f/5 focal ratio and let’s assume the filter glass has a refractive index of around 1.5 which is typical for glass.
This leads to an expected halo diameter of 0.49mm which is very close to the observed halos.
I therefore consider it likely that the larger halos are caused by internal reflections within the filter glass itself.
Dave Stirling · Jun 21, 2026, 02:47 AM
I have the L-Extreme on a redcat51 and have included an original stack and an inspector panel set for comparison. I have never seen an offset with this filter like your zoom. My nemesis for halos was the Celestron-branded Ha-Hb-OIII triband for the RASA, which seemed inclined to halo just about any bright star… Haven’t seen anything like that with the L-Extreme. Maybe there’s a quality issue?
📷 stacked.jpg
indeed, there is no halo like mine. now it’s really make me thinking is my L-extreme issue. will try to use other filter to check it out again.