Chroma 3nm halo

[ollypenrice]

We are very exacting in our requirements (reasonably so, given what we pay) but with so many optical elements in the train it is difficult to know what causes what. It might be that the tight bandpass produced by the filters is eliminating a blurring of the same phenomenon when the bandpass is wider. Very hard to know. I would begin by asking Chroma.

Olly

[Whirlwind]

4 hours ago, souls33k3r said:

Unfortunately they are worthless to me if it doesn't work the way they are intended. I don't have to put up with software wizardry to fix something that shouldn't even be present in the first place. I really can't put up with this especially I paid nearly £500 per filter. If I was imaging a bright star then yes it makes sense for the microlensing effect to be very much visible and may even have the newtonian rings but on a small star? Certainly something is not right here. 

Newtons rings is a different from the more traditional microlensing effect you might get with and ASI1600.  In fact that you don't see it on the bright stars makes me more certain that Newton's rings are the cause.  The more traditional microlens effect is a result of pure reflection from surfaces that have less than ideal coatings (and hence are more obvious around brighter stars).   The newtons rings arise because there the you have a variable boundary between a planar and spherical surface resulting in constructive and destructive interference arising from reflection at the boundaries.  

The radius of any given ring is proportional to only the radius of the spherical surface and the wavelength of the light being observed.  This gives an explanation as to why very bright stars don't show the effect.  Regardless of the brightness of the star any given ring is at the same distance from the star.  However the flux of a much brighter star is 'scattered' over a wider radius.  This flux hence overwhelms the effect of the newtons rings - it's still there but is simply swamped by the actual signal.  For faint stars there is too little flux to detect above the background.  It's only the medium bright stars where there is enough flux but are still relatively small.  

I am assuming that you have moved to narrower filters than previously.  Broader filters are likely to have hidden the effect as well.  Newton's rings are wavelength dependent and as such each wavelength would constructively and destructively interfere at different radii from the star.  When you conflate the various wavelengths together they balance out across the same radius and it all merges (so the effect is masked).  

So where could this come from. If it is the filter then it would needed to have been made poorly as you would need part of the surface to be spherical and have pulled away from another planar element of the filter.  As it is an interference filter this is not impossible.  However, as it is present in all three filters then it would imply quality control at Chroma has gone down the pan and the lack of other similar issues reported elsewhere suggests it is unlikely or that you were very unlucky to get this with three filters.  Conversely we do know of an area of your system where this is a known planar and spherical touching surface.  This being the cover slip and the microlens. In probability terms given this is 'a known' for the sensor it is more likely it is arising at this location (it doesn't matter which filters you use it is always there but may just be washed out where broader filters are used).  To an extent each of these options can be tested.  The formula for Newton's rings is known.  As you know the radius of a number of rings for each wavelength, you could measure these and then calculate the radius of the spherical surface causing the effect for each filter band.  If this comes out as approximately the same then that would imply the same source (and more likely to be from the sensor).  If each were widely different then that would suggest another source (as the radius of the microlens would be the same regardless of wavelength and hence more likely to be the filters).  Note you would need to measure closest to the centre of the optics to limit optical distortion (i.e. near centre of the chip).

 

Edited November 15, 2020 by Whirlwind

[Adam J]

I dont see this at all on my Astrodons with ASI1600MM Pro so its not to do with other filters masking the issue. It could be a result of the low F-ratio optics and large apperture resulting in newtons rings...The only time I have ever had this effect was with a coma corrector, I sent it back and it turned out that they had not coated two of the lens surfaces.

Adam

Edited November 15, 2020 by Adam J

[Whirlwind]

1 hour ago, Adam J said:

I dont see this at all on my Astrodons with ASI1600MM Pro so its not to do with other filters masking the issue. It could be a result of the low F-ratio optics and large aperture resulting in newtons rings...The only time I have ever had this effect was with a coma corrector, I sent it back and it turned out that they had not coated two of the lens surfaces.

Adam

So just working on your signature, there are two things to note.  Firstly your Astrodons are 5nm, the extra width could be enough to 'bloat' the medium stars just enough to hide the effect.  Secondly you are imaging with a newtonian + coma corrector which may again bloat the stars slightly compared to the EdgeHD as I have no idea which produces smaller stars (also the airy disc size could be different/larger again masking the effect - airy disc is naturally smaller in a larger telescope/but have to factor in CO).  Another possibility is that the cover slip on your camera is tilted enough compared to the OP to remove the effect.  Without a side by side comparison and literally swap the cameras it is difficult to tell. I would still suggest running the numbers to see if we can find whether the sphere radius causing the issue is the same in all filters.

[MattJenko]

Not the same scope by any stretch of the imagination (TS60ED reduced to 260 FL), but the exact same 3nm Chroma Ha and ASI1600Cool - older one, not the Pro. Could be argued there are some blurry halos around my stars but at this resolution its hard to tell. I would tend to attribute to the camera given my experience with it as opposed to the filter as I have used it with an Atik 414ex and a 460ex and not a hint of halo with those.

 

 

[souls33k3r]

I guess I'll email FLO tomorrow and bring forth this issue to them. Let's see where this leads me because I'm just not pleased with the results no matter how I look at it. 

[Adam J]

3 hours ago, Whirlwind said:

So just working on your signature, there are two things to note.  Firstly your Astrodons are 5nm, the extra width could be enough to 'bloat' the medium stars just enough to hide the effect.  Secondly you are imaging with a newtonian + coma corrector which may again bloat the stars slightly compared to the EdgeHD as I have no idea which produces smaller stars (also the airy disc size could be different/larger again masking the effect - airy disc is naturally smaller in a larger telescope/but have to factor in CO).  Another possibility is that the cover slip on your camera is tilted enough compared to the OP to remove the effect.  Without a side by side comparison and literally swap the cameras it is difficult to tell. I would still suggest running the numbers to see if we can find whether the sphere radius causing the issue is the same in all filters.

My sig is 2 years out of date so you can't work anything off my signature...

One thing I would say is that the place I have seen this effect more than any other is in narrow band images taken by the Hubble space telescope and I am sure there are no issues with its camera or filters. It will be a combination of  factors acting together as opposed to any single bit of kit being at fault. Hence I suspect op will just have to live with the effect. 

I'll ll be interested to hear what Chroma say none the less. 

Adam

 

Edited November 16, 2020 by Adam J

[souls33k3r]

5 hours ago, Adam J said:

My sig is 2 years out of date so you can't work anything off my signature...

One thing I would say is that the place I have seen this effect more than any other is in narrow band images taken by the Hubble space telescope and I am sure there are no issues with its camera or filters. It will be a combination of  factors acting together as opposed to any single bit of kit being at fault. Hence I suspect op will just have to live with the effect. 

I'll ll be interested to hear what Chroma say none the less. 

Adam

 

Most certainly not just going to "live with the effect" if it doesn't work, they're going back and I'd be happy to buy the cheaper filters that don't have this effect/issue. 

[souls33k3r]

I found someone on Instagram who luckily has the absolute exact same setup as mine, even to the second scope. I've been exchanging messages with him and he was kind enough to share some single subs, stacked masters and processed image and they don't exhibit the same issue. 

Just wanted to put this out there. 

[Adam J]

3 hours ago, souls33k3r said:

Most certainly not just going to "live with the effect" if it doesn't work, they're going back and I'd be happy to buy the cheaper filters that don't have this effect/issue. 

My point was only that it may be a combination of factors so not the fault of the filters as such. It's up to you if you want to keep them of course.  

[souls33k3r]

22 minutes ago, Adam J said:

My point was only that it may be a combination of factors so not the fault of the filters as such. It's up to you if you want to keep them of course.  

I totally get what you mean mate. Of course I spent top dollar to keep the filters and if they had worked with the gear combination that I have then I would have no leg to stand on. I'll be happy to have this set returned and to be replaced with another set. Not sure there's more I can do at this point. 

[Whirlwind]

17 hours ago, Adam J said:

My sig is 2 years out of date so you can't work anything off my signature...

One thing I would say is that the place I have seen this effect more than any other is in narrow band images taken by the Hubble space telescope and I am sure there are no issues with its camera or filters. It will be a combination of  factors acting together as opposed to any single bit of kit being at fault. Hence I suspect op will just have to live with the effect. 

Yeah, I did note that it was based on your signature, so if it is out of date then less can be inferred.  But the principles still stand.  

As for space telescopes they don't tend to have cover slips that consumer versions do.  They are prepared in clean rooms so whereas consumer versions have to take some abuse from the environment.  They tend to introduce issues in the far red and infra-red which isn't great for photometry and spectroscopy of cool (or distant) objects.

[Whirlwind]

9 hours ago, souls33k3r said:

I found someone on Instagram who luckily has the absolute exact same setup as mine, even to the second scope. I've been exchanging messages with him and he was kind enough to share some single subs, stacked masters and processed image and they don't exhibit the same issue. 

That's fortunate and interesting because that would suggest a different manufacturing tolerance level.  For example it could be that the chip is tilted slightly or even that the cover slip isn't lying against the micro-lenses.  Still think the best option would be to run the numbers and see whether you get the same radius causing the effect in each filter as that would point to a specific piece of equipment.

[Adam J]

28 minutes ago, Whirlwind said:

As for space telescopes they don't tend to have cover slips that consumer versions do.  They are prepared in clean rooms so whereas consumer versions have to take some abuse from the environment.  They tend to introduce issues in the far red and infra-red which isn't great for photometry and spectroscopy of cool (or distant) objects.

and yet the HST has newtons rings. My point was that there are things appart from the cover slip and micro lenses that will cause that and that its possible to get that effect even with as good an optical system as you can make.

Edited November 16, 2020 by Adam J

[tomato]

I don’t think the  HST has the best optical system you can make, hasn’t it got extra bits of glass in the optical train to cope with a primary mirror that has spherical aberration?

[souls33k3r]

1 hour ago, Whirlwind said:

That's fortunate and interesting because that would suggest a different manufacturing tolerance level.  For example it could be that the chip is tilted slightly or even that the cover slip isn't lying against the micro-lenses.  Still think the best option would be to run the numbers and see whether you get the same radius causing the effect in each filter as that would point to a specific piece of equipment.

You will have to probably dumb it down for me. Run what numbers and how? 

[Whirlwind]

23 hours ago, souls33k3r said:

You will have to probably dumb it down for me. Run what numbers and how? 

So if we assume it is Newton's rings then there is a specific equation that can be run which is where the radius of the nth bright ring is given by multiplying the wavelength observed the radius of the spherical surface multiplied by (the ring number measuring - 0.5) all to the power of 0.5 (easier to read here https://en.wikipedia.org/wiki/Newton's_rings (first equation).

As such what we need is a distance measurement from the centre to the centre of a bright ring (and knowing which one) and as we have a specific wavelength we should then be able to determine the radius of the spherical surface. If this is run for each filter then we should be able to determine whether the radius of the spherical surface is the same.  If it is then that is a strong indicator that it is newtons rings and that it has one specific cause.  If it isn't the same then that might imply that Newton's rings isn't the cause or that it is a different source.  As the filters would be the only thing that was changing that would give a lot more empirical evidence that it is the filters at fault.

To start you could count the pixels from the centre to which ever ring you choose (and count which ring).  With the pixel scale that will give a distance.  You can run this for each filter (note you need one in the centre of the field of view so other optic distortions don't come into play).

If you have a solar telescope you could also use the camera on the sun.  It passes the same wavelength but you can remove the filters as potential cause if the same effect is seen.  On the other hand no effect would more strongly suggest a filter or other problem (or isn't N'rings).

 

[groberts]

Souls: I wondered if you've seen this thread on CD on this issue, it's excellent and couldn't be clearer + seems to be a common problem:

https://www.cloudynights.com/topic/715162-chroma-3nm-orientation/

Meanwhile, I also heard back from Chroma who say: "In most cases orientation does not matter with these types of filters, but if you want the filter-coated side to face the sensor, if you read the writing on the edge of the filter, the filter coating will be right side up." 

This corresponds with the aforesaid CN thread. 

Good luck.

Graham

 

I

[souls33k3r]

1 hour ago, groberts said:

Souls: I wondered if you've seen this thread on CD on this issue, it's excellent and couldn't be clearer + seems to be a common problem:

https://www.cloudynights.com/topic/715162-chroma-3nm-orientation/

Meanwhile, I also heard back from Chroma who say: "In most cases orientation does not matter with these types of filters, but if you want the filter-coated side to face the sensor, if you read the writing on the edge of the filter, the filter coating will be right side up." 

This corresponds with the aforesaid CN thread. 

Good luck.

Graham

 

I

LOL mate, look back at the previous page and you asked me about this link and I gave it to you

That is exactly how I had mine fitted. 

My filters are definitely showing something just more than these concentric circles, it shows these weird halos around the stars at the edge of the field. All three filters. 

I've sent my images to Chroma and they are looking at it. Not sure if I can keep up with this if they come back to say that this is normal especially after what I've paid for them.

[groberts]

Doh!  Ah well, hope it works out, will be following your events. 

I'll be fitting mine soon + then need some clear skies , which on recent evidence seems unlikely.

Graham   

[souls33k3r]

4 hours ago, groberts said:

Doh!  Ah well, hope it works out, will be following your events. 

I'll be fitting mine soon + then need some clear skies , which on recent evidence seems unlikely.

Graham   

Cheers matey. I have emailed FLO with my findings who in turn have emailed Chroma who are inspecting the subs and stacked results. As soon as I hear back from them on this, I shall be updating. 

Yeah unfortunately the skies don't look promising for the upcoming weeks and I fear that if Chroma asks me to make a few more tests, it might be weeks if not a month at least before I can get back to them. 

[Ken82]

Hope you get it sorted souls 👍

Just of interest what magnitude star are we talking about ? 
 

Would you mind uploading a single sub ?

Ken 

[Ken82]

Souls you had me thinking for a minute. I can see a small ring type artefact on the garnet star in my elephant image which is mag 4. Its very acceptable and only noticed under extreme zoom. So after finishing my pacman last night i pointed to alnitak and got a single HA + OII sub. No sign at all of it here. So apart from the microlensing id expect yours to be similar. 

 

[souls33k3r]

1 hour ago, Ken82 said:

Souls you had me thinking for a minute. I can see a small ring type artefact on the garnet star in my elephant image which is mag 4. Its very acceptable and only noticed under extreme zoom. So after finishing my pacman last night i pointed to alnitak and got a single HA + OII sub. No sign at all of it here. So apart from the microlensing id expect yours to be similar. 

 

Apologies for the delay in replying, just had a busy few days. 

Here are the single and stacked Ha subs. Look at the bottom right hand corner star which like I said is bigger of the bunch. 

Single:

 

Stacked:

No processing has been done apart from calibration frames applied.

[Whirlwind]

20 hours ago, souls33k3r said:

Apologies for the delay in replying, just had a busy few days. 

Here are the single and stacked Ha subs. Look at the bottom right hand corner star which like I said is bigger of the bunch. 

I'm a bit confused but I don't see any ringing on these images?