20 replies to this topic

[BackyardSpaceDude]

Hello everyone!

 

I'm mid-way through my first SHO project and I've noticed something odd with Sadr. It does show up in my Ha stack but even more so in my Sii:

 

Processed stack:

 

ASI1600MM Pro

ZWO 7nm Sii filter

SW ED80 DS-Pro

93x 180s (Stacked in Siril, processed in PS)

Gain 139

Temp -20

 

It shows up immediately upon the initial levels stretching. I've never had this problem with DSLR, so I'm quite unfamiliar! 

 

I assume it's as a result of the ZWO filters but there are loads of possibilities, so wanted to check the wealth of knowledge on here!

[Craig H]

Do you have previous experience with extremely bright stars in your photos?  Their shear brightness tends to show up internal reflections in your imaging train that are otherwise not an issue.

 

Craig.

[rockstarbill]

Diffraction artifact from the Panasonic sensor in the 1600 camera.

[scadvice]

This has come up a few times here on CN. I have not seen it yet with my 1600 but if we assume it's going to happen on bright stars with that sensor at some point how do we go about minimizing the possibility of that artifact? That's where I think most of us would to carry this discussion further toward now.

[rockstarbill]

There really is no way to get around it on very bright stars. Some folks have used Photoshop or clone stamping to fix it manually to some degree of success. 

[scadvice]

That's what I've read also. Something sticks in my brain about a PI video were someone separated out the stars and some fancy masking then using clone stamp cleaned the areas up. Another was removing the star completely then in some method of replace it with fewer of the same image re-stacked.

 

I need to try and find those videos. 

[ChrisWhite]

The curse strikes again....

 

Search for "microlens diffraction" here on CN, and you will find some interesting (and often colorful) threads on this.  Frank (Freestar8n) and SharkMelly have both done some analysis on this and modeled the pattern (separately). 

 

It's interesting stuff...

Edited by ChrisWhite, 10 August 2020 - 06:07 PM.

[Michael Harris]

I have a different model ZWO camera, the ASI294MC Pro one shot color. It does not have this microlensing artifact but Sadr is so bright that I get a reflection ring from the L-enhance dual band filter. I kind of like the effect, but there are probably ways to correct it that I don’t know yet.

[rockstarbill]

I have a different model ZWO camera, the ASI294MC Pro one shot color. It does not have this microlensing artifact but Sadr is so bright that I get a reflection ring from the L-enhance dual band filter. I kind of like the effect, but there are probably ways to correct it that I don’t know yet.

Use a different filter.  

[RJF-Astro]

Besides the diffration pattern there is also a circular reflection caused bij the filter. This can give you problems, especially if it varies between the narrowband filters. A real pain to process. That is why I went with Chroma narrowband in the end. I have done several images with Sadr in the past two months and reflections were not an issue (microlensing is). You are fine though if they do not bother you or if you avoid really brights stars like Sadr, Alnitak, Y cas, μ Gem etc.

[BackyardSpaceDude]

Thank you all so much for your input. Apologies, another forum noob strikes with an already long-since answered question! 

 

Chroma filters definitely on the cards to reduce some artefacts (I didn't really need a big push) and simply avoiding bright stars seems to be the way forward. I would like to watch those videos on how to process it out, though!

[schmeah]

I suspect if I read through all the threads on this, I could probably find the answer, but is there any way to predict with a given set up when this will likely happen, ie: how bright a star with a given focal length / image scale / filter configuration? A lot of targets have bright stars. 
 

Derek

[TareqPhoto]

One day i will try bright stars and see, with two "microlensing" cameras.

[ChrisWhite]

I suspect if I read through all the threads on this, I could probably find the answer, but is there any way to predict with a given set up when this will likely happen, ie: how bright a star with a given focal length / image scale / filter configuration? A lot of targets have bright stars. 
 

Derek

 

In my experience Aperture plays a role.  I had a powerful pattern with my 8in Newt, but not so much on smaller aperture scopes.  I dont have an example for the latter but the former is here:  https://www.astrobin...page=2&nc=&nce=

 

For fun I tested on Gamma Cas.  The pattern was monstrous!

Edited by ChrisWhite, 13 August 2020 - 06:26 AM.

[Toxic Coolaid]

My 1600 produced quite a disco ball around Alnitak when I shot the Horsehead.  This was with a AT65EDQ so it was a fairly small aperture.

 

https://astrob.in/ja3d8c/0/

[ChrisWhite]

My 1600 produced quite a disco ball around Alnitak when I shot the Horsehead.  This was with a AT65EDQ so it was a fairly small aperture.

 

https://astrob.in/ja3d8c/0/

The magnitude of a star also plays a significant role of course.  Alnitak being 1.74mag compared to Propus in the image I shared at "only" 3.31mag.

 

It would be interesting to see what your pattern looks like with a mag ~3.5 star. 

[RJF-Astro]

This is what I got on my 5" newt (130PDS). That reflection was really horrible by the way, after this picture I decided to ditch the Baader and get Chroma. And this was Ha, not even O3.

 

[TareqPhoto]

This is what I got on my 5" newt (130PDS). That reflection was really horrible by the way, after this picture I decided to ditch the Baader and get Chroma. And this was Ha, not even O3.

 

20200118 IC443.jpg

Did Chroma filter solve the problem?

[RJF-Astro]

Did Chroma filter solve the problem?

I have done some testing so far, but nothing definitive. I did some subs on in March the Horsehead and they had no appearant halos, although it was not enough for a good stacked image as I could only get 2 subs.

 

Most recently I did the Butterly nebula with the 130PDS. Sadr is just on the edge of the frame and I cut it out in the final image, but I see no signs of halos. That bright spot below Sadr is part of the nebula.

 

 

 

I want to do more testing, but I only have camera lenses at the moment. I sold my scopes and bought a 6" UNC, which I had to return to TS because of a bad primary mirror cell. The camera lenses (135-200mm) had no issues at all on Sadr, Deneb and the Veil, both Ha and O3. But I do not know if halos show up to the same extent with these smaller apertures.
 

[TareqPhoto]

I have done some testing so far, but nothing definitive. I did some subs on in March the Horsehead and they had no appearant halos, although it was not enough for a good stacked image as I could only get 2 subs.

 

Most recently I did the Butterly nebula with the 130PDS. Sadr is just on the edge of the frame and I cut it out in the final image, but I see no signs of halos. That bright spot below Sadr is part of the nebula.

 

20200624 IC 1318 Sadr dust lane 6h.jpg

 

 

I want to do more testing, but I only have camera lenses at the moment. I sold my scopes and bought a 6" UNC, which I had to return to TS because of a bad primary mirror cell. The camera lenses (135-200mm) had no issues at all on Sadr, Deneb and the Veil, both Ha and O3. But I do not know if halos show up to the same extent with these smaller apertures.
 

We have some similar items, i also got 6" Newt but from GSO 2 months ago, i got my Chroma filters while ago with first OIII last year and next SII 3 months ago i think, but didn't test them as well, only left is Ha, i only have Astrodon Ha 5nm, not sure if this is enough to cut halo at least, or just buy a cheap 3.5nm Ha filter.

[ruben1999]

I got the exact same pattern on sadr with my asi1600mm. Most likely the sensor.