Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

ASI1600MM Pro - EDGE HD 8 - .7 Reducer - Triangular Reflection Artifacts

Celestron filters imaging
  • Please log in to reply
8 replies to this topic

#1 RianBergenAstro

RianBergenAstro

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 13 Apr 2020

Posted 16 September 2020 - 05:52 PM

I seem to be encountering some weird Triangular Reflection Artifacts as well as some HALOS around Stars as well as a grid of Halos throughout the image.

My current Image Train is:
EDGE HD 8

.7 Reducer

Celestron T-Adapter (with the extension attached)

ZWO 8 Position Filter Wheel (contains the ZWO 31mm filter set)

ASI1600mm Pro

 

Autosave.jpg

This image was reduced in size and quality to follow upload rules.

 

I have no idea where this is coming from at the moment. Has anyone else encountered this?

 

Dropbox link to fits files for all filters plus the empty filter slot: https://www.dropbox....QocNQaC5Fa?dl=0


Edited by RianBergenAstro, 16 September 2020 - 05:53 PM.


#2 RianBergenAstro

RianBergenAstro

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 13 Apr 2020

Posted 16 September 2020 - 05:55 PM

I stretched the above image to better show all artifacts.

All subs in dropbox link are 30 seconds long at 139 gain and 50 offset.



#3 petert913

petert913

    Skylab

  • *****
  • Posts: 4,342
  • Joined: 27 May 2013
  • Loc: Silverton, OR

Posted 16 September 2020 - 07:01 PM

Have you taken frames without the reducer?  And then remove filters from the light path.   Just trying to eliminate possible reflection sources.



#4 Stelios

Stelios

    Voyager 1

  • *****
  • Moderators
  • Posts: 10,241
  • Joined: 04 Oct 2003
  • Loc: West Hills, CA

Posted 16 September 2020 - 07:10 PM

Your collimation is very suspect. Also I think (hard to tell for sure) that your spacing may be a bit over what's needed for best corner stars. 

 

And then there's the microlensing effect. And then there's some problem with filter (I checked out Lum, and the *second* brightest star has a halo that it shouldn't have).

 

But basically, it would take a very high quality setup indeed to image a star this bright properly, with a camera with perfect anti-reflection coatings, and expensive filters. Not at this price point. 

 

IMO, if you fix your collimation, upgrade your filters (is this the *new* ZWO set, or an older one? Doesn't look much improved from my old one) and avoid super-bright stars, you'll get some very nice images.



#5 Astrojedi

Astrojedi

    Aurora

  • *****
  • Posts: 4,820
  • Joined: 27 May 2015
  • Loc: SoCal

Posted 16 September 2020 - 07:31 PM

I seem to be encountering some weird Triangular Reflection Artifacts as well as some HALOS around Stars as well as a grid of Halos throughout the image.

My current Image Train is:
EDGE HD 8

.7 Reducer

Celestron T-Adapter (with the extension attached)

ZWO 8 Position Filter Wheel (contains the ZWO 31mm filter set)

ASI1600mm Pro

 

attachicon.gifAutosave.jpg

This image was reduced in size and quality to follow upload rules.

 

I have no idea where this is coming from at the moment. Has anyone else encountered this?

 

Dropbox link to fits files for all filters plus the empty filter slot: https://www.dropbox....QocNQaC5Fa?dl=0

 

Which filter was this image taken with? Are you experiencing it with all filters?

You need to follow a process of elimination to isolate the source. For e.g. try without the reducer, try without a filter etc.



#6 RianBergenAstro

RianBergenAstro

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 13 Apr 2020

Posted 16 September 2020 - 07:32 PM

Have you taken frames without the reducer?  And then remove filters from the light path.   Just trying to eliminate possible reflection sources.

I was imaging for roughly 2 months without the .7 reducer and never noticed the triangle or the dimmer repeated halos.

 

 

Your collimation is very suspect. Also I think (hard to tell for sure) that your spacing may be a bit over what's needed for best corner stars. 

 

And then there's the microlensing effect. And then there's some problem with filter (I checked out Lum, and the *second* brightest star has a halo that it shouldn't have).

 

But basically, it would take a very high quality setup indeed to image a star this bright properly, with a camera with perfect anti-reflection coatings, and expensive filters. Not at this price point. 

 

IMO, if you fix your collimation, upgrade your filters (is this the *new* ZWO set, or an older one? Doesn't look much improved from my old one) and avoid super-bright stars, you'll get some very nice images.

My collimation was definitely off as I didn't have enough time to collimate when I took these test shots. This is definitely still a problem even when collimated correctly. My guiding was also off as I had removed an OAG that I would usually have in the optical path to test if my reflections were coming from the OAG (they weren't).

 

My spacing is exactly at 105 not accounting for filter (which would put it at 106ish). It's not perfect, but as close as I could get it for the purposes of running this test:

With Celestron 0.7x reducer: Recommended 105 mm

Celestron T-Adapter: 50mm

Adapter extension (comes with Celestron T-Adapter): 28.5mm

ZWO 8 Position Filter Wheel: 20mm

ZWO ASI1600MM-cooled: 6.5 mm

 

I'm aware of the mirco-lensing as that is an artifact from the ASI1600mm Pro. Not the prettiest stuff, but I can live with it.

 

I bought the filter set this year in February from OPT. Not sure what I got. Is there anyway to check?

I also double checked the Filter Sides as well as reversing the filters. I also tried the empty slot on the filter wheel to see what happens there.The triangle is still there as well as one of the reflection donuts.

 

My main concern at the moment is that it might be the .7 reducer as I've never had the triangle thing before this. The star in the image is VEGA which is usually one of my focusing and star alignment stars.



#7 RianBergenAstro

RianBergenAstro

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 13 Apr 2020

Posted 16 September 2020 - 07:39 PM

Which filter was this image taken with? Are you experiencing it with all filters?

You need to follow a process of elimination to isolate the source. For e.g. try without the reducer, try without a filter etc.

The triangle artifact happens with LRGB, Ha, SII, OIII, as well as the 1 empty slot on my EFW.

I just got the reducer, and I never encountered the triangle artifact before I got the reducer.

(Or at least, I never saw it)

 

It just started raining, so I have to wait. As soon as it clears, I am planning on running some more tests by removing different components (I've already removed the OAG as I thought that was the problem).

 

The drop box link contains the original fit files for all filters as well as the empty slot.



#8 dswtan

dswtan

    Mariner 2

  • *****
  • Posts: 242
  • Joined: 29 Oct 2006
  • Loc: Morgan Hill, CA

Posted 16 September 2020 - 10:15 PM

Maybe best not to over-think this beyond "it's a normal artifact to be expected when you exceed the capabilities of the optical train". As Stelios said more gracefully "avoid super-bright stars". Analogy -- turn your hifi up to max volume - do you get any distortion?

 

Since it's not been mentioned, I believe the technical name for this effect is a type of caustic: https://en.wikipedia...austic_(optics). As you've already determined, it's most likely from reflections interacting with the multiple lenses of the reducer. It's possible that other alignment issues are emphasizing it, fair enough, so maybe you're considering it as a diagnostic tool for that.

 

Here's my version, probably coming from a Hyperstar (not unlike your reducer internally) and multiple bad alignment sources in the optical train:

https://www.cloudyni...n/#entry9789713



#9 RianBergenAstro

RianBergenAstro

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 13 Apr 2020

Posted 21 September 2020 - 01:54 PM

Maybe best not to over-think this beyond "it's a normal artifact to be expected when you exceed the capabilities of the optical train". As Stelios said more gracefully "avoid super-bright stars". Analogy -- turn your hifi up to max volume - do you get any distortion?

 

Since it's not been mentioned, I believe the technical name for this effect is a type of caustic: https://en.wikipedia...austic_(optics). As you've already determined, it's most likely from reflections interacting with the multiple lenses of the reducer. It's possible that other alignment issues are emphasizing it, fair enough, so maybe you're considering it as a diagnostic tool for that.

 

Here's my version, probably coming from a Hyperstar (not unlike your reducer internally) and multiple bad alignment sources in the optical train:

https://www.cloudyni...n/#entry9789713

I know I am pushing what I have to an extreme by pointing it at Vega. I did want to see if there was a way to minimize and reduce it. What really scared me was seeing the reflections without any filters. This plus the fact that I've never noticed it without the reducer...

 

I just ordered Bob's Collimation Knobs. This should make it easier to collimate. I have added better filters to my wish list for the next upgrade as well.

Since I just bought the reducer, would you recommend maybe getting it replaced (just in case)?




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: Celestron, filters, imaging



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics