We use 14 Chroma filters for my astrophotography; 7 are 36mm LRGBSHO, 7 are 50mm LRGBSHO. The narrowband filters are 5nm (SII and OIII) and 3nm (Ha). In this post, we present two issues occurring with two different telescopes, both of which have the same (everything but size) filters.
1) Narrowband Issues With Chroma SHO Filters (see equipment for more information) on C14 EdgeHD
I, along with @Tamas Kriska, have detected some odd separation issues that grow particularly pronounced between the SII and OIII filters. Essentially, the centroids are WAY off, with the red (SII) and blue (OIII) channels almost completely separated. See the pictures below:
Image 1: Melotte 15 stars
The very far right is a star on the SHO frame, which has a sharp, bright Ha star with more diffuse blue (OIII) and red (SII) glows in the background. The two combined issues made an image of Melotte 15, whose frames were truly exceptional, unsalvageable. For an example of this issue with Ha and OII, see:
Image 2: Horsehead Nebula in HOO
Horsehead Nebula (IC 434) and Reflection Nebula NGC 2023 in HOO
For the images above, we used this equipment:
* Image 1: all images registered, stacked, and aligned with PixInsight
^ Image 2: all images registered, stacked, and aligned with DeepSkyStacker
We have yet to image, stack, and align in RGB on the 14" Celestron EdgeHD, but an issue on another scope forebodes a similar issue on the 14".
NOTE: Images are binned 2x2, so the scale is about .56"/pixel, and the pixel size is 7.52 microns; seeing is about 1.5-2", so we assume that our atmosphere is not the issue (see below). We are probably not too oversampled either.
2) Broadband Issues With Chroma RGB Filters on Stellarvue SVQ100
I have collected dozens of hours of data since we installed the new camera, the ZWO ASI2600MM, on our 100mm refractor in October. When I imaged the Pleiades, I discovered that the stars in the RGB channels were completely off.
Image 3: Messier 45 RGB stars*
* Registering, aligning, and stacking done with DeepSkyStacker
Image 4: Messier 45 RGB Stars*
* Registering, aligning, and stacking done with PixInsight
For the images above, we used the following equipment:
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The red and blue are virtually separate in Image 4; thus, even with two different telescopes, the red and blue channels are off. We likely can rule out processing, for we used two different applications to register, align, and stack the subs. The only consistent pieces of equipment between the two scopes are the Electronic Filter Wheel (ZWO), the OAG (ZWO), the cameras (from my knowledge, the 2600MM and 6200MM have the same specs outside of the sensor size), and the filters. We assume that the issue is the filters, for monochrome cameras should not have centroid issues like this, and the channel separation is consistent between both scopes, where red and blue are essentially mismatched. Tilt is probably not an issue, also.
Does anyone know what our issue could be? Has anyone had similar issues with their Chroma filters? We'd like to be able to take full advantage of our equipment!
Regards,
@William Gottemoller
1) Narrowband Issues With Chroma SHO Filters (see equipment for more information) on C14 EdgeHD
I, along with @Tamas Kriska, have detected some odd separation issues that grow particularly pronounced between the SII and OIII filters. Essentially, the centroids are WAY off, with the red (SII) and blue (OIII) channels almost completely separated. See the pictures below:
Image 1: Melotte 15 stars
The very far right is a star on the SHO frame, which has a sharp, bright Ha star with more diffuse blue (OIII) and red (SII) glows in the background. The two combined issues made an image of Melotte 15, whose frames were truly exceptional, unsalvageable. For an example of this issue with Ha and OII, see:
Image 2: Horsehead Nebula in HOO
Horsehead Nebula (IC 434) and Reflection Nebula NGC 2023 in HOO
For the images above, we used this equipment:
- Scope: Celestron 14" EdgeHD
- Camera: ZWO ASI6200MM
- Mount: Astro-Physics 1600GTO
- Filters: 50mm Chroma LRGBSHO
- SII: 5nm
- OIII: 5nm
- Ha: 3nm
- Focuser: MoonLite CHL 2.5 inch
- Reducer: Celestron .7x Reducer for C14
- Software: SGP, TheSkyX, PHD2
- Processing: PixInsight*, DeepSkyStacker^, Photoshop
* Image 1: all images registered, stacked, and aligned with PixInsight
^ Image 2: all images registered, stacked, and aligned with DeepSkyStacker
We have yet to image, stack, and align in RGB on the 14" Celestron EdgeHD, but an issue on another scope forebodes a similar issue on the 14".
NOTE: Images are binned 2x2, so the scale is about .56"/pixel, and the pixel size is 7.52 microns; seeing is about 1.5-2", so we assume that our atmosphere is not the issue (see below). We are probably not too oversampled either.
2) Broadband Issues With Chroma RGB Filters on Stellarvue SVQ100
I have collected dozens of hours of data since we installed the new camera, the ZWO ASI2600MM, on our 100mm refractor in October. When I imaged the Pleiades, I discovered that the stars in the RGB channels were completely off.
Image 3: Messier 45 RGB stars*
* Registering, aligning, and stacking done with DeepSkyStacker
Image 4: Messier 45 RGB Stars*
* Registering, aligning, and stacking done with PixInsight
For the images above, we used the following equipment:
- Scope: Stellarvue SVQ100 f/5.8 Apochromatic Refractor
- Camera: ZWO ASI2600MM
- Mount: Astro-Physics 900GTO
- Filters: 36mm Chroma LRGBSHO
- SII: 5nm
- OIII: 5nm
- Ha: 3nm
- Focuser: Starizona MicroTouch
- Software: SGP, TheSkyX, PHD2
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The red and blue are virtually separate in Image 4; thus, even with two different telescopes, the red and blue channels are off. We likely can rule out processing, for we used two different applications to register, align, and stack the subs. The only consistent pieces of equipment between the two scopes are the Electronic Filter Wheel (ZWO), the OAG (ZWO), the cameras (from my knowledge, the 2600MM and 6200MM have the same specs outside of the sensor size), and the filters. We assume that the issue is the filters, for monochrome cameras should not have centroid issues like this, and the channel separation is consistent between both scopes, where red and blue are essentially mismatched. Tilt is probably not an issue, also.
Does anyone know what our issue could be? Has anyone had similar issues with their Chroma filters? We'd like to be able to take full advantage of our equipment!
Regards,
@William Gottemoller
While it could be an issue with the filters, it is very unlikely. More likely is that this is the aberration of the Edge 14 at the corners when used with a full frame sensor. Looking at the spot diagrams from Celestron's own white paper shows that the stars get pretty distorted at 20mm from the center which is close to the edge of a FF sensor. Your corner stars look similar to the spot diagrams and will show color distortions accordingly when they are combined.
