I am seeing an issue that I don't understand, which is a single-corner vignette that appears to be changing over time. Below are a sampling of images I've taken with generally the same setup. Relevant details are included. I would greatly appreciate any help that you all can offer, as this is really driving me mad.
Details:
In chronological order:
The Crescent Nebula. No field flattener. 5m exposure @ 300 gain. This was overexposed, and you can see some amp glow in both the right corners.
The Bubble Nebula. No Flattener. 4m exposure @ 200 gain. Here you can see an obvious vignette in the top right corner.
The Tadpoles. We added an Astrophysics Quad TCC .72x reducer. 4m exposure @ 200 gain. It actually looks like the amp glow creeped back in. My suspicion is that I didn't account for the lower F-stop after adding the TCC, so it's overexposed again.
Veil Nebula. Quad TCC. 105s exposure @ 200 gain. Here you can see it's now the bottom right corner that has the issue.
Horsehead. Quad TCC. 25s exposure @ 139 gain. Finally, some consistency. The bottom right corner looks off again.
The kicker is that I don't own the telescope, so I can't completely test this on my own. A friend owns the scope, I own the rest of the imaging equipment, and we meet when there's a clear night to image. So this weekend I've been testing what I can at home, sans-telescope, basically pointing the camera at a white wall with the filter wheel attached, but nothing else. Taking 1s exposures through the O-III filter and 0.0058s exposures through the L filter, which looks... interesting. I have no idea if these are of any value, but you can pretty clearly see the lower right corner looks darker in both. Again, these have a PixInsight auto-stretch applied.
Of note: I have tried these with multiple filters and multiple orientations of the camera with respect to the filter. The corner in question is always the bottom right. The lone exception is the Bubble Nebula above, which I cannot explain.
O-III:
L:
My questions are:
1. Can anyone explain what's going on? Is this a "feature" of the camera sensor, or something else?
2. In your opinion, would this calibrate out if we took flats? We don't typically take flat frames, but I'd be more than happy to make time for them if they would calibrate out these horrid corners.
Happy to try anything people would suggest given the limitation of not having the telescope in my physical presence. Also happy to take notes for test shots to take next time we have the scope out. Thanks much for any ideas or suggestions!
Details:
- These were all imaged from the the same location.
- These were all imaged with the same camera, a ZWO ASI160mm-c pro. I think @ the same temperature of -20, with the exception of the Horsehead for which I forgot to turn on the fan.
- These were all imaged with the same filter wheel, a Starlight XPress 7-position wheel.
- All but the Horsehead nebula were imaged through an Astrodon O-III filter. The Horsehead was imaged through an Astrodon L filter.
- The same scope was used in each image, an Astrophysics StarFire GTX Refractor
- Each image below is a single sub auto stretched in PixInsight.
In chronological order:
The Crescent Nebula. No field flattener. 5m exposure @ 300 gain. This was overexposed, and you can see some amp glow in both the right corners.
The Bubble Nebula. No Flattener. 4m exposure @ 200 gain. Here you can see an obvious vignette in the top right corner.
The Tadpoles. We added an Astrophysics Quad TCC .72x reducer. 4m exposure @ 200 gain. It actually looks like the amp glow creeped back in. My suspicion is that I didn't account for the lower F-stop after adding the TCC, so it's overexposed again.
Veil Nebula. Quad TCC. 105s exposure @ 200 gain. Here you can see it's now the bottom right corner that has the issue.
Horsehead. Quad TCC. 25s exposure @ 139 gain. Finally, some consistency. The bottom right corner looks off again.
The kicker is that I don't own the telescope, so I can't completely test this on my own. A friend owns the scope, I own the rest of the imaging equipment, and we meet when there's a clear night to image. So this weekend I've been testing what I can at home, sans-telescope, basically pointing the camera at a white wall with the filter wheel attached, but nothing else. Taking 1s exposures through the O-III filter and 0.0058s exposures through the L filter, which looks... interesting. I have no idea if these are of any value, but you can pretty clearly see the lower right corner looks darker in both. Again, these have a PixInsight auto-stretch applied.
Of note: I have tried these with multiple filters and multiple orientations of the camera with respect to the filter. The corner in question is always the bottom right. The lone exception is the Bubble Nebula above, which I cannot explain.
O-III:
L:
My questions are:
1. Can anyone explain what's going on? Is this a "feature" of the camera sensor, or something else?
2. In your opinion, would this calibrate out if we took flats? We don't typically take flat frames, but I'd be more than happy to make time for them if they would calibrate out these horrid corners.
Happy to try anything people would suggest given the limitation of not having the telescope in my physical presence. Also happy to take notes for test shots to take next time we have the scope out. Thanks much for any ideas or suggestions!
