I captured this in Williston on 8/14/22. The moon was fairly bright for part of the session, but I think the Optolong L-eXtreme filter damped the effect of the moon's brightness a bit. This is a cropped version of my original image.
AT60ED w/ field flattener and Tele Vue PowerMate (2X) [Effective focal length with camera crop factor taken into account was about 1,080 mm]
ASI2600MC Pro (OSC camera)
SkyGuider Pro with guiding via ASIAir Plus using an ASI120mm mini and a 30mm F4 guide scope
Optolong L-Extreme dual-band filter (H-alpha, O-III)
240 second exposures x 30 (2 hrs total), with dark, flat, and bias calibration frames
Stacked in Astro Pixel Processor and processed in Photoshop
It may be just an extension of the Bubble Nebula, but there's a small cloud of nebulosity at about 3:30 from the Bubble nebula. Not sure what it is, and I was hoping someone could tell me. Astrometry.net didn't flag it as anything when I submitted the image for annotation.
I'm going to process this a bit more (and differently) as soon as my computer arrives. The computer I'm using now is just not up to the task so I can't do too much with it.
I reprocessed this image a bit and rotated it to appear like it would in the night sky. Still trying to figure out what the small nebulosity is that's now about 12:30 from the Bubble Nebula... 🤥
Great image capture and processing Greg, the bubble is very clear and nice colors for both the nebulosity and the stars. Stars and nice and round as well, bravo! You get the same artifact I see with my 80mm skywatcher in your stars, and that is a cone artifact pointing towards the middle of the star. I've looked into this in the past and even had skywatcher replace my scope once, only to have the new scope be exactly the same. I don't see this in larger aperture scopes.
Terri
Great image capture and processing Greg, the bubble is very clear and nice colors for both the nebulosity and the stars. Stars and nice and round as well, bravo! You get the same artifact I see with my 80mm skywatcher in your stars, and that is a cone artifact pointing towards the middle of the star. I've looked into this in the past and even had skywatcher replace my scope once, only to have the new scope be exactly the same. I don't see this in larger aperture scopes.
Terri
Thanks for taking a look, Terri! Does the artifact you get always go in the same direction as mine: looks like from the right side? I don't usually bother too much about the stars, to be honest, since I assume that with a doublet refractor I'll just get some bloating and with the L-eXtreme I'll have some halos. I wonder if it's due to the filter? In the attached zoomed in photo of Bode's galaxy where I didn't use a filter, the stars still have weirdness but I don't see the cones (I could be missing them, though).
Great image capture and processing Greg, the bubble is very clear and nice colors for both the nebulosity and the stars. Stars and nice and round as well, bravo! You get the same artifact I see with my 80mm skywatcher in your stars, and that is a cone artifact pointing towards the middle of the star. I've looked into this in the past and even had skywatcher replace my scope once, only to have the new scope be exactly the same. I don't see this in larger aperture scopes.
Terri
I looked back at the stars in my images of the NA/Pelican and the Elephant's Trunk Nebula and I don't see those cones in the stars, Terri! (Take a look at those previous images if you have time -- your eyes are more attuned to these images than mine.) I used the same L-eXtreme filter for all those targets but the difference between those images and the Bubble nebula is that I used a Tele Vue PowerMate for the Bubble Nebula. I wonder if it has anything to do with that.
Greg
Hi Greg, I just looked in the bodes image, but the stars are mostly saturated.. so that'll blow out any detail like the artifact. Exposing for the galaxies is the quickest way to get an image with minimal exposure, but you then risk having stars that are more saturated. Exposing for only a few stars saturated will usually force you to do more integration.. it's all a balance. Given you're using such a small aperture scope, I think you are doing the right thing. So I think they're still there, just can't see them. I need to look into that further myself.. I don't see those kinds of artifacts from my Stowaway 92mm/660mm fl scope and with reducer it's around 500mm. SO I haven't used my 400mm for a long time due to this.
Terri
Hi Greg, so I just searched and looked up again, because I wanted to remember the root cause.. it's aperture vignetting but the cause isn't all that clear. Maybe it is your reducer or barlow or powermate (whatever you use). The aperture vignetting causes an almond shaped star shape, but i'm unclear on why certain scopes have it. It seems the wider angle are more prone to this (my 80mm, your 60mm, and even the Tak FSQ scopes).
T
Hi Greg, so I just searched and looked up again, because I wanted to remember the root cause.. it's aperture vignetting but the cause isn't all that clear. Maybe it is your reducer or barlow or powermate (whatever you use). The aperture vignetting causes an almond shaped star shape, but i'm unclear on why certain scopes have it. It seems the wider angle are more prone to this (my 80mm, your 60mm, and even the Tak FSQ scopes).
T
I saw an old post referring to this on Cloudy Nights. Guess it's just a fact of life with smaller aperture, wide angle scopes. Maybe on the next clear night, I'll take some images of the same target with and without the TV PowerMate to see if it exacerbates the problem. I can adjust my field flattener, but only a couple of mm so I don't think that would do anything. Thanks so much for the input and research, Terri! I appreciate it.
Greg
