What might be causing these image artifacts?

[eneilson]

Hi Everyone,

I'm relatively new to PixInsight and astrophotography in general. I've done a number of practice image processing for the past few months with good results.  This weekend I took my first ever image on my own equipment.  This was a test exposure so I kept things fairly simple: 10 exposures at 30 seconds each no flats, biases or darks (my equipment details are below).  After stacking and applying a DBE, I see an odd set of artifacts in my image that I've not seen before when working with other images. I suspect this is equipment related and I'm wondering if someone here can discern the issue by looking at the artifacts. The photos below show before-DBE and after-DBE images, both heavily stretched and thanks in advance for the help.

Equipment used:
Canon 60D
EdgeHD 11 with Hyperstar
AP mount
10 30-second exposures at ISO 400 (in heavy light pollution)

[pfile]

the banding is unfortunately a well-known problem with canon cameras. the source of the problem seems to be the bias, and the best way to attack it is to make a master bias from an insane number of bias subs - like 150 or 200. the pattern is also in the lights of course but with a small master bias stack you end up injecting more of it into the calibrated frames.

there's a script in PI (that Georg wrote) that's called CanonBandingReduction and it can help. but with an object with a bright core you will have to take care with the "protect from highlights" setting, tweaking it to get a good result. the image has to be oriented so that the banding is horizontal before you try the script.

anyway your stack may improve with good calibration. with just 30s exposures you can probably make a master dark from 100-200 frames without spending all day on it.

mainly it looks to me like you are removing vignetting with that DBE so you might try 'division' as the background correction method. also i'd reduce the number of DBE samples so that your background model is not 'lumpy'. just hit the corners and the top/bottom/left/right centers inside and outside of the vignetting.

rob

[eneilson]

That's fantastic advice, thanks.  I will give this a go and post a follow-up.

Eric

[pfile]

also even though flats are sometimes a pain in the butt with OSC cameras, it's worth trying to get some flats, mainly so you can concentrate on removing real gradients from the image rather than vignetting.

rob

[eneilson]

Regarding flats, I'll certainly give those a try at some point.  From reading the literature it sounds like DSLR flats require the scope to be at the same focus as the lights and also for the camera to be in the same orientation.  I believe a light box is in my future.

[pfile]

yes, good points - this is true of any flat image, dslr or not. precise focus is probably not super important, but you should not be wildly out of focus. most important is the camera angle, as the shape of the vignetting will change with the angle and any dust motes that are on optical surfaces in front of the sensor will move as the angle changes. there's nothing worse than a dust donut that's just slightly off - it ends up looking "embossed" on the calibrated image...

so if you've removed the camera from the OTA then it's probably better to just take flats next time rather than trying to replicate your camera angle.

with the lightbox be careful that your flat exposure is long enough to average out any flickering in your light source. for instance a fluorescent light has a 60hz frequency so short flat exposures will not be evenly illuminated. if you have to lower the ISO, that's okay, just calibrate the flat subs with bias frames (or dark flats) taken at the same ISO.

rob