SharpCap Forums

Dr. Glover, I’m not sure this is possible, but is there any way to add an RGB Align feature to the Enhancements tab while live stacking?

I live at 54°north latitude, and many of the best targets barely cross 20° above my horizon. The atmospheric dispersion causes some serious chromatic aberration, resulting in red/blue haloes and bloating around brighter stars.

Thanks for your consideration.

Trent

Hi Trent,

it's not an impossible feature to add, but actually you would do better with an ADC (atmospheric dispersion corrector) if you can fit one into your imaging system. Normally they are used for planetary, but unless you are using a large sensor (?bigger than APS?) then they might work for deep sky. The advantage of an ADC is that it should bring all wavelengths back to the same point, whereas the alignment of the 3 colour channels can line up red with green with blue, but can't do anything about the smearing that will be caused by the dispersion within the individual channels.

cheers,

Robin

I use a ZWO ADC when I’m imaging planets, but that’s with an ASI178MC camera. When I’m stacking deep sky, my imaging train is 2” (including reducer on my C11) and an ASI294MC.

I guess I’m just looking for an easy fix for EAA purposes. On the occasions that stack something I’m really happy with and want to take it further, I’ll use RGB Align tools to clean it up. It’s not nearly as good as a hardware solution, but it helps a lot.

I’m just making the assumption that aligning each sub as they come in would be even better at correction than doing the final image as a whole.

Hi,

yes, aligning each sub would probably help a bit. I think it depends on whether the direction/amount of dispersion remains constant during stacking... If it does remain constant then aligning the final result would be fine, if it changes significantly in either direction or amount then aligning the individual frames would be better.

cheers,

Robin

As I get closer to the horizon, my FWHM climbs from an average of ~5.0 at over 60° to over 10.5 at 20°, and it fluctuates wildly; occasionally over 12, then below 10.

I’m curious if the dispersion is causing that as well…?

Hi,

my guess is that dispersion is hurting you a bit, but you are probably also getting more spread from seeing as the light is going through more air. What happens if you look at

a) the FWHM of a frame without colour alignment
b) the FWHM of a frame after aligning the channels?

That would reveal how much the misalignment is hurting you - at least the part between the colour channels.

cheers,

Robin

I picked 2 random (consecutive) frames of a recent capture of the Lagoon nebula.

The second screenshot is after an RGB alignment. Originally, SharpCap picked up more stars but after I cycled it a couple of times, it levelled out, but the FWHM is tighter afterwards.