LRGB Comparison, issue with Blue

[04Stefan07]

Here are my LRGB of the Trifid. I Noticed my blue channel always looks out of focus/blurry and not as sharp as my other channels. Is this due to the channel or another issue I may have? See below.

 

L

 

B

 

G

 

R

Edited October 3, 2020 by 04Stefan07

[steppenwolf]

This is quite typical - blue light suffers greater dispersion through the atmosphere than the other colours. Always aim to capture the blue data when the object is at its highest point in the sky.

[Skipper Billy]

Are you refocussing on each filter change??  Even sets of filters advertised as parfocal rarely actually are parfocal.

[04Stefan07]

Interesting.

Yeah refocusing on each filter change and I think every 5-8 shots as well.

These are the 31mm ZWO filters.

[ollypenrice]

Steve has it. Actually I think that most cases of non-parfocality arise not from the filters but from the optics. No Apos are literally apochromatic so different wavelenths have slightly different focal lengths. The blue channel always sorts the men from the boys amongst the apos! They have to focus all the blue wavelengths to the same point and can struggle. On top of that you may be picking up a little poorly focused signal from the violet.

Like a number of TEC140 users I find that the official field flattenener reduces bloat in the blue even though the manufacturer insists that it doesn't.

Anyway, the great thing about LRGB is that the L channel controls the final sharpness and, although it obviously contains blue, it isn't dominated by it.

Olly