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M1 Crab Nebula


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Hello All

Imaged the excellent M1 nebula last year, but only now managed to process.

Equipment used: OO 12" F4, QSI583WSG, QHY5 (guide cam), 

Ha: 3x 1200s

OIII: 3x 1200s

Color combination was R- Ha, G- Ha+OIII, B- OIII


It is interesting that the OIII data is less sharp - looking at stars - than Ha - they was taken on different days. I am sure that focus was good enough to not have caused this. Filter seems looked to be ok and seeing was also ok as Ha of some other targets taken on same day was comparable. Guiding was not that worse. Is this normal for OIII frames?

Ha: 3x 1200s


OIII: 3x 1200s


Comments welcomed.

Best regards


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That's interesting about the OIII data with this target. I have just imaged it myself in narrowband and did think that the OIII stack looked very soft and cloudy when processing it. The Ha is very crisp and sharp, as is the SII data. I'm sure it's not a focussing issue. As for why this might be... We need a scientist to offer some explanations!

Nice image, though the OIII appears to me to be drowning out the Ha. How similar are the stretched stacks before you combine them? I try and get the background value to be almost the same before combination. It could of course use loads more data to reduce the noise too!

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Both of my filters are 5nm Astrodon.

Focus was definitely as good as possible, as the OIII data was taken after some hours of imaging, so there is usually not much change because of temperature any more and refocused just before that.

Maybe sometime I can get a 3nm version to compare.

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