M82 Cigar galaxy

[Tommohawk]

M82 seems very popular at the moment and I've always found it fascinating since the supernova a couple of years back, so thought I'd give it another go.

I recently acquired a Quattro 10S which I'd been on the look out for for some months - and when one came up just 10 minutes drive away I though it must be a sign and bought it. The guy I got it from admitted he'd always struggled with it for imaging, but I though my collimation skills would soon sort it. Not so easy though - as it turns out I reckon I spent about 12 hours fiddling with it but now it's about there I think. Slightly off centre maybe.

So I chose M82 partly because it's not too far from the pole and I wasn't able to guide as the HEQ was seriously overweight with just the Quattro. If the Quattro performs well, I'll lash out on a new mount - which is probably overdue anyhow - and F4 coma corrector. BTW I tried the SW CC which works fine with the SW200P but is horrible with the Quattro - too much chromatic aberration mostly I think, though to be fair when I tried it the collimation was miles off. For this image I took great care to ensure the subject was bang on in the middle to avoid too much coma.

I went with 30S subs at unity for all LRGB to avoid any trailing - none binned - and did a good PA for each session - some subs were iffy, but generally the poor ones had other issues rather than eggy stars. Having got a passable result in LRGB, I though I'd try and add some Ha - I experimented with high gain 2 minute but this seemed way too noisy and about half were unusable due to tracking issues.

So then I heard about a local Astrocamp in a dark site just 20 minutes away, and came up wit the idea of using the SW200P guided for the Ha. (No coma corrector to keep the image scale the same)

The Astrocamp was great - fabulous site, great views and great to chat with real people rather than you virtual types - no offense intended!

One snag - I'd recently switched the filters from a 5 posn wheel to an 8 posn wheel, and somehow got the Ha and the OIII muddled. So I spent the first couple of hours at Astrocamp just sorting the filters by experimenting with the heart nebula. I think I've got it right - the OIII is easy to tell because of the colour but I wasnt sure if I'd switched the Ha with the SII. Take home message is think twice before buying unmounted filters, especially as they need to go the right way round - and I'm not sure I've got that right either!!

Anyhow the processing was the main issue and I'm not sure I got it right at all. The Ha element seems more red than it should be - I was aiming for something like Jens's excellent rendition here.

I blended the Ha on top of the LUM using lighten mode - does that sound right? No Ha in the red though. The RGBs I tried some at high and some low gain - generally Hi looked better but only if there was more of them - so I used just whatever seemed to work.

I've posted the Ha also - my impression is that the Ha just needs more or longer subs. I've done OK with 5 mins subs for SHO in the past, but that was at F4/300mm.

Quattro 10S unguided for the LRGB, SW200P guided  for the Ha, ASI1600MM at -10deg, ZWO filters.

LUM = 104x30s 139 gain, Red = 90x30S 300 gain, GRN = 82x30S 139 gain, BLU = 46x30S 139 gain + 26x30S unity gain. Ha = 58x300S 300 gain

Usually I say any comment / criticism cheerfully received, hoping for nothing negative - this time I'll take it on the chin though - the detail isnt bad but it doesn't look quite right - so whats adrift? thanks for looking!

 

 

 

[carastro]

I'd say you've safely identified the Ha filter Tom.  I am not familiar with the ZWO cameras, but with a CCD camera I would say the longer the better for the Ha.

Some would say to add Ha to the Red channel and blend mode lighten.

This is a method I devised for myself previously which seemed to work for Ha highlights, might be worth a try:

"Convert Ha to RGB then put the RGB channel over the top of the Ha channel and combining as blend mode "lighten"  I switched off the upper layer (RGB) and increased the red in the Ha layer in curves (first anchoring down the Black and white points).  Switch on the RGB later again and the Ha "highlights" should show through. "

I didn't notice the mount you had at camp, was it really a 200PDS on an HEQ5 - Wow?

You are certainly the right tracks.  Look forward to seeing you at another camp.

Carole 

 

[Tommohawk]

5 hours ago, carastro said:

I'd say you've safely identified the Ha filter Tom.  I am not familiar with the ZWO cameras, but with a CCD camera I would say the longer the better for the Ha.

Some would say to add Ha to the Red channel and blend mode lighten.

This is a method I devised for myself previously which seemed to work for Ha highlights, might be worth a try:

"Convert Ha to RGB then put the RGB channel over the top of the Ha channel and combining as blend mode "lighten"  I switched off the upper layer (RGB) and increased the red in the Ha layer in curves (first anchoring down the Black and white points).  Switch on the RGB later again and the Ha "highlights" should show through. "

I didn't notice the mount you had at camp, was it really a 200PDS on an HEQ5 - Wow?

You are certainly the right tracks.  Look forward to seeing you at another camp.

Carole 

 

Hi Carole - thanks for that. I tried blending the Ha into the R as you describe but somehow that just made the Ha sections very red. Maybe if there's some spare time at the next Astrocamp we can compare notes on this. 

Yes the 200P runs OK on the HEQ5, though its a bit on the limit. Autoguiding log shows a total RMS error of 0.80" for the six hour session, but this includes a couple of big wobbles at startup and tear-down and a windy period around 1.20am, so not too bad - I think! Probably just matches my imaging scale.

Fingers crossed for clear sky next time! I have that weekend clear so hopefully either Friday or Sat would be good. 

[Tommohawk]

Quick follow on - thanks for the likes folks, much appreciated.

I've come to the conclusion that the Ha just needs more data - using 300s subs even with high gain isn't enough. That said and looking at some other renditions, its easy to lose a lot of the detail in the background if the Ha is used unblended - thats why I liked Jens's version which I linked to in post#1. Even the hubble image seems to lack some of the background detail, though it looks more natural somehow - makes you wonder exactly what data is real in all this!! I see Jens has entered his M82 for the SGL Galaxy imaging challenge - don't think I'll bother with mine!

Another point - using the Quattro 10 with 30s subs to avoid guiding clearly does work - but the file folder is now at 15GB (including the processed layer file and the Ha data) which is a bit of a monster for 1 image.

Maybe longer term I'll settle for a Quattro 8in in carbon fibre to keep the weight down so I can add the guiding gear .... but I dont want to reduce the FL as I want to keep to small targets like M82... so maybe a MakCass..... or an SCT .......