M101 - Pinwheel Galaxy, not quite as planned

[James]

I got a chance to image on Sunday night for the first time in quite a while, got setup and decided to image M101.

I'm using a new set of Baader LRGBC filters, replacing the Astronomik set I had but I left the Astronomik Ha filter in my filter wheel and in doing so set myself up for my second error of the night but more in a minute.

I got an hour of luminance, 30 minutes each of Red, Green & Blue and 30 mins of Ha. I 2x binned the Green and Blue but for reasons that escape me now I didn't bin the red. I had a chance before I took the kit down to get more red but made an elementary error in thinking that by not 2x binning I was getting half the data. As I was gently reminded the factor is 4 so I got barely any red... first error of the night.

My second error was in forgetting to refocus when I switched to the Ha filter... so my Ha data was soft and out of focus so that's an hour wasted...sigh...

I thought I'd post what I did get so here's the luminance data (and there's nothing wrong with black and white images ).

As usual, taken using our WO FLT110 using a Starlight Xpress SXV-H9 and guided using a DMK31AF03. All subs were 5 minutes and an Astronomik CLS filter was used to help reduce Taunton's orange glow...

Once again, thanks to SteveL for his processing help and his patience when I keep throwing problematic data at him

James

[Tim]

James, it's a very familiar tale, the details change but the errors are roughly the same I put it down to tiredness. Even so, it's a very fine image, loads of detail.

I note with interest that point about not refocussing for Ha. I dont really understand about lenses and things, but do you have to refocus for each colour too? I was under the impression that triplet APO's would make sure all colours were focussed at the same point, have I got that right? If that is right, then does Ha have a different focal point?

Sorry for all the questions, but I am thinking of swapping my c9.25 for an APO, to go with my OSC camera, but want to make sure there's not too much faffing about with focussing etc, and also to be certain that all colours (inc narrowband wavelengths) are all brought to focus together. Is that possible???

Tim

[James]

I think the focusing issue is one of brands of filters. The RGB and L filters were Baader and parfocal whereas the Ha filter was an Astronomik. I didn't have to refocus between the R, G & B filters just between them and the Ha.

If I use a Baader Ha filter I should only have to focus once during the session unless conditions change/focuser shifts etc etc.

James

[Tim]

ah. The plot thickens then. Again, as regards filters etc, I am under the impression that the glass in them has varying focal lengths. Is that right? Doesnt half make it awkward when trying to work out spacing for coma correctors etc.

Thanks James.

[James]

..... I am under the impression that the glass in them has varying focal lengths. Is that right?

....

TBH I don't know, hopefully one of our resident experts will help here! I must admit that I was surprised to find that if I looked through the R G & B filters in turn the focus to my eye was different for each but isn't in the scope. Maybe one day we'll all be able to get triplet corneas or suchlike.

I haven't dared get into any imaging requiring an MPCC yet although I'm tempted just for the fun of it to see what I can get with my 10" Newt. The next step for me has got to be processing at which point I'll be stepping well outside my comfort zone!

James

[Dangerous-Dave]

Cracking shot James. Taunton is big enough for its own orange glow?!

[James]

Cracking shot James. Taunton is big enough for its own orange glow?!

It's got 58,000 people and I'm only a mile from the town centre so there's plenty of orange. Luckily there's no streetlights on my street and the countryside is fairly near to the south and west so I can still see the milky way overhead on a reasonable night.

James

[barkis]

Whatever the problems were James, the image looks just fine.

Ron.

[Tim]

TBH I don't know, hopefully one of our resident experts will help here! I must admit that I was surprised to find that if I looked through the R G & B filters in turn the focus to my eye was different for each but isn't in the scope. Maybe one day we'll all be able to get triplet corneas or suchlike.

I haven't dared get into any imaging requiring an MPCC yet although I'm tempted just for the fun of it to see what I can get with my 10" Newt. The next step for me has got to be processing at which point I'll be stepping well outside my comfort zone!

James

I have a spare MPCC, I can take it to Lucksall if you like. Sometimes the problem with the newts for imaging is the size of the secondary, but it depends on the camera I think.

Processing! That'll be both feet firmly planted in the dark side!!!

[FLO]

... I'm tempted just for the fun of it to see what I can get with my 10" Newt.

From what I hear the Skywatcher/Celestron 10" f4.8 Newtonian hits the Sony 285 sensor's 'sweet spot'. Steppenwolf's and Yfronto's images certainly seemed to confirm that.

[Whippy]

That's still a cracking effort despite the errors James .

Tim, if you get a 'frac with good colour correction, you'll be fine and dandy. I tried using an 8" newt twice for imaging and hated it, using my Zenithstars is so much easier in comparison. No cooldown time, no collimation, no real issues with focus travel. The only thing you'd probably need is a field flattener with that big chip camera of yours.

Tony..