M31 luminance from Blacklands

[Carole]

When M101 disappeared behind the trees it was still clear so rather than waste clear skies I did M31 which was a better size for the WO ZS71.

Les for your info this is full frame to give you an idea of scale.

Atik383L Luminance 500secs x 12 & 12 x 30secs for the core
WO ZS71 with focal reducer giving F4.8
Guided with finderguider/QHY5 and NEQ6

Looking forward to adding RGB to this:

Full size:
http://gallery.orpington-astronomy.org.uk/albums/userpics/10047/M31_Blacklands_main_and_core_aug_2013.png


 

[mickw]

That's looking good Carole and nice detail

Stars are a bit misshapen on the left though - everything seated squarely ?

[Carole]

Thanks Mick,

Stars are a bit misshapen on the left though - everything seated squarely ?

Yes I noticed that Mick, well as far as I can tell it was all seated squarely, I wonder sometimes if it's to do with the tightening nuts on the drawtube that clamp the camera in place.  The spacing wasn't spot on about 3mm too much, I thought I had the right size spacers, but seems I don't, but surely that would make all four corners misshapen.

Carole

[mickw]

Was the orientation of the camera vertical when aligned on the subject or "up" pointing to the left or right ?

I'm thinking the camera was "drooping" slightly.

[The Thing]

Looks good to me. Maybe stars aren't all round - in fact it's well known that there are fast rotating oblate stars and ones that have companions pulling them out of shape, I'm not going to worry about round stars in my images any more!

[Carole]

Thanks Duncan. 

I'm thinking the camera was "drooping" slightly.

It's occured to me that the filterwheel is heavy and lopsided on the camera, I wonder whether that could pull it over slightly.

Carole

[MarkS]

Carole,

That has the makings of a great image.  Add some decent colour data and this could be your all time best image.

Mick is right about star elongations on the left side but that is not the whole story - I've done an analysis here:
http://www.markshelley.co.uk/webdisk/Carole_M31_elongations.jpg

It analyses the stars in the corners, the centre and mid edges of the image.  Roughly speaking the elongation is left/right at the left of the image and up/down on the right, though the elongations are worse at the top than the bottom.

What changed between the M101 image and this one?  I analysed the M101 image and it didn't show this weirdness.

But all this is minor quibbling - you've captured some great luminance data there.

You say 500x12sec?  That's a huge number of very short images!  I guess you meant 12x500sec?

Mark

[Carole]

Wow, thanks for that analysis Mark.  Looking at it things are actually worse than I thought, so maybe it could partly be down to the 3mm spacing error. 

Yes I made an error in the first post (now corrected) yes it is 500secs x 12.

What changed between the M101 image and this one? 

M101 is a crop so you don't see all the far corners and I also did a tiny bit of photoshop magic to round the stars up which I didn't do with M31.

Carole

[JohnP]

Very nice Carole - Lovely FOV & excellent detail - You must be chuffed with this one - john

[Carole]

Thanks John, yes I am chuffed with this one.
Always some bits you wish were better though.

Carole

[Fay]

that is very nice indeed Carole

Fay

[Carole]

Thank you Fay.

Carole