A very sad M78

[MarkS]

In theory the conditions were ideal - SQM-L reading of 20.8 (slightly darker than October's DSC) and the temperature was 4C.
I shot 50 subs of 5 min.
BUT - the night was extremely dewy and the secondary mirror fogged up after 18 subs, meaning that most of the night's acquisition was wasted.  So the only reasonable subs were when Orion and M78 were low in the sky - hence severe background gradients.

H-alpha modded Canon 350D on Tak Epsilon 180ED with IR/UV filter.  18 x 5min subs at ISO 800.

Here is the result of processing the 18 subs.  The red gradient at the bottom left is genuine - it is part of Barnard's Loop.  The top left gradient is spurious.



Larger version is here (but I've binned by a factor of 3 to reduce noise):
http://www.markshelley.co.uk/Astronomy/2011/m78_01112011.jpg

I certainly think M78 is interesting enough to warrant another attempt.

Mark

[JohnP]

Like you say not your best but shows loads of promise & a lovely FOV - John

[Fay]

Yes I think that looks a very promising subject. The dew was very bad last night!

[Carole]

That's a shame Mark, all that hard work.  Still looks a nice image though.

I was wondering about dew with Newtonians as a young man at Salisbury had a dewed up mirror, and no dew heaters, I wasn't sure whether you could put dew heaters on Newtonians seeing as the mirror is not actually attached to the sides of the tube like a refractor lens is, or is there a different method for Newtonians?

Carole

[RobertM]

Yep, I echo John's comments.

It's been on my list for years but the weather's always been in the way.

Robert

[MarkS]

I wasn't sure whether you could put dew heaters on Newtonians seeing as the mirror is not actually attached to the sides of the tube like a refractor lens is, or is there a different method for Newtonians?

I use a dew heating band around the tube next to the primary and this is sufficient to keep the primary clear.  But because of the design of the Tak's secondary, I don't know if there's a way to get a heating element anywhere near the secondary mirror surface.  However, secondary only tend to dew up on VERY dewy nights - like last night

Mark

[MarkS]

I've completely reprocessed this - the most difficult reprocess ever!
I've added in another 16 subs - which were badly affected by the dewing up but where the signal had not been attenuated too much.  The remaining subs of the 50 were too badly attenuated to be of any use.  Using the first 18 subs as a reference, I subtracted the extra fuzziness introduced by the dew in the next 16 subs.  The technique actually worked quite well but, in the end, you can't make a silk purse from a sow's ear.

So, 34 x 5min:


Larger version (but binned by factor of 2):
http://www.markshelley.co.uk/Astronomy/2011/m78_01112011v2.jpg

Mark

[RobertM]

A lot of people would be much more than happy with that result Mark !

The noise has reduced considerably with those extra subs you managed to use.  I think as a result you've managed to tame some colour gradients and make it look more natural.  Overall I think the reprocess has worked very well.  It's a beautiful area of sky around M78...

Robert

[julian]

Well worth the extra work in re-processing the image.  It looks great!

Regarding the secondary mirror dewing up, would you be able to put resistors on the back of the mirror and control it with a pulse width modulator, running the cables along the top of the mirror veins and maybe wiring the resistors up in a star form so it looks like the letter Y?

Julian

[Carole]

Great re-process Mark. 

Carole

[Fay]

Well the conditions are not good lately, Mark, & I think you have done a very good job, as ever

Fay

[Mac]

Considering the amount of problems you had, and the loss of subs, ect
thats a pretty good result,

Mac.

[mickw]

Very nice reprocess, less noisy and the colours look more natural.