NGC7000 with Warts

[MarkS]

A quick attempt at the North American and the Pelican Nebulae last night.

DIY modded Sony A7S on Tak Epsilon 180ED.  80x90sec dithered subs at ISO 2000 giving 3 hours of total integration time.  Sky Quality was 20.7 according to my meter and ambient temperature 8C.  Lights were calibrated with Darks, Flats and Bias frames then sigma rejection stacked in PixInsight but no other noise reduction has been applied.



Larger version is here:
http://www.markshelley.co.uk/Astronomy/2015/ngc7000_a7s_20150615.jpg

I haven't cropped this image, so you can see the warts i.e. what on earth are those crescent moon shaped artefacts?  Possibly some kind of internal reflection?  They're especially noticeable in the top right and top left corners.  I never had them when using the Canon 350 on the Tak but they are outside the area of the Canon's APS-C sensor. Also there is some multi-coloured streaking coming in from the right hand side, near the top.  I think this is probably caused by Deneb, which is just out of the frame.

I reckon the quality of data in this 3 hour image with Sony A7S is far superior to a 9 hour image I did last year using the modded Canon 350D on the same scope.  It was certainly a lot easier to work with:
http://www.markshelley.co.uk/Astronomy/2014/pelican.html


Mark

[Carole]

It certainly is remarkable the amount of data you have captured with the A7S in 1 1/2 hours compared to the 9 hour canon image.
Those Warts are very odd, as you say some sort of reflection.

Carole

[Fay]

Very nice Mark, great image, colour and only 1 1/2 hours capture, cant be bad

Fay

[The Thing]

Fantastic colours and such a lot else, any defects are swamped by the good stuff. And maybe you have discovered a load of stars with big crescent bow shocks!

[MarkS]

I'm going mad.  80x90sec is only 2 hours - not 3 hours.

[The Thing]

I'm going mad.  80x90sec is only 2 hours - not 3 hours.

Everybody else worked it out as 1 1/2 so it's not only you

[JohnP]

Mark that is pretty amazing - warts & all - strange reflections - do you have any idea what might be causing them? - Without them it definitely is an APOD contender... The amount of stars recorded is amazing - thousands of little feint yellow ones..

I din't know you were using Pixinsight now...?

John

[MarkS]

John,  I think those crescents are caused by internal reflections either in the built-in field flattener or within the Sony/Canon adapter.  I want to see if each crescent has a matching star inside or outside the image.

I dip in and out of PixInsight.  In this example I calibrated and aligned the images in IRIS then did only the image integration in PI because it is very powerful.

Mark

[JohnP]

well its a really cool image... one shot colour as well... darn shame the camera is so expensive else I could be tempted...!

[RobertM]

Very nice Mark

I've had reflections but nothing like that yet.  I've found reflections off brighter off image stars cause much larger arcs.

Robert

[MarkS]

I've just done a quick experiment that proves the crescents come from stars outside the sensor area.  I just need to determine the "mechanism" behind it.

[Later Edit]

Here is the problem:



The red arrows show how reflective the inner ring of this Sony to Canon adaptor is.  So stars which would otherwise form an image just outside the sensor are hitting this ring and being reflected onto the sensor as a crescent.  I need a different adaptor - designed to prevent all internal reflection.

What a pain!

Mark

[JohnP]

cant you use some mat black paint....

[Kenny]

Apart from the crescent shapes, where are the warts?

Fantastic image!

[Carole]

cant you use some mat black paint....

I was wondering that too.

Carole

[MarkS]

cant you use some mat black paint....

Possibly, but it's a very smooth surface  and the light hits it at an extremely shallow angle so there will still be reflections.  It needs roughening up.

[RobertM]

Roughened up then painted.  This is what you need:



http://www.patrolbase.co.uk/krylon-spray-paint/KrylonBlackSprayPaint#.VYMhilKkqnM

Chris put me on to it a while back.

Robert

[The Thing]

This paint looks good, as used by Teleskop Service on their scopes

[MarkS]

Thanks, Robert & Duncan.

One of those should do the trick after roughening or grinding down the surface first.

Mark

[MarkS]

I actually found some Halfords ultra-matt black camouflage paint in the garage.  I tried it out last night.  Using an artificial star it made a huge difference - completely eliminating the crescents and significantly reducing the flare.  The flare results from the very low glancing arrows of the light paths - I don't think any paint would totally eliminate that.

Mark

[MarkS]

What I forgot to say is that I could see the nebulosity in live view.  I was pretty impressed by that!  It made framing very easy.

Mark

[The Thing]

What I forgot to say is that I could see the nebulosity in live view.  I was pretty impressed by that!  It made framing very easy.

Mark

I don't see nebulosity in 5 minute subs with my 1000D and 8" SCT @f6, let alone LiveView.     Obsy first, rest of it second.