Very trying Veil Nebula

[Hagar]

A section of the Veil Nebula.

A compilation of 7 X 15 minute exposures fully calibrated.
The image was a trying image to process without going to far and looking grossly overprocessed. The image was taken from my observatory but was very low in the sky at about 15 degrees above the horizon. The image suffered from a major gradient problem thanks to a street light in line with the target.
I experimented with a couple of settings for the flats for this image with the first (first image) with a saturation of about 18000 and the second (second image) at about 28000. The diference was noticable but either would have created a usable final image.

Take a look at both images and tell me what you think.

[spearo]

Nice work
second one for me
frank

[Tilt]

Very nice doug. Both are fine images, however I'm leaning towards the 2nd one.

Michael

[Craig_L]

A hard one to shoot to be sure. Second one has more nebulousity but there's a colour cast on the stars. The levels look a bit clipped to me but I'm sure there's some better people to comment on this. Still very good.

[gregbradley]

A fantastic image of a very low object.

Greg.

[Ric]

Hi Doug, great looking images, both of them.

The second one definitely has the more detail but seems a bit redder.

Cheers

[monoxide]

nice Doug, looks like you should be able to stretch it a bit more though

hope you dont mind :thumbsup:

[Hagar]

Thanks everyone for the comments. I am leaning towards the second one myself which is the way I will probably go with my Flat files. There has been a lot of talk about the saturation of flat files for the QHY8 on this and other forums without any real resolution to what is best.
Be my Guest to tinker with the images. The only way we learn is by listening and watching others attempts at the same task. A different perspective to an image is never a waste.

Thanks Again.

[leon]

Have to agree Doug, they both are fine images, however I do like the second one just that bit over the other, well done indeed.

Leon

[Terry B]

Doug.
I like the second one.
As for the flats, the flat needs to be in the linear part of your sensor otherwise when you divide by them they will give an incorrect result. This was discussed on one of the photometry groups as the linearity is important for photometry.
Your sensor on the QHY8 is an antiblooming sensor and is probably not particularly linear above about 1/2 the saturation level.
You could try and measure the linearity by taking a series of images of the same star field with a bright star that will saturate the sensor and some dimmer ones that don't. Expose for increasing times in ~10 sec increments. ie 10,20,30,40,50 sec etc until you have saturated the bright star. You need to start with an exposure that doesn't saturate the stars.
You then measure the flux of a few stars in the images and graph the results against time.
This assumes that the stars you are imaging are not variable in the short term and that no clouds etc have stuffed up some of the images.
The results you get will look like the attached charts.
After doing this you can pick what intensity is linear for your CCD and keep the flats within that range.

Cheers

[Hagar]

Thanks Terry. That will keep me occupied for an evening. May also improve the quality of my shots after calibration.
Many thanks.

[Lester]

Wonderful image of this low faint object Doug.

The second image is very good and doesn't (to me) look over processed in any way, showing more detail. I feel that if one captures the detail do what you can to bring it out, without introducing any harshness of over sharpening, etc.

On ya Doug.

[RobF]

Wow. 2 very nice pics for the tricky circumstance. :thumbsup:

[Jen]

:thumbsup::thumbsup:very nice pics Doug keep up the great work cheers :thumbsup:

[Kevnool]

Poor ole 1st one dont get much of a mention but hey a pic is for eternity and no matter how good they are or how bad they are there still there for life.

I enjoy them all Doug....... Cheers Kev.

[winensky]

Another votefor number 2. You are choosing somelow targets Doug. Thanks Terry for the info on the linearity of flats.