Iris Neb NGC 7023

[Keiran]

Its been quite a long time since I've been out with the scope, decorating the house etc. Saturday night i managed to get 5+hrs of imaging. Unfortunately this is from my light polluted garden.

Equipment:

Scope: WO GT-81

Flattener: WO FFII

Camera: Canon 500 D (Unmodded)

Guiding: ST80 and QHY5

Mount: HEQ5 Pro

97x180 second Subs @ iso 400

25 x 180 seconds Darks to match

Stacked in DSS, and converted in PS

My garden, and thats not the sun, but the motorway light (taken at 2230 tonight)

Light Pollution by keiran_bernstein, on Flickr

Iris Neb NGC7023 4hr51min 97 lights 3mins ISO 400 by keiran_bernstein, on Flickr

I was rather disappointed with what i got, but i will give it another go soon (hopefully) from a darker site...

Thanks for looking

Keiran

[laser_jock99]

That's a fair bit of LP in the garden there- still not a bad effort on the Iris, it's not the brightest of objects.

[Keiran]

Thanks very much... Its the first time trying, and i didnt know what i would get, but i was expecting a little more.

[squeaky]

That's a tough target. Any haze, and with that amount of LP it's going to be difficult to capture the nebula.

I'm with you in thinking that for 47 mins worth there should be more nebula - at least on first sight - but honest guv, that's a pretty fair result given the conditions and the target.

[squeaky]

EDIT:

Actually you've got a whole lot more data there than your post shows. I "equalised" the image in PS to see how much faint background stuff there was....

So while the equalised version is no good as an image it shows that a bit of work with levels and curves should show more stars and more nebula than you currently have.

[squeaky]

As in something like this...

[Keiran]

Cheers richard, it was a total of 4hr 51 mins. I will have another play in PS, but whether i get a usable image or not thats another thing Im not the greates with PS, so i dont expect miracles

[squeaky]

Oops OK.... four hours worth!

ISO 400 ?

Maybe try 800 or even 1600 next time?

There are LOADS of video tutorials on levels and curves available on youtube. Do search on something like ... photoshop tutorial levels

If you want a dead simple VERY basic starter for ten on those I did a couple of step by step photo posts a while back:-

Levels

====

Curves

=====

Then once you get the hang of those - Mark (Quatermas) from here has done a whole bunch of good stuff:

Mark's tutorials

=====================

http://www.youtube.com/results?search_query=boodlewoodle&page=1

After that it's just a mere matter of hours and hours of viewing and playing

[Gina]

Good result for the circumstances It's a very faint object. You don't mention any light pollution filter - I recommend a CLS filter as that does a great lob at removing the sodium and mercury emissions that you get from most street lights. I was quite suprrised when I compared a with and without comparison

[Keiran]

Good result for the circumstances It's a very faint object. You don't mention any light pollution filter - I recommend a CLS filter as that does a great lob at removing the sodium and mercury emissions that you get from most street lights. I was quite suprrised when I compared a with and without comparison

Thanks Gina, I did forget to mention i do have a Skywatcher 2" LP filter, and i am looking at getting my camera modded and doing NB, but funds are very short currently.

Richard, the reason i chose iso400, was i did a test of iso 800 @ 180secs and the LP overwhelmed the image. So instead of dropping the sub time to 120s i chose to drop the iso, hoping to improve image quality.

I will take a look at them link you posted and if i get time tonight i will have another look at it.

Thanks for the help and advice all

Keiran

[squeaky]

Yes, if you use your LP filter I think you'd have to up the ISO anyway. Only tests will show you your best option.

That's the fun of this astro-photography lark - all by God and by guess with lots of trial and error. In my case - mostly error

[Keiran]

Why would i need to up the ISO?

The iso allows you to take photos with lower light conditions, reducing the capture time. but in doing so you increase the noise.

I set the ISO to 800 and took a 3 min sub. The light polution over whelmed the photo. I could have dropped the exposre time to 2 mins, but instead i lowered the ISO reducing the noise, and the image was nolonger bleached by the LP.

Atleast this is my understand of it. Is that right?

[squeaky]

I thought that using a filter not only cuts out pollution but reduces the overall amount of light as well? If not, I'm sorry for confusing the issue.

[Keiran]

The Skywatcher LP filter is not very dark, it doesnt really effect the the image. When i took the first test image (iso800 3mins) it was almost like taking an image of a piece of white paper. Not quite as white, but not far off. It was just too over exposed. If you can afford to drop you ISO, the its always best to do it. It reduces alot of the noise and make the final image alot cleaner and easier to work with.

If i had dropped the ISO and i needed to increase the image time by 2mins to get a usable image then it wouldnt be worth it.

Thanks for your help though Richard.

[squeaky]

Fairy nuff

[Shibby]

Looking good... I think you might be able to extract a bit more with some more aggressive processing. I would have through the reflection nebulosity is separable from the generally red glow of LP, but I know just how difficult it can be.

Your garden situation looks very similar to mine!

[badgers]

I'm with squeaky on this, upping the ISO is pretty much required for a DSLR to get the sensitivity you need out of 3-10 minute shots.

I remember being devastated when I took my first DSLR shots at 800 ISO in Cambridge the RAW pictures looked awful, but careful tweaking of RGB levels and white balance gave me really acceptable shots even at higher ISOs.

Biggest life saver for me was the Baader UHC-S filter I use for Light Pollution. I am in the centre of a city and like you have a few sodium lamps within metres of my imaging site.

I think it might not just be LP though at the moment. It's still fairly warm and I found my sensor didn't respond well above 20 degrees, in the winter it usually was much less noisy. The moon may have been washing things out or even a light haze high in the atmosphere.

[Keiran]

I'm with squeaky on this, upping the ISO is pretty much required for a DSLR to get the sensitivity you need out of 3-10 minute shots.

I agree if you were at a dark site, but not for a LP area. I could never get 3min - 10mins from my garden. You might as well shine a torch down the scope.

Thanks Lewis. I dows make things alot more difficult.

[Gina]

I swear by the Astronomik CLS CCD clip filter for stopping LP with a DSLR - exceedingly good attenuation of sodium and mercury emission lines and virtually unattenuated fo all the astronomical emissions we are interested in. Not cheap but very good and well worth the cost IMO.

[Keiran]

I swear by the Astronomik CLS CCD clip filter for stopping LP with a DSLR - exceedingly good attenuation of sodium and mercury emission lines and virtually unattenuated fo all the astronomical emissions we are interested in. Not cheap but very good and well worth the cost IMO.

I have heard they are very good, It would be interesting to be able to test one. At the moment money is a real issue, so astro goodies come bottom of the pile.