The annoying orange

[bri]

A few snaps to give an idea of what I'm up against.

single 90sec sub at iso 1600 17mm to the south. SE, S, SW is my good side of the sky. I wouldn't normally go that sensitive, 400-800 normally and have had pleasing results. Now I have an upgraded mount, I eventually will be performing longer subs but am worried about the annoying orange.

This is the main culprit! This thing is to the north and without it, would have a very nice area of sky to work with. Never had a decent sub if pointing W N E. Shame as there are a few targets that I'm interesting in but their out of reach!

1. With the equipment in my signature, I would like to know which filter would give the best results against this menace.

2. Will any of these give a significant reduction?

3. Any other examples on the market?

4. Will it be ok to be used with a SW coma corrector? (2", screwed directly into it with any negative effects)

http://www.firstlightoptics.com/light-pollution-reduction-imaging/baader-neodymium-filter.html

http://www.firstlightoptics.com/light-pollution-reduction-imaging/skywatcher-light-pollution-filter.html

I know there is price diffrence between the two and normally would assume the dearer the better, but would like some views from users, first hand before purchasing.

Does anybody have any before and after shots with settings/details? This would be most useful.

Thanks

Bri

[steppenwolf]

If you really want to cure this, what you need is a Hutech IDAS LP Filter which I know is more expensive but it just does the job properly. It should screw into the Sky-Watcher coma corrector OK.

Careful post processing will also make a huge difference using levels (working on each colour separately) and curves (to boost contrast) to remove the orange glow. I also used Gradient Xterminator to remove the gradient in the background. Here's a 'down and dirty' quick process to give an idea:-

[bri]

Thanks for the reply Steppenwolf. There are 3 sizes available. I take it that I need the 48mm version and that would screw directly to the CC on the end that goes into the focus tube? I ask as there is not much available thread at the 'tube' end because of the corrector lens (about 2 full turns available) and if it went on the other end it may cause me some focus issues.

Once fitted, the filter casing will not be any wider than the CC barrel? As the CC only just slides into the focus tube.

Once again, many thanks

Bri

[steppenwolf]

If the tolerance is that close, I would advise further research but the 48.0mm filter should be the right one for a 2" (50.8mm) nosepiece and having measured mine, the IDAS filter outside diameter is 49.9mm so plenty of clearance. This should be fitted at the furthest end from the sensor to avoid reflections.

[bri]

Pic of the available threads. There is something already screwed in there but that would be to hold the lens in place i would think.

Is there enough thread there to secure a filter?

[steppenwolf]

Two threads is enough and, yes, the other item is a securing collar.

[bri]

Thanks for the help, much appreciated.

[russellhq]

If you really want to cure this, what you need is a Hutech IDAS LP Filter which I know is more expensive but it just does the job properly. It should screw into the Sky-Watcher coma corrector OK.

Careful post processing will also make a huge difference using levels (working on each colour separately) and curves (to boost contrast) to remove the orange glow. I also used Gradient Xterminator to remove the gradient in the background. Here's a 'down and dirty' quick process to give an idea:-

Great work steppenwolf, any chance you could post a link to a guide or tutorial that takes you step-by-step through the process of eliminating sky glow?

[steppenwolf]

Sorry for the late reply, Russell but I have been away on holiday for a week.

The key to post processing this particular image was to get the colour balance right from the start. In PhotoShop:-

1. Select Window - Histogram and choose 'Channel' - colors

2. Select Image - Adjustment - Levels

3. You'll notice that the green channel is flanked by blue to the left and red to the right. Choose the blue channel from the Levels dialogue box

4. Move the centre slider of the input levels until the blue channel lies 'over' the green channel

5. Choose the red channel from the Levels dialogue box

6. Move the centre slider of the input levels until the red channel lies 'over' the green channel - but note that this predominant channel overhangs both the left and right edges of the green and blue channels

7. Next, adjust the red 'overhang' by sliding the left and right sliders of the output levels inwards until the overhang is removed. The image will still be too bright but the colours will be better presented.

8. Click OK

9. Now Select Image - Adjustment - Levels again but leave the default RGB channel selected

10. Slide the left hand slider of the input levels to the right until it just touches the left hand 'slope' of the histogram - this darkens the background. Click OK

11. Select Image - Adjustment - Curves and pull the left hand quarter point down a fraction to darken the image and pull the right hand three quarter point up a little to increase the contrast. This gives a good base point from which to start from.

Hope that helps.

[peem]

HI I have just found this tutorial by steppenwolf about elimingating sky glow . Exellent step by step guide for a novice like me . Thanks

[kirkster501]

HI I have just found this tutorial by steppenwolf about elimingating sky glow . Exellent step by step guide for a novice like me . Thanks

I just bumped into this as well. A super lesson from Steppenwolf here. Many thanks.

Rgds, Steve