The Heart Nebula, IC 1805

Carl

If one is using HA filter as a strategy to reduce light pollution - from moon or skyglow - then surely using luminance images would be counter productive. I would have thought that the image would have to be taken purely in the narrowband.

Mark

Hi Mark,

Sorry for getting back to you so late. As you probably know H Alpha is visible in the red part of the spectrum. Hydrogen is the primary component of nebulae, therefore the H-alpha line occurs where hydrogen is being ionized. So if you use a H alpha filter on a galaxy all you'll pick up is the hydrogen regions and noting else. Luminance is essential when imaging galaxies you can have some problems with light pollution / moonlight. You can get a CLS filter that are very good but you can still get a Gradient in the image.
Here is an example. At the moment I'm working on M33 spiral galaxy witch is very rich in H alpha so my plan is to get 4 hours luminance, 2hours H alpha and RGB 2hours on each colour.

If I was imaging a nebula I would go for 7 hours H alpha.1hour red, 2hours green and blue. So when I'm combining the image I'll add some h alpha to the red channel. I hope this makes sense It's very hard to explain like this it would be much easer to explain over a few pints.

Carl

Thanks Carl

Is the essence of this: You play down the red channel a bit and compensate with more H-Alpha so sky background has a bit less light pollution (at least in red) but the target suffers a lesser reduction in red as some of the detail in the red is in H-Alpha not otherwise present in the light pollution?

Mark

have being experimenting with various methods to combine HA data with the Colour Data captured with my Astronomik CLS filter.

This is the result of using 50% HA mixed with CLS Red to produce a Red Channel, 25% HA with CLS Blue Channel to create a new Blue Channel, Green was left as is. The HA - Red channel was also used for Luminosity.



Larger version here:
farm3.static.flickr.com/2477/4012212966_864c68af0d_o.jpg

Colour Data: Camera: Canon 350D (IR Filter removed) c/w an Astronomik CLS CCD Filter. A Stack of 49 x 180 second exposures taken on the 25th and 26th of September, 2009

HA Data: Camera: Canon 350D (IR Filter removed) c/w an Astronomik 12nm H-Alpha fil Filter. A Stack of 30 x 300 second exposures taken on the 8th and 9th of October, 2009

Total Exposure Time: 4 Hours and 57 Minutes

Taken from Cherrymount, Waterford, Ireland.

Thanks for looking
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Steve

Jeez Steve, you're going hammer & tongs at this one :woohoo: I don't hink that I've seen an image with the two filters combined before. I know how bad you rlight pollution is, good luck with getting more exposures.

How do you combine the images? In PS or deep sky stacker?

Keith.

Many thanks Keith,

As you know the direction of this target is towards town, complete with lots of Sky glow and the usual Light Pollution. I got the HA filter to try and compensate for this. The 6nm was way out of my budget, Keith, so I got the 12nm one and even with that, it is competing with lots of sky glow and haze. The RAW frames look very red!! However you can see it is picking up the target.

In fact during an imaging run earlier this week, the area got fogged over with no stars visible in the sky to the eye ( a complete haze, even Jupiter was invisible), and with the HA filter it was still registering the target (with much less contrast however).

I have been experimenting with what software is best to use, this image is a result of Stacking the CLS filtered data in DSS, also Stacking the HA filtered data in DSS, separately.

I then Opened the CLS Filtered colour image in Photoshop and split the RGB channels. Saved them as separate Monochrome RGB files.

With the HA Data, I converted to greyscale, then stacked and saved. Converted it to a Greyscale image in PS.

I then mixed 50% HA Monochrome with the CLS Monochrome Red. The original CLS Green Channel was left as is, And 25% HA monochrome with the CLS Monochrome Blue.

I then Flattened the files and ensured they were in greyscale mode. Then combined in Photoshop. Also I then used the HA-Red combination for luminosity.

I am still trying to work out the best work flow and processes for this type of imaging so any tips are very welcome.

Cheers