A Coma Corrected View of Eta Carina - Thanks Guys!

[2020BC]

Many thanks to the folks here and on Cloudy Nights for pointing me in the right direction for fixing my coma problems.

Installing a Baader MPCC Coma Corrector, and the helpful information about collimation has all but eliminated coma from my images - right out to the edge of field. If you use a DSLR for imaging in a Meade SN-8 (or I'd guess any Newtonian) you MUST get the MPCC. It didn't cost a lot.

The next thing I have to do is to acquire a guidescope. The few remaining aberrations in my images now appear to be related to tracking.

This example is an unguided image raised from a stack of 44x30secs ISO1600 with Noise reduction on. Canon 350D (unmod) in LXD-75 SN-8 with the MPCC Coma Corrector.

You can view a larger version here (http://www.zodiaclight.com/images/EtaCarina44x30secs27aApr06PosterWeb .jpg) and see a closeup of the stars here. (http://www.zodiaclight.com/images/EtaCarina44x30secs27bApr06PosterWeb .jpg)

[EzyStyles]

Beautiful Bill! very nice indeed. is it because your camera is unmodded thats why the colours came out like that?

[2020BC]

Thanks. I believe so. I've read lots that the unmodified Canon is only so-so sensitive at Ha, but it seems to work just fine for me. I know that if I modified it (removed the IR filter) there would be a great boost to Ha sensitivity, and one day in the future I'm going to do that. Anyhow, for now, I don't mess with the colors, because I don't know enough about the physics of the light coming out of the different nebulae. I do know that it is not just red light. I try to represent the images close to what the camera captured them. I love the idea of creating images that resemble how the objects would look if we could see them in person and up close.

Eta Carina has its own peculiar look while the Lagoon nebula appears to be a really Red/pink nebula (see the attached shot for an example). I processed that image pretty much the same as I do for Eta Carina. The two nebulae are obviously quite different color-wise. The Lagoon is very red/pink. A good test is going to come when I get around to doing M20 (Trifid) which has really stark Red and Blue components.

My processing consists of 1. Establishing color balance so the seperate R,G &B histogram peaks are coincident. 2. Raise Black Point (the RGB curve) to the left knee of histogram curve. 3. Lower RGB white-point enough to increase overall brightness without blowing out the bright areas. 4. Set the RGB mid-point somewhere in the middle (subjective) - this is usually somewhere near the right knee of the histogram. 5. For this particular image of Eta Carina because I had a large stack to play with (and so less noise) I was able to increase the brightness quite a lot and brought the white point and mid-point more over to the left. This brought out the fine detail in the outer arms. Because this burns out the small area around the core I then used a mask on it and was more gentle with the core. Feathering the mask eliminates any 'joint' between the core and the rest of the image.

If there's an error in the logic of what I do it may be at step 1, but for now I think the physics of it is that the peaks of the seperate R,G & B curves should be relatively close together on the histogram. If one doesn't do this then the stars and the picture in general get tinted. This's why you see some guys photos have red stars when they try too hard (cranking up the Red) to bring out the red nebulosity.

The way I look at it is that if the Eta Carina nebula wasn't pumping out a shed load of blue and green light the camera wouldn't be recording those colors. The data is definitely there.

An unmodded Canon is a very sensitive camera at any visible color wavelength, Hutech modification notwithstanding. I'm loving this camera and the detail that I can capture with it.:)

p.s. I've noticed that with the Baader MPCC coma corrector installed (combined with much better scope collimation) the colors are more vivid. The reds darker and the blues bluer. Certainly there's now more detail in my shots now than in previous attempts. I'm thinking that poor collimation and bad coma smudges one's images like smudging wet paint - the colors and the detail get blurred somewhat.

[beren]

:) Excellent image mate , well done on getting all the gear together and making it work :thumbsup: to my eyes anywhy i prefer the unmodded look

[Lester]

Fantastic Bill, unmodded cameras cirtainly have their place. The intricate fine detail and colour variation in the nebula is stunning. These are eye catching images.

[tornado33]

Great shots there, yes the MPCC is great, they work great on all SN's as well as standard newtonians. They may possibly correct coma on some refractors too, I guess that remains to be tested. If you can get a guidescope going and can guide for 5 to 10 mins at a time, then I thouroughly recommend either a 2 inch Lumicon Deep Sky, or Baader UHCS filter. Using such filters along with the MPCC and shooting 10 mins @ISO 1600 will blow you away with how much nebulae can be recorded, it seems to suck the nebulosity from the background, making up for the lost Ha sensitivity, and at the same time, the images will have a bluish cast, neutralising that further brings out the reds., examples, taken with my Unmodified 300D and 10 inch F5.6telescope (no MPCC at the time)
http://www.users.on.net/~josiah/temp/NGC6164-65small.jpg unfiltered
http://www.users.on.net/~josiah/baader/6164-5_filteredsmall.jpg filtered
http://www.users.on.net/~josiah/temp/lagoon%20final.jpg unfiltered
http://www.users.on.net/~josiah/baader/Lagoon%20deep_filtered2.jpg filtered
The nebula filter makes a HUGE difference.
Scott