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NGC 4631, The ‘Whale’ galaxy.

RobH

By RobH
in Imaging - Deep Sky

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RobH

RobH

Posted
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It seems like ages since I've posted anything, what with work and the rotten weather! Anyway, here's something I've finally put together from April.

This is an edge-on spiral, similar in size to the milky way, some 21 million light years away from us.

It does look a lot like a whale, or a shark, or some other denizen of the deep :cool:

The small companion elliptical galaxy is NGC 4627.

There is lots of activity in the centre of the ‘Whale’….it’s thought that so many supernovae have exploded in this region that gas is being blown out of the plane of the galaxy. This can be seen in X-ray emissions.

This image was taken with 2 cameras, a mono Atik 16HR for luminance and H-alpha, and an OSC 16HRC for the colour data.

I borrowed the OSC camera as I didn’t have much time available and wanted to grab the colour data quickly.

While this worked OK on the galaxy itself, the star colours are not correct, and I really noticed the difference here as compared to using coloured filters when it came to processing.

It’s not a route I’ll be taking again…personally, I prefer mono with filters.

Imaged with a TMB152 @ F8

L.20 x 6 minutes

RGB 17 x 5 minutes

Ha 11 x 6 minutes binned 2x2

Ha was added to the red channel in ‘LIGHTEN’ mode at 50% opacity.

L /Ha imaged on April 1st 2009

RGB imaged on April 27th 2009

Hope you like it :)

Cheers

Rob

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barkis

barkis

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Outstanding work Rob. It's certainly a beauty, and plenty of action has taken place within that star Island.

Was any part of the image data captured via the newly acquired equipment The mount perhaps?

Ron.:cool::icon_salut:

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RobH

RobH

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Thankyou folks :)

Alan, I'd not thought much to this one before either, but when the Ha subs came in they were really interesting, and I'm pleased the way it's come out with this added.

Ron, no, it's not done with the new mount, still the very heavily loaded CGE!

The 'whale' of a mount may be here by the end of the month :)

My plan when I changed from the big SCT to the TMB was to have the possibility of putting a 1.5x barlow on it to get a similar image scale to the SCT at about F6, as I liked working at that scale for galaxies etc.

This would need much longer exposures with a 6 inch scope of course, but I've not been able to manage it as the CGE has a max payload of 60lbs, and I'm quite close to this. Not an issue visually, but a big factor when imaging.

I'll be able to hang 140lbs off the AP so the mount won't be pushed at all. Plus I can save up again and get another big SCT OTA to put on it too :cool:

Cheers

Rob

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albedo0.39

albedo0.39

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Fantastic image Rob. I'm going to ask a daft one:-

Regarding this lot:-

Imaged with a TMB152 @ F8

L.20 x 6 minutes

RGB 17 x 5 minutes

Ha 11 x 6 minutes binned 2x2

Ha was added to the red channel in ‘LIGHTEN’ mode at 50% opacity.

How do you know that the colour you get from all this is "real" - i.e. the right amount of time ? I've done no imaging whatsoever, but curious to know when to stop adding time etc...

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RobH

RobH

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Hello Albedo,

Good question :cool:

When I look at these objects through the eyepiece, if I can see them at all, they look like grey smudges, so what is 'real'?

The RGB shots were taken with a camera that has been calibrated against a star of the same type as the sun, a G2V star, so I know I'm in the right ballpark, the added Ha has emphasised the Ha regions somewhat, but after that it's down to interpretation, and getting to know, over a long time and many different images, how my particular imaging setup relates to others, using commonly imaged objects as a guide.

The hubble images are often done in a completely false colour, where the RGB channels don't relate to the wavelengths that the eye percieves as RGB.

I'm on record as saying that these (in general) don't personally appeal to me in an aesthetic respect, and all of my images, unless started otherwise, use red for red, green for green etc etc.

Regarding how many images to take....in this coun try especially, it often comes down to how many you can fit in before the clouds roll in, but as a rule I try to get a similar amount of RGB, as much luminance as I can get, and enough of any other band to get a good signal to noise ratio...same with the RGB.

Once you have this, you have a lot of room to manoeuver during processing.

Cheers

Rob

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RichieJarvis

RichieJarvis

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Very very nice as usual Rob....

Your Ha additions to galaxies I am finding very inspiring - I keep meaning to give it a go, maybe seeing this will push me over the edge! :cool:

Any particular reason why you bin 2x2 for Ha? Also - how are you blending the Ha data - with the Red, or with the Luminance (or both!)

Cheers,

Richie

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RobH

RobH

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Thanks again guys :cool:

Richie, the Ha was blended into the red channel with the layer blend mode set to 'LIGHTEN' and then the opacity reduced to 50% as the Ha was very dominant. The layers were then flattened and the result was used as red.

Nothing was added to the luminance layer.

I binned the Ha in this case to increase the sensitivity by a factor of 4, and thus cut down on exposure time. The loss of resolution isn't important in this case as the Ha is just being used to enhance the red.

If I'm shooting an emission nebula though, I shoot the Ha at full resolution as it'll probably be used as luminance.

Cheers

Rob

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