M31 and M33

[Jay-qu]

Recently got some time to do some more imaging and was excited to have M31 and M33 nice and high in the sky. I spent about an hour on each of the below (90sec subs for M31 and 60sec subs for M33), but they definitely needed more data.. I just got a bit impatient :P

Both were taken with a Skywatcher 100ED atop a CG5-GT mount, using a Canon 60D at ISO6400. The images were stacked in DeepSkyStacker with darks and bias applied.

I had a little bit of trouble with the colour balance post stacking.. any tips for maintaining a nice but realistic look in the colours with DSLRs?

It was my first time shooting with the 60D and I am quite happy with the noise performance at such a high ISO, looking forward to guiding (next project) and getting the ISO down to a more reasonable level.

Thanks for looking!
Jay

[Larryp]

Nice images, Jay!:thumbsup:

[blink138]

hi jay.... where do you live that these objects are high in the sky?
nice images by the way but in perth they never get more than about 15 deg above the northern horizon unfortunately
pat

[loki78]

Yeah I think they look good also, am also curious where they were taken from.

[cmknight]

Hmmm ... Nice and high in the sky, and with a name like "Jay qu", I'd have to hazard an guess and say ... somewhere north of the 49th parallel? Possibly ... China? Am I close, Jay?:D

[Jay-qu]

The name is just a nickname, I am from Australia but currently in Arizona, enjoying some clear desert skies ;)

[Screwdriverone]

Hi Jay,

For colour balance, I use levels in Photoshop CS3.

I make sure the histogram is visible on the right and then select each individual channel and then adjust the middle (grey slider) until they all line up on the histogram.

A few passes normally does the trick.

Free programs like GIMP can also do this.

Looking good, need more data and colour balance away from blue.

Cheers

Chris

[naskies]

My post-stacking workflow in DSS is:

1. Look at the histogram and figure out which colour channel has the most data on the left edge. Move the black point (left slider) for that colour to the right until it just starts to clip - you'll see this in the histogram with a vertical line on the left edge that starts to go higher and higher. Next, move the black points for each of the two remaining colours to the right until the main histogram peak is in the same location as the first colour's peak.

^ Note that your histogram will look a bit funny if you have a light pollution gradient, vignetting, etc.

2. Repeat Step #1 for the highlights if necessary. The stars are usually grossly overexposed with DSLRs, so I tend not to touch this. I usually leave the midpoint slider alone too (if the white balance was set reasonably well).

3. When you hit Apply, you should get a fairly colourless (black-and-white) image. Set Saturation to 20% and hit Apply. If your colour balance is out, it will look absolutely horrible. Carefully adjust the black point / highlight clipping sliders to remove any colour casts. You should have a reasonably colourful image at this point.

4. Use the Luminance tab to bring out the colours and details in the nebulosity. This usually gets me pretty close to my final result - I just do final tweaking in Photoshop.

Note that if you have a red background due to light pollution, it's best to remove it by clipping the red channel - don't try to remove it by adjusting the middle slider or you'll never be able to fix the colour balance.

I've attached an example of Sculptor Galaxy - raw stacking output on the left, stretched version on the right. Hope this helps! :)

[Screwdriverone]

Nice tips Dave,

Good to know that I am not the only one who saturates the stacked output by 15-20%.

Interesting about the luminance clipping on red, I might have to retry this on some stacks to see how it goes.

Thanks for posting this,

Cheers

Chris

[Jay-qu]

Thanks for the tips, I'll give it a go ;)

[cmknight]

Oh, man. I couldn't have been more wrong if I'd tried. Sorry bud. I'm from Vancouver, British Columbia, Canada, but currently (for the last 10 years, actually LOL) in Changchun, China.

Since you're in Arizona, you ought to try to make it up north for the annual Table Mountain (Washington) and Mt. Kobau (Osoyoos, British Columbia) star parties.