M 13

[Jim McMillan]

I'm probably over-sharing again, but we just had 2 clear nights in a row after being rained on for 40 of 50 days!

This is a "one night" image. M 13 is quite bright so it doesn't need a lot of exposure time unless you're trying to show the faintest of the stars. I also don't think it benefits all that much from taking luminance images, so this is just a straight RGB. It is 11 x 10 min each R, G, B (5.5 hrs total).

Processing globular clusters creates a fair amount of opportunity for making choices:

1) How much stretching to show faint stars?
2) How much stretching on the core?
3) How much sharpening on the core?
4) How much color saturation?
5) Where to set the black point?

I tried to create a "balanced" image, not pushing anything too far (except perhaps the color saturation). Astronomy Tools for Photoshop (Elements) eliminated any color gradients and helped with the star saturation.

Of course, everything was acquired via ACP (including dawn flats). I used 100% of the images - things worked 100% perfectly.

Jim

[Russell Archer]

Hi Jim

Wow! Another beautiful image. I can really appreciate it as I've had a go at imaging a couple of globular clusters (M3 and M13) recently myself (I've attached my image of M3 for comparison - my M13 didn't come out too well). There's so much more depth and '3-D'-ness to your image. And I really like the way you've captured colors of both the blue and yellow stars. My image of M3 was 10 x 300-secs Luminance, 5 x 120-secs RGB.

Unlike in my image, you haven't over-done the sharpening of the core (you can start to see dark halos around the core stars in my image). Looking at your image, it's almost like the core is slightly sharper than the rest of the image, which gives it that 3D feel.

Thanks very much for sharing your wonderful image

Russ

p.s. Meant to say that all my subs were taken with ACP 6 - I too was able to use of of the exposures (thanks to ACP and the SX AO!)

[Jim McMillan]

Hi Russ,

I think your image is very good! It looks like you've got your AO working well. That's no small feat!

Even though this is a bright object, a little more exposure will do 2 things:

1) Bring out the dimmer stars a little bit.
2) Improve the star color saturation.

For globulars, I usually forgo the luminance and use the extra time to add to the RGB.

Regarding the deeper color of mine, I just pushed the color saturation in MaxIm, then used "increase star colors" in Astronomy Tools. I suspect you could do the same things with your image successfully. With respect to sharpening, I think it's just a metter of taste.

Try as I might, I couldn't figure out your FOV versus mine. My FOV is about 28 arcmin x 19 arcmin. I'm guessing yours is somewhat smaller? I also wonder if your AO, with its mirror, is giving a mirror image to mine...

Anyway, very good job! You've made great strides!

Regards,

Jim

[Russell Archer]

Hi Jim

Many thanks for your comments.And sorry, I think I confused things - my image was of M3, not M13. I had recently tried to take an image of M13 but had problems because of a lack of guide stars ... you wouldn't think it with a globular cluster!

I can absolutely see now why one needs a rotator. That's on my shopping list for the future. My FoV by the way is 13.2' x 10' and an image scale of 0.57" per pixel.

And yes, I think I have got the AO working very reliably - it makes such a difference compared with normal guiding. Your advice was really, really helpful and saved me a lot of trial and error. I can't thank you enough for that

Russ