The swan nebula M17 last night

[5ash (Philip)]

This completes the series of pics I have taken in the last week or so ( Triffid, lagoon and eagle nebulas in time for moonlit evenings. This one of the swan comprises 15 X 400 second exposures through SW 120 ED using the nightscape camera. Have uploaded two pics , one more stretched than the other. Which do you think looks the best?
regards philip

[cometcatcher (Kevin)]

Beautiful image Philip!

As you can see, the more stretched image shows better detail in darker areas but burns out the bright regions to white. There's a couple of ways to address this. It's much like processing an image of the Orion nebula where there is extreme contrast between shadow and highlights.

In Photoshop, or your favourite processing program, the most popular way is to mask out the bright core while stretching the rest of the pic. There's lots of ways of doing that, but I just lasso the bright area, feather the edges of the selection so that it's not a hard line, invert the selection and stretch the rest. You may need to do this a couple of times as regions reach white point.

Another way is to only expose long enough to stop short of white point clipping, eg stop just before the white burns out in initial exposure with shorter subs. In processing, instead of doing a linear stretch, use a midtone stretch. The downside to this method is that it can lack the "punch" of a linear stretch. Or you can use a combination of both.

Selections, layers, masks all help make the most of an image.

[tilbrook@rbe.ne (Justin Tilbrook)]

Good work Phillip!

Both have good points, first shows the middle of the swan without blowing the core.
The second shows the fainter out lying nebulosity.
Are you into layering and blending yet?

If so layer and blend the first into the second.

Here's a link to Louie Atalasidis page on processing tutorials for photoshop if your using it.
http://www.atalas.net/

Cheers,

Justin.

[5ash (Philip)]

Thanks Kevin and Justin I'll try to follow your advice and perhaps repost the result.
Regards philip

[Jon (Jonathan)]

Lovely images, Philip.Tell me more about the "Nightscape" camera?

[5ash (Philip)]

Originally Posted by Jon

Lovely images, Philip.Tell me more about the "Nightscape" camera?

Hi Jon,
I bought the 10.7 Mp celestron nightscape OSC 3rd hand from an IIS member who used it on a fastar setup.You can find more info on the celestron website. They are a budget , large size sensor camera with cooling down to 20 degrees below ambient. The images are quite noisy compared to similar expensive brands but the resulting pictures are quite pleasing. The supplied capture and processing software (astrofx) is apparently a cut down Maxim dl . The work flow for processing produces stacked and processed images in a matter of minutes. All the pictures I have posted have used this software with tweaks in PS.
Regards philip