Cygnus Loop

[gthomas]

This Canon EF 200mm lens continues to impress me.

One hour and fourty minutes of 2 and 3 minutes subs, stacked in DSS and some processing with pixInsight gave the following.

The whole loop is nicely captured with plenty of detail and there are a shed load of stars which are nice and round right out to the corners even though the lens was only stopped to f3.5!

Those stars are the problem though. I've not yet found a way to lift the nebula while keeping the background stars down. There are just so many that the loop gets kinda lost in there.

[Gina]

Great images I'm planning to do some wide-field stuff a bit later. I don't know PixInSight, I use PS sand in that I use Curves to bring up the fainter stuff while keeping the bright stars at bay. The technique is to lift the curve near the bottom (right hand) end but lower it near the upper (left hand) end. That lifts the brightness/contrast of the darker parts while lowering that of the lighter parts. Hope that makes sense.

[gthomas]

Thanks Gina,

Do you mean like the usual S curve but upside down?

[Steve Ward]

Just been watching this , may be useful to you .

http://www.astronomyshed.co.uk/forum/viewtopic.php?f=19&t=10593

[gthomas]

Thanks for that Steve,

I've tried star masks and, following Gina's idea, also some really bizarre curves but all to no avail. The problem is that the many small stars are at a signal level that is in the middle of the range covered by the nebula. Normally the problem is the other way around with the nebula far lower.

[Mark72]

Glyn,

This is not a great deal in PI. Create a star mask, apply to linear image, go to a stretched mask script, set to 100 iterations, watch the whole football game; when it's over, PI will be ready with a lot of nebula and suppressed stars.

You can also reduce them with Morphological transformation. May look like this in the end - http://astrobin.com/2546/

[gthomas]

Thank you Mark.

I am fairly new to PixInsight and so was not familiar with those two functions. I've had a bit a play with them but with only limited success so far. I guess I need to do some more research and practice.

[gthomas]

Well after playing with various masks and transforms and on-line tutorials I think this is a lot better.

[Mark72]

Yes, much better!

[gthomas]

Thanks for your help Mark

[Psychobilly]

Fits nicely in the FOV doesnt it...

I'm using mine at f2.8 these days...

http://stargazerslounge.com/index.php?/topic/150462-Canon-200/2.8L-can-you-get-decent-star-shapes-at-f2.8#entry1514700

Peter...

[gthomas]

I find that at f2.8 I get some vignetting in the corners, but that can be corrected with Canon Photo Professional. At f3.5 or f4 I don't need to do that extra step plus, to be honest, I rather like the diffraction pattern on the brighter stars

[Psychobilly]

And i lke the fact you can grab those photons more quickly

Flats soon sort out any uneven illumination issues as well as sny dust bunnies etc...

Pesonally i hate the multiline diffraction pattern and used to use front aperture rings to stop the lend down... but each to their own...

Peter...