another try at The Helix

[raymo]

Unfortunately this imaging session coincided with a bright moon.
30 x 60 secs, 5 x 75, 2 x 105, all at 1600 ISO. It has a magentaish
bloom at right of object; I don't know what caused it, or how to get rid of it.
raymo

[Retrograde]

That's disappointing raymo. It looks like a nice image otherwise.

My guess would be a touch of dew but of course it could be any number of things.

[raymo]

Thanks Peter. I 'll have to wait until there is no moon, get a good PA,
and do a load of 120 sec subs. Actually, last night was the first time in ages that I've had a dew free session. The humidity was very low.
raymo

[5ash]

Hi Raymo,
Looks like some detail was starting to show , I think with more exposure you'll get a great image . Can't think what that greenish glow was from.
Regards philip

[cometcatcher]

That's one of the many reasons I dislike Newtonians. It does happen with refractors, but less often.

You have light getting in from somewhere. Could be indirectly from the bright moon, reflecting off the front of your tube / shield. It's more obvious now that you are pushing the envelope. The deeper you go, the more you will notice things like this happening. Something that was minor before, now becomes much more noticeable. Even the slightest glimmer of light from something (I think probably moonlight in this case) will stretch out bright along with the image.

It's a result of you progressing Ray as you advance in astrophotography. If you want to progress further, your going to have to learn new Photoshop tricks. Flats probably won't help this sort of thing, but are a good idea anyway to minimise uneven field illumination. DSS is for basic processing and can't handle uneven fields. Photoshop can, even old versions. Software flat fields in photoshop are even more essential if you don't shoot real flats. However heavily processed images from DSS are no good to photoshop. To avoid the bright areas, you have to move away from processing in DSS and process in third party software. Either astronomy friendly software or learn photoshop skills.

[raymo]

Thanks for all the advice, I shall take it to heart. I might have found the culprit. The moon was high, but behind me, and I forgot to fit the
rubber viewfinder cover. I don't think it was at the other end of the optical train, as I have a very long matt painted dew shield, and the moon was behind the scope.

Thanks Philip, hopefully I'll get there in the end.
raymo

[cometcatcher]

I meant to put the reply in the bloom thread, not this one. Anyway...

You have a lot of nice data there Ray, just have to work on a few things.

[Rex]

That's a nice shot Raymo. Pretty clean, hardly any noise. It's a shame about the glow. I would have said dew also, however you have said that wasn't possible on this night. Other than that the only other possibility is stray light as Kevin has said. Hope you get it sorted because that is a really good image.

[Bassnut]

Nice work Raymo. It was easy to fix, a bit of selective curving in PS.

[raymo]

Thank you very much Kevin, Rex, and Fred. That looks much better.
Now to wait for a moon free night, lots of 120sec subs, and see what I get.
raymo [exciting, ain't it].

[BruceG]

Waiting for another moon free clear night? exciting or frustrating?
Ok, a bit of both I guess. Great work Raymo by the way...
Bruce.

[raymo]

Thanks Bruce; yes the waiting is frustrating, but I can see the detail in
the image tantalising me. I just need more, longer, subs.
raymo

[LightningNZ]

That's a nice picture there Raymo - things are really coming along for you.
Cheers,
Cam

[raymo]

Thanks Cam, slowly getting there. Gotta learn some PS processing.
raymo

[rustigsmed]

hi ray, nice job.

here is a good guide to PS processing
http://sharmaastronet.ipage.com/PS1.pdf

I use the gradient removal method suggested above but i found it black clipped my image. I found another way which adds another layer but stops the black clipping. However I don't like the first few steps in version below so combined the first half from the version above with the later steps in the one below

http://starryvistas.net/articles/GradientSubtract/GradientSubtract.aspx

hope this helps.

Rusty

[raymo]

Thanks again Rusty.
raymo