Astroimage processing

Re: Enhancing Nebulae while reducing Star bloat?

Locoweed — Thu, 27 Nov 2008 03:23:56 GMT

IMHO, that is a pretty tought object to work with. Starting on something with less stars to deal with will be easier.

Russ

Re: Enhancing Nebulae while reducing Star bloat?

lothar22 — Mon, 04 Aug 2008 23:45:14 GMT

Thanks for all your help!

Re: Enhancing Nebulae while reducing Star bloat?

jballauer — Mon, 04 Aug 2008 04:42:59 GMT

Nice result! Congrats!

Re: Enhancing Nebulae while reducing Star bloat?

lothar22 — Sat, 02 Aug 2008 16:05:45 GMT

Set the scope up:

Checked Collimation, aligned, focusing with eyepiece para focal to my DSI, Adjusted anti-backlash settings, Found my guide star, inserted camera, imaged this.

Jay's knowledge and information really helped me process this one much better than the last.

No vignetting in the image this time. I used my OIII filter, which might have eliminated vignetting.

I decided not to use flat frames and just keep my optics clean and use at least a pollution filter.

Those two things will let me sneak by without taking flat frames, at least for now.

When I get a wedge and go for longer exposures, vignetting may become more of an issue.

Anyway, I'm happy with my results...

Re: Enhancing Nebulae while reducing Star bloat?

lothar22 — Thu, 31 Jul 2008 18:07:04 GMT

Flat Field question:

From what I've read about taking flat frames, is that the optical path must not be changed from imaging an object to taking a flat frame (focus, orientation of the camera).

So, how do you do that? It's 1:00am, I'm done taking my images, then I put a T-shirt over the end of the scope and point a lightsource at it then take the flat frames?

Should this be done at the end of every session?

How are these flat frames applied to the actual astro images?

???

Re: Enhancing Nebulae while reducing Star bloat?

lothar22 — Thu, 31 Jul 2008 12:31:33 GMT

My mount is Alt-Z, and my scope does all it can do just to keep the object in view, meaning it moves around quite a bit in an imaging session. When stacking, the registration image has the object at the middle of the view, but the object in the images towards the end of the session are at tht bottom of the view. That's why the bottom of the images don't have much data.

I excluded a good many exposures due to field rotation.

I have to tweak the anti-backlash settings to make the movement steadier. I've done it before, and it does help. I was experimenting with some telescope control software and inadvertently reset the anti-backlash settings to 0.

The vignetting isn't always an issue. Some shots I've taken have very little or no vignetting, with or without the reducer, and others it is very bad. It's probably like you said, light pollution or stray light from my laptop. I will try the T-shirt flat to see if that helps.

thank you very much for taking the time to process the images and provide feedback!

Re: Enhancing Nebulae while reducing Star bloat?

jballauer — Thu, 31 Jul 2008 03:20:08 GMT

Okay, here's what I came up with...

In short, you've done a pretty good job of processing it yourself!

Of course, the real weak point is not your processing, but rather the data. You'd be amazed at how easy it is to process good data. In fact, I'd encourage you to try your hand at processing some of the data that Jim Misti has made available here...

http://www.mistisoftware.com/Astronomy/index_fits.htm

Now, back to the data...

I'm wondering about the parts of the image I had to crop. The top part of the FITS files you sent me were striated and unusable. I wonder what would have caused that? As far as the vignetting, I would make sure there is no direct lighting around, including the laptop. For 30 second images, your background levels are extremely high, meaning you most certainly are shooting in some bright conditions...assuming the master files you sent were averaged rather than added.

Yes, flat fields would certainly help. Try shooting sky flats in the early morning...or doing "T-shirt" flats, stretching a t-shirt over the aperture end. However, I would resolve to figure out why you have that much vignetting in the first place. I'm not sure it's mechanical vignetting (something cutting into the light cone), but rather than you have a hot spot in the optics (all scopes have such a spot) and it just becomes more pronounced with light pollution. Though, again, that striated part concerns me...don't know what could have caused that.

Just a few tips once you acquire the data...

- Don't use luminance data if it doesn't help the image. Honestly, the green channel was your best data...if you are going to use a luminance, just duplicate your green channel. I know your L layer was probably synthetic, due to the single shot color camera, but I'm talking conceptually here. When you process with an L layer, you are telling the software that you want your details FROM that layer. So, you'd be certainly that your L layer has details worth detailing!

- Be picky about the images you use in your stacks. If you shoot 90 images per channel, chances are VERY likely that MANY of those images are blurred, with oval stars. In that case, including them actually kills your S/N level in the image. You are better off selecting the best 10 or 20 of them.

- I don't know what type of reducer you are using, but be sure you have the right distance between the reducer and the chip...if not, then you won't have the right reduction and you add aberrations to the image. More than likely, you have one of the .5 reducers that screws into the eyepiece, which kinda negates the point. However, it's good to double check that.

- Don't fall in love with the reducer. When shooting single objects like this, it doesn't "speed" up anything. You are often better off shooting natively. Now, if you are doing it because you need the forgiveness offered by that image scale, then it's a different story. But the point is, if you have the gear to shoot at the longer focal length, the results will be better on an object like this if you do it.

It's really good to work on your processing...you are beginning to understand the importance of the white and blackpoints, and what we call "logarithmic curves" - namely, boosting the shadow areas more than the highlights. But I think you are at the point where you need to work hard to get better data...that's what will really improve your images.

Hope this helps!

Re: Enhancing Nebulae while reducing Star bloat?

lothar22 — Thu, 31 Jul 2008 01:53:12 GMT

Images sent.

Re: Enhancing Nebulae while reducing Star bloat?

jballauer — Wed, 30 Jul 2008 21:31:36 GMT

Exactly. Just the master files for each of the channels.

Re: Enhancing Nebulae while reducing Star bloat?

lothar22 — Wed, 30 Jul 2008 17:42:36 GMT

Thanks. Thanks again for sharing your knowledge!

I stretched the 2nd attempt much more than the first, so I think I kept the star bloat to a minimum.

Do yo want all the exposures? 109 FITS exposures for each; L,R,G, and B. That would be a lot.

How about the 4 FITS files that are the product of combining each of the color exposures?

Re: Enhancing Nebulae while reducing Star bloat?

jballauer — Wed, 30 Jul 2008 05:05:39 GMT

Oh, a definite improvement! You've managed to show the colors a bit more true. Your first effort did do a better job of controllling the stars, though...not bad at all!

If you'd like, send me your raw data to my email at jballauer at gmail dot com. I'll work it up for you so we can see the potential that's there.

Re: Enhancing Nebulae while reducing Star bloat?

jballauer — Wed, 30 Jul 2008 05:01:28 GMT

LOL, I'd expect that from you, john.

Good to see you!

Re: Enhancing Nebulae while reducing Star bloat?

lothar22 — Wed, 30 Jul 2008 04:36:11 GMT

I followed your advice and re-processed the bit 'o veil I imaged.

Here is my first attempt, before reading through your tips...

Not bad, but here's after following (and practicing) the techniques you shared...

Although it may not be that apparent, I think it's a definite improvement.

Thanks Jay!

Re: Enhancing Nebulae while reducing Star bloat?

tasco-60mm — Tue, 29 Jul 2008 23:46:36 GMT

hi jay- hows it going?- you know, this thread gave me an idea, i might add some nebula enchancing ATN's on the the next issue of spitfire's scopestuff- LOL

Re: Enhancing Nebulae while reducing Star bloat?

jballauer — Tue, 29 Jul 2008 22:32:19 GMT

Good to see you, Steve....been too long.

Hopefully, I'll spend more time out of my hole!

And, BTW, I can't imagine you'd have much more to learn. I've never seen anybody get the data you get from so little exposure time!