Scott Tilley Posted December 9, 2015 Share Posted December 9, 2015 As we had clear sky for what seems like the first time in ages I decided to point at a nice easy reliable target. Managed 90x75 sec images with 30 dark and 10 flats. All done with Star adventurer, 70d and Tamron 90mm macro lens. I even got a shadow of the Witchead Nebula! Link to comment Share on other sites More sharing options...
wimvb Posted December 9, 2015 Share Posted December 9, 2015 Very nice. Sooo many stars! What is the cause of the circular star pattern? Natural or due do equipment? Link to comment Share on other sites More sharing options...
Scott Tilley Posted December 10, 2015 Author Share Posted December 10, 2015 Very nice. Sooo many stars! What is the cause of the circular star pattern? Natural or due do equipment?Hi wim, I'm not sure to be honest as my processing skills are very basic at the minute. It could be the remnants of light pollution after I have run the photoshop plug in to get rid of it. I'm hoping to add some more data to this and reprocess it,although that could make it better or worse!!!Scott Link to comment Share on other sites More sharing options...
wimvb Posted December 10, 2015 Share Posted December 10, 2015 I saw another image of yours somewhere around here that seems to have the same flaw. There seems to be a rainbow effect over the width of the image. It might be the lens you're using. If you have the possibility to use another lens, you can find out if this is the case. I have never seen the colour banding this way. I have had colour gradients (blotches really) in my images after background extraction and stretching, but never in a circular pattern. If it is software related, you can try to just play with the histogram and not use the LP plugin. I'm not familiar with PS though.Good luck and clear skiesPS just saw the other image I referred to and saw that you use another lens, but of the same brand. The circular pattern may be software related, so you might try stretching a raw image, without background correction first.. Just a thought. Link to comment Share on other sites More sharing options...
Scott Tilley Posted December 11, 2015 Author Share Posted December 11, 2015 I saw another image of yours somewhere around here that seems to have the same flaw. There seems to be a rainbow effect over the width of the image. It might be the lens you're using. If you have the possibility to use another lens, you can find out if this is the case. I have never seen the colour banding this way. I have had colour gradients (blotches really) in my images after background extraction and stretching, but never in a circular pattern. If it is software related, you can try to just play with the histogram and not use the LP plugin. I'm not familiar with PS though.Good luck and clear skiesPS just saw the other image I referred to and saw that you use another lens, but of the same brand. The circular pattern may be software related, so you might try stretching a raw image, without background correction first.. Just a thought.Thanks Wim. Its the processing bit I find most difficult.I will go through a couple of tutorials and see if I can re-work the image.All the best.Scott Link to comment Share on other sites More sharing options...
Scott Tilley Posted December 11, 2015 Author Share Posted December 11, 2015 I saw another image of yours somewhere around here that seems to have the same flaw. There seems to be a rainbow effect over the width of the image. It might be the lens you're using. If you have the possibility to use another lens, you can find out if this is the case. I have never seen the colour banding this way. I have had colour gradients (blotches really) in my images after background extraction and stretching, but never in a circular pattern. If it is software related, you can try to just play with the histogram and not use the LP plugin. I'm not familiar with PS though.Good luck and clear skiesPS just saw the other image I referred to and saw that you use another lens, but of the same brand. The circular pattern may be software related, so you might try stretching a raw image, without background correction first.. Just a thought.Hi Wim,I'm not sure what you mean with regard to background correction. My processing basically (and I mean basic) consists of stacking in DSS and then doing multiple small stretches in PS and then darkening in curves as the background gets too light. I have just got the Prodigital software plug ins specifically for astro-photography so may also use these to get rid of light pollution or noise etc.Scott Link to comment Share on other sites More sharing options...
wimvb Posted December 12, 2015 Share Posted December 12, 2015 Background correction means that you somehow create an image that holds information about your images background. Most images contain background gradients. Just in the same way that daytime cloudless sky isn't a uniform blue, so it is at night for various reasons. (light pollution, moon glow, etc). In image processing you take samples of your background in the original image, create a new image by interpolation, and subtract that image from your original. That way, you even out the background of your original. Pixinsight has a tool that does all this. I believe that the process in Photoshop is more elaborate. I don't know exactly how it's done there.After this correction you have to make your background a neutral colour. Because of light pollution and depending on your camera, it usually is not neutral. This would be equivalent to setting the white balance in daytime picures.My advice is that you google for tutorials on astrophotography in whatever tool you are using for processing your images.I use pixinsight for all my processing, but there are other good tools available. Choose whatever works for you and is within your budget, and learn all you can.Good luck and clear skiesWimsent from my mobile device Link to comment Share on other sites More sharing options...
wimvb Posted December 14, 2015 Share Posted December 14, 2015 If you make the stacked image available to me, I can have a go at it using PixInsight. Just put the autosave.tif file that DSS creates in a public folder (Dropbox or Google Drive). Now that I'm finished grading I have more time to spend on the fun stuff. Link to comment Share on other sites More sharing options...
Scott Tilley Posted December 15, 2015 Author Share Posted December 15, 2015 If you make the stacked image available to me, I can have a go at it using PixInsight. Just put the autosave.tif file that DSS creates in a public folder (Dropbox or Google Drive). Now that I'm finished grading I have more time to spend on the fun stuff.Hi Wim, than you so much for the offer. I have uploaded the 16 bit tiff to my google drive. I just need to know how I give you access to it.many ThanksScott Link to comment Share on other sites More sharing options...
wimvb Posted December 15, 2015 Share Posted December 15, 2015 I just sent you a PM with my google account information. Just let me know (PM or this thread) when it's available Link to comment Share on other sites More sharing options...
wimvb Posted December 15, 2015 Share Posted December 15, 2015 Summary:Background extraction in several passes with different number of samples and varying sample parametersStretchingLuminance extraction and combinationHDR transformationCurvestransformationColour saturationI got rid of most of the background gradients and stretched the image less than in the original post.Then applied LRGB combination in several passes, using luminance and red channel as L, to enhance the horsehead nebula.Finally coloursaturation.It was difficult to tame the Orion nebula, while enhancing the horsehead and flame.When doing LRGB combination with R as luminance, some of the stars came out a little too blue. I tried to minimise this by first averaging the L and R channels using pixelmath.Thanks for letting me have a go at this wonderful, but challenging image.Btw: the forum software deteriorates the final result. On my computer screen the image (8 MB jpeg) is less noisy and has more subtle colour changes, while the backgound is less pronounced red. Link to comment Share on other sites More sharing options...
Scott Tilley Posted December 17, 2015 Author Share Posted December 17, 2015 Hi Wim, thanks for taking the time. Your workflow is really useful, I've printed it out to try and work through on the next image I produce. That's presuming we ever see a clear sky again!Thanks AgainScott Link to comment Share on other sites More sharing options...
wimvb Posted December 17, 2015 Share Posted December 17, 2015 You're welcome. Processing your image benefits me as well. This way I practice processing and I get a feel for how different cameras/lenses capture a scene. From the processing I have done for others recently I conclude that (modern) Canon cameras are much better noise-wise than my trusty Pentax (which is getting old). Technology is leaping forward.As for my processing flow; I usually do noise reduction before stretching, but that was not a problem in your image.I do believe however that you should try to figure out what causes the circular background pattern in your images. My guess is that it is your Tamron lens that is the culprit. Lenses that are good quality for daylight photography, may show flaws in low light conditions. Remember that astrophotography is done under optically extreme conditions; dark background and bright pointlike lightsources is not what these lenses were designed for.If this is the case, you should se a similar pattern if you process raw unstacked images. You can also use other lenses and see if your images still suffer from this effect.Good luck and clear skies Link to comment Share on other sites More sharing options...
Pete Presland Posted December 18, 2015 Share Posted December 18, 2015 Very impressive final image! Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.