Astrosurf Posted August 11, 2014 Share Posted August 11, 2014 Hi all,This image of Cygnus was taken with an old F4-5.6, 17mm-85mm Canon EFS lens, set at 17mm, on my modded Canon and Astrotrac. I didn't use a LPF as the lens has a rubber ring that protrudes inwards so it wouldn't fit. Melsky suggested Custom White Balance, which was good. But I get sooooo fed up with the red halos around the stars. I thought it was the Astronomic LPF but it's still happening here. Must be that the red end of the spectrum in the modded camera isn't focusing the same as the other colours. I've softened the red halos in processing but they're still a blasted nuisance. How to I get rid of them?Alexxx Link to comment Share on other sites More sharing options...
Leveye Posted August 11, 2014 Share Posted August 11, 2014 You can isolate just the stars in photoshop and invert selection then refine the edge and desaturate a selected color with the eyedropper or replace color at will. Link to comment Share on other sites More sharing options...
Astrosurf Posted August 11, 2014 Author Share Posted August 11, 2014 This shows what I mean. Link to comment Share on other sites More sharing options...
Astrosurf Posted August 11, 2014 Author Share Posted August 11, 2014 You can isolate just the stars in photoshop and invert selection then refine the edge and desaturate a selected color with the eyedropper or replace color at will.Thanks Leveye. I tried that with Colour Balance but didn't want to lose any natural colour. I didn't include Deneb and the other bright stars. Maybe I should force it a bit more. Link to comment Share on other sites More sharing options...
Thalestris24 Posted August 11, 2014 Share Posted August 11, 2014 HiI'm not experienced enough to help but the problem looks quite similar to the effect I've seen when I've overstretched/overexposed stars and tried to replenish the colours by increasing saturation and colour bias. I've only really used StarTools plus tweaking with cs2. I'm sure I've read another thread about reducing the prominence of stars in order to increase nebulosity - some actions in PS?Also this one: http://stargazerslounge.com/topic/221052-red-fringing-on-bright-stars-after-dslr-mod/page-2?hl=%2Breducing+%2Bstars#entry2378924Sorry I'm not much help!Louise Link to comment Share on other sites More sharing options...
Astrosurf Posted August 11, 2014 Author Share Posted August 11, 2014 That's interesting. Thank Louise. The red is already in the RAW images and stretching just brings them out. I did use custom white balance but I didn't look at the channels. I'll have a closer read of that thread to see if I can understand it all! Link to comment Share on other sites More sharing options...
ronin Posted August 11, 2014 Share Posted August 11, 2014 The additional red allowed through by the modified camera will not focus to the same plane.The design specification on the lens would have been for something like 650-400nm to be at the same plane.You have now allowed 700nm to get through and that was never in the original design of the lens.The filter took out these wavelengths so the lens was never designed to handle them.Think about it, why design a lens to handle a wavelength that is not (should not) be present? Link to comment Share on other sites More sharing options...
Astrosurf Posted August 11, 2014 Author Share Posted August 11, 2014 Good point Ronin. Link to comment Share on other sites More sharing options...
Thalestris24 Posted August 11, 2014 Share Posted August 11, 2014 Ah - if this is correct http://www.astrosurf.com/buil/baader/eval_us.htm then the problem is caused by lack of anti-aliasing capability with the Baader filter but can be improved by dithering.HthLouise Link to comment Share on other sites More sharing options...
Astrosurf Posted August 11, 2014 Author Share Posted August 11, 2014 That looks good. Thanks Louise. It's very wordy so I'll have a look tomorrow! Link to comment Share on other sites More sharing options...
Thalestris24 Posted August 11, 2014 Share Posted August 11, 2014 HiIt's really just the bit at the bottom - sorry, I should have said!Louise Link to comment Share on other sites More sharing options...
Astrosurf Posted August 11, 2014 Author Share Posted August 11, 2014 Thanks Louise. I did sort of see that, just not in detail! Link to comment Share on other sites More sharing options...
wxsatuser Posted August 12, 2014 Share Posted August 12, 2014 http://budgetastro.com/micro/articals/red_halos/red_halos.html Link to comment Share on other sites More sharing options...
Astrosurf Posted August 12, 2014 Author Share Posted August 12, 2014 Absolutely marvellous! Thanks! I'll let you know how it goes. Link to comment Share on other sites More sharing options...
Astrosurf Posted August 17, 2014 Author Share Posted August 17, 2014 I tried the tutorial to reduce halos but one part wouldn't work, so I used the Magic Wand to select the stars and made the stars smaller as on the tutorial. Still a lot to learn with processing!What do you think? Link to comment Share on other sites More sharing options...
toxic Posted August 17, 2014 Share Posted August 17, 2014 have you tried a normal ir filter for the lens i know its a modded camera but it will be worth a try at least you could take some with the filter on the lens and use them as a color layer mask. Link to comment Share on other sites More sharing options...
Astrosurf Posted August 17, 2014 Author Share Posted August 17, 2014 That's a good idea. Thanks for the tip! Link to comment Share on other sites More sharing options...
toxic Posted August 17, 2014 Share Posted August 17, 2014 oh btw its a very nice image sorry i never mentioned that Link to comment Share on other sites More sharing options...
Astrosurf Posted August 18, 2014 Author Share Posted August 18, 2014 Awwww, thanks toxic! Link to comment Share on other sites More sharing options...
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