RyanParle Posted February 28, 2019 Share Posted February 28, 2019 Hi All. After a few years away from astronomy & astroimaging I have now found the time & motivation to get the telescope out and do some imaging. I started out spending a few evenings getting my guiding, Focusmax, Platesolves & image rotator working in symphony with CCDC, I also spent some time building up an extensive calibration image library. Once everything was running right and could be fully automated I set about imaging a few objects, I was impressed with my guiding and could happily take subs up to 30 minutes with round stars. I grabbed a few 10 minute & 30 minute subs of M81 & M82. When i try to convert them to colour am having issues in getting a decent colour balance. I have attached a couple of screen grabs & one of the FITS Subs & a sample Flat Frame one of the image with the scaling set at 1:1:1 & Auto background levels, where most of the image looks quite naturally coloured however the stars are all pink. The other has had the white balance set by using one of my flat frames shot on a 80% grey card during daylight, here you can see that the whole image has a green tint to it, the colour of the stars is slightly better but now they have a green tint as well The images were shot on a Canon EOS 50d with a Baader Neodymium Filter. Can anyone offer any advice on getting a natural colour balance for this Camera / Filter combo? M81 & M82_600s_90.0deg_20190227_1933_000000642.RAW.FIT EOS_50d_Flat-Field_90.0deg_20190223__000000519.FIT Link to comment Share on other sites More sharing options...
alan4908 Posted March 1, 2019 Share Posted March 1, 2019 Obtaining a good colour balance is one of things I struggled with when I started astrophotography - the issue is that if you don't get it approximately correct at the start, then balance will only get worse the more you process the image..... The way I used to obtain a colour balance with my camera is to work out the corresponding filter balancing coefficients (eg the RBG factors). If you know these you can insert them into MaximDL. You can do this with a piece of free software called Excalibrator - what it does is to take you image and compare it to some known data and then work out the correct balancing coefficients see http://bf-astro.com/excalibrator/excalibrator.htm - I found that this works quite well. I way I do it now is to use Pixinsight's Photometric Colour Calibration tool - you can you download Pixinsight as a free trial. Pixinsight is quite a challenging software package to use but it is extremely powerful once you get the hang of things. Alan Link to comment Share on other sites More sharing options...
Davey-T Posted March 1, 2019 Share Posted March 1, 2019 Maxim does a pretty poor job of displaying images, colour or greyscale so it's difficult to see what they actually look like without transferring them to something like Photoshop. Dave Link to comment Share on other sites More sharing options...
RyanParle Posted March 1, 2019 Author Share Posted March 1, 2019 1 hour ago, alan4908 said: Obtaining a good colour balance is one of things I struggled with when I started astrophotography - the issue is that if you don't get it approximately correct at the start, then balance will only get worse the more you process the image..... The way I used to obtain a colour balance with my camera is to work out the corresponding filter balancing coefficients (eg the RBG factors). If you know these you can insert them into MaximDL. You can do this with a piece of free software called Excalibrator - what it does is to take you image and compare it to some known data and then work out the correct balancing coefficients see http://bf-astro.com/excalibrator/excalibrator.htm - I found that this works quite well. I way I do it now is to use Pixinsight's Photometric Colour Calibration tool - you can you download Pixinsight as a free trial. Pixinsight is quite a challenging software package to use but it is extremely powerful once you get the hang of things. Alan I tried eXcalibrator last night & it ended up very green (so green that it looked as if the red & blue channels were switched off!) I don't have a sample image at the moment as I am at work, I'll post one tonight. Link to comment Share on other sites More sharing options...
Davey-T Posted March 1, 2019 Share Posted March 1, 2019 You can use what's called a " G2V " star to calibrate your camera [ sensor ] this in theory is a standard white light that can be analysed to work out the settings for RGB in Maxim though many folk only stack the RGB images separately then do further processing in other software. Dave Link to comment Share on other sites More sharing options...
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