Redness to stars

[RedLeader1]

Been playing around with various settings (histogram) trying to calm down the excess redness that is appearing on my images. The attached image is of the Owl Nebula and as you can see that is quite red and the stars have too much redness them. My telescope is a Celestron C8 and Celestron F/6.3 reducer with an SVBony sv405CC camera which uses the same sensor as the ZWO ASI294MC Pro. I am using a CLS-CCD filter.

Any ideas or suggestions would be greatly appreciated.

Thanks.

[admin]

Hi,

I would suggest testing on a terrestrial view (point your telescope/camera at a distant tree, building, hill, etc) to see how the colour comes out in that image. The filter will give a colour cast to the image, but you should hopefully be able to clearly see that reds/greens/blues at least are roughly right, and that confirms that the image from the camera is being processed correctly. If you see odd colours (red/blue seem to be swapped) or a purple tone to the image with a fine checker grid visible at the pixel level then the images may be being processed with the wrong bayer pattern. Shining a red torch (if you have one) into the telescope is another way to check - if the image shows red bright patches from the torch light then the bayer pattern is right.

Beyond that, it's worth checking the colours of stars in an unstretched image (not live stacked, etc). The stretching applied as part of live stacking or processing in general to bring out faint detail can also exaggerate small colour balance problems to appear much bigger. If you are live stacking then you have colour balance sliders available to the right of the histogram that allow you to try to correct any colour cast.

cheers,

Robin

[Menno555]

To add what Robin says: it could be you are capturing too much infrared (IR). When using no IR Cut filter, especially stars can have a red "glow" surrounding them. Your camera is sensitive in the IR range and the protection window before the sensor doesn't have an IR Cut in it.
And as I understand it, the used filter also doesn't block IR. So another option you can try, is to use an IR/UV Cut filter. I have the one from Baader and it does the job it is suppose to do.

Menno

[RedLeader1]

Thanks Robin and Menno, I will give those things a try.

@Robin - with shining red light what other settings such as exposure etc need to be set to and do i just point the telescope at the red light in the dark? As understand it the red patches are the red pixels coming to life?

[admin]

Hi,

with the red torch trick, you will probably need to drop the exposure quite a bit to see the correct effect... The torchlight is a lot brighter than starlight, and even though it is more red than other colours, there is enough green/blue light in it that the whole image will show up white on long exposures. If you start with a short exposure (maybe 20ms) and see if you see anything, then gradually turn up until you do see something.

cheers,

Robin