red caste

[adamsp123]

As I am slowely struggleing my way into AP I have a number of questions which you marvelous folk may have the answer. Rather than post a whole list of Q's I will ask one for now.

When I use my canon 1000D at iso 1600 on my meade 10" SNT at 1 min exposures and above the pic has a strong red caste due I think my light pollution. So specifically must I use a filter and if so which type, or can I process this colour caste out or must I do both.

Thanks Pete

[Kaptain Klevtsov]

You can do either or both. The usual way round this is to set the black point during processing so that the red disappears. In Photoshop go into levels (Cntrl + L) and select each channel individually. Slide the left slider up to the edge of the hump in the histogram for the red, green and blue and the colour cast should go away.

Alternately you can use a light pollution filter such as a Baader neodymium or similar. The CLS filter is quite good for longer exposures of several minutes, but up to a minute the Baader one is good. The Baader is cheaper too.

Kaptain klevtsov

[adamsp123]

Thanks KK for that, Had a go with the black point seems to dramatically improve things, unfortunately the photos I took of M51 weren't exactly "exciting".. more effort needed

Pete