Hi just thought I would ask , this is probably a noob question but why do I get a red colour about half way up the sky from buildings and trees  in my photos when I try to take skyscapes from my backyard over my house using exposures of around 25 seconds . I am using a Nikon d90 with standard kit lens 18-105 set at 22mm f4.5, ISO 400 , NR on .

Thanks Mark

Are you near a big city? If so, my guess is it's a cloud layer, or maybe smog or pollution thats reflecting light from the city lights, and your camera is picking it up.

I have seen the same thing on occasion when using a my DSI first generation Color CCD camera.

I only noticed it though when the sky has to much moisture content or poor transparency, or in the winter months when an upper layer of the atmosphere has ice crystals floating about.

On nights with good transparency it does not show up at all.

I now use the DSI II Pro in Mono, even though I have the RGB filter set, and on bad nights, I get a light gradient in my images that is just too hard for me to remove without losing detail.

I have to agree with the last post that blames the sky conditions.

Dennis

Thanks Dennis I have noticed it is worse in nights that have  a lot of moister in the air but even in nights that are very clear of moister  its still there but not as prominent .

Worked the problem out guys the D 90 has a function called active D lighting which retains lost shadows in photos I always leave it on auto . I just turned it off and the problem is much better not completely gone but I think that is like you guys said low lying cloud reflecting the light . Thanks Mark .