How can I avoid getting a grainy sky when shooting photos at night?

Question

Say I am trying to get an HDR of skyscrapers at night. If I get the buildings to look nice, the sky generally ends up looking orange and grainy.

Answer 1

Most likely your camera is set (or is automatically choosing) to use a higher iso. Grain starts getting noticeable at 400iso and gets more and more obvious at 800, 1600 and 3200.
If you can change the ISO make it 100 or 200 and you should get rid of the noise (but you'll probably need a tripod since the shutter speed will be low-otherwise you'll get camera shake)
The link will give more info on ISO.

Answer 2

What time of night do you need to shoot? Twilight, midnight? How bright is the sky due to city lights? I would imagine you are shooting early nightime when most office lights are still on. And the sky may be colored due to sodium vapor or mercury streetlights. They tend to throw an ugly color cast and you may need to adjust the white setting to overcome that. As mentioned above, shoot at lower speeds. If you can do this on film, it may be better. For long exposures...more than a few seconds, faster film cannot compete with slower films due to reciprocity failure, and slow film has much better grain. You can always convert a film print to digital via scanning.

Answer 3

If you have a SLR camera, change the aperture and shutter speed to allow more light into the camera if you want to use a slower film speed (if you have a film camera). Using a tripod is pretty much a must.