Light pollution questions

[Tony_]

G'day,

I have a few questions regarding imaging in light polluted skies (of course dark skies would be the best option - but not practical for me):

Given all things being equal (eg. exposure times etc.) what is the best way to handle general light pollution (I use a modded dslr):

1. Use a custom white balance (eg. white paper photographed in sunlight). (or other custom white setting)?
2. Use a LP filter (I have a Hutech IDAS).
3. Other settings in camera?
4. Use nothing and balance the colour in processing?

Also in regards to LP filters I have read 2 theories on exposure times, which one is correct?

1. Light Pollution filters basically remove light therefore the exposure time will need to be longer.
2. Light Pollution filters remove mostly (hopefully) unwanted background light which improves the contrast for the wanted light, therefore exposure time is decreased.

Thank you for any input.

Regards,
Tony.

[cometcatcher]

It depends how bad your LP is, to how you handle it. With mild LP you may not need a filter at all and only need to adjust camera settings. With more severe LP a filter will help, especially with nebula, less well with stars and galaxies. The best LP filter depends on how severe your LP is. At the lower end a wideband filter will be fine. If it's severe you may need something more narrow. Specifically which IDAS filter do you have?

Since LP filters don't increase the overall light, I don't see how exposure times can be shortened. In real world results with broadband OSC filters, some LP will still get through, but you will get an increase in contrast between nebula and background light which would allow you to increase exposure time.

Just experiment with and without your filter and see what happens.

[malau]

Hi Tony,

I have a 600D with Astronomik CLS filter for LP. I am a beginner so my info may not be 100% correct. However as far as I understand filters (including narrow band) are filtered out certain wave length of light (depending on your filter purpose) therefore those not filtered out (e.g. the light from star) still be able to pass thru. For your question I guess #2 (for both) is correct