How do you combat light pollution? / concentric light circles what are they?

[wouter]

Hello all,

After an imaging session last night I wanted to ask the people who are not fortunate to live in a dark area far away from any major urban cities,

How do you "fight" the light pollution for your imaging?

Do you use any filters / equipment to keep the street light / sky glow out?

Last night was a rather clear night, except for some thin high clouds and the inevitable light pollution / sky glow around Brussels.

This brings me to my other question, What are these conentric light circles, which get brighter near the center on any of the images I take?

I have noticed that the intensity of the light circles depends on the ISO and / or the exposure time.

Logically I would think that is merely the effect of LP, but why do they appear as circles getting brighter to the center of the image?

near the edges of the image field you can see they are nearly gone.

The following images are from the ring nebula last night, both 120sec exposure, the first one at ISO 100 the second at ISO 400.

Next is an even more remarkable image attempt of M33, it was close to the zenit and had the least LP (most of the LP here is near the Southern horizon as I live about 8 miles away from Brussels city center)

ISO 200, 8min exposure (if you look clearly, you can see faint details of the spiral arms, but the core which should be brighter is completely washed out near the center of the image)

Could there be a problem with my equipment?

The optics I use are a Celestron C9.25, f/6.3 focal reducer / flattener, prime focus Canon Eos 550D without any filter.

I really hope someone can explain me what these gradient light circles are.

And I really hope there is no damage / problem to my equipment...

One more question I have, I am seriously concerned about my DSLR (it's actually my dad's one, if something happens to it he will eat me alive lol)

When I brought it back in last night after 3 hours of imaging several degrees below zero, it didn't want to auto focus anymore when I put the camera lens on it again. I had to wait half an hour before the auto focus mechanism started working again

Seriously worried about that.

Any ideas what could have caused this? It's not because of dew, there was no dew on the mirror, I could perfectly manual focus.

It's a rather new camera (bought 1 year ago)

So, I'd like to protect my camera, I think I need some filter to stop damp air entering the body.

At the same time I really want something to keep the LP / sky glow out a bit.

Would a normal skywatcher LP filter do that for me? Or is it solely for visual use?

Could somebody recommend me a good filter?

Many thanks in advance for reading and any advice or answers to my questions

Wouter

[Gonzo]

What is your White Balance set as on your DSLR?

[wouter]

it's set on daylight.

Could that be the problem?

[Zakalwe]

it's set on daylight.

Could that be the problem?

As long as you are shooting in RAW mode (and you should be) then the WB setting can be altered in software afterwards. The in-camera setting only affects JPEGs.

[GlassWalker]

The bright middle/dark corners effect is usually vignetting due to the optics. I'm not familiar with the C9 so couldn't say 100% that was the case. The fix for this is to use flats in processing.

Regarding the AF not working after you bought it in, I'd suspect condensation which is to be expected when moving an item from a cold place to a warm one. Nothing to worry about, just let it evaporate.

Light pollution filters can be very useful at killing the orange glow. The best one around is probably the Hutech IDAS. I personally use Astronomik CLS-CCD since they were more easily available at the time I got it.

[Gonzo]

it's set on daylight.

Could that be the problem?

I would say yes, do not set it to "auto" or "daylight", set to "Color Temperature" (or what-ever it's called on your camera) and pick the lowest: ie on mine it's set to 2500K.

It will make a huge difference in your pictures, I'm not saying it will remove the light pollution but it's a start.

edit:

or shoot RAW