light pollution filters.

[Galen Gilmore]

Ok, what I thought I knew about Light pollution filters is now apparently false.

I've been researching a bit about light pollution filters. From what I've read it says that LPF's reduce light pollution, but require longer exposure times for them to be effective. Is this accurate? If so by how much? Because with my lack of guiding longer exposures might not be possible.

Someone educate me.

[PeterCPC]

LPFs are only going to reduce light pollution from the Orange sodium lights. If you have the more modern white lights they won't do anything other than make the sky a bit darker. Any filter will mean increasing exposure times. If you have the white lights then a UHC filter may help. That's what I use but it will still mean longer exposures which may be double the time. HTH

Peter

 

[Galen Gilmore]

2 hours ago, PeterCPC said:

LPFs are only going to reduce light pollution from the Orange sodium lights. If you have the more modern white lights they won't do anything other than make the sky a bit darker. Any filter will mean increasing exposure times. If you have the white lights then a UHC filter may help. That's what I use but it will still mean longer exposures which may be double the time. HTH

Peter

 

I understand that they only reduce orange light pollution, but is the exposure time really going to need to be double the normal for it to have any effect? So far I have been doing 120s, would I need to do 180-240s to see any effect?

[alacant]

Hi. I don't think it would be double the exposure. What you avoid is filling the pixels with orange and green e.g. the crescent nebula. Say you have x minutes unfiltered and the histogram is right of centre. x minutes with CLS gives you about the same intensity nebula with less pollution to have to gradient away and the histogram back left. What I find becomes impossible is the colour balance when processing; I suppose there's a big chunk of spectrum missing. All is not lost however since these days it seems ok to choose whatever colour you like anyway! HTH.

[Galen Gilmore]

59 minutes ago, alacant said:

Hi. I don't think it would be double the exposure. What you avoid is filling the pixels with orange and green e.g. the crescent nebula. Say you have x minutes unfiltered and the histogram is right of centre. x minutes with CLS gives you about the same intensity nebula with less pollution to have to gradient away and the histogram back left. What I find becomes impossible is the colour balance when processing; I suppose there's a big chunk of spectrum missing. All is not lost however since these days it seems ok to choose whatever colour you like anyway! HTH.

Ah, I see. So basically the brightness of said object stays the same filtered or not. But what does change is the amount of obnoxious colors surrounding it.

[PeterCPC]

I said double to make it clear that it would be much more exposure. It may not be that much but it depends on the filter to some extent. If you are doing 120s exposures I would expect that to go to 180s or so to keep the histogram over the 1/3 of the way across. The colour balance will change but that can be adjusted in post processing. You need to experiment. If you are going to be using the Canon I would suggest an Astronomik clip filter.

Peter

[Galen Gilmore]

6 hours ago, PeterCPC said:

I said double to make it clear that it would be much more exposure. It may not be that much but it depends on the filter to some extent. If you are doing 120s exposures I would expect that to go to 180s or so to keep the histogram over the 1/3 of the way across. The colour balance will change but that can be adjusted in post processing. You need to experiment. If you are going to be using the Canon I would suggest an Astronomik clip filter.

Peter

Ah ok, that helps a lot. Thanks.

[Starwiz]

The transmission curve of the filter should help you decide.  If, for instance, it lets through 90% at the wavelength of the light you're trying to image, then you should only need to increase the exposure by around 10% or so.

[Starwiz]

1 minute ago, Starwiz said:

The transmission curve of the filter should help you decide.  If, for instance, it lets through 90% at the wavelength of the light you're trying to image, then you should only need to increase the exposure by around 10% or so.

Of course, the LP filter will allow you to do longer exposures in light polluted areas as the LP becomes less of a limitation.

[Galen Gilmore]

3 hours ago, Starwiz said:

Of course, the LP filter will allow you to do longer exposures in light polluted areas as the LP becomes less of a limitation.

Oh, that makes sense, I'll have a look.