LP and modded cameras

[Dave_D]

Does removing the IR filer from a Dslr make it more suseptible to light pollution? In particular, low pressure sodium?

[opticalpath]

Low pressure sodium light is concentrated in a very narrow wavelength band in the yellow part of the visible spectrum, so removing an IR filter will make no difference to how bright it appears.

The main reason for removing the IR filter is because the filter doesn't only block invisible IR (which messes up daylight colour balance), it also blocks the very desirable deep red H-alpha visible light. The replacement filters available DO allow H-alpha wavelengths to pass while still blocking unwanted IR. But neither option will make the LP sodium glow better or worse; modern light-pollution filters can be effective in reducing LP sodium pollution.

Adrian

[Dave_D]

yeah i was just wondering... modded my 1100d yesterday and last nights session subs were showing a lot more LP, maybe just the conditions but i wasn't sure

[Chris]

Your subs will appear more pink with a modded camera, not to be confused with the orange glow of LP. When it comes to LP I use a cheap Skywatcher LP filter for mine and it works wonders and keeps the colour balance quite well, I recommend them:

http://www.firstlightoptics.com/light-pollution-reduction/skywatcher-light-pollution-filter.html

hth

Chris

[opticalpath]

yeah i was just wondering... modded my 1100d yesterday and last nights session subs were showing a lot more LP, maybe just the conditions but i wasn't sure

If your mod was filter removal, rather than replacement, your camera will be sensitive to IR now.  You may be picking up some extra sky background in near infra-red from atmospheric water though I don't know from experience how big an issue this is.  You might benefit from a LP filter to cut out the sodium and a IR cut-off filter.  There is some info here that might help:

http://www.astrosurf.com/buil/city/result.htm

Adrian

[RobertC]

I modified my 60d and noticed no difference in changes to the LP.

-Rob

[opticalpath]

I modified my 60d and noticed no difference in changes to the LP.

 

-Rob

Did you remove the filter altogether, Rob, or replace it with a Baader or other similar type for astro use? 

 

Adrian

[lensman57]

If your mod was filter removal, rather than replacement, your camera will be sensitive to IR now.  You may be picking up some extra sky background in near infra-red from atmospheric water though I don't know from experience how big an issue this is.  You might benefit from a LP filter to cut out the sodium and a IR cut-off filter.  There is some info here that might help:

http://www.astrosurf.com/buil/city/result.htm

Adrian

That is a very good point, there is concern over IR causing bloating as it can not be focused by FRACS at the same point as RGB. Also the new IDAS D1 LP filter now has much earlier cut off just past the Ha waveband, to eliminate the red background glow that affects OSC CCDs and DSLR to a greater extent.

A.G

[RobertC]

Did you remove the filter altogether, Rob, or replace it with a Baader or other similar type for astro use? 

Adrian

I took it out and didn't replace it with anything. 

-Rob