RGB filter question

[hickeydp]

I have a set of LRGB filters I know little about brand wise. They are made by Orange Bright Optics. Anyone know anything about them?
 
My issue is the green filter seems very broadband, in that it has no effect on the low pressure sodium street lights used where I live. By this I mean it does not reject (dim) the light at all.
 
Is this typical for a green filter in a RGB set?
 
For information, I tested this by simply closing one eye and putting the green filter over the other and looking at the light and the reflected light from a silver car parked underneath it. There is a porch light on a door just beyond the street light. The porch light turns green but the sodium light is unaffected. The red and blue filters reject the sodium light leaving only the core of the bulb visible.

[theastrodragon]

It depends on the brand. On some, there is no real gap between the red and green filters. On others, there is a deliberate small gap to block the Sodium D lines.

However looking at a street light doesn't work well, they are too bright. If you can, try looking at some low-altitude orange sky glow and see if it does much to that.

[Physopto]

Yes it is typical. You will need another band pass filter to filter out the Sodium and possibly the Mercury wavelengths. An IDAS or LPS type filter should do that for you.

The usual method though if you have a major problem with these unwanted frequencies of light is to use narrowband but this is more expensive and also requires longer exposures to acquire the data.

If you add a band pass filter it is cheaper in the long run but you will need it fitted before the RGB filters. This usually means some method of fitting the larger filter somewhere in the light train as close to the LRGB filters as possible.

Have a look at the Astronomik website for filter graphs showing the band pass characteristics. Here is one for their RGB filters and will be similar to yours I suspect. Overlay the CLS on top and you will get an idea of what wavelengths are passed.

 

Derek