LPF + RGB

[Earl]

If I use RGB filters do i still use a LPF?

I was thinkng of getting a 2" CLS filter, would I get the IR block version?

This would fit on the two inch adapter part of my filter wheel which goes into the focuser.

[AndyUK]

Hi Earl - I had this conundrum - Which filters have you got...?

Some filters (ie the posh Baader's, Astrodon's) have a gap in the spectrum coverage between the red and green filters which effectively means they cut out the common LP bandwidth (Sodium/Mercury).

However, if you use a Luminance filter then obviously there's no LP cut... So, if you take LRGB, and decide to use a LP filter (as you've described) then in order to ensure colour consistency when combining the channels apparently you really should use if for all 4 filters, not just the one... And the downside is that it's yet another dust trap, and the luminance layer can tend to "wash out" the colour.

In order to get around this, I was given the tip to use just RGB (to maintain the colour) and then, if I wanted to, use all the RGB subs, stack them all together and use that at the luminance layer. That way you're still getting the detail of a luminance layer but cutting out the light pollution. I've only tried it myself once mind, but it did seem to work quite well...!

[Earl]

I have yet to decide which RGB filter im going to go for.

I have my narrownband set which no LPF is needed, so im a pondering.

[Psychobilly]

My 2" IDAS P2 LPF used to stay on the front of the FFIII all the time and any other filters get added infront of it...

Taking a simplistic approach (ignoring relection losses) the transmission at any wavelength is the product of the transmission of each filter at that wavelenght...

Peter...

[Whippy]

In a word, yes. If you have to use a LP filter when imaging OSC or mono, then use it for the RGB too.

Tony..