LPS filters

technofetishism (Nick) · #1 15-10-2012, 01:38 PM

Currently looking at getting some form of light pollution filter for a modded 350d. I'm thinking of heading down the path of using one of the IDAS-LPS-P2 filters. However I want to check whether theres any traps in going down that path, such as IR issues with modded cameras, or performance in comparison to competing options such as the CLS-CCD.

cometcatcher (Kevin) · #2 16-10-2012, 06:41 PM

The IDAS-LPS-P2 is one of those multiband filters with peaks and troughs all over the spectrum. At 44.9% photopic transmission, I don't think it would be as effective as the Astronomik CLS for LP reduction. And with the CLS CCD you know for sure it will block IR and UV. I'd go for the CLS CCD personally. Oh wait I did.

ZeroID (Brent) · #3 18-10-2012, 09:44 AM

Quote:

Originally Posted by cometcatcher

The IDAS-LPS-P2 is one of those multiband filters with peaks and troughs all over the spectrum. At 44.9% photopic transmission, I don't think it would be as effective as the Astronomik CLS for LP reduction. And with the CLS CCD you know for sure it will block IR and UV. I'd go for the CLS CCD personally. Oh wait I did.

+1 here. Astronomik CLS is working for me in LP situation.

technofetishism (Nick) · #4 18-10-2012, 10:42 AM

Have any issues with color balancing?

cometcatcher (Kevin) · #5 18-10-2012, 12:49 PM

Quote:

Originally Posted by technofetishism

Have any issues with color balancing?

I know IDAS advertise that their filter produces neutral colour, and I suppose the Baader Semi-APO is in the same "no colour shift" category, but when more colours are removed from the spectrum there is bound to be some colour shift.

I find the CLS produces a slightly blue overall colour cast compared to no filter. However it's very easy to correct post processing. It's literally a single eyedropper click in Photoshop. Takes half a second to do.

I'll upload some comparison photos. These are single 3 minute exposures of M42. One with the CLS straight out of the camera with no processing, one with the CLS and single click background adjustment and one with no filter at all and no processing. The frame with no filter shows red sky glow from street lights and is only 2 minutes of exposure.

Edit, I should also add it depends what you're shooting. The CLS is a nebula filter, designed to bring out OIII and Ha in photos. It's not designed with star clusters in mind. For those you may be better off with the IDAS filter.

technofetishism (Nick) · #6 18-10-2012, 09:16 PM

Hmm, how bad is IR LP in the suburbs in reality, figured out a way to mount a straight CLS 1.25" filter in the imaging train without too much vignetting.

loki78 (Jon) · #7 18-10-2012, 10:08 PM

Kevin, those 3 side by side comparisons are perfect and a huge help to people weighing up their options. Great to see.

cometcatcher (Kevin) · #8 18-10-2012, 10:53 PM

Quote:

Originally Posted by technofetishism

Hmm, how bad is IR LP in the suburbs in reality, figured out a way to mount a straight CLS 1.25" filter in the imaging train without too much vignetting.

The IR block on the CLS-CCD filter is not for LP, it's for imaging with a CCD camera or modified DSLR to prevent bloat effects. For unmodified DSLR cameras the IR block component is not necessary so a standard CLS will work fine.

M42 and nearby nebula like the running man NGC1977 is probably not the best example of the power of a nebula filter. Blue reflection nebula isn't well enhanced. However nebula strong in Ha like Eta Carina shows great enhancement.

This example taken with a 135mm lens. Left pic with no filter, right pic with a Lumicon Deep Sky filter. The Lumicon Deep Sky is very similar to the Astronomik CLS.

technofetishism (Nick) · #9 18-10-2012, 11:02 PM

I currently have a full spectrum modified 350d, so the IR is a bit of concern with relation to this task. Ah well, a bit of bloat isnt the end of the world.

Very useful pics none the less.

alistairsam · #10 19-10-2012, 12:29 AM

Hi
Any experience with the baader UHC-s filters?
Thanks

cometcatcher (Kevin) · #11 19-10-2012, 10:45 AM

Quote:

Originally Posted by alistairsam

Hi
Any experience with the baader UHC-s filters?
Thanks

I don't have one, was going to get one but got a bit side tracked. However I've looked at the spectrogram and it seems like a more narrow band nebula filter compared to the CLS. Theoretically it would give more contrast but at the same time need a longer exposure time. The Baader UHC-S has a photopic transmittance of 22.5% so it does kill a lot of light.