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Old 08-08-2013, 09:57 AM
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PRejto (Peter)
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H694 Camera + Filters: Question re LP

I'm close to pulling the trigger on an SXVR-H694 + filter wheel to use with my TEC140. My question is primarily about LRGB filters for this camera. As I image from a moderately light polluted spot I have been considering the Astrondon Series E II. While the price is higher they seem to offer a bit of LP suppression in RGB due to the "gap" in transmission between G&R. Then the idea (I'm sure not original) occured to me that perhaps I could use an IDAS LP filter for luminance directly on the filter wheel rather than in front of the wheel (which for many reasons with my imaging train is not ideal). I would of course lose parfocability with luminance. Is this likely to work? Is there enough cut in lum. IR/UV for my TEC140? I also like the idea because there is less glass, less dust, fewer possible reflections. Good idea? Bad idea?

THANKS!!
Peter
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Old 08-08-2013, 10:34 AM
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strongmanmike (Michael)
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Good choice of camera there

As I mentioned I recon it's worth a try, not hard to change it out either. The Astronomik CLS CCD filter is parfocal with other Astronomik filters too. Regarding suitability, it says: "CCD photography: Very good, optimized rejection of light pollution"

Mike
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Old 08-08-2013, 12:25 PM
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Quote:
Originally Posted by strongmanmike View Post
Good choice of camera there

As I mentioned I recon it's worth a try, not hard to change it out either. The Astronomik CLS CCD filter is parfocal with other Astronomik filters too. Regarding suitability, it says: "CCD photography: Very good, optimized rejection of light pollution"

Mike
Mike, I appreciate your thinking here! However, the Astronomik filters don't appear to have the "gap" in-between R & G like the Astrodon do, so without a LP filter the Astronomik filters are likely to show more effect of LP. At least that is my thinking here until I'm told otherwise. The whole idea is to find a way to deal with LP without having the LP filter "added" to the whole set of LRGB.

Peter

Last edited by PRejto; 08-08-2013 at 02:32 PM.
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Old 11-08-2013, 11:15 AM
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The Baader filters claim to be optimised to reduce some effects of light pollution. In my experience light pollution seems to effect the green channel the most so check out the specs of the green filter most heavily. They are worth checking out as well.

Greg.
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Old 11-08-2013, 01:53 PM
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According to the Astronomik transmission curves, the major artificial light pollution emission lines for mercury at 435.8, 546.1, 577.0, and 578.1 nm, and for sodium at 589.0, 589.6, 615.4, and 616.1 nm.

It looks like the Astrodons cut out everything from 570 to 620 nm (i.e. a substantial amount of light pollution), although the B and G filters will still pick up the other wavelengths.

The IDAS LP spectrum is very similar to the Astrodon/Astronomik L spectrum, but it blocks the major light pollution wavelengths. Assuming reflections aren't a problem, I would imagine that you'd see a huge benefit with the IDAS in front of the Astronomik RGB filters.

Your idea of replacing the L filter with the IDAS seems sound in theory to me, but you'd still get some light pollution in the B and G filters.

Anyhow, I would have thought that a 48 mm threaded filter would be easy to add into your optical train? Many nosepieces and connectors are threaded for 48 mm filters.


Quote:
Originally Posted by gregbradley View Post
The Baader filters claim to be optimised to reduce some effects of light pollution. In my experience light pollution seems to effect the green channel the most so check out the specs of the green filter most heavily.
I'm using Baader filters with my SBIG STF-8300M. There's a gap between R and G at 580 nm, but all other Hg/Na wavelengths are passed through. It's certainly better than imaging with a DSLR (red channel is nowhere near as bad), but the green channel seems most severely affected as you pointed out.

Hmmm I might have to try putting an LPS filter in my nosepiece. (I sold my Lumicon a little prematurely... oops.)
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Old 11-08-2013, 10:54 PM
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Thanks Greg and Dave!

I've been looking at the Baader filters and they are of interest. I took note of some very nice examples done with a TEC140.

It does look like the Astrodon filters would give perhaps the best protection against LP, but would allow LP in the green channel. It seems my "idea" woud only be partially successful.

I have been imaging with the Hutech IDAS LP filter in front of Astronomik filters with my KAF8300 chip camera. It does work, but I want to use the ONAG guider and this is a difficult solution as the fitting to the camera/filter wheel is T-thread and my filter is 48mm. The filter cannot go in front of the ONAG as there will then be no IR light to guide on! So, putting the LP filter in the wheel solves that not little issue, but creates a problem in green and maybe red. Perhaps Precise Parts can make some sort of adapter. I suppose I can just try out the idea and if the LP is too hard to control try to find an alternate solution.

Peter
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