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Old 28-06-2021, 09:32 PM
Hans Tucker (Hans)
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L-Luminance vs Clear

Rummaging through my Astro gear for stuff to sell I found a set of Astrodon I-Series Filters (LRGB) Generation 1 I think. Now these apparently are NIR Blocked. I also found a Astrodon Tru-Balance Clear Filter .. can I assume this is not NIR Blocked and if so what imaging advantage/disadvantage does a Clear have over a Luminance?
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Old 28-06-2021, 09:59 PM
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Peter Ward
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Clear = More flux.... but if your optics can't focus IR/UV at the same time, could be a case of careful what you wish for
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Old 08-07-2021, 02:32 PM
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I used a Clear filter for a while. Stars are slightly more bloated but not objectionably so.

A bit more light gets through. Does it make much difference? Slight, but we spend a lot for small improvements so perhaps worthwhile for those faint galaxies etc.

Greg.
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Old 08-07-2021, 03:10 PM
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multiweb (Marc)
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Yes clear will let everything in so the only limitation is the wavelengths your camera and optics can collect. LUM will wrap and envelope as close as possible to your RGB set so it's bell shaped, shaving a little UV and IR on the end of the spectrum.
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Old 10-07-2021, 02:59 PM
ericwbenson (Eric)
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Hi,

The answer of course is, it depends...

As pointed out earlier in the thread your optical system must be up to it, collecting extra photons but piling them up in a disk around the star doesn't really help.

So assuming the optics are OK, next up is the target, does it emit more in the NIR (limited to 700-1000nm for us amateurs using Si based cameras) than the background sky? The natural sky brightness increases dramatically as the wavelength increases, see Table 1 here:

https://academic.oup.com/mnras/article/386/1/47/976996

So the short answer is: your signal will increase with clear vs Lum, but your contrast might not.

Cheers,
EB
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Old 11-07-2021, 10:12 AM
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The_bluester (Paul)
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If I ever get some clear sky I should make some experiments on both my SVX80T and 10"F4 newt. I currently have an Astronomik L-RGB set plus HA and Oii and a clear that I bought at the time I bought the HA (To be able to focus through the clear and be closely parfocal with the HA)

I should pick a nice couple of nights and do say 60 X 60s subs through both the clear and lum with both scopes to get a good average HFR for each filter on both systems. Then when Fedex finally decide to deliver my Sii filter (Instead of sending it to the wrong city and leaving it there until I started making phone calls, then leaving it there for another week so far, I am about to tell them to hold it there as I will be passing the depot that they reckon has it this Wednesday!) I can make a choice between witch of the lum of clear to leave in the wheel. If neither show a significant increase in HFR and no reflection issues with the clear I should leave that one in to get whatever extra light I can.
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