Moon glow filter advice

Dear all,
in the last 8 months, despite having bortle3-4 locations quite close, it seems that the ecosystem wanted to punish me for starting astrophoto with cloudy skies and unusual cold weather 90% of the time

. And when sky was clear, moon was out.

All this to kindly ask about your experiences with astrophotography in the presence of the moon glow (>=50%). Which filters do you use? narrow or broad band? Do they really work with the moon or are they only useful with artificial light pollution?

Thank you very much.

Hi Alvise,

I have the same luxury problem: Bortle 4 but when the weather allows, the Moon is out. Yet, I see only a few solutions:
1. Shoot (with a camera) the moon.
2. If available planetary photography.
3. Star clusters.
4. Narrowband imaging.

Everything else isn't working, IMHO. The moon is a broad spectrum emitter/reflector. It's essentially the sun but only dimmer. So, there is no specific filter to it.
Also with the artificial light pollution: all filters that claim to block artificial light pollution refer implicitly to emitters with well defined spectra (like sodium-vapor etc.). The newer LED-based light pollution is a "nice" mixture of broad band signal that nicely reaches into the transmission spectra of the light pollution filters. Sorry for the sarcasm but I still don't get why some mayors believe that they need to make day out of the night.

CS!

Björn

Thanks Björn! I suspected about the moon broadband (it's, after all, a sun's reflector), but I wanted to ask, just in case. I will eventually buy a l-eXtreme narrowband… I bought ASI294MC 1 month ago, and not yet chance to even try it

I image in all sky conditions as clear skies are at premium where I live. The L-PRO is permanently mounted on the ASI294MC and I can go after galaxies (i.e. broadband emitters) with full moon no question asked. Obviously moon best kept at safe distance (>40 deg away) but can be done, as there are plenty of objects that fits the bill. I'd not be to sure of the L-extreme, weird results with that sensor. I'd get the L- eNhance instead but only because works better for PNs and emission nebulae in general.

andrea tasselli:
I image in all sky conditions as clear skies are at premium where I live. The L-PRO is permanently mounted on the ASI294MC and I can go after galaxies (i.e. broadband emitters) with full moon no question asked. Obviously moon best kept at safe distance (>40 deg away) but can be done, as there are plenty of objects that fits the bill. I'd not be to sure of the L-extreme, weird results with that sensor. I'd get the L- eNhance instead but only because works better for PNs and emission nebulae in general.

Thanks Andrea! Not sure what do you mean by PN (Planetary?)... I am still building up the astro-terminology

So: as its name suggests, l-eXtreme is too extreme (especially for a beginner like me). You definitely suggest l-Pro/eNhance... don't you?

Hi Alvise (curiously same name of one of my cousins, pretty rare these days!). PN stands for Planetary Nebulae, as you rightly guessed. Yeah, the L-extreme cuts lots more and may not work as intended for some OSC camera, like the ASI294MC. L-Pro is the Swiss army knife/jack of all trades kind of filter. Works like a charm. For dedicated emission (H-alpha, H-beta, OIII) stuff then the L-enHance. Works best for PNs but can be used quite effectively also on diffuse nebulae. Does not retain true star colour however. I'm going to get one as well, come this summer.

Hi @andrea tasselli,

I've taken a look at the spectra of the L-eXtreme and L-eNhance. The major difference is that the eXtreme is narrowing down to the OIII line in the Blue-Green band of the spectrum. In that case, if you use a color camera (with Bayer matrix), you are not exposing the blue pixels of the sensor but only the red and green. The white balance will hence be completely off. The eNhance transmits some blue color and therefore, the colors will not look that weird as compared to the eXtreme. But that's my theory as I haven't tried these two myself. In case you have some subs for both filters, you might check the blue channel for both images and you should see that for the extreme, the blue channel should be extremely dark.

Björn

Hi Björn,

How much the OIII and the H-beta will split between the G and B pixels of an OSC camera depends a lot on the actual dyes used in the sensor. In my ASI294MC that seem pretty even, although this is based on qualitative evaluation rather than actual measurements (I don't have the required 2" filters to do that). I suspect that H-beta would tend to end more in the B than in the G pixel but with just 10-15 nm difference between the two/three emission line peaks I suspect there would be cross-over spillage even for the H-beta.

@Björn Arnold we can assume that for OSC camera l-eXtreme, Triad quad-band and similar are a no-go, 'cause they will produce un-manageable pictures during post-processing. The only option that seems feasible remains l-Pro and/or l-eNhance... but there is still the point about LED pollution. As usual, there is not any only-win solution.
I found this filter: IDAS LPS-D2 (https://www.astroshop.eu/broadband-filters/idas-filters-nebula-filter-lps-d2-2-/p,57331). Looking at the transmission graphs it seems (claims) to be able to also stops some wavelenght coming from LED (the "white" ones), but of course not perfectly because LED spectrum is quite broad. Does anybody know it ?

andrea tasselli:
Hi Björn,

How much the OIII and the H-beta will split between the G and B pixels of an OSC camera depends a lot on the actual dyes used in the sensor. In my ASI294MC that seem pretty even, although this is based on qualitative evaluation rather than actual measurements (I don't have the required 2" filters to do that). I suspect that H-beta would tend to end more in the B than in the G pixel but with just 10-15 nm difference between the two/three emission line peaks I suspect there would be cross-over spillage even for the H-beta.

I once did an analysis to compute the RGB values for Hb and OIII in the sRGB-Color space. Interestingly, there is a cross-over of blue and green right between Hb and OIII, i.e. on the Hb side, the blue increases drastically while the green decays quickly. On the OIII side of this cross-over wavelength its just the other way around.
But as I said, my comment was just a theory based on that. One would indeed have to measure it.

Alvise Dorigo:
As usual, there is not any only-win solution.

If it were, there forums were quite a lot emptier, right?

Björn Arnold:
Alvise Dorigo:
Does anybody know it ?

As far as I've seen it in industry documentation, the spectrum shown in the link you've provided seems to be very representative.

@Björn Arnold by "representative" you mean "effective" for LED too ? Even if I trusted them, it would be nice to find someone using it in medium/full moon. I'll have to dig here and some other picture repository... not a problem with cloudy nights

Alvise Dorigo:
Björn Arnold:
Alvise Dorigo:
Does anybody know it ?

As far as I've seen it in industry documentation, the spectrum shown in the link you've provided seems to be very representative.

@Björn Arnold by "representative" you mean "effective" for LED too ? Even if I trusted them, it would be nice to find someone using it in medium/full moon. I'll have to dig here and some other picture repository... not a problem with cloudy nights

Sorry, I've misinterpreted your question. I thought you referred to the LED light spectrum. Since I couldn't delete my post, I edited it to ***deleted***. Can one delete your own post here on AstroBin?

@Alvise Dorigo I would like to elaborate more on this "they will produce un-manageable pictures during post-processing"... I'd like to understand what happens there in detail.

Björn Arnold:
@Alvise Dorigo I would like to elaborate more on this "they will produce un-manageable pictures during post-processing"... I'd like to understand what happens there in detail.

Simply I mean: how difficult is to make colors appear and pop from data taken with OSC+narrowband... My understanding so far is that is much more difficult than using a broadband filter... I do not know yet, because I've never tried yet. I'am trying to collect idea, experience, opinions to do the best buy and not to waste money.

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