Filters and Moonlight

[cometcatcher]

Hi all. For 7nm SII, Ha and OIII filters, what percentage of Moonlight can they be imaged in before Moonlight becomes a problem. I've heard a few different things. Obviously proximity of Moon to target will be a thing also.

[Camelopardalis]

Kevin, I use the Astronomik 6nm set, so very similar.

I've found I need to stay well away from the Moon, even in Ha, like 45+ degrees away. OIII is futile with any significant illumination of the Moon because of how it washes out the sky. Around full Moon is a forget-it situation for me. Anyone who says the Moon doesn't reflect Ha obviously hasn't tried it!

And then there are the gradients. Depending on the filter, the Moon can create additional gradients in an image due to it's floodlighting, on top of any local gradients from LP and horizon-dependent gradients.

I'd be interested in hearing from anyone with the 3nm for Ha, out of curiosity. Regardless, they're cost prohibitive for me at the moment, especially with the current exchange rate :eyepop:

[glend]

As Dunk has said, forget shooting Oiii with the Moon up. I have shot Ha and Sii when the Moon was up, but my rule was to stay 90 degrees away if possible, so no moonlight can spill into the front light shield and reflect around. And forget doing any imaging around the full Moon, there are plenty of other nights, and the stars aren't going anywhere, don't rush, it only compromises your final result.

[cometcatcher]

Thanks Dunk and Glen. I've noticed even in Ha the sky brightness creeping up as the Moon waxes. The thing is, I swear it's clear more often during a full Moon. I don't want to waste the sky. Wish 3nm were cheaper.

[lazjen]

I generally use the full moon time to test things out, rather than imaging. Having said that I was even too lazy to do that tonight. :)

[cometcatcher]

I suppose I could always image planets, but they are out rather early.

[Atmos]

I find that the best thing to photograph during a full moon is either really bright nebula where the moon has no real effect. Either that or shoot star clusters.

To give an example, this Eta Carina image (https://www.astrobin.com/full/16yxz3/0/) was shot under full moon from my bortle 7 backyard. It's bright enough that a lot of the nebulosity isn't hugely affected. Yes, it would have stronger signal and less noise under dark moonless skies but you take what you're given sometimes.

As another example, NGC 253 (https://www.astrobin.com/full/idw6ol/C/) was not only shot under a near full moon but the moon was only some 20º away if memory serves; this kinda makes the light polluted backyard meaningless. I did this mostly because I was curious about how close I could get to the moon and still achieve a result.

Star clusters are the best to chase though as light pollution and the moon don't do anything other than potentially wreck some havoc with colour calibration as you're not worrying about the background signal.

[cometcatcher]

Thanks Colin, your full Moon examples look like my no moon shots. But I was thinking more about narrow band. You have the 3nm filters. Does the Moon still affect 3nm Ha much?

[Atmos]

I haven’t done a comparison between full moon and no moon with the 3nm filters. I definitely would attempt OIII or possibly even SII as it’s already quite faint. Ha is always going to be stronger so I guess it would depend on what you’re chasing. If it’s a bright Ha object as opposed to attempting to capture the faintest of details.

I’ve never let the moon get in the way of some great Ha data!

[Andy01]

Yep! I guarantee Murphy is in charge of the weather :lol:



I purchased a top of the range $$ 3nm Chroma O3 filter (https://www.tolgaastro.com/store/filters/chroma/chroma-filters-48mm-mounted-round-193.html) so can I shoot whenever it's clear - for instance this image (https://www.astrobin.com/full/1owi5g/0/) was recently taken under a full moon. :thumbsup:

Astrodon or Chroma are the filter brand kings for a very good reason, you get what you pay for. I have also found Chroma to be as good as and better priced than the Dons. :thumbsup:

[codemonkey]

I haven't really done that much narrowband imaging... it was mostly a thing that I did when the moon was more than 50% full and I didn't want to image galaxies.

I've been pretty happy with my narrowband data, often taken on or near full moon with total disregard to how far away the moon is from the target. You can definitely get good results.

Is it a good idea to try and go deep, digging for faint nebulae in such conditions? Probably not... but can you get usable, even great results with many targets? Absolutely!

I think people worry too much about the moon... if it's clear and I can be bothered, I'm imaging something. Just try to pick the target that will be compromised the least by the moon.

[cometcatcher]

Thanks Andy. Wow those dragons are nice. Seems as though I liked it before, which may have inspired me to have a go at the dragons and 6164 in the same field also. I'm doing it with an F4.5 ED80 and ASI 183mm Pro, but it doesn't look as nice as yours. I need much more data.

And that was with full Moon... So possible with good quality 3nm filters.

[cometcatcher]

Thanks Lee. Yeah I think that's the thing, to image something even with full Moon.