Imaging when moon is up (80% and more) with 6nm narrowband filters - Looking for feedback - Forums

Hi all,

I remotely image with 6nm narrowband filters and tend to avoid shooting when the moon is up. As a result, I miss every months between 8-10 nights (at least). I am tryging to figure out whether I could still image and benefit from clear nights. Hence this thread.

My acquisition sotware has an outstanding features (Voyager, Moon avoidance) which calculates the minimum distance of an object from the moon as per the moon phase. I am about to use it.

Meanwhile, and based on a few tests that I performed lastly (Ha only), I must say that the results were disappointing. Most of the images looked a bit washed out, although the respective objects were at decent distances from the moon (i.e. min 60 degrees away from it).

I am curious about how you guys are dealing with the moon.

Thanks for your feedback, for any tips, best practices.

Aygen

There isn't a lot you can do about the moon. a 100% moon makes the entire sky many times brighter than it would be without especially when the moon is at high altitude like it is now. HA is still viable for targets that are bright and a decent distance away from the moon. Of course even those targets may require some additional care during post-processing though.

Here's an HA stack of the NGC 1027 area I captured last night (99% moon). It was about 40° from the moon. After some background extraction is looks pretty decent because the HA here is quite bright. You really have to take things on a case by case basis.

I image *every* single time is clear outside, moon or no moon (did the day before yesterday with 93% phase). Respectable distance (4 hours offset) and with NB filters but if the object is intrinsically bright I'd go with clear (e.g., L-Pro) filters too. What limits me isn't the Moon but rather sky transparency and about that there isn't much you can do about it.

Reg Pratt:
There isn't a lot you can do about the moon. a 100% moon makes the entire sky many times brighter than it would be without especially when the moon is at high altitude like it is now. HA is still viable for targets that are bright and a decent distance away from the moon. Of course even those targets may require some additional care during post-processing though.

Here's an HA stack of the NGC 1027 area I captured last night (99% moon). It was about 40° from the moon. After some background extraction is looks pretty decent because the HA here is quite bright. You really have to take things on a case by case basis.

Many thanks Reg for your feedback. And what a decent result ! Can you tell me what filters did you use ?

andrea tasselli:
I image *every* single time is clear outside, moon or no moon (did the day before yesterday with 93% phase). Respectable distance (4 hours offset) and with NB filters but if the object is intrinsically bright I'd go with clear (e.g., L-Pro) filters too. What limits me isn't the Moon but rather sky transparency and about that there isn't much you can do about it.

Thank you Andrea. Never really thought about making the difference between "bright" and "faint" objects. Very interesting. I will defintely shoot no matter what provided the respetive object is bright enough (for example, I will avoid very faint object while the moon is around and mostly use Ha).

Reg Pratt:
There isn't a lot you can do about the moon. a 100% moon makes the entire sky many times brighter than it would be without especially when the moon is at high altitude like it is now. HA is still viable for targets that are bright and a decent distance away from the moon. Of course even those targets may require some additional care during post-processing though.

Here's an HA stack of the NGC 1027 area I captured last night (99% moon). It was about 40° from the moon. After some background extraction is looks pretty decent because the HA here is quite bright. You really have to take things on a case by case basis.

Many thanks Reg for your feedback. And what a decent result ! Can you tell me what filters did you use ?

Antlia 3nm.

I am in the camp that I will shoot with moon as well. I not to image right next to the moon. I use Antlia 3nm filters as well. The only filter I won't shoot with full moon is Oiii. My Ha performs very well moon or not.

Jeff Horn:
I am in the camp that I will shoot with moon as well. I not to image right next to the moon. I use Antlia 3nm filters as well. The only filter I won't shoot with full moon is Oiii. My Ha performs very well moon or not.

Good to know Jeff. I am quite tempted to upgrade my filter to get 3nm. However, that would require to tweak a bit my back focus and probably take care again of the tilt. Since my rig is in Chile - and I am located in the middle of Europe - that makes me thing twice before proceeding. What a headache

I shoot SHO with the moon at up to 100% It helps to have high quality 3nm filters but depending on the signal strength of the object it certainly is doable. Actually, I end up only shooting my SHO with the Moon up because I shoot my RGB with the Moon up to 50% illuminated. I do require the moon be 60 degrees away for RGB. With Ha I use >20 degrees and with OIII and SII I use >30 degrees away.

But it I was looking for some really faint OIII structures I would shoot moonless. That's what I do for PN searches.

Regarding the filters; the bandpass is important but also the shape of the transmission curve. If the sides of the bandpass curve are nearly vertical you will block more moonlight and continuum than if the transmission curve is more bell shaped. Both would have the same FWHM calculated bandpass of say 3nm but the bell shaped curve would not be as good. And wouldn't you know those filters with the more sharply defined bandpass curves cost more!

Kevin

Great explanation Kevin, much appreciated.

Very informative and interesting to see that you shoot your Ha with such a « small » distance from the moon. It’s eye-opening. I thing I might finally get (again) Chroma filters which should allow me to image during moon !

Many thanks 🙏

Kevin Morefield:
Regarding the filters; the bandpass is important but also the shape of the transmission curve. If the sides of the bandpass curve are nearly vertical you will block more moonlight and continuum than if the transmission curve is more bell shaped. Both would have the same FWHM calculated bandpass of say 3nm but the bell shaped curve would not be as good. And wouldn't you know those filters with the more sharply defined bandpass curves cost more!

I would think the integrated transmission would matter way more...

Great explanation Kevin, much appreciated.

Very informative and interesting to see that you shoot your Ha with such a « small » distance from the moon. It’s eye-opening. I thing I might finally get (again) Chroma filters which should allow me to image during moon !

Many thanks 🙏

One thing to keep in mind - the alternative to shooting with a full Moon is not to shoot at all. So nothing to lose, but it is probably good to compare the best and worst subs and be sure you are using SNR based weighting during integration.

Kevin Morefield:
Great explanation Kevin, much appreciated.

Very informative and interesting to see that you shoot your Ha with such a « small » distance from the moon. It’s eye-opening. I thing I might finally get (again) Chroma filters which should allow me to image during moon !

Many thanks 🙏

One thing to keep in mind - the alternative to shooting with a full Moon is not to shoot at all. So nothing to lose, but it is probably good to compare the best and worst subs and be sure you are using SNR based weighting during integration.

Thanks for the input ! Makes sense.

I need to think about the 3nm filters. Things would be easier if Chroma had 1mm thick filters 😂. My filters are 1mm, and by getting thicker ones, I need to consider the slight and still important impact on the back focus (I shoot at F/3).

andrea tasselli:
I would think the integrated transmission would matter way more...

Since all you care about is that one single wavelength (essentially a bandwidth of zero), you want very high peak transmission and the rest of the wavelengths dropping off to zero as quickly as possible since all they are doing is admitting light pollution. So no, it isn't the integrated transmission.

Arun H:
Since all you care about is that one single wavelength (essentially a bandwidth of zero), you want very high peak transmission and the rest of the wavelengths dropping off to zero as quickly as possible since all they are doing is admitting light pollution. So no, it isn't the integrated transmission.

I think the argument was about transmission of *unwanted* light, not the peak transmission at the emission wavelength.

andrea tasselli:
I think the argument was about transmission of *unwanted* light, not the peak transmission at the emission wavelength.

Ah, ok, that makes more sense. I think Kevin's argument still holds. A very sharp bell curve would give you near zero integrated transmission everywhere except at the desired wavelength.

Arun H:
andrea tasselli:
I think the argument was about transmission of *unwanted* light, not the peak transmission at the emission wavelength.

Ah, ok, that makes more sense. I think Kevin's argument still holds. A very sharp bell curve would give you near zero integrated transmission everywhere except at the desired wavelength.

Absolutely. This what I will be aiming for.

Arun H:
Ah, ok, that makes more sense. I think Kevin's argument still holds. A very sharp bell curve would give you near zero integrated transmission everywhere except at the desired wavelength.

While they have the same FWHM (Kevin's original proposition) the argument cannot be settled so easily. One might have more integrated transmission than the other and thus it can only be decided by carrying out the integration across the spectrum (wavelength) of interest, IMHO. Otherwise, yes, obviously.

Practically, the shape of the transmission curve is another reason why Chromas cost twice as much as Antillas. And another reason why they might be worth it depending on your use case. And this is additional difference is seldom discussed. That was my observation.

Kevin Morefield:
Practically, the shape of the transmission curve is another reason why Chromas cost twice as much as Antillas. And another reason why they might be worth it depending on your use case. And this is additional difference is seldom discussed. That was my observation.

I used to have Chroma's filters with my former rig. I start regretting not having invested in the optmized version for fast astrograph. I am now processing it again.

During full moon periods I shoot bright narrowband, RGB stars for narrowband images, open clusters or globular clusters.

I used to image in >60% moon, but no longer do so. The biggest issue for me was guiding. Unless one is lucky to have bright guide stars in the f.o.v., guiding is poorer. This leader to larger FWHM on the image, which combined with the increased sky background, simply makes it no sufficient return on my time investment to try any longer.

With an 80% or brighter Moon, I typically limit myself to Sii (on bright targets) or I'll shoot star clusters.

If I stopped imaging with the moon out, my total imaging time per year would go down from 20 nights to 10 or less. I wish I had the luxury to skip imaging in non-perfect conditions

Imaging when moon is up (80% and more) with 6nm narrowband filters - Looking for feedback

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