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Narrowband

Pesky Moon!


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Last night was a lovely cloud free night here and I was planning to add some quality data to my latest DSO but I bargained without the Moon! I used a UHC and a dew shield to cut glare and got 11 X 10 minute subs of the Iris nebula.

When I came to process them, a couple of very small Curves applications revealed an image with horrendous horizontal gradients! The image also lacked any depth so I have wasted nearly three hours of valuable cloud free time! Lol.

I did try to take a few subs of M31 at about 3.00am but the camera battery packed up after a minutes exposure. That one looked very good. ha ha.

So it looks like short exposures are the way to go when the moon is doing its business. Anyone got any other tips for imaging in moonlight?

Never thought to image to moon itself!  Tim. 

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The moon is a horrible source of unwanted light. A bright moon creates more trouble than all the urban light pollution that is always here.

Two options come to mind:

1) Brighter planets and the moon itself won't be swamped.

2) Narrowband imaging, e.g. Ha and/or OIII filters.

Option two comes with extra challenges from needing very long exposures and expense. Still, works better on a moonless dark night for the feint stuff.

Andy M

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I don't even try to do DS in the moonlight. You can do Ha but OIII is very badly affected and not, in my view, worth bothering with. The big bonus of a monochrome CCD is that it can take decent Ha in the moon though, even, then, there's a week straddling full moon when you'll be big on noise and low on contrast.

Olly

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I agree with the above comments.. I had great success in imaging Ha and SII in near full moon light... OIII is effected by moon light for me to bother with... and Ha & SII only work if you're not imaging near the moon itself. Unfortunately when the moon is out you're limited to imaging it, the planets and only in the deep red narrowband away from the moon.

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I don't even try to do DS in the moonlight. You can do Ha but OIII is very badly affected and not, in my view, worth bothering with. The big bonus of a monochrome CCD is that it can take decent Ha in the moon though, even, then, there's a week straddling full moon when you'll be big on noise and low on contrast.

Olly

The moon is a horrible source of unwanted light. A bright moon creates more trouble than all the urban light pollution that is always here.

Two options come to mind:

1) Brighter planets and the moon itself won't be swamped.

2) Narrowband imaging, e.g. Ha and/or OIII filters.

Option two comes with extra challenges from needing very long exposures and expense. Still, works better on a moonless dark night for the feint stuff.

Andy M

Not sure if it OK to ask this in this thread, But is it possible to just attach an Ha filter to a DSLR (I have a modded and unmodded one) and image? If so, what length of exposures would you need and how many for a worthwhile image?

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It is possible to image Ha on an astro-modded camera, exposure times will be long. Unmodded the sensor has almost no sensitivity to the wavelength.

Don't know how long you will need on your camera, probably tens of minutes for each sub. I've done all my narrowband on a CCD camera.

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Just for the hell of it I set up my Atik One 6.0 with an 85mm Canon lens and 5nm HA filter on my Astrotrac last night and shot off 18 x 360sec frames unguided to see what I could get under a full moon from my back garden in a small town... It was better than I was expecting :)

Mel

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Ive never seen an image where the Moon has caused so much unwanted LP. I think the underlying image of the Iris nebula though is pretty good. I am guessing if AP is your thing then there are ways around the LP from the Moon in post processing. 

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Ive never seen an image where the Moon has caused so much unwanted LP. I think the underlying image of the Iris nebula though is pretty good. I am guessing if AP is your thing then there are ways around the LP from the Moon in post processing. 

I did have a go, using DBE and Photoshop, but the result is not worthy to be in the same thread as Mel's stunning image!

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Ive never seen an image where the Moon has caused so much unwanted LP. I think the underlying image of the Iris nebula though is pretty good. I am guessing if AP is your thing then there are ways around the LP from the Moon in post processing. 

Nope, I don't think so. It's important to understand that, while post processing involves a set of skills, it cannot invent. You have to have real and genuine information to start with.

The worst possible target for shooting in moonlight might well be (sorry!) the Iris. It's a reflection nebula so it has no emission nebulosity to pass through an Ha filter. (Actually not quite true becaue it does have a whiff of Ha emission but it's on the seriously subtle side!) And the nice faint dusty stuff lying around it will be totally overwhelmed by skyglow/moonglow. This is a dark site and dark night target. When the moon is around a DS imager with mono and NB filters should be looking to the opposite side of the sky to the moon and shooting in Ha. Plenty to go at in Cygnus and Cepheus. Me? Bed time!!

Olly

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Nope, I don't think so. It's important to understand that, while post processing involves a set of skills, it cannot invent. You have to have real and genuine information to start with.

The worst possible target for shooting in moonlight might well be (sorry!) the Iris. It's a reflection nebula so it has no emission nebulosity to pass through an Ha filter. (Actually not quite true becaue it does have a whiff of Ha emission but it's on the seriously subtle side!) And the nice faint dusty stuff lying around it will be totally overwhelmed by skyglow/moonglow. This is a dark site and dark night target. When the moon is around a DS imager with mono and NB filters should be looking to the opposite side of the sky to the moon and shooting in Ha. Plenty to go at in Cygnus and Cepheus. Me? Bed time!!

Olly

I simply cant/wont argue with anything you say Olly. You are a master of your craft.

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Well I tried again last night... targeted Sould Nebula.... short 2.5 min exposures * 20.... iso 800.....   Same result!

A little nebulosity was captured but small stretches revealed horrendous gradients. The gradients can be alleviated to some extent but the processing leaves the image noisy and lacking any detail.

I have learnt a bit over the last couple of nights....  mainly DO NOT IMAGE WHEN THE MOON IS UP!

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