More on the 3Nm Astrodon.

[ollypenrice]

I'm getting the hang of this filter now. It is fantastic. Not only is it more more contrasty but it can be used as luminance at a far higher opacity then is possible with the 7Nm I used before. The 'pink with blue haloes' syndrome of Ha as Lum is vastly reduced. Also, the 3Nm as lum reduces star sizes spectaularly well. I'm now getting RGB stars this way which are not much bigger than NB stars. I'm even wondering if I could use it to make a star mask for non Ha targets. Hmmm...

Olly

[RikM]

Do you have to increase the exposure time to compensate for the narrower passband, or does it not work like that?

[ollypenrice]

I remember not understanding a thread on this subject a few years ago! The argument was that you didn't. I think that you do but am not yet certain. The thing is that the darker regions of a target are darker in the 3Nm and darkness arises (you amaze me Holmes!) from low signal and low signal means noise. So where there is strong signal the 3 may be as fast as the 7 but the darker parts will need more time. Then again, if your intention is to use blend mode lighten to add Ha to red then the darker signal won't get applied. Most of this is conjecture. I intend to do a hard nosed comparison though, but only when I intend to use the data for real. I don't like testing in imaging time!

Olly

[Merlin66]

If you are imaging primarily at Ha, the Ha emission is only a couple of A wide (<0.5nm)

So the same amount of Ha will pass with a 3nm/ 7nm/12nm filter. The only difference would be the amount of non-Ha "background" recorded by the wider filters.

[RikM]

That was the argument used by a friend of mine for sticking with the 35nm. If the Ha is a line signal and you are going to blend it anyway, it doesn't much matter. However, I do know that said friend is now using a 7nm!

[ollypenrice]

That was the argument used by a friend of mine for sticking with the 35nm. If the Ha is a line signal and you are going to blend it anyway, it doesn't much matter. However, I do know that said friend is now using a 7nm!

Yup, so you need to ask the friend what was wrong with his red filter.

Olly

[johnrt]

I've moved from a 12nm Astronomik to a 3nm Astrodon and kept my exposures the same at 10 minutes. I don't need to push the exposure time further, I feel the detail and depth is there and the background is darker, smoother and so much less noise than with the 12nm. I "think" it's letting everything through I want and suppressing everything I don't meaning imaging time in unaffected. That's just how I feel it's working for me though, your milage may of course vary

[Gina]

I just wonder if there would be a worthwhile difference between a 5nm Ha and a 3nm Ha

[Whirlwind]

The 3nm should exclude any NII so you should get a purer Ha sampling.  Of course if there is no NII in the object then it doesn't really make any difference!

Ian

[NickK]

Still want to see a M81/M82 shot with Ha 35nm, 7nm and 3nm... then colour'd with red, white and blue..

[johnrt]

Crikey this filter doesn't care about moonlight, just tried a 30 minute exposure just to see what it would look like under some pretty bright moonlit skies and I'm a little taken aback!!

Uncalibrated and just stretched in Pixinsight.

[Merlin66]

John,

Moonlight is just reflected sunlight.

It's only the residual continuum spectrum around the Ha emission which could/ would make the difference.

[Gib007]

Oh my, $925 for one narrowband filter. I can safely say my career won't push me to buy these at any point, hahaha. Good to hear they're excellent though. I use Baader ones myself.

[ollypenrice]

Oh my, $925 for one narrowband filter. I can safely say my career won't push me to buy these at any point, hahaha. Good to hear they're excellent though. I use Baader ones myself.

Tell me about it! However, since I do AP for a living in various ways the investment has been worthwhile. It has taken me six years to pluck up the courage, though!!

Olly

[opticalpath]

I need to upgrade from my ancient 12nm Ha filter but am swithering between the 3nm and 5 nm Astrodons.  Help me decide!

The 3nm excludes NII emission: is that a good thing or a bad thing?  Any reduction in (wanted) signal presumably reduces S/N, so do I want to gather up the extra NII photons (5nm) or exclude them (3nm)?  I guess it boils down to whether the NII represents wanted or unwanted signal.   I have pretty light-polluted suburban skies - does that outweigh all other factors and make it a no-brainer to opt for the ultra narrow filter?  I'm not into full NB; this will be used just for Ha-only or Ha-RGB images.

Any advice welcome

Adrian 

[Gib007]

Tell me about it! However, since I do AP for a living in various ways the investment has been worthwhile. It has taken me six years to pluck up the courage, though!!

Olly

I admire that. I'd love to take this hobby much further. I'm a secondary school teacher but once I retire, who knows, South France looks mighty tempting as a retirement location. Gibraltar is small and buzzing with development, with the light pollution to go with it. Spain is next door, yes, but accessibility depends on how the Spanish government feel about my mere existence as a Gibraltarian, hehe.

[ollypenrice]

Another escapee from secondary school here!

Olly

[RikM]

I'm married to a secondary school science teacher. Does that count?

[ollypenrice]

Last night, in what felt like broad daylight, we ran off 4 hours of Ha on the same side of the sky as the moon. It looks OK, though we haven't processed it yet. Remarkable.

Whatever the reason, I'm sure the 3 is more moon proof than the 7.

Olly

[Tom OD]

Right 3nm O3 for Christmas it is then.

[ollypenrice]

Right 3nm O3 for Christmas it is then.

A joint present for us! Heh heh.

Olly

[Gina]

Just before I bought my 5nm Astrodon Ha filter I was humming and harring about 5 or 3nm.  From reading the Astrodon web site I decided on the 5nm thinking the NII was mworth having.  But I now think I made the wrong decision (with hindsight and a lot more experience - both mine and other people's).  I would think the amount of NII emission would be negligible compared with the Ha.  And even with a relatively dark sky, I think the extra cut in background and reduction in star sizes would have been worth the extra money.  Plus, of course, the extra moonlight reduction.

I had a go at the Melotte 15 area in the heart of the Heart Nebula last night in spite of a full moon.  Unfortunately, mistiness and high cloud put a stop to that (but that's another story).  I was getting a considerable background gradient from the moonlight which clearly would have been less with a narrower filter.

This is a 5n Ha sub which clearly shows the gradient and then processed using GradientXterminator in Ps.  MN190 with Atik 460EX and Astrodon 5nm Ha filter bin 2x2 (transparency was poor giving 3-4 FWHM unbinned).

 

[johnrt]

I've just bought a 5nm OIII to go with my 3nm Ha Astrodon, crazy? Well my reasoning is that imaging OIII under bright moonlight is never going to be a good idea no matter what the bandpass is, so the extra 2nm isn't going to do anything for me.

How many subs in the second image Gina?

[Gina]

I've just bought a 5nm OIII to go with my 3nm Ha Astrodon, crazy? Well my reasoning is that imaging OIII under bright moonlight is never going to be a good idea no matter what the bandpass is, so the extra 2nm isn't going to do anything for me.

How many subs in the second image Gina?

Just the one.

[steppenwolf]

My own take on this as I currently ponder the purchase of a couple of Astrodon filters is this:-

I can't justify the purchase of an NII but I do want to capture NII data (try comparing the detail in images of M27 taken with NII data included and without to see why). OIII data is normally much noisier than Ha data from the same object. Sooo, my simple brain says 5nm Ha and 3nm OIII,

Gins, I really don't think you have made a mistake.

Sent from my iPhone from somewhere dark .....