Astrodon Narrow Band Filters

[Gina]

I'm thinking about which OIII filter to get - 5nm or 3nm. Now I know this is my own personal decision but comments from the experts would be welcome.

I have always found in life that it pays to go for the best you can afford. Also, it often pays to save up for something better than rush ahead with a lesser item and then feel the need to upgrade later. I applied that principle when I bought my NEQ6 mount. I guess in some ways that's answering my question but I would still like other opinions.

I have decided to go for the best in NB filters as I gather there is a big difference between Astrodon and other makes. I intend later on to buy an astro CCD camera but in the meantime I'm using DSLRs (1100D). I have been doing NB DSO imaging with a twin wide-field rig with a pair of 1100Ds (modded and cooled) and a pair of Vivitar 200mm f3.5 telephoto lenses (with home-made remote electric focussing) using Astronomik clip filters (Ha and OIII). I've decided to go much narrower in bandwidth and have found that 1.25" mounted filters will fit very nicely in the end of the lenses with just a sliver of plastic to hold them in place. This way the filter more than covers the aperture and enables the use of smaller filters.

So far I have bought a 5nm Ha Astrodon filter from Ian King. This covers both Ha and NII whereas if I want to cover NII (apparently quite a common DSO emission) I would need 2 3nm filters - one for each waveband. That would be stretching things too far.

Next to consider - and this is where I'd appreciate orther views - is the OIII filter. Looking at Astrodon's web site, the benefit of the 3nm over the 5nm is made very clear. Ian King doesn't have these in stock ATM and the delay is expected to be a few weeks. That's why I decided to go ahead with the Ha filter rather than an OIII, at least I can get some better Ha images. I know narrower bandwidth helps with the brightness of the very bright stars that can be such a nuisance in NB images. So now I have time to contemplate which OIII filter to get - the top end 3nm or save over a ton on the 5nm.

As I see it the pros for a 3nm are tighter stars and better moonlight rejection and the con is half as much again in price or £114.

Any comments please.

[davew]

Hi Gina,

I'm no expert but spent a great deal of time investigating this very dilemma. I went for Astrodon 5nm filters.

On looking around I saw many images damaged by internal reflections. There are a few causes but good anti reflection coatings on the filters will help. Over all I discovered that Astrodon were regarded as being about the best from the main stream. You have to be careful though when looking at images out there. Quality of equipment and processing ability come in as do F/R and F/L.

O111 seems to be affected by moon light and some other light pollution so the narrower the better I assume. I won't be able to find the links again but there were some experiments done in the USA. They discovered that 3nm O111 and 5nm Ha stars match up very well. You can of course manipulate the stars in software and as I've got a 5nm O111 filter this is ok for me.

When you see the differences on the Astrodon site between 3nm and 5nm, be aware they weren't done via a DSLR through camera lenses !

I think you'd have to have a very compelling reason to image N11. For this you would need the 3nm Ha as you say.

I can't say that Astrodon is better than any other from experience, because I haven't tried them all. I have spoken to others that have and they say that they are indeed better all round filters. They do cost a bit though. The trouble is that it's difficult to get a truly unbiased opinion. Why would someone who has bought, say Baader, tell you that they aren't much cop ? Why would rich kids like me ( ) tell you I made an awful mistake ?

Another thing to be wary of is that 3nm filters won't like very fast lenses. f2.8 seems to be ok with 5nm but I don't think you'd get much joy at f2 and 3nm. Also be aware that the filters need to be square on to the chip. The faster the lens and the narrower the pass band the more it will show.

I'd go back to Ian King and have a proper talk with him as I did. I value his advice very highly.

I don't think you'll see a great difference until you change over to CCD imaging.

Finally..... Don't believe all the manufacturers say about their products. For instance, Astrodon claim no IR leak like some others but when analysed someone found IR leak that was worse than Baader. It didn't bother me because the chips we use don't go too long into the red.

Fingers are tired now !

Dave.

[Gina]

Hi Gina,

I'm no expert but spent a great deal of time investigating this very dilemma. I went for Astrodon 5nm filters.

Thank you for your reply That's very interesting

On looking around I saw many images damaged by internal reflections. There are a few causes but good anti reflection coatings on the filters will help. Over all I discovered that Astrodon were regarded as being about the best from the main stream. You have to be careful though when looking at images out there. Quality of equipment and processing ability come in as do F/R and F/L.

O111 seems to be affected by moon light and some other light pollution so the narrower the better I assume. I won't be able to find the links again but there were some experiments done in the USA. They discovered that 3nm O111 and 5nm Ha stars match up very well. You can of course manipulate the stars in software and as I've got a 5nm O111 filter this is ok for me.

Interesting - thank you

When you see the differences on the Astrodon site between 3nm and 5nm, be aware they weren't done via a DSLR through camera lenses !

No, I realise that - I'm mainly thinking of the future when I plan to buy an Atik 314L+.

I think you'd have to have a very compelling reason to image N11. For this you would need the 3nm Ha as you say.

Yes. Quite.

I can't say that Astrodon is better than any other from experience, because I haven't tried them all. I have spoken to others that have and they say that they are indeed better all round filters. They do cost a bit though. The trouble is that it's difficult to get a truly unbiased opinion. Why would someone who has bought, say Baader, tell you that they aren't much cop ? Why would rich kids like me ( ) tell you I made an awful mistake ?

Yes, I know what you mean.

Another thing to be wary of is that 3nm filters won't like very fast lenses. f2.8 seems to be ok with 5nm but I don't think you'd get much joy at f2 and 3nm. Also be aware that the filters need to be square on to the chip. The faster the lens and the narrower the pass band the more it will show.

Yes, I am aware of that.

I'd go back to Ian King and have a proper talk with him as I did. I value his advice very highly.

Yes, I think you're probably right there.

I don't think you'll see a great difference until you change over to CCD imaging.

No, maybe not.

Finally..... Don't believe all the manufacturers say about their products. For instance, Astrodon claim no IR leak like some others but when analysed someone found IR leak that was worse than Baader. It didn't bother me because the chips we use don't go too long into the red.

That's a very good point! I also noticed that Astrodon were comparing their newer 3nm OIII filter with their older 6nm one rather than their current replacement 5nm one. That makes me a bit suspicious. And, of course, they will want to make out their dearer one are better than their cheaper one. It all makes me wonder if going for the "top end product" is a good use of the extra money.

Fingers are tired now !

Dave.

Thank you again for your thoughts it's just the sort of thing I wanted It's oh-so-easy to get stuck in a rut!

[Gina]

Nobody else have anything to add to the discussion? Please?

[jjongmans]

I only use the 3nm filters. They are absolutely great, the contrast is amazing and no halos. Out of Ha, OIII and SII, the OIII is most influenced by moonlight and LP, so 3nm will help you there. I won't use it with a DSLR, but you know why I think.

[GlassWalker]

This is something I've been looking at for a long time, but my interest is slightly different. My main driver for going narrower is to improve light pollution rejection. The difference from 5nm to 3nm should be significant enough to be worth going for, although I'm still trying to work out how "fast" an optical system I can get away with while retaining the benefit of 3nm filters. I think going as slow as f/4 should be ok.

[jjongmans]

Astrodon claims f/3, I only used them on f/5.4 and slower.

[Gina]

I only use the 3nm filters. They are absolutely great, the contrast is amazing and no halos. Out of Ha, OIII and SII, the OIII is most influenced by moonlight and LP, so 3nm will help you there. I won't use it with a DSLR, but you know why I think.

Thank you I gather you don't like DSLRs but I can't yet afford a half decent CCD. Maybe I should hold fire on the OIII until after I get a CCD camera - it is about a third of the price of an Atik 314L Plus.

[Gina]

This is something I've been looking at for a long time, but my interest is slightly different. My main driver for going narrower is to improve light pollution rejection. The difference from 5nm to 3nm should be significant enough to be worth going for, although I'm still trying to work out how "fast" an optical system I can get away with while retaining the benefit of 3nm filters. I think going as slow as f/4 should be ok.

Thank you for that LP from the moon severely limits imaging when it's around but otherwise my LP is very slight and then mainly distant street lights.

The main thing I'm looking at ATM is replacing the Astronomik 12nm OIII clip filter I'm using in one of my WF DSO cameras which is pretty dreadful - too wide and star halos. Maybe I'd be better just replacing that with a much cheaper Baader 1.25" filter fitted into the end of the lens and leave the Astrodon until after I have a CCD camera for the scope.

[GlassWalker]

Gina, I'm curious about the halos you say you get with the Astronomik OIII filter. Got any examples? Astronomik's site say in the past there may have had some problems with halos caused by their filter, but that was some time ago and they do free replacements for them if that is the case, and not some other cause.

[Gina]

I was going to post a crop of the stacked and Photoshopped Cygnus Loop, Witch's Broom section to show this but the SGL uploader isn't working so here's a finished combined Ha + OIII Cygnus Loop linked from Photobucket. I believe this shows a halo from the bright star in the Brroom.

[GlassWalker]

Gina, hard to tell on your photo but I see what appears to be a bit of star bloat, and what appears to be a bubble offset from the star?

A quick crop from one of mine, left is OIII on a stock 600D, Astronomik 12nm OIII and Sigma 120-300mm OS at 300mm f/2.8. Right is Astronomik 12nm Ha on modified 450D upsized to same scale as OIII for comparison. Not entirely clear on mine, but there may be a faint halo around my OIII shot, or could it be a trick of the eye from a detail of the nebula?

[Gina]

Yours doesn't show that bubble like artefact that I'm getting. Still no upload working so here's a link to one I've uploaded to Photobucket.

[davew]

That's drastic Gina !

I've posted here a single slightly cropped sub of Sadr taken with my 5nm O111 filter for 15 minutes. I chose to upload Sadr because it's so bright.

Straight single sub not callibrated or messed with other than levels so there's no hiding place. Hot pixels free of charge

Not a hint of halo. Would another make serve me as well as the Astrodon ? No idea.

Dave.

[GlassWalker]

Gina, I don't think an offset bubble is a direct filter performance problem as such. More likely some unwanted reflection in the optical chain when combined with the filter, and changing to a different filter is no guarantee of fixing that.

[davew]

I agree about no guarantees 100%

The rub is that there aren't too many of us who can afford to experiment with different filters.

If someone would like to send me a few to try then I would post the results. Cloud permitting Not going to happen though.

Dave.

[Gina]

Gina, I don't think an offset bubble is a direct filter performance problem as such. More likely some unwanted reflection in the optical chain when combined with the filter, and changing to a different filter is no guarantee of fixing that.

I wondered that but there's no sign of it in the Ha image. OK it's a different sample of lens though the same make. Maybe I should swap over.

OTOH it's not just the halo, I'd like a narrower bandwidth to cut down star brightness and moonlight when the moon's out. I'm now considering a much cheaper option and leaving the Astrodon until I've got an astro CCD camera viz. a Baader 8.5nm OIII at £81 - a lot wider than the 3nm Astrodon but a big difference from £359 at over 4 times the price. I shall probably want to do wide-field NB DSO AP anyway and I won't want to take the Asdrodon out of the filter wheel to do it. OTOH I wonder if I'd notice the difference between 12nm Astronomik and 8.5 Baader.

[Martin-Devon]

Gina, I have the full set of 5nM Astrodon filters. The Astrodon HA 5nM filter is an absolute stunner - it's fantastically impressive with sharpness and clarity. The 5nM Astrodon OIII is more fussy and I suspect that this is the case with all OIII filters. Others have already raised the issues, but mainly Moonlight is the biggest problem with OIII filters and the stars tend to bloat a tad more as well compared to a HA filter. If I were buying right now, I'd go for a 3nM OIII - it's just more critical with this filter I think.

[Gina]

Gina, I have the full set of 5nM Astrodon filters. The Astrodon HA 5nM filter is an absolute stunner - it's fantastically impressive with sharpness and clarity. The 5nM Astrodon OIII is more fussy and I suspect that this is the case with all OIII filters. Others have already raised the issues, but mainly Moonlight is the biggest problem with OIII filters and the stars tend to bloat a tad more as well compared to a HA filter. If I were buying right now, I'd go for a 3nM OIII - it's just more critical with this filter I think.

Thank you Martin Yes, I'm coming to the conclusion that I should go for the 3nm OIII but after I get an astro CCD.

[Gina]

I think I have come to a decision. I shall not buy an Astrodon OIII filter until after I have an astro CCD and then it will probably be the 3nm one. As I think I mentioned, I shall have a set of Baader 36mm NB filters for the 1100D (Ha and SII already with OIII on backorder). I can use those initially with the CCD and upgrade to Astrodon later.

Thank you everyone for your comments and suggestions, it has helped my with my decision