Comparison between 7nm Ha filter and 3nm Ha filter

[swag72]

I have been using the 7nm Baader Ha filter since I started in CCD imaging about 18 months ago. I fancied trying a 3nm Astrodon Ha filter, so bit the bullet and bought one. I decided that I'd do a comparison for my own interest to see just what the difference was.

This comparison is not absolutely scientific as the data for each was taken on different nights, but I have tried to ensure that is the only changed variable.

• Capture details - M: HEQ5, T: Tak FSQ85 and C: Atik 460EX
  
• Each night the imaging was started at about the same time
  
• 11x1800s stacked in PI using the same bias frames and the same stacking settings
  
• Stetched using the automatic STF in PixInsight, so that both images recieved the same stretch
  

No other processing has been done, no cropping, sharpening - Nothing.

I am hoping that this gives as good a comparison I can do between the 2 filters. The first image is the 7nm Baader filter and the second one is the 3nm Astrodon.

I hope that this is a useful insight into the two filters for others.

[johnrt]

Interesting, there seems to be a much bigger reduction in small and medium stars in the 3nm version, it also looks like it has less noise and is smoother, this could just be the illusion of the star reduction.

What are your thoughts Sara having looked at the originals close up?

[ollypenrice]

Good post, Sara. Thanks.

Mildly underwhelming on this target? I agree with John's observations of the images and share his questions. This does come as a bit of a relief since I've just bought the 2 inch Baader and wouldn't want to be cursing it for the next few years!

I wonder how they compare in moonlight and LP?

NB imagers may well really like the small stars though for me they don't matter because the Ha stars are smaller than the RGB anyway and, properly processed, have no effect on them. I only apply NB to RGB.

I've done a couple of images with a guest's Astrodon LRGB set. While many of the best imagers swear by them (and I defer to their expertise) I'm afraid I disliked them in the end. I couldn't get on with the teal blue which they claim as a virtue and I also felt, somehow, that there was a red-blue bipolarity in the colour as if green wasn't playing along. It could just be unfamiliarity.

Olly

[swag72]

Looking at these close up, the 3nm is definitely smoother overall, less noisy and easier to process. I like the smaller stars on the 3nm.

Underwhelming Olly? Yes perhaps I should have done a comparison on a far feinter target as this is where the 3nm is supposed to have the edge. But I had the IC1396 from the night before!

Am I glad that I've got the 3nm? Looking at the data at this stage, yes I am. This is a bright target, not the particular strong point of the 3nm and already I like what I see.

I've processed the data better now and yes, I like it! The down side is that looking at the size of those stars there's no way the Baader OIII and SII will match this filter, so I guess I'll have to buy the Astrodons!

[Catanonia]

TBH apart from the smaller stars I am struggling to see the difference.

[swag72]

Here's something of a massive crop between the two.

I hope that this will help people to decide whether the Astrodon's are worth it for them. It's certainly something that I wondered about. I'm hoping to do some fainter targets soon, but these won't be as a comparison. My thoughts are that this filter will increase the contrast for the fainter stuff and will also be a little more forgiving in the full moon periods.

[Mark72]

I'd agree with Sara,

The second image looks smoother. I guess should mean less noise and better details with fainter objects.

3mm O3 filter does not even care about the full Moon. So I guess Ha would not even notice it if the object is far from it.

Mark

[Gina]

Yes, I imaged with the Astrodon 3nm OIII filter during full moon in the same sector. After using GradientXterminator the result was great I went for the 5nm Ha and SII filters from Astrodon. I have Baader 7nm Ha and 8.5nm OIII and SII as well as the Adtrodons and will be able to do a direct comparison shortly when I have my dual imaging rig fully set up. I'm expecting the second Evostar 80 ED DS Pro plus matching reducer on Wednesday and a filter tray for my second widefield imager tomorrow. I got my second Super Takumar 105mm f2.8 lens today. I already have a second 314L+ mono CCDs thanks to Sara

[Catanonia]

Ah that's better Sara with the crop, couldn't really tell at work. Yes smoother as well.

[billhinge]

Just for fun as an unscientific testI loaded them both into Pixinsight's Blink tool and set the blink rate to 0.1 sec, there doesn't appear to be any difference in the nebulosity but on the 7nm filter the foreground stars are much brighter and it makes the image busier when viewed normally - I didn't go down to pixel peeping level so the 3nm may be less noisier ?

I printed the following blink report - I'll leave it to someone more knowledgeable to interpret

FileName # Ch Exposure Mean Median AvgDev StdDev Minimum Maximum

IC1396_3nm_SGL 0 L 0.000 15016.625 15934.000 7487.861 8752.982 0.000 65535.000

IC1396_7nm_SGL 1 L 0.000 15530.451 16448.000 7738.645 9328.284 0.000 65535.000

[davew]

That is very interesting.

I can see a few pros and cons though.

Pros - Tighter stars with no fuzz round them. Better demarcation between dark and light giving a harder edge ( I think it's a pro ). Seen above the head and trunk area. Detail appearing in the dark areas. Double stars look like doubles. Smoother bright areas.

Cons - Star eater ! Some of the smaller stars are disappearing and if this was a Nikon / Canon comparison there would be howls of outrage ! No O111 filter you are likely to buy will produce small enough stars meaning more work in processing. You may end up with quite a few bright blue stars. Greater guiding accuracy will be required. Eggs will show up straight away. ( Pix has a decon routine that may solve this )

Give me more time and I could find more of each.

I would like to see these images done with flats. I'm sure I can see a pattern appearing in one of them. No pressure

On a personal level, if I was doing just Ha, as I do, then the 3nm is very good indeed. In " Normal " narrowband imaging the 3nm O111 filter would be used with the 5nm Ha filter.

So far so good. Show us the way Sara,

Dave.

[swag72]

Thanks for the thoughts everyone - Hopefully this will make interesting reading for someone in a dilemma one day!

@Dave - Can you see the banding that is starting to appear in the 3nm one? Something to do with the bias as it goes when I restack without the bias. I has a stacking artifact like this before and solved it by ditching Maxim for data capture. I'm not going to do this again as I really want the dithering that Maxim gives me.

I'm thinking that the 3nm OIII should be a match for the 3nm Ha. And they're small enough to fit in my handbag on my next UK trip. No one need ever know!!!

[davew]

It is on the 3nm side by side image. Only just, so could be a genuine feature.

So..... he doesn't know yet ?

Dave.

[swag72]

Funny Dave, I only noticed it on the 3nm and PI has been merrily stacking and calibrating my other subs from the 460EX and taken in Maxim. That's an odd feature if it's natural!!

Shhh, no he doesn't know yet and at such a small container size, there's every chance that he won't know!!

[ollypenrice]

One of the best threads in a long time. Bravo Sara. What any one individual chooses to conclude is not that important. It's having the information that matters. This is great inforamation.

Just a repeat thought though; moonlight?

Olly

[swag72]

Thanks Olly - I will have a go at something similar when the full moon is about and hopefully clear skies!

[opticalpath]

Really useful thread, Sara ..... and highlights for me the long-overdue upgrade required to my old Astronomik 11nm filters.

Can anyone comment on how they find different brands of Ha filter compare with regard to annoying halos around bright stars (which I get with the Astronomik Ha)? How do the Baader and Astrodon filters perform?

Thanks

Adrian

[swag72]

Can anyone comment on how they find different brands of Ha filter compare with regard to annoying halos around bright stars (which I get with the Astronomik Ha)? How do the Baader and Astrodon filters perform?

Is that another request Adrian?!!! I'm guessing that there's not too many people with both to compare?

[opticalpath]

Is that another request Adrian?!!! I'm guessing that there's not too many people with both to compare?

No! Sorry, let me rephrase that ........

Anyone using Baader or Astrodon Ha filters like to comment on their performance regarding halos around bright stars? (to help me make my own comparison )

Adrian

[davew]

I use Astrodon 5nm and haven't noticed any.... yet.

The CCD and CCD window may play a part so be careful comparing results.

Dave.

[johnrt]

Really useful thread, Sara ..... and highlights for me the long-overdue upgrade required to my old Astronomik 11nm filters.

Can anyone comment on how they find different brands of Ha filter compare with regard to annoying halos around bright stars (which I get with the Astronomik Ha)? How do the Baader and Astrodon filters perform?

Thanks

Adrian

If you get halos with the Astronomik filters contact them directly for a return and replacement of the filter for new, they will swap it totally free of charge. I swapped out my Ha & OIII due to this issue.

http://www.astronomik.com/en/news/astronomik_halo_free_filter_halo_problem

[ollypenrice]

If you get halos with the Astronomik filters contact them directly for a return and replacement of the filter for new, they will swap it totally free of charge. I swapped out my Ha & OIII due to this issue.

http://www.astronomi...er_halo_problem

So did I and I got smaller haloes. I use the Baaders, though I own both. I personally feel they are better.

Olly

[Gina]

I get no haloes with the Astrodons.

[billhinge]

Hmm, I've looked at this a few times and apart from more brighter stars on the 7mm I don't see any difference, not saying there isn't just I can't see it so for me and possibly others the 7nm would be good enough

So as an experiment I did a straight subtraction 7nm - 3nm in Pixinsight using pixelmath and I'm only left with stars ?

Surely the 7nm is catching all the Ha light that the 3nm catches plus a few more non Ha photons coming from the stars which what I see in the pic?

[Gina]

Where you have the case of a very bright star in the midst of faint nebulosity, the narrower passband helps reduce the brightness and bloating (eg, Alnitak with The Flame and Horsehead Nebulae). It also helps when the moon is out by reducing the amount of wideband emissions getting through.