Which Ha Filter

[blinky]

My Orion Starshoot deep space mono imager should be arriving tomorrow morning, many thanks to Sky@Night and Simon @ The Widescreen Cenrte:icon_cheers:

Anyway I am looking to get an Ha filter so that I can do some narrowband 'stuff' and also it seems the only time the sky is clear is when Luna is out!

Which one to get though...

Options are:

Baader 7nM

Baader 35nM

Astronomik 13nM

So whats the thoughts? Currently I am edging towards the Astronomik 13nM.

1. It is a larger bandpass than the Baader 7nM so should give slightly shorter exposures. Also the camera I am getting is one of the cheaper ones so I assume does not have the same sensitivity etc of more expensive ones.

2. Astronomik are one of the bigger names is Astro filters so they must be good?

3. The 35nM is a bit too big a bandpass and a full moon may start to interfere?

Whats everybody elses thoughts on this?

[narrowbandpaul]

Low cost doesnt mean low sensitivity, the sony 285 is small, but pretty responsive over the visible range. Where the sony chips do lack is well depth. Only around 25000e for a 7.4um? pixels.

The narrower you go the better SNR you will get, as you get lower background levels.

I would go for the baader 7nm, hands down.

The peak transmission should be very similar to the 13nm, so there will be almost no difference in attenuation as the light passes through the filter.

35nm is a no-no. I have used it in moon conditions, but it wasnt nearly as good as a true narrowband filter.

hope this helps....

[blinky]

Cheers for the info Paul. It is about the same price as the 7nM one so maybe makes more sese to go for the narrower transmisison.

[Merlin66]

Unless you have some major issues with light pollution any one will do the job.

You must remember that Ha emits light in a VERY narrow bandwidth, so ideally a 1nm will pass ALL the Ha light emitted by nebulae.

There's not too much (if any) artificial light which emits close to the Ha wavelength so anything will do the job.

Bang per buck (unless you're using extreme wide fields ie > 5 degree) the narrower the better ( why not??)

[blinky]

Somebody told me that the 7nM meant that a lot of stars would be very dim.

[Whippy]

I don't think that's the case Craig, Kai uses a Baader filter and I've never heard if him complaining about that.

TBH, the only issue you may want to take into account is the Astronomik filters may give you a 'halo' effect around the brighter stars in your images although I'm sure I read somewhere that they've brought out (or about to) bring out a new version that eliminates this.

Other than that, either the Baader or the Astronomik would do you just fine.

Tony..

[Kai]

Craig

As Tony says i use the Baader 7nm and to be honest i find it very easy to get on with.Take a look at my Dso Album and you will get a idea of what it can do.

I havent had chance to compare it to others but i also see no reason why when i get results that im happy with

[blinky]

I think I am going to go for the 7nm Baader. Kai, can you post a link to your album?

[Merlin66]

The filter will ONLY pass the Ha light whether it comes from a star or nebulae. Most stars don't give a lot of light in Ha, so unfortunately they will appear very dim.

[Kai]

I think I am going to go for the 7nm Baader. Kai, can you post a link to your album?

http://stargazerslounge.com/album.php?albumid=19

There you go

[MartinB]

The only Ha filter I've ever used is the Astronomik 13nm. It's performance has always seemed excellent and although I've thought about trying th 7nm I've never really felt the need.

The Astronomic is very tough and can be cleaned, within reason, without worrying about the coatings. This is important since dust bunnies on filters will show up on your image.

Ha filters do attenuate the stars. Not sure whether there would be any difference between the 13nm and the 7nm. It isn't a great issue for Ha mono images - just saves you having to run through star bloat routines! The main problem comes when using an Ha luminence with RGB or more still when adding Ha data to the red channel. Again, not a huge problem.

The halos can be a problem and my impression is that it is very dependent on the spacing between the chip and the filter. I never had a problem with my SXV H9 in a couple of filter wheels or with a QSI532 with an integrated wheel. I do get some small halos with a QHY8 and a filter held in a seperate filter drawer. Because of the QHY8 nosepiece the filter is quite a long way from the chip.

The 35nm is designed for fast astrographs below F5. With fast scopes, when the light is coming in at an angle the is a shift in the band pass meaning that the filter is capturing the wrong bit of the spectrum. A 7nm filter will be affected more by this with faster scopes than the 13nm.

My rough guestimate would be F<4 go for 35nm. F4-7 use 13nm and >7 7nm should be fine. This is only very rough thinking but is how I would go if buying new.

[DIYASTRO]

Craig,

Just looking through some of my notes and I have scribed 'require 12nm Ha for webcam imaging'. Cannot remember why? Looking through my other notes just now to find answer!

Boyd

[blinky]

Martin,

I am intending to image with the ZS66 and a 0.5 reducer, this would bring the F ratio down to about 4.5, even if I use the 0.8 WO Reducer it's still under F5, so maybe the 12nm is the way to go????

I had no idea this would be so tricky to sort out!

[MartinB]

Nick Syzmenek and Ian King have both produced amazing images using an Astronomk 13nm Ha filter with a ZS66 and an AP 0.67 reducer. With the focal ratio you are planning I would definitely go for the 13nm rather than the 7nm.

[blinky]

Well thats that decided then Martin. Thanks very much for the advice.

[blinky]

Just bought the Astronomik 12nM from Bern! Thanks to everyone for the advice.