Alternative Narrow Band Filter Suppliers - H-Alpha

[John K]

Hi guys,

I am doing some research on getting a narrow band 3nm HA filter for mono imaging from severely light polluted Brunswick here in Melbourne.

So imagine the shock I got when I saw the cost of these things! My goodness!

Although they are cheaper in say the higher HA range like 6nm, 10, 12nm, seeing that I am only 5.5 KM from Melbourne CBD, wanting to go as narrow as I can if possible to 3nm in HA.

Has anyone sourced filters and used filters from OMEGA:

http://www.ebay.com/usr/bjomejag?_trksid=p2047675.l2559

http://www.omegafilters.com/products...ss/588bp5.html

Clear skies,

John K.

[Merlin66 (Ken)]

John,
The filters from Omega Bob are very good. But they are all 25mm diameter.
He has supplied replacement ITF filters for the PST and more recently some interesting CaK narrowband filters.

[John K]

Originally Posted by Merlin66

John,
The filters from Omega Bob are very good. But they are all 25mm diameter.
He has supplied replacement ITF filters for the PST and more recently some interesting CaK narrowband filters.

Well actually Ken - if you click on the link clearly says 33mm mounted. Have sent them an email and good to know about the quality.

[Merlin66 (Ken)]

John,
the link is for a 588nm filter not Ha.....
All the filters I've found so far are 25mm sometimes mounted in a 28mm threaded frame.

[John K]

Originally Posted by Merlin66

John,
the link is for a 588nm filter not Ha.....
All the filters I've found so far are 25mm sometimes mounted in a 28mm threaded frame.

No worries Ken - I have sent them an email and perhaps they can provide a quote for me? Certainly a market for 3-4nm low end narrow band filters!

[clive milne]

Originally Posted by John K

wanting to go as narrow as I can if possible to 3nm in HA.

Omega do a very competitively priced 0.7nm filter all be it in a 1" format:

http://www.ebay.com/itm/Optical-Inte...fs99IT3LHLhxzw

Alluxa do larger (and custom) formats at a price.
The transmission curves are impressive in as much as they are mesa shaped (as distinct from a bell curve)

http://buy.alluxa.com/656-3-1-od4-ul...-bandpass.html

As with any interference filter of such narrow bandwidth, neither of these would be a sensible option at focal ratios much faster than F7. - The angle of incidence shifts the band pass too much to capture the emission line at faster focal ratios.

Also, there is inevitably some degree of variation in any given production run with respect to the wavelength at the peak of the transmission curve.
If you are given a choice, the best filter (within sensible parameters) will be the one where the the peak wavelength is approximately 1/2 the bandwidth of the filter
towards the red end of the spectrum.
For example, for a 656.3nm filter with a 1nm band pass, the best filter in the bunch will be the one with the peak transmission at 656.8nm (or there abouts)
Caveat: this advice is relevant to fast optical systems and very narrow band filters. Ignore it for 3nm and f9.

[codemonkey (Lee)]

Ahh, that's interesting. I contacted these guys back in Feb to see if they could do some narrowband filters in 3nm-5nm with 90%+ transmission and they couldn't do it. Said they could do +/- 15% of the center wavelength with that kind of transmission, but no better.

Could be worth a look. I'd be interested to see how they go with halos. I'd go in expecting disappointment with something this cheap, but hoping for something decent.

[Andy01 (Andy)]

Don't forget that you get what you pay for John.
My Astrodon 5nms were not cheap but they are parfocal, top quality and a once in a lifetime purchase that have enabled me to achieve considerable enjoyment and some degree of success with my images.
At the end of the day though we must ask ourselves what is our motivation for taking space pictures and how much money do we want to throw at it?
What is the best bang for your buck?
Just m 2C worth

[Slawomir (Suavi)]

What's also important is good out-of-band blocking across a wide range of wavelengths (300 to 1100nm), otherwise a filter won't provide expected contrast.

I believe that currently 3nm Astrodons are as narrow as practically possible while keeping important emission at circa 97% at f9 and with effective out-of-band blocking.

[John K]

Well, I never got a response from OMEGA - so be it.

As I cannot justify the expenditure with premium Astrodon filters as my CCD camera is only worth $1k, from those using 6-7nm filters from light polluted inner Melbourne or Sydney, what have been your experiences?

I could justify something like this 7nm from Optolong:

https://www.myastroshop.com.au/produ...p?id=MAS-001K3

http://astronomyconnect.com/forums/a...rgb-filters.9/


John K.

[Peter.M]

Originally Posted by John K

Well, I never got a response from OMEGA - so be it.

As I cannot justify the expenditure with premium Astrodon filters as my CCD camera is only worth $1k, from those using 6-7nm filters from light polluted inner Melbourne or Sydney, what have been your experiences?

I could justify something like this 7nm from Optolong:

https://www.myastroshop.com.au/produ...p?id=MAS-001K3

http://astronomyconnect.com/forums/a...rgb-filters.9/


John K.

I have bought filters from Peter Tan before, The Baader 7nm which would be the proven entry level filter is around the same price as the one you quoted above.

http://www.tan14.com/Baader.htm

[John K]

Originally Posted by Peter.M

I have bought filters from Peter Tan before, The Baader 7nm which would be the proven entry level filter is around the same price as the one you quoted above.

http://www.tan14.com/Baader.htm

Cheers Peter - I was aware of Peter Tan's range and he modified my DSLR.

The question I was really asking is if 7nm works effectively from severely light polluted skies for narrowband vs 3nm? I live in Brunswick which is 5.5km from Melbourne's CBD.

[Slawomir (Suavi)]

Originally Posted by John K

The question I was really asking is if 7nm works effectively from severely light polluted skies for narrowband vs 3nm? I live in Brunswick which is 5.5km from Melbourne's CBD.

Hi John,

I have used 12nm for some time and then gradually over time upgraded to 3nm due to heavy light pollution - I image from a very close proximity to Brisbane's CBD. The difference was astounding. If you have severely light polluted skies, then 3nm will give better contrast and detail than 7nm filter, or even 5nm filter. Such narrow filters will also lessen the effects of the moon light. To me it was no brainer. 3nm filters are relatively expensive, but with such filters you know you are collecting the best data you can from your site and with your gear.

Maybe 5nm Ha filter would yield comparable results to a 3nm one due to inclusion of nitrogen emission line, but in severely light polluted skies 3nm might be a better option. Oxygen and Sulfur - 3nm will yield higher contrast than filters with wider bandwidths, unless one is using a very fast system (under about f/4).

IMO the importance of filters in astrophotography is too often underestimated. Just my five cents

[rustigsmed (Russell)]

hi John,

what filter size were you going to use? will you need to be larger than 1.25" for the dslr?

I haven't heard much on those optolong ones... have you seen any real life examples of images taken with them?

I went with the baader HaSIIOiii (~7-8nm) as they were the narrowest for the money (and proven in the field - halo/reflection free).

I think it is a case of the narrowest you can afford/willing to part with. Are you going to shoot at f5?

Russ

[John K]

Originally Posted by rustigsmed

hi John,

what filter size were you going to use? will you need to be larger than 1.25" for the dslr?

I haven't heard much on those optolong ones... have you seen any real life examples of images taken with them?

I went with the baader HaSIIOiii (~7-8nm) as they were the narrowest for the money (and proven in the field - halo/reflection free).

I think it is a case of the narrowest you can afford/willing to part with. Are you going to shoot at f5?

Russ

G'day Russell,

All I need is 1.25" - will not be using my DSLR but a new cooled ASI174mm CMOS camera, so 1.25" filters is all I need together with LRGB filters I have - yep - 12.5" f/5 scope.

How are you finding the Baaders?

John K.

[rustigsmed (Russell)]

nice, you'll save some cash with the 1.25". so you intend on doing some deep sky with the 174?

had no problems with the baaders, mind you I do live a lot further out than you do and haven't used them as much as would like to have yet. but no reflections or haloing. I was quite impressed with the Ha under full moon conditions though, just have to aim south away from the elliptic.

[stevous67 (Steve M)]

Hello John,

I have the Baarders and they work nicely from 30km out of Melbourne.

The only thing to consider is whether you have any LED lighting in your area? Ha won't filter that out.

Steve

[Merlin66 (Ken)]

I got a reply from Omega on a 10A (1nm) Ha 1.25" filter - us$377