Should I buy an Ha filter?

[Ovi]

Hello! I have a modified Canon 60D, Nikkor 135mm f/2.8 lens and Omegon MiniTrack LX2 tracker. Would 1 min long exposures (the limit with my mount) be enough to collect meaningful Ha data? Thanks! 

[rickwayne]

For what it's worth, I did this image of the West Veil with an f/4.5 scope one night when guiding failed and I was limited to 60 seconds. Dunno if it's "meaningful" but there's certainly a signal, even in O-III which as you know is always much weaker than Ha.

Likewise this Elephant's Trunk is also composed of 60" exposures.

 

Edited November 30, 2020 by rickwayne

[Ovi]

Those are some nice photos

[rnobleeddy]

I'ma big fan of the dual band filters for a DSLR. They effectively split the Ha signal to the red pixels and the O-III to the G/B pixels. The width of the Ha  pass band aside, as far as I can tell, the concept is strictly better than Ha for DSLR's because you don't lose any Ha, and gain O-III for free. Practically, I imagine the Ha band is a lot wider in the dual band filters than a quality Ha filter though.

I'm always wary of posting images as I have a lot to learn - but this was less than hour of dual band data with a 450D on a night with 90% moon.

 

 

 

[Ovi]

23 hours ago, rnobleeddy said:

I'ma big fan of the dual band filters for a DSLR. They effectively split the Ha signal to the red pixels and the O-III to the G/B pixels. The width of the Ha  pass band aside, as far as I can tell, the concept is strictly better than Ha for DSLR's because you don't lose any Ha, and gain O-III for free. Practically, I imagine the Ha band is a lot wider in the dual band filters than a quality Ha filter though.

I'm always wary of posting images as I have a lot to learn - but this was less than hour of dual band data with a 450D on a night with 90% moon.

 

 

 

What dual bandpass filter would you recommend?

[nephilim]

2 hours ago, Ovi said:

What dual bandpass filter would you recommend?

Optolong L-eXtreme looks a great filter with a very narrow band pass of 6nm in Ha & Olll it's not cheap but they never are.

[Jm1973]

There are quite a few dual-bandpass type filters now, often confusingly marketed as tri-band or even quad-band, but apart from the OPT Triad Ultra Quad-band, they are all just dual bandpass.

Sometimes the oiii band is wide enough to allow hb to pass as well, and a bit of clever marketing is to call these tri-band filters, rather than dual band filters with a less restrictive band-pass. 

If the Ha band is also a bit wide, enough to include sii then they call it a quad band filter.

In reality though, these tri and quad band filters are just less restrictive dual band filters - althought they may confer other qualities such as more natural star colour.

The l-extreme as it has two 7nm bandpasses, is good enough to filter out most light pollution, even moonlight, which most of the others won't block. The STC duo-narrowband is similar but more expensive.

The OPT Triad Ultra Quad-band actually has 4 separate bandpasses, one for each of the emission lines, but that is massively more expensive.

If you just want to dip your toe in the water, so to speak, the Altair Astro tri-band and the ZWO duo-band filters are the cheapest, at around £80 for the 1.25" version. They have, I think, 15nm ha and 35nm oiii/hb bandpasses.

The good thing about these filters is you can split out the oiii and ha into two channels and do dual-narrowband imaging in APP or PI.

 

 

Edited December 2, 2020 by Jm1973

[Jm1973]

On 01/12/2020 at 09:19, rnobleeddy said:

I'ma big fan of the dual band filters for a DSLR. They effectively split the Ha signal to the red pixels and the O-III to the G/B pixels. The width of the Ha  pass band aside, as far as I can tell, the concept is strictly better than Ha for DSLR's because you don't lose any Ha, and gain O-III for free. Practically, I imagine the Ha band is a lot wider in the dual band filters than a quality Ha filter though.

I'm always wary of posting images as I have a lot to learn - but this was less than hour of dual band data with a 450D on a night with 90% moon.

 

 

 

That's a nice East Veil pic. Which filter did you use?

[rnobleeddy]

5 hours ago, nephilim said:

Optolong L-eXtreme looks a great filter with a very narrow band pass of 6nm in Ha & Olll it's not cheap but they never are.

 

1 hour ago, Jm1973 said:

That's a nice East Veil pic. Which filter did you use?

I'm using the STC filter (https://www.rothervalleyoptics.co.uk/stc-astro-duo-narrowband-filter-2.html)  but only because it came up 2nd hand cheaper than the a new Optolong extreme (https://www.firstlightoptics.com/narrowband/optolong-dual-band-l-extreme-filter.html). 

 

I was about to write something very similar about tri-band and so on, but @Jm1973 beat me to it! 

 

The veil seems to be a particularly good target. I've since collected more data on the East and the West and it seems react well to these filters. Nothing else I've imaged so far as as strong an O-III signal. I was also pleased with the Ha response from the elephant trunk nebula, but will admit that star colors can be an issue for other targets. I haven't quite mastered aligning RGB subs, but for example, I want to try combining Ha from the red channel using the dual band with RGB data using a different filter.

Edited December 2, 2020 by rnobleeddy

[Snooze]

I'm in a similar situation as OP and very interested in this thread. 

Correct me if I'm wrong but a 1min exposure without an Ha filter should contain the same Ha signal as a 1min exposure with a filter right? As far as I understand it, the point of narrowband filters is to let you expose for longer thereby increasing the useful signal(the DSO) compared to unwanted signal such as light pollution or sky glow. Is that correct?

[Jm1973]

46 minutes ago, Snooze said:

I'm in a similar situation as OP and very interested in this thread. 

Correct me if I'm wrong but a 1min exposure without an Ha filter should contain the same Ha signal as a 1min exposure with a filter right? As far as I understand it, the point of narrowband filters is to let you expose for longer thereby increasing the useful signal(the DSO) compared to unwanted signal such as light pollution or sky glow. Is that correct?

A one minute exposure with an ha filter will actually have less signal, than a 1 minute exposure without one.

But for me,  even a two minute exposure, without a filter, is ruined by skyglow and LP.

Edited December 2, 2020 by Jm1973

[SmokeyJoe]

Sorry to but in but I have a quick question, is there any point in using such a filter with an UNmodded DSLR?  I have seen a number of images on places such as Astrobackyard but there is no mention of the camera being astro modded. 

[TerryMcK]

Best to get a DSLR astro modded if you want to take advantage of Ha filtering. All of Trevors cameras that he uses for Astrophotography are modded or are made specifically for the task including his latest mirrorless Canon.

Edited December 3, 2020 by TerryMcK

[rnobleeddy]

On 02/12/2020 at 22:57, Snooze said:

I'm in a similar situation as OP and very interested in this thread. 

Correct me if I'm wrong but a 1min exposure without an Ha filter should contain the same Ha signal as a 1min exposure with a filter right? As far as I understand it, the point of narrowband filters is to let you expose for longer thereby increasing the useful signal(the DSO) compared to unwanted signal such as light pollution or sky glow. Is that correct?

I don't think it's necessary to expose for longer, although that's how many people in areas with heavy light pollution will use them. Even keeping exposure constant, you're getting a better signal to noise ratio. 

[Jm1973]

15 hours ago, rnobleeddy said:

I don't think it's necessary to expose for longer, although that's how many people in areas with heavy light pollution will use them. Even keeping exposure constant, you're getting a better signal to noise ratio. 

For me, it's not so much that I would make longer subs with a filter... it's that I have to make shorter subs without one.

Semantics I know, but it's an important distinction I think. I would be making longer subs anyway if it wasn't for the LP, and the filter facilitates this.

Not that I've actually got one yet (I've one on order), but that is the hope.

Edited December 4, 2020 by Jm1973

[Ovi]

On 03/12/2020 at 21:34, SmokeyJoe said:

Sorry to but in but I have a quick question, is there any point in using such a filter with an UNmodded DSLR?  I have seen a number of images on places such as Astrobackyard but there is no mention of the camera being astro modded. 

Unmodded DSLR block around 75% of Ha signal IIRC so it wouldn't really make sense to use an Ha filter with one.