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H-Alpha filter with DSLR cameras

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#1 Reece

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Posted 08 April 2021 - 10:04 AM

Would an h-alpha filter make sense for nebula imaging with my Canon 20Da? I know it would be at least 4 times more inefficient than a monochrome camera (which I do not own). Would 30 second h-alpha filter subs be an improvement versus no filter nebula imaging in Bortle 8 skies? Thank you so much for your help! 



#2 qswat72

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Posted 08 April 2021 - 10:07 AM

I’d go with a duo-narrowband. You get the narrower bandpasses to cut out LP, but don’t take the efficiency hits that you would from just an Ha filter.
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#3 bobzeq25

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Posted 08 April 2021 - 10:13 AM

Would an h-alpha filter make sense for nebula imaging with my Canon 20Da? I know it would be at least 4 times more inefficient than a monochrome camera (which I do not own). Would 30 second h-alpha filter subs be an improvement versus no filter nebula imaging in Bortle 8 skies? Thank you so much for your help! 

It will work some.  The duoband filters like the LEnhance  or LExtreme will work better.

 

Ha is made for mono cameras.  The LEnhance and LExtreme were designed for one shot color.  They all work better with the right camera.  You can try weird combinations, they're not going to be better.  How much difference there will be is target dependent.  There will be a difference.

 

In any case 30 second subs are very short with these dark filters.


Edited by bobzeq25, 08 April 2021 - 10:16 AM.

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#4 DubbelDerp

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Posted 08 April 2021 - 10:14 AM

+1 for the dual narrowband. I'd look into clip-in filters too if you're planning on continuing to shoot with a DSLR. I have a 2" l-enhance that works great, but causes some wonky stars when I stick it on the front of a lens. Wish I had held out for a clip-in model...


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#5 Reece

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Posted 08 April 2021 - 10:28 AM

Thank you all so much for your replies! I was worried about what bobzeq25 ended his post with: "In any case 30 second subs are very short with these dark filters." 

 

My Vixen Polarie mount does not have periodic error correction nor do I autoguide. I further do not have a polar scope and I can't manage to get my intervalometer to work with my Canon 20Da. Despite these limitations, 30 second subs turn out quite nice however I am not sure how much longer I could make the sub exposures. I have read in other Cloudy Nights forum threads that narrowband subs are supposed to be considerably longer which mine would not be. 



#6 T~Stew

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Posted 08 April 2021 - 10:30 AM

+1 for the dual narrowband. I'd look into clip-in filters too if you're planning on continuing to shoot with a DSLR. I have a 2" l-enhance that works great, but causes some wonky stars when I stick it on the front of a lens. Wish I had held out for a clip-in model...

Interesting, the clip on mine intrudes terrible vignetting at top and bottom of frame, I don't want to mess with clips again lol and got a lens with a filter drawer so hopefully can use regular 2" telescope filters and not have to mess with clips.

 

If I may piggyback related question... yes narrowband is better on astro camera, but if you have dslr and plan on trying to use narrowband to be able to shoot during bright moon, would these duo-narrowbands still work with the moon? I'm not sure how much the moon effects the Oiii wavelengths versus Ha...


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#7 Reece

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Posted 08 April 2021 - 10:32 AM

Great question T~Stew and one I would love to know the answer to as well! 

 

 

Interesting, the clip on mine intrudes terrible vignetting at top and bottom of frame, I don't want to mess with clips again lol and got a lens with a filter drawer so hopefully can use regular 2" telescope filters and not have to mess with clips.

 

If I may piggyback related question... yes narrowband is better on astro camera, but if you have dslr and plan on trying to use narrowband to be able to shoot during bright moon, would these duo-narrowbands still work with the moon? I'm not sure how much the moon effects the Oiii wavelengths versus Ha...



#8 DubbelDerp

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Posted 08 April 2021 - 10:42 AM

Interesting, the clip on mine intrudes terrible vignetting at top and bottom of frame, I don't want to mess with clips again lol and got a lens with a filter drawer so hopefully can use regular 2" telescope filters and not have to mess with clips.

 

If I may piggyback related question... yes narrowband is better on astro camera, but if you have dslr and plan on trying to use narrowband to be able to shoot during bright moon, would these duo-narrowbands still work with the moon? I'm not sure how much the moon effects the Oiii wavelengths versus Ha...

Which filter were you using that caused this problem? I don't have any experience with clip filters yet, but the round filter is a bit of a hassle with mounting to the front of a lens. The filter drawer would fix this for sure. Was it with full frame or APS-C sensor?

 

The OIII will be affected by moonlight for sure. But it'll be useable data versus unfiltered during the full moon. Your H-a data will be great. The emission nebulae I've shot during full moon with the l-enhance filter have been decent.


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#9 DubbelDerp

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Posted 08 April 2021 - 10:45 AM

Thank you all so much for your replies! I was worried about what bobzeq25 ended his post with: "In any case 30 second subs are very short with these dark filters." 

 

My Vixen Polarie mount does not have periodic error correction nor do I autoguide. I further do not have a polar scope and I can't manage to get my intervalometer to work with my Canon 20Da. Despite these limitations, 30 second subs turn out quite nice however I am not sure how much longer I could make the sub exposures. I have read in other Cloudy Nights forum threads that narrowband subs are supposed to be considerably longer which mine would not be. 

30 seconds is pretty short.. how fast are your optics? At f/2.4 I can get useable subs at 30 seconds, although I usually use closer to 120 seconds.


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#10 Reece

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Posted 08 April 2021 - 10:50 AM

F/2.8. Thank you DubbelDerp.

 

30 seconds is pretty short.. how fast are your optics? At f/2.4 I can get useable subs at 30 seconds, although I usually use closer to 120 seconds.



#11 bobzeq25

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Posted 08 April 2021 - 10:51 AM

Thank you all so much for your replies! I was worried about what bobzeq25 ended his post with: "In any case 30 second subs are very short with these dark filters." 

 

My Vixen Polarie mount does not have periodic error correction nor do I autoguide. I further do not have a polar scope and I can't manage to get my intervalometer to work with my Canon 20Da. Despite these limitations, 30 second subs turn out quite nice however I am not sure how much longer I could make the sub exposures. I have read in other Cloudy Nights forum threads that narrowband subs are supposed to be considerably longer which mine would not be. 

Doing any kind of narrowband with a Polarie will be a compromise.  I'd _definitely_ get the duoband, probably the LEnhance.  Figure an absolute minimum of 100 subs.  As stated above, fast optics will be better.

 

Unfortunately this business is not cheap.  There are no magic solutions.


Edited by bobzeq25, 08 April 2021 - 10:52 AM.

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#12 klaussius

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Posted 08 April 2021 - 10:55 AM

Thank you all so much for your replies! I was worried about what bobzeq25 ended his post with: "In any case 30 second subs are very short with these dark filters." 

 

My Vixen Polarie mount does not have periodic error correction nor do I autoguide. I further do not have a polar scope and I can't manage to get my intervalometer to work with my Canon 20Da. Despite these limitations, 30 second subs turn out quite nice however I am not sure how much longer I could make the sub exposures. I have read in other Cloudy Nights forum threads that narrowband subs are supposed to be considerably longer which mine would not be. 

H-alpha imaging requires long exposure times, about 3 minutes on bright targets, 5 minutes on most, maybe 10 minutes on very dim ones.

 

You will need a better mount and autoguiding I believe. Or substantially faster optics.


Edited by klaussius, 08 April 2021 - 10:55 AM.

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#13 DubbelDerp

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Posted 08 April 2021 - 11:00 AM

I suspect that you would be ok. I should have mentioned, by the time I put a 48mm filter on the front of my lens, I'm closer to f/3.

 

Here's a single sub of NGC 1499 through my l-enhance filter, 60 seconds at ISO 1600. If you were to *gasp* increase your ISO to 3200, you would have a similar exposure. Not ideal, but neither are B-8 skies, right? This was at full moon, so the skies were incredibly washed out. Hard to believe there's a nebula in there...

 

Annotation 2021-04-08 120004.jpg


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#14 Reece

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Posted 08 April 2021 - 11:03 AM

Thank you bobzeq25 and DubbelDerp.

 

Unfortunately, this all gets very expensive very fast if I upgrade my camera lens to a telescope which is then too heavy for my mount. I will be staying with my Vixen Polarie + camera lenses permanently I am afraid. 

 

This limits me to perhaps only 20-30 targets which I can get nice images of. I intend to make "mini-projects" out of them and do not mind spending an entire week imaging the same object if it will give me a nice image in the end.


Edited by Reece, 08 April 2021 - 11:06 AM.


#15 klaussius

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Posted 08 April 2021 - 11:08 AM

Thank you bobzeq25 and DubbelDerp.

 

Unfortunately, this all gets very expensive very fast if I upgrade my camera lens to a telescope which is then too heavy for my mount. I will be staying with my Vixen Polarie + camera lenses permanently I am afraid. 

 

This limits me to perhaps only 20-30 targets which I can get nice images of. I intend to make "mini-projects" out of them and do not mind spending an entire week imaging the same object if it will give me a nice image in the end.

How fast does your lens go?

 

If it's around F/2 you may be able to get usable subs.



#16 Reece

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Posted 08 April 2021 - 11:17 AM

F/2.8. It is a Canon 200mm F/2.8.

 

If I follow some of the advice I have received on this forum recently and stop imaging targets at 30-45 degree declination and begin imaging them more at ~ 75 degree declination, perhaps 45-60 second sub exposures should be possible even without a polar scope based on how polar alignment error is punished as tracking error more severely at lower declination.

 

How fast does your lens go?

 

If it's around F/2 you may be able to get usable subs.



#17 klaussius

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Posted 08 April 2021 - 11:22 AM

F/2.8. It is a Canon 200mm F/2.8.

 

If I follow some of the advice I have received on this forum recently and stop imaging targets at 30-45 degree declination and begin imaging them more at ~ 75 degree declination, perhaps 45-60 second sub exposures should be possible even without a polar scope based on how polar alignment error is punished as tracking error more severely at lower declination.

Um... that's about 3x as fast as my F/5. It would be marginal, but you may be able to pull some signal. Only trying will tell you for sure.


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#18 Reece

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Posted 08 April 2021 - 11:34 AM

Thanks klaussius.

 

I guess there would be no harm in purchasing a duoband filter from a retailer who has a return policy in case I am not happy with the performance. It is quite difficult to figure out how much money it makes sense to put into my current setup. I think buying a $300 Polarscope for my Vixen Polarie for example would probably be best set aside instead for a mount upgrade if I did choose to invest more in this at some point. 

 

If money were not a concern, I know the correct answer would probably be:

Trade my Canon 200mm F/2.8 for a used Canon 300mm F/4 (so more objects would have satisfactory size)

Trade my Vixen Polarie for a used HEQ5

Trade my Canon 20Da for a used ZWO 1600mm Pro Monochrome

 

Unfortunately quite an expenditure even if purchased "Used" !!


Edited by Reece, 08 April 2021 - 11:39 AM.


#19 DubbelDerp

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Posted 08 April 2021 - 11:39 AM

F/2.8. It is a Canon 200mm F/2.8.

 

If I follow some of the advice I have received on this forum recently and stop imaging targets at 30-45 degree declination and begin imaging them more at ~ 75 degree declination, perhaps 45-60 second sub exposures should be possible even without a polar scope based on how polar alignment error is punished as tracking error more severely at lower declination.

I'm not sure how your tracker works, but it is possible to polar align a non-goto tracker by using your DSLR via the polar alignment routine in Ekos, assuming you can connect your camera to a computer. You point the tracker towards the pole, and aim your DSLR towards Polaris. The software takes an exposure, plate solves it, and then prompts you to rotate the tracker in RA. Then takes another photo, plate solves it, and repeat. You have to take three exposures, but it compares the position of the pole versus the center of rotation, and gives you a "correction" vector to improve your polar alignment.

 

Just something to consider, and does not add a whole lot of cost to your set-up depending on what you already have on hand.


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#20 Reece

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Posted 08 April 2021 - 11:44 AM

DubbelDerp, that is absolutely wonderful. Thank you so much! I have an old laptop that I would be happy to try this with. smile.gif


Edited by Reece, 08 April 2021 - 11:44 AM.


#21 DubbelDerp

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Posted 08 April 2021 - 11:48 AM

The one caveat is that Ekos runs on Mac and Linux. Windows not so much. If you have a windows machine, an easy solution is to pick up a Raspberry Pi and run astroberry server. You connect your camera's USB to the raspberry pi, and then remote control the pi from your windows laptop. But the advantage here is that you could use the pi to control your camera's shutter, so no need for an intervalometer. And if you have an autofocus lens, you can focus through the software without having to touch the lens.


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#22 klaussius

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Posted 08 April 2021 - 11:49 AM

Thanks klaussius.

 

I guess there would be no harm in purchasing a duoband filter from a retailer who has a return policy in case I am not happy with the performance. It is quite difficult to figure out how much money it makes sense to put into my current setup. I think buying a $300 Polarscope for my Vixen Polarie for example would probably be best set aside instead for a mount upgrade if I did choose to invest more in this at some point.

A duo-band filter is optimal, but they can be expensive if you're not sure to be able to take advantage of it.

 

What I did when I found myself in a similar situation, is get a used, cheap 12nm H-alpha filter. It was really cheap, and my experience with it was awesome, and convinced me to get a proper narrowband imaging setup. If things had gone the other way and not worked, it wasn't a lot of money to throw into an experiment either.


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#23 Reece

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Posted 08 April 2021 - 11:57 AM

I have a 2012 MacBook Pro which refuses to die smile.gif

 

It seems to me (with my admittedly very limited understanding) that even a 12nm h-alpha filter would be a large upgrade on the full spectrum Bortle 8 LED light pollution I am experiencing at present. 



#24 DubbelDerp

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Posted 08 April 2021 - 12:07 PM

Don't hesitate to reach out if you need help getting it working. Kstars/Ekos can seem a bit intimidating at first, but once you get a feel for it, it's very easy to use. And if you upgrade to a full goto mount, or guide camera, or whatever, it can control everything for you.


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#25 Reece

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Posted 08 April 2021 - 12:15 PM

Thank you so much DubbelDerp!

 

I think bringing a laptop outside will be very good practice for what I would have to do every time if I decided to purchase a monochrome astro camera at some point. 


Edited by Reece, 08 April 2021 - 12:17 PM.



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