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Hello everyone,

 

I recently bought a Svbony 7nm H-alpha filter and I have been playing around with it with my modded DSLR. Since I'm new to narrowband imaging, I have a couple of questions regarding the results I obtained:

1/ Here is a stack of 7x7min exposures ISO800 (red channel only). Is it normal that my background is not dark and very grainy with the filter? Maybe it's because I'm using a DSLR which I know is not the best way to do things but I was hoping there would be more contrast?

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Here is a stretched version:

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2/ How should I stack the images? Just throw everything(whole image with B and G channels) in DSS or isolate the red channel from each sub first and then stack those grey images?

 

Thanks in advance for the help.

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I'd say that is a 'normal' result looking at the time and number of subs. DSLRs often produce these rain like streaks and I never found a good way around it in processing. I had some software that had an anti-streak routine but can't remember which one it was. 

For stacking, you are limited by your data. With that I mean that after stacking you will be able to pull out whatever it is you are looking for. But for this target, very Ha rich, I see no reason why you couldn't stack the whole lot AND separately stack the red channel to have a look at what's in there. You can use this as a separate layer, if layers are something you are familiar with.

/Jessun

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As Jessun says, this looks pretty normal for a DSLR with that amount of data. To reduce the streaking effects you could increase the aggressiveness of your dithering. It may not completely remove the issue - it doesn't with my 600D - but it may make it better. For a better signal to noise ratio, you just need a lot more data.

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On 17/02/2021 at 22:34, Snooze said:

How should I stack the images? Just throw everything(whole image with B and G channels) in DSS or isolate the red channel from each sub first and then stack those grey images?

I don't know the process for colour cameras but I assume that the blue and green channels contain no signal due to the the Ha filter.

I would then assume that by stacking the B and G channels you would just be diminishing the signal from the red channel.

Someone knowledgeable in the DLSR process can comment better than me - so just a thought 😁

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5 hours ago, Mr Thingy said:

I don't know the process for colour cameras but I assume that the blue and green channels contain no signal due to the the Ha filter.

I would then assume that by stacking the B and G channels you would just be diminishing the signal from the red channel.

Someone knowledgeable in the DLSR process can comment better than me - so just a thought 😁

I was about to say the same. With a Ha filter, there will be no signal in G/B, so all that can add is noise.

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Yep.  You've essentially  turned your DSLR into a mono camera with 3/4 of its photosites inactive (most Bayer filters have double G sites, e.g. my Pentax is BGGR). So you'll need a lot of integration time to pull up the Ha signal, and only the red channel will contribute anything.

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Thanks everyone for the input. I do know that I'm only using 1 out of 4 pixels but it should not matter in my case since it is the same wether I use the Ha filter or not (The Ha is still mapped to the red pixels even without the filter). What I was hoping to achieve was get a better signal to noise ratio without having to expose for ridiculous amounts of time. I will try to add more 7min subs and see if I can get a better result but so far it does not look better than my stack of 3min subs without the filter.

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I agree with what is said above by other members.  It's been some time since I used my Canon DSLR so my advice about stacking was not clear. I assumed a run with the filter and another without it.

Sorry for the confusion.

As to the rain effect, I'm sure you can search for 'rain' or something and find some threads on the topic.

/Jessun

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After you've stacked your images open your image, go to channels, select just the red layer. Now copy and paste that into a new, grey scale clipboard.

Now you'll have only the ha data and none of the noise from the green and blue channels.

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15 hours ago, geordie85 said:

After you've stacked your images open your image, go to channels, select just the red layer. Now copy and paste that into a new, grey scale clipboard.

Now you'll have only the ha data and none of the noise from the green and blue channels.

This is what I did with the pictures in the orignal post. I will add more 7min exposures to see if i get something better but so far my 3min no filter stack looks better. 

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