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HII filter for imaging

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Hi everyone,

First off I hope you all had a great Christmas!

Back to the main point, I live In the outskirts of Coventry, so I have a bit of LP but not loads. It could be better however, anyway, I've just got into Astrophotography, and want to image galaxies more than anything, so would an HII filter be useful for that?

If so, why would be the best way to utilise it?

Thanks!

Cam

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Do you mean Ha or SII? I'm not sure there is HII. I assume this would be with the DSLR in your sig?

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also called H-beta i think? its used for revealing ionized hyrogen gas in nebulae i believe

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People would tend to add Ha to an RGB image to bring out the star forming regions in the galaxies. This is an RGB with the Ha blended to the red.

gallery_7987_2089_498728.png

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yeah thats the kinda thing i mean! would it be worth getting one do you think?

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If you suffer from light pollution, I think you'd be better off with a LP filter. The IDAS Hutech ones are very good. Ha filters are a good way to cut through light pollution, but they are better used on nebula's and a bit tricky on a DSLR.

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i have an LP filter! bought it at Astrofest.

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HII is found in emission nebula, it has roughly the same distribution as Ha but with about 30% of the brightness. It is used to make more natural colour images of emission nebula rather than the false colour Hubble style images. It will not add anything of use to imaging galaxies which require broadband LRGB treatment, with a dash of Ha too if you like to bring out the star forming regions.

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HII isn't the correct term. It's H_beta. HII is a term that describes areas of ionised hydrogen. It's a general term. Ha and Hb describe transitions of ionised hydrogen. In Ha it's the n=3 to n=2 transition at 656nm (red) and Hb is n=4 to n=2 at 486nm.

Ha is the stronger emission by roughly a factor of 3. Your camera though is more sensitive at Hb than Ha. This is certainly true for a DSLR. With a CCD the difference usually isn't as pronounced. The question is whether the efficiency of your camera is 3x higher or more at Hb than Ha. Might be true for a DSLR, especially I modded, but I can't see it ever being true for a CCD that normally peaks around the 550nm mark.

I suppose Hb is the second transition in the Balmer series though, maybe that's where the term HII came from, though I have never heard HII being used for Hb.

Hope that was informative

Paul

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I checked APOD, was it the M33 image you are referring to? They used the term HII region, which is an area of ionised hydrogen that emits Ha, Hb, Hgamma, Hdelta and so on. That's those pink regions. We have them too in our galaxy, areas like the heart nebula, North American and so on...

So HII regions are types of objects and Ha, Hb are particular emission lines. The emission lines are useful for highlighting these areas, Ha being the most useful (as it brightest).

Hope that helps

Paul

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Yeah!

Ok I must have just got confused then. I was still half asleep when I read it :)

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Hi everyone,

First off I hope you all had a great Christmas!

Back to the main point, I live In the outskirts of Coventry, so I have a bit of LP but not loads. It could be better however, anyway, I've just got into Astrophotography, and want to image galaxies more than anything, so would an HII filter be useful for that?

If so, why would be the best way to utilise it?

Thanks!

Cam

Sent from my iPhone using Tapatalk

Galaxies emit light through the spectrum, Ha, Hb, Sii and Oiii are narrow band filters designed to isolate the light emitted by nebulea. As these filters block all other but the one thay have been designed to pass through, at times  they are used as LP filters in particular the Ha filter . Ha is also used  to enhance the light from the star forming regions of galaxy but this is added to an RGB image of the galaxy as either LUM or to RED channelt, You could try and use NB filter to image galaxies but you'd blocking all other lights coming from the target. I have learnt to my financial cost that not a lot can be done about LP zone AP. The only satisfactory solution is a true dark site which is a rare as hen's teeth where I live. Aiternatively you could try good LP filters such as Astronomik Clip CCD or the IDAS P2 or D1 and then try and remove the remaining gradients post capture.

A.G

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What is an NB filter? It's going to be something really obvious :p

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What is an NB filter? It's going to be something really obvious :p

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Narrow Band, as in H alpha 7nm or 12 nm, the numbers are the width of the filter's pass band of light. I have an Ha 35nm and an Ha 7nm, the 35 nm passes a broader width of the Ha through.

A.G

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Oh ok. I'm new to this as you can tell :) so which would you recommend?

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on the sensor

Oh ok. I'm new to this as you can tell :) so which would you recommend?


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Hi,

I would say that you should first try an inexpensive LP filter such the one from SW, at around £40.00  for a 2" version it is very good value for the performance it offers. Then you  can judge the result and see how much of a difference it has made. I would not advocate using an Ha filter on an unmodded DSLR as you would get very littlle on the sensor.

Regards,

A.G

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I use my LP filter on images anyway. Ok will bear that it mind

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Understanding how all these things work I find very beneficial in imaging. Doing something without understanding what it does is a no no for me. I'm not advocating becoming a scientist or anything but a little understanding will go a long way. Learning a little about how stellar spectra differ from nebula spectra will tell you why NB filters are good for nebulae but of less use for galaxies, except in the star forming regions. Understanding a little about how light becomes an image in your camera and what kinda of noise there is and how it's dealt with will improve your imaging. Fact.

These concepts aren't too difficult to understand. The answers already exist on google and SGL so a simple search will answer the questions.

Having a basic understanding of the imaging process, from polar alignment to telescope optics, from filters to camera, from image calibration to processing and from stars to nebula is, in my opinion, essential. Some say that it's not required. That you don't need to understand any of it, even at a basic level. That doesn't wash with me. It's nonsense. Look at the big guns. I don't know of many top imagers how don't have a reasonable understanding of what's going on either in space or in their telescope or camera. That's not to say that they know it all. Some imagers, including the top ones don't have a grasp on things that they probably should. I'm not saying that I do. I'm not as arrogant as that. In fact I know what I don't know. Some people don't know what they don't know. They are the dangerous ones. They say things that are unjustified and people swallow it up because if "he" said then they must be right. My original point is that most of the top guys know what's going on to some level. This is the common factor.

Having the right tools for the job is not guarantee for success. A good set of golf clubs doesn't make you Tiger Woods. You need to know how to use the equipment to get the most out of it.

So my advice is to keep asking questions and read up in things. The more you know the better your images will be. Fact.

I'm not sure if I went off topic here, I lost track.....

Cheers

Paul

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