M42 - Narrowband Experiment using Hbeta.

[MarsG76]

Hi All,

When it comes to deep sky imaging in light polluted locations such as near city lights, the only option to get the faint details for imagers is narrowband. That of course renders images that are false color. I think that when balanced properly false color images look great but what if someone wants to image the same detail as narrowband but retain the natural look?

I'm trying to emulate natural color by using Halpha as red, OIII as green and Hbeta as blue... the closest I got is the image I attached which looks pale in comparison to the red associated with the Great Orion nebula.

My theory is that 656.28nm, 501nm and 485nm is closest to the (more or less) 600nm, 540nm and 450nm center frequencies of RGB except that the narrowband will reject all of the unwanted light pollution. Unfortunately a lot of wanted light is also rejected but perhaps the price paid for suburban skies.

Has anyone tried Ha OIII Hb instead of SII Ha OIII narrowband imaging?

Mariusz

[dementedgr]

Did you shoot with a Hb filter or simulated it from the Ha data? I am interested to see if there is any difference in the data!

I don't think I can help you with the colour balance, but my guess is that it is hard to retain the natural colour since, with narrowband,

you are only capturing light that is emitted while at the same time you are losing most of the light that is reflected. And in such complex

nebulae with star clusters all over the place, reflection nebulae play a significant part in the colour that you see in an RGB image...

Perhaps shoot R & B to capture reflection nebulae and add them to the mix as most light pollution lies in the G spectrum?     

I don't know, just my 0.02$... Great shot by the way, nice to see M42 in a different way! Any info on the equipment used?

[steppenwolf]

I have used Hb as the 'blue' channel with some success in the past with certain objects especially planetary nebulae and the Rosette Nebula however, I get very satisfactory results using just Ha (mapped to red) OIII (mapped to green) OIII (also mapped to blue) and find that this gives a very 'natural colouring.

That said, I LOVE the colours in your image and the sensitive processing that you have applied - there is, however, a reflection artefact that I have seen before (on an SCT) that you might wish to check out.

[MarsG76]

I agree, I knew that I'm losing too much data to retain natural look... perhaps lots of RGB short subs stacked and stretched, then the narrowband corresponding added to the R, G & B channels but only a 30-50% mix.... I need to wait for Orion to be in the sky again to try that or your suggestion with imaging R & B channels...

I imaged using a Baader Hbeta filter, and I do find a difference between the theoretical 30% intensity of Halpha to emulate hbeta.. there definitely is a difference.. I makes sense though, one is 656.28nm and the other 485nm... there has to be, it's different data.

I used a Celestron Nexstar 8SE on a CGEM mount, through a f6.3 focal reducer and a full spectrum modded Canon 40D. Guider was a Celestron NexGuide unit.
 

I prefer to use low sensitivity setting, ISO400 max and long subs, mostly 30 minute subs. I expose shorter only if there is a overexposed part and need to tone it down a bit. I find that this combination gives me the best results over shorter subs and higher gain (ISO).
 

[MarsG76]

I have used Hb as the 'blue' channel with some success in the past with certain objects especially planetary nebulae and the Rosette Nebula however, I get very satisfactory results using just Ha (mapped to red) OIII (mapped to green) OIII (also mapped to blue) and find that this gives a very 'natural colouring.

That said, I LOVE the colours in your image and the sensitive processing that you have applied - there is, however, a reflection artefact that I have seen before (on an SCT) that you might wish to check out.

OIII in green and blue?? interesting.. worth a try....

I think that reflection is caused by a bright star not far out of the field of view... the long subs I take just amplifies the effect..... It does make sense that the phenomenon is a SCT  related occurence since I'm sure the corrector plate refracts the light (especially on bright point of light) to a certain degree.. also seeing that the "loops" are different sizes/position in each filter since each frequency of light would refract slightly differently.

[dementedgr]

Well technically Ha & Hb comes from the same data, as a hydrogen cloud is a hydrogen cloud even though it might emit in different parts of the spectrum from different ioniziation processes.

What I am most interested in is if there are any differences in it's brightness in some parts of the cloud i.e. some parts emit more in the Ha region and others in the Hb region...

I don't know, maybe a comparison between the subs can answer my question... Or a (brightness balanced Ha/Hb)  Hb(B)Ha® and a synthetic G can show something?

Or perhaps subtracting x% Ha from the Hb sub? I honestly have no idea, just throwing stuff out!   

It is just that most would be like "Hb is a waste of time, its the same as Ha", however, I 've never really seen a comparison between them to trust that premise...

PS: I hope my scientific curiosity is not taken as hijacking your thread, it's just that Hb rarely shows up! 

[MarsG76]

Well technically Ha & Hb comes from the same data, as a hydrogen cloud is a hydrogen cloud even though it might emit in different parts of the spectrum from different ioniziation processes.

What I am most interested in is if there are any differences in it's brightness in some parts of the cloud i.e. some parts emit more in the Ha region and others in the Hb region...

I don't know, maybe a comparison between the subs can answer my question... Or a (brightness balanced Ha/Hb)  Hb(B)Ha® and a synthetic G can show something?

Or perhaps subtracting x% Ha from the Hb sub? I honestly have no idea, just throwing stuff out!   

It is just that most would be like "Hb is a waste of time, its the same as Ha", however, I 've never really seen a comparison between them to trust that premise...

PS: I hope my scientific curiosity is not taken as hijacking your thread, it's just that Hb rarely shows up! 

You know, I might just do that with my Ha & Hb data next time I'm infront of my PC. I'll combine the comparison pics and post here. Results will be interesting, might reveal that either the majority opinion of it being the same as halpha is correct or open a new door to narrowband imaging.

It's true that Hb is rarely used in imaging, I imagine it's because it's not a popular filter, advertised as only useful on a few objects and quite expensive.

[buikimaging]

Wow, I do like the looks of that indeed, taken with a canon I see?

I'm thinking of the same; doing narrowband with a modded DSLR, I'll have a Sony Alpha to do it with. And maybe I'll need to use the Quattro to get the same detail for the NB images instead of using the 80 ED.

Great example you have there and will certainly be on the guidelines for my images in the future.

I'm interested to see the how the beta and alpha data correspond to each other.

Keep up the good work!

[MarsG76]

Wow, I do like the looks of that indeed, taken with a canon I see?

I'm thinking of the same; doing narrowband with a modded DSLR, I'll have a Sony Alpha to do it with. And maybe I'll need to use the Quattro to get the same detail for the NB images instead of using the 80 ED.

Great example you have there and will certainly be on the guidelines for my images in the future.

I'm interested to see the how the beta and alpha data correspond to each other.

Keep up the good work!

Thanks for the feedback. You'll find a pleasant surprise with the results a DSLR will produce. Even a 80mm refractor is more than good enough to image NB with a DSLR, I done a couple and I'm happy with my result.

The only thing is to get best detail vs noise subs you will need to image at lowish ISO/gain and long exposures, in the order of 30-45 minutes... Especially SII. Generally I do Halpha/OIII 15-30 mins at ISO200-400 and SII 30-45mins at ISO800 for the best balance. OIII needs moonless skies for best result but I imaged Ha and SII during full moon and it was fine as long as the moon is not close to the object imaged.

[buikimaging]

Thanks for the feedback. You'll find a pleasant surprise with the results a DSLR will produce. Even a 80mm refractor is more than good enough to image NB with a DSLR, I done a couple and I'm happy with my result.

The only thing is to get best detail vs noise subs you will need to image at lowish ISO/gain and long exposures, in the order of 30-45 minutes... Especially SII. Generally I do Halpha/OIII 15-30 mins at ISO200-400 and SII 30-45mins at ISO800 for the best balance. OIII needs moonless skies for best result but I imaged Ha and SII during full moon and it was fine as long as the moon is not close to the object imaged.

I don't know if I can manage those exposures with the Sony, its quite noisy in 2,5 minute subs already so I will definitely need to get into cooling! But that's another challenge to achieve maybe I will contact my old physics teacher to help me with adding cooling to it with peltiers and adding incandescent satchels to keep it all moist free!

Anywho, this image will remain one of my goals to achieve with a DSLR.

[MarsG76]

On 20/07/2015 at 05:31, buikimaging said:

I don't know if I can manage those exposures with the Sony, its quite noisy in 2,5 minute subs already so I will definitely need to get into cooling! But that's another challenge to achieve maybe I will contact my old physics teacher to help me with adding cooling to it with peltiers and adding incandescent satchels to keep it all moist free!

Anywho, this image will remain one of my goals to achieve with a DSLR.

How did you go with your imaging? Did you image the Orion Nebula? Did you cool your SONY or get a cooled CCD?

Im attempting to cool my 40D with some successes and failures but feel like it's moving slowly in the right direction..

 

 

[Ruud]

You used such a beautiful pallet of colours . It's amazing how warm and rich it is.

Wonderful.

[buikimaging]

On 11/01/2019 at 01:55, MarsG76 said:

How did you go with your imaging? Did you image the Orion Nebula? Did you cool your SONY or get a cooled CCD?

Im attempting to cool my 40D with some successes and failures but feel like it's moving slowly in the right direction..

 

 

Sorry for the very very late response, I've not been on this forum the past 3 years. 

In the end I ended up getting a ZWO asi 1600mm-c with LRGB and Narrowband filters which I'm still rocking. Together with a takahashi FS-60CB (still need to work out some spacing issues because takahashi doesn't like off brand adapters) 

The Sony hasn't seen light since 2015 I think, has since been replaced with a Nikon D750 and 24-70 F2.8 Tamron. An adapter is underway to get the ZWO on the Nikon lens.