Ha with a DSLR (Non Modded)

[blinky]

The more I think about modded camera's the more I cannot figure out why it is necessary Surely Ha light is visible to the hunan eye, therfor surely there must be 'things' that are Ha coloured....say a nice red jumper! Anyway if you took a picture of said Ha coloured jumper it would turn out red in the image, yes?

So......I read the canons are not sensitive to Ha BUT I assume this is compensated for in the colour balance setting of the camera SO why mod them

[SteveL]

because non-modded Canons only allow 25% of the Ha wavelength through the filter to the sensor.

http://www.12dstring.me.uk/350dmod.htm

Its not that the CCD isnt sensitve to it, its the filter that is installed that filters so much of it out

[blinky]

Yeah but as I was saying if you had a jumper on that was Ha coloured and took a picture if it then it would look natural. I assume that although the sensor only gets 20% of the light that it is compensated for somehow? I dont think I am explaining this right!

What I mean is that something completly Ha coloured would produce a normal picture not a 20% bright picture, you know where I am coming from?

[SteveL]

Isnt that what custom white balance is for?

[blinky]

Arrgggggg!! I cannot explain what I mean!

OK I have a jumper that is the same colour as Ha Light. If you take a picure of me wearing it then the picture will look fine. The red jumper wont be really faint or anything. The camera knows it is getting less light at this wavelenght and the white balance is already compensating for it. Am I making any more sense?

[SteveL]

wouldnt it actually be better to get 100% of the available Ha recorded by the CCD, rather than the 25% being digitally altered and increased by the white balance? (and in the process, introducing noise?)

[blinky]

:scratch: Yeah I suppose :? Seems like a silly question now :oops:

[Kai]

Or another way to think about it would mean that you would have to dramatically increase your exposures to bring detail to a image , compared to a modded sensor.

[Jamie]

Hi Craig.

Can you please please show us this jumper of yours. (must be out of this world)

Sorry I;ll get me coat.....

[Kai]

:laughing3: :laughing3: :laughing3: :laughing3:

Makes him sound like Joseph

[SteveL]

Makes him sound like Joseph

Joseph and his Hubble Pallette dreamcoat

[Kai]

Very Astro

[blinky]

right lets put this down to a moment of madness :oops: :oops: :oops:

[kev 102 42]

if i thought of this,id ask for it to be deleted ..kev

[dph1nm]

Actually the human eye is not very good at H-alpha either. The response has fallen to about 10% of its peak value by 6500 Angstroms. So your average unmodded camera is probably a good match!

NigelM

[blinky]

That was kind of what I was saying, the response must match the human eye and we can see Ha but as we dont have much sensitivity either I can see why you would mod it.

Still cannot afford it though....

[Sam]

I've got a question related to this:

When you record Ha on a CCD and then produce the image on the screen, the original Ha is then represented in a red colour that the human eye can see, is that right??? My monitor doesn't blast Ha into my eyeball does it??? So if I got in my space ship and flew to the Rosette Nebulae I wouldn't see the lovely red gas clouds, or would I?

Sam

[barkis]

Probably look Green Sam. I'm sure Hydrogen is green to the eye. Maybe wrong, I just recall reading this somewhere. I have seen a greenish hue in the Orion Neb. in a large Newt.

Ron.

[Sam]

Probably look Green Sam. I'm sure Hydrogen is green to the eye. Maybe wrong, I just recall reading this somewhere. I have seen a greenish hue in the Orion Neb. in a large Newt.

Ron.

I think you are right Ron, Orion Neb looks green in my 16".

[Keagle]

I've got a question related to this:

When you record Ha on a CCD and then produce the image on the screen, the original Ha is then represented in a red colour that the human eye can see, is that right??? My monitor doesn't blast Ha into my eyeball does it??? So if I got in my space ship and flew to the Rosette Nebulae I wouldn't see the lovely red gas clouds, or would I?

Sam

I thought it was caused by an electon in an Ha atom gets given energy and jumps up to the next orbital, but then falls back down and releases this energy back and this energy is emitted as light, at a certain wavelength and we just associate that wavelength as Ha?

So it is light you are seeing. Not Hydrogen Atoms beamed into your eyes.

Kurt

[Sam]

I've got a question related to this:

When you record Ha on a CCD and then produce the image on the screen, the original Ha is then represented in a red colour that the human eye can see, is that right??? My monitor doesn't blast Ha into my eyeball does it??? So if I got in my space ship and flew to the Rosette Nebulae I wouldn't see the lovely red gas clouds, or would I?

Sam

I thought it was caused by an electon in an Ha atom gets given energy and jumps up to the next orbital, but then falls back down and releases this energy back and this energy is emitted as light, at a certain wavelength and we just associate that wavelength as Ha?

So it is light you are seeing. Not Hydrogen Atoms beamed into your eyes.

Kurt

I realised it wasn't H atoms flying into my eyeball, I need to type clearer, but the the light at that particular frequency - caused by what you said.

[SteveL]

Hydrogen Alpha is Red

Sulpher II is also red

Oxygen III is green

As the human eye is far more senstive to green, its easier to see visually. The eye is least sensitive to red... why do you think you are using red screen covers and red torches, eh?

[narrowbandpaul]

the green will be a mix of Hbeta...n=4 to n=2 (vs n=3 to n=2 for Ha), and O[iII] which id green at 500.7nm

The green seen from m42 isd in no way attributable to Ha emission...Hbeta yes O[iII] yes, but Ha is red

Like craigs jumper!

Hope that helps

Paul

[dph1nm]

Just for fun, I asked my psychologist friend about this, and it turns out the colour response of the eye is all Very Complicated. Apparently the three colour cones all overlap in response, so H-alpha is likely to trigger a green response at some level and maybe even blue! Then some fancy differencing goes on in the brain to decide what colour you actually see. One consequence of all this is that if you do an experiment to illuminate just an individual red cone (which is possible, apparantly) you do not see red.

NigelM

[themos]

I think colour response of the eye would be pretty straightforward, but colour perception is where it gets complicated.