Tarantula Nebula, Why Green?

[eavaria]

Hello,

I'm new here, and wanted to know something I couldn't google for...

Attached is one of the exposures I took from NGC2070, and it's completely green. I haven't done any processing. This frame is directly from the raw file (I have like 2 hours that plan to process soon), the issue is that every resource I've found on the internet says it should be seen on "normal" colors, not this glowing green, that I understand it's rare on DSOs...

The image was taken with a chinese Jintu lens at 800mm F/16, 30s exposure on a Canon SL3 using N.I.N.A. I believe on ISO 6400

It was my first time using N.I.N.A., so I thought the software did something, but yesterday I took a clear wide field (50 mm) photo of the area, and it shows clear green too...

Anyone can explain me why I see it ccompletely different than the whole Internet?

I'm in central Chile (about -34, -71)

(couldn't attach files, so here are the links to my drive)

Wide Field: Small green spot in the edge of the LMC

https://drive.google.com/file/d/1MJRl6DRvgPOgzF9jkzOkqnNFC7YvY4DJ/view?usp=sharing

Light frame: 

https://drive.google.com/file/d/1Wmd7ou1042ex1JoU_D_Vo-yxWdfpe_T7/view?usp=sharing

 

For reference, this  and this is how it should look... I have raw images if anyone want's them... 

[vlaiv]

Issue of color in astrophotography is somewhat controversial.

In this particular case - you took raw data from camera and just convert it to image, right?

Raw data from camera is not:

1. color balanced

2. color corrected

3. gamma corrected

In order to get true color from raw data from DSLR you need to perform above steps. Camera firmware does this for you when you select to shoot image as .jpg instead of raw format. You can also use Canon software to convert raw image to proper color.

Colors that you see in images online are not true colors of objects in space. There are several reasons for this:

- Most astrophotographers don't understand above color management or don't care about it

- Very often astrophotographers use modified cameras and don't adjust for color correction in those

- Some of the images are actually narrowband images where false color models are used to emphasize gas distribution rather than produce natural looking color.

- People get creative with their astrophotography and do color balance manually for artistic look rather than to produce actual color.

In the end - it is actually quite normal for nebula to be greenish in visual appearance if one wants to display true color as would be seen by humans. This is because humans are much more sensitive in green part of the spectrum than in far red. Most emission type nebulae radiate in Ha, OIII and Hb wavelengths. Ha is deep red and we are not as sensitive to it. OIII is mixture of blue and green and Hb is more to blue part of spectrum.

Here it is chromaticity diagram:

Triangle is sRGB color space (that can be shown on computer images). Outer line is spectral locus - where individual spectral colors lie in this XY diagram. Note that computer screens can't display any pure spectral color. All colors produced by combining sources of particular colors - lie within area made up from these color sources (for that reason all sRGB colors fall within triangle in this image because we use particular red, green and blue colors to synthesize them on screen). I've marked another triangle where all colors that can be made by mixing Ha, OIII and Hb wavelengths lie.

You can have any of those colors present in nebula that consists mostly out of Hydrogen and Oxygen gas. If Hydrogen beta is not strong - there won't be much blue in the image. I suspect that this rendition of tarantula is pretty good representation of true color of the object:

 

 

[eavaria]

I did some minor processing on lightroom when exporting to jpg, but indeed, the nebula is mostly green, with some blue present in the center. I believe mine matches your image way better than any other in the internet. Thanks for your answer. Will try to remove noise and try to get some natural colors . 😀

[vlaiv]

1 minute ago, eavaria said:

I believe mine matches your image way better than any other in the internet.

Just to be clear, above image is not mine - it was just image that I found in google search and I thought has good color representation of the object.

Image is found on abc.net.au domain (Which I believe is ABC network domain in Australia, right?).