Re: M27 and filters: It's the colors, Dumbbell!


You confirm what I've suspected. I think that if one could travel in light years most objects would appear grey much like the moon except for those objects that emit wavelengths of light in the [hence] visable spectrum. You mentioned the Andromeda Galaxy and I have long thought the photos were very heavily processed. I had not considered its dynamic range was beyond human vision or how that is possible for those wavelenghts within human comprehension. -Best, Robert

On 08/04/2022 8:32 PM W Hilmo <y.groups@...> wrote:

On 8/4/22 4:21 PM, ROBERT WYNNE wrote:
...I don't know if the image I've captured is what the image would realistically appear in space to the human eye. The moon and planets are straightforward but DSO is entirely another matter.-Best, Robert

No processed deep sky image shows how the object would realistically appear in space to the human eye.  The human eye simply doesn't capture the really faint stuff very well.  Getting closer to another galaxy, for example, would not make it brighter, and it would not reveal color to the naked eye.  For a demonstration of this, consider the Milky Way.  We are inside of it, yet it only appears as a faint, grey band across the sky.  The Andromeda Galaxy is another good example.  Even if you got closer to it, it would mostly look like it does from a super dark site with very transparent skies.

It's reasonable to process deep sky images in a way that is "true to the data".  By that, I mean that it is possible to calibrate the colors so that they match the photons that the sensor picked up.  For narrow band, it's possible to map the data to the RGB channels to reproduce their "proper" color.  I actually try to do that with my images, but the colors just don't pop the way that they do if I exercise some artistic license.

The other thing that we do in processing that is very different from what the naked eye would see is how we stretch the brightness. The dynamic range of many deep sky targets is huge.  Your eyes are much better than a computer monitor at handling this, but in most cases, your eye would not be capable of managing the full dynamic range.  If the faintest parts of a galaxy's spiral arms were somehow bright enough to be visible to the naked eye, the core would be painfully bright.

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