View Full Version here: : astrophotography and how we see it
03-05-2012, 12:24 PM
(sorry about the first person preample to the question)
recently i was looking at some solar imaging done with a lunt and was struck by the fascinatingly subtle differences between the lunt image and what i see through the eyepiece of my pst having had it for about a year now and developed an appreciation of the finer optical details available (to my eye) as seeing oscillates.
so i made a enthusied comment to the person who had posted the image and just after that remembered having had an identical feeling about a book i had read several nights before. the book is quite old (medieval) and written in another language.
so the way i was reading it was by comparing a number of various translations as a way of trying to get my head around it
the process and the feeling was identical to the way i saw/responded to the solar images, so i immediately wondered if i was "seeing" through the same mental synapses/processes as i had been using to study the book.
i have often wondered, looking at astrophotography to what extent the objects viewed are actually out there.
would at any point as you drew closer to a astronomical object such as a spiral galaxy would it look like the spectacluar images we see.
the question isn't about authenticity, its more a philosphical curiousity to know where they actually are.
what is out there, what is in the computer processing and what is us at that moment looking inwardly at our capacity to comprehend (among other factors).
is the distinction definable?
science or poetry they are still great
i just laughed to myself when realizing this question is an extension of what the story in the book was pointing to,
needless to say i found it pretty absorbing.
03-05-2012, 01:18 PM
Colin you are quite correct.
Our senses are limited by their physical reality. For example colour does not exist! It is merely the ratio of three different sensing molecules in your eye's cones that are sensitive to different wavelengths that enable the brain to synthesise the sensation of colour.
Other species have up to and more than five 'colour' receptors.
Your brain is a superb computer working in real time to extract all the available information of what you see. From the very dim scene of the proverbial black cat in a coal mine to the bright Sun drenched savanna. The large bit at the back of your head contains the very large part of your brain that does this processing in real time. The conjecture is that even Fourier enhancement is going on in real time as the resolving power of your eyes lens and photoreceptors is far poorer than what you sense.
Modern digital cameras have an advantage our eyesight does not, and that is a long integration time. This of course loses temporal information. Our eyes and brain are exquisitely tuned for the slightest movement. It is this difference that has evolved over many millions of years between having a dinner and being dinner!
Our visual senses have also evolved with a limited spectral sensitivity as our atmosphere blocks both short and long wavelengths.
Stars and thus galaxies etc emit a far larger range of EM radiation and high energy particles. That is why one mob of smart apes on a tiny third rock from a nondescript star are still inventing better detectors than their eyes.
How to present this data is matter for argument amongst ourselves. There is no 'correct' method. Just specify the conditions.
03-05-2012, 02:02 PM
Bert, that is an interesting point that colours don't exist.
But as far as what we'd see if we approach a galaxy, I think that's limited to "how" we see. We either look at the object with our eyes or use sensitive cameras to look at the same object and since both methods use our eyes, I think its safe to say that astrophotography images are a close enough representation of what's visually there, with variations in sensitivity / colour interpretation.
when we're looking at the light from a galaxy that left millions of years ago, its pretty much an extension of that galaxy and would be the same if we were to use the same camera in a spacecraft close to the galaxy millions of years ago.
I've always wondered about post processing AP images and how we tweak colours to achieve a pleasant or "correct" colour interpretation, but if our OSC cameras are correctly designed, do we really need to correct colour that much?
Its like audio amplifiers, you could have a 25 band graphic equalizer to adjust various frequencies, but the professional ones don't use tone controls and are designed to have a flat response at all frequencies and that delivers a natural output.
Only difference is that our ears are less sensitive to the lows and highs and that's why you'll see the graphic equalizer sliders adjusted to a "U", where the lows and highs are amplified relative to mids for our ears.
again, modifying the signal to suit our ears.
03-05-2012, 02:18 PM
The reality is that our eyes have a huge dynamic range from starlight bathed scenes to Sunlight. It is almost impossible to portray this realistically with 8 bit or even 16 bit depth.
The aim of astrophotography is to try and convey information about the object. Stars record in less than a few seconds. Dim emission nebulae and reflection nebulae and illuminated dust can take many minutes. Dust in front of stars or emission nebulae is just very dark.
03-05-2012, 02:29 PM
Very interesting concept put forward.
For me using a Mono plus filter CCD, i love seeing the differences in the data before i push the image together. blinking though you see the different wave lengths, but in black and white.
At the end of the day astrophotography (the pretty pictures variant) is nothing more than technical art. I use it to record what I see so i can show friends and loved ones the wonders of what is out there.
Astronomy should be for everybody not just somebody with good equipment and the time to go out. :)
03-05-2012, 03:11 PM
There are a number of web pages about the perception and reality of colour in astro images.
I was having this discussion the other day on another forum where people debated that as I could see green in an image they said it was my monitor. Although the green was apparent on three different monitors I used to view the image.
I argued that this was not the case but my eyes are green channel dominant
Anyone who's had an eye test will remember the red/green screens and which appeared more clearer to you.
Colour perception in an image is in the eye of the beholder, and much of what we do in astro photography, as Brendan stated is art
03-05-2012, 03:17 PM
What book were you reading? Not Montaillou, by any chance?
03-05-2012, 05:10 PM
no but close....
03-05-2012, 05:26 PM
Montaillou did my head in.
I think it may have been the fact the footnotes took up 80% of the page. :)
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