A basic question about colour ...

[kev100]

Hiya. Although I've stayed away from imaging, and concentrated on visual observing, I have to say, I have felt the lure of the imaging side of things. It is a tantalising and somewhat mysterious practice, arcane even.

Anyway, last night I thought I'd just stick my 400D on a tripod, point it up and see what happened. I took a few single shots (8 second exposures, 1600 ISO) of the double cluster in Perseus (it happened to be directly opposite our front door). When I had a look this morning I was amazed to see so much colour! Visually, most stars look white, at least through my 10 inch dob.

I know the experience of colour is a subjective thing, but is this what the stars would look like if we only had the eyes to see?

Cheers,

Kev.

Sent from my iPad using Tapatalk

[michael.h.f.wilkinson]

At night the colour-sensitive cones in the retina largely shut down. Only the brightest objects aver show colour. If our cones were as sensitve as rods, we would see much more colour

[kev100]

Ah, the image didn't attach. Here it is:

https://www.dropbox.com/s/o8b9ilswe43th9o/Double%20cluster%20Lo_res.jpg?dl=0

[kev100]

Hi Michael,

Thanks. I'm used to seeing pretty much everything in black and white (with just a few exceptions), but I was amazed at how much colour the camera seemed to pick up. Just wondered really if the pic is at all 'accurate', or is it inserting colour in some way.

Kev.

[kev100]

It might not be too apparent in the low res pic I uploaded, but there's yellows, blues, purples, oranges, reds ... 

[glowingturnip]

yep, the colours really are there !  I think there's a tendency in processing of astrophotos to not bring out enough colour, because we anthropomorphise what the camera is showing - because the eyeball can't see it, the camera must have got it wrong, whereas it's actually the other way round.

Imagine what the night sky would like like if you had colour-sensitive dark vision - are there animals who have that ?

[ollypenrice]

On a course some years ago we were asked to rank a list of bright stars in order of spectral type (essentially colour along the spectrum from red to blue.) It was, in fact, prefectly possible to do this and get it pretty much right. The trick is to compare one with another by going back and forth. This was naked eye.

In a scope it can help to see colour if you make the tube vibrate or go slightly out of focus. The obvious star to try this out on is the double, Albireo. Beautiful!

CCD cameras do better than DSLRs on star colour because the greater well depth helps to avoid saturating the cores and burning them to white. Keeping exposure times down helps rather than hinders star colour.

Olly

[Dave Lloyd]

Plus the fact your eyes see in real time. They are unable to build up an image as film or sensor can.

[kev100]

Hiya. I have seen coloured stars, Alberio being an obvious one. Antares, betelguese, etc, but I was totally amazed to see so much colour in an area that, when viewed with the scope or binoculars, appears just white, or bluish white.

In all the images I've seen, the stars tend to me mostly white, too.

I thought my camera was throwing in artifacts, but its good to know the colours are actually there. It's amazing!

[Nathan_Pembs]

To keep stars colour you keep the exposure length down, but if you're imaging something faint like a galaxy then surely you need the longer exposures?

Seems like you can't do right for doing wrong lol