Colours in different scopes

[MattJenko]

I have just come back from a very pleasant evening at an observatory where I got the chance to use my little reflecting scope and compare it to much bigger scopes. I did notice that the large SCT scope there did not seen to show the colours of the stars as clearly as my much smaller reflector. Is this generally the case that for observing, reflectors highlight the colour more than SCTs, or is this just something to do with the setups of the scopes on this particular night?

[cutepetgroomer]

I have noticed that different telescopes on one night will show things differently . my 50mm scope doesn't show planets as brightly as say my 70mm scope does but I have noticed they are on same show of color just the brightness varies. 

[Pondus]

Maybe some stars in large telescopes get so bright that the colors get hard to see? washed out?

[ronin]

Tend to agree with Pondus, the bigger scope will collect more light and eventually it just becomes "white".

[MattJenko]

The more light  = whiter light theory sounds extremely plausible to me - thanks. Raises the interesting question about using the right power of scope to look at particular objects - ie bigger aperture for dimmer objects, less light gathering scopes for brighter object. Implies that bigger is not always better, which is nice.

[brantuk]

Yup - larger apertures will let you see fainter, more distant objects - so you can peer deeper into space. But you do have to compare the magnification and fov too - not just the aperture. Higher mag often results in a dimmer more grainy view - even of bright objects like planets - but a narrower field of view. It also depends on the prevailing conditions and type of scope used. A smaller but more contrasty, clear, low power view can be better than a larger, dimmer, high mag view.

[ronin]

I suspect that it is how the eye works. The eye tends to scan so even when you look at something the images is actually all ove the place so assorted rod and cones get splattered with light. Also in actual fact actually the eye/brain uses only a small amount of information, the brain literally makes the rest up. Think along the lines of "Stars are white points of light in the night sky" so the brain translates them into white points in the sky.

I recall seeing some "old" sky images taken on 35mm colour film, there were (appeared to be) a lot more coloured stars in the final result then I can see by eye today and it is the same stars and the same colour.

[MattJenko]

Indeed - especially at low light, the colour receptors in the eye (cones) simply don't fire as much as the rods as there are not as many of them, so things appear more monochrome. Also the light from stars varies across the spectrum in 10:1 ratios in most cases which still means a full range (white) light from what I have read (Handbook of Astronomical Image Processing).