planetary colour

Any tips for improving visual observation of planetary colour?
I'm using a 222mm reflector which I have finally adjusted to give some
crisp images of Mars, Saturn and now Jupiter. Unfortunately they are
very bright and although I can resolve some surface features they are
basically B/W images. Same problem for nebulae.

Mark

"Mark Parrish" wrote in message
...
Any tips for improving visual observation of planetary colour?
I'm using a 222mm reflector which I have finally adjusted to give some
crisp images of Mars, Saturn and now Jupiter. Unfortunately they are
very bright and although I can resolve some surface features they are
basically B/W images. Same problem for nebulae.

Do telescopes have something similar to a polarising filter? I'm more used
to cameras than scopes and I always use a polarising filter in bright
sunlight to cut down on the glare from reflective objects nearby. Using it
when I've been skiing has allowed me to get deep blue skies and real detail
on the snow without the glare and light saturation I'd get without it. But
also, it doesn't affect the colour of the object your photographing. It just
blocks excessive light.

What filters, if any, can you get for scopes?

"Mark Parrish" wrote in message
...
Any tips for improving visual observation of planetary colour?
I'm using a 222mm reflector which I have finally adjusted to give some
crisp images of Mars, Saturn and now Jupiter. Unfortunately they are
very bright and although I can resolve some surface features they are
basically B/W images. Same problem for nebulae.

Hi Mark,

Have you tried using colour filters to view the planets? - Certain filters
are good at bringing out features on the surface and in the rings.

As regards nebulae - Most will look like grey smudges to the human eye. The
nice colourful pictures you see are normally long exposure photographs which
can detect the colour. Our eyes aren't built like that! You might detect
faint hints of colour, but nothing like the blaze of colour you see in many
photographs.

John.

Mark Parrish wrote in message . ..
Any tips for improving visual observation of planetary colour?
I'm using a 222mm reflector which I have finally adjusted to give some
crisp images of Mars, Saturn and now Jupiter. Unfortunately they are
very bright and although I can resolve some surface features they are
basically B/W images. Same problem for nebulae.

Mark

The planets are brighter at lower magnifications. Once you get above
150x the brightness tends to fall off in average apertures. At 240x in
my 6" refractor Saturn and Mars are very comfortable though the full
moon was still bright. The trouble is getting the fine seeing
conditions to push magnification that high.
Use ND (neutrel density) filters to maintain reasonably accurate
colour rendition while reducing brightness. These can be stacked if
necessary simply by being screwed into each other then into the
eyepiece thread.
Seeing colour in DSOs (Deep Sky Objects:Galaxies, nebulae etc) at
low light levels is not possible with the human eye because different
receptors in the retina are used for sensitivity and colour. (Rods and
cones)

Chris.B

http://hyperphysics.phy-astr.gsu.edu...n/rodcone.html

Schneck wrote:
[...]
Do telescopes have something similar to a polarising filter? I'm more used
to cameras than scopes and I always use a polarising filter in bright
sunlight to cut down on the glare from reflective objects nearby. Using it
when I've been skiing has allowed me to get deep blue skies and real detail
on the snow without the glare and light saturation I'd get without it. But
also, it doesn't affect the colour of the object your photographing. It just
blocks excessive light.

A polarising filter does not simply block excessive light (how would it
know which light was excessive?). To attenuate excessive light one
reduces aperture or exposure time or both. A polarising filter
attenuates light that is polarised in one direction more than it does
the light that is polarised in a direction perpendicular to the first
direction. It is useful because of the manner in which light is
polarised by reflection but if it is orientated to (say) attenuate light
reflected from snow-covered ground, it will be sensibly ineffective
against light reflected from (say) the vertical glass of a building.
Look through one and rotate it to see what I mean.

AIUI, the light from a planet is not selectively polarised except
possibly in its crescent phase (has anyone tried this?), so a polarising
filter would not be useful as a polariser, although it would have some
value as an ND filter.

What filters, if any, can you get for scopes?

ND filters
Colour filters
LPR filters (including "deep sky" filters)
Line filters (usually O-III and H-beta for nebulae; H-alpha)
Variable filters
Solar filters (e.g. Baader)


For more details, see the FAQ.


Best,
Stephen

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Forgot about minus violet filters.

(If I forgot any others, someone else will probably fill the gaps)

Best,
Stephen

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On 18 Dec 2003 01:06:22 -0800, (Chris.B) wrote:



The planets are brighter at lower magnifications. Once you get above
150x the brightness tends to fall off in average apertures. At 240x in
my 6" refractor Saturn and Mars are very comfortable though the full
moon was still bright. The trouble is getting the fine seeing
conditions to push magnification that high.
Use ND (neutrel density) filters to maintain reasonably accurate
colour rendition while reducing brightness. These can be stacked if
necessary simply by being screwed into each other then into the
eyepiece thread.
Seeing colour in DSOs (Deep Sky Objects:Galaxies, nebulae etc) at
low light levels is not possible with the human eye because different
receptors in the retina are used for sensitivity and colour. (Rods and
cones)

Chris.B

http://hyperphysics.phy-astr.gsu.edu...n/rodcone.html

thanks for those answers. I suspected that those lovely coloured
photos in the books weren't what one would normally expect to see! I
will experiment with some filters though.

Most of the astronomy books I have seen are full of those brightly
coloured images - I guess they sell more copies that way.

I know that by the very nature of most photographic and digital
imaging techniques the captured images must be different to those seen
visually but I wonder if there are any resources that give a close
approximation to what you should resonably expect to see when using a
medium sized scope to observe typical objects?

Mark

On Fri, 19 Dec 2003 10:28:22 +0000, Mark Parrish
wrote:

http://hyperphysics.phy-astr.gsu.edu...n/rodcone.html

thanks for those answers. I suspected that those lovely coloured
photos in the books weren't what one would normally expect to see! I
will experiment with some filters though.

Most of the astronomy books I have seen are full of those brightly
coloured images - I guess they sell more copies that way.

I know that by the very nature of most photographic and digital
imaging techniques the captured images must be different to those seen
visually but I wonder if there are any resources that give a close
approximation to what you should resonably expect to see when using a
medium sized scope to observe typical objects?

Well you could look at the nice detail images in books after a heavy
pub session ;-)

Scope images tend to be pretty devoid of colour as you have
discovered. The direct view through a scope also has a quality that
you can't replicate in a photo - motion. Seeing wobbles and
defocusses/re-focusses an image so that you are not looking at a
static picture. As such your eyes and brain have to do a bit of work
on the image to get the best from it.

Therefore if you try and reproduce a visual experience in a
diagram/sketch/photo - it's pretty much impossible. Sure you can show
the sort of detail that you would see, but the dynamic nature of the
visual image is part of the experience.

I think the closest you can get is to take a small (dimensionally)
video sequence and squint at it while it plays.

--
Pete Lawrence
http://www.pbl33.co.uk
Home of the Lunar Parallax Demonstration Project

In message , Mark Parrish
writes

thanks for those answers. I suspected that those lovely coloured
photos in the books weren't what one would normally expect to see! I
will experiment with some filters though.

Most of the astronomy books I have seen are full of those brightly
coloured images - I guess they sell more copies that way.

I know that by the very nature of most photographic and digital
imaging techniques the captured images must be different to those seen
visually but I wonder if there are any resources that give a close
approximation to what you should resonably expect to see when using a
medium sized scope to observe typical objects?

The best collection of drawings I know of is in David Eicher's "The
universe from your backyard", published by Kalmbach.
Lots of sketches, mostly done with a 8 inch SCT. The photos are amateur
too, rather than from places like Palomar, though they are by the
experts such as Jack Newton.
I don't know if it's in print but it seems a common item in second-hand
bookshops and library sales.
--
Rabbit arithmetic - 1 plus 1 equals 10
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Mark Parrish wrote:
I wonder if there are any resources that give a close approximation to
what you should resonably expect to see when using a medium sized scope
to observe typical objects?

Yes. There is a Webb Society publication, written by Faith Jordan and
which deserves to be far better known, called _An Introduction to Visual
Deep-Sky Observing_. Faith's sketches are excellent and almost certainly
meet your requirements. More details at:
http://www.webbsociety.freeserve.co....alDeepSky.html

Best,
Stephen

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