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Colours why and why not?


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Hi All,

Why is it that I can see colours on planets and stars through my scope but not colours of nebulas like the orion nebula just looks gery. And how do people take coloured pics of nebulars with dslrs if colours can not be seen?

And please dont say you see grey and that is a colour LOL

Kev

Edited by Kevdan
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Our eyes can't compete with CCD's and the combination often of many hours of exposures Kev. The colors on planets and stars are subtle but we can detect those. Colours in deep space objects are much, much fainter so, with the exception of a little lime green in the Orion Nebula, our eyes just can't perceive them.

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Could I recommend the excellent thread on night vision over in the primers section?

You'll see there that in low light conditions our eyes basically work in black and white (of course you know this from your own experience). A bright planet like Jupiter seen through a telescope is bright enough to activate some of the cones in your eyes and detect colour but for nebula and the like, they just ain't bright enough (though I am sure you can detect the red tinge to Betelguese and that some stars look bluer than others so you can see colour in those bright objects as well).

DSLRs and CCDs can collect the light over a period of time and do register the colour of the light they gather...

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great Qs this was the main reson o got a camera so i could se the images in color ,but still m42 is a great view even in grey/white and black this is my fav neb i have other fav ones but this one is magical and draws me every night am out when its in view

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Here is a picture with some movement so focus not great of M42 and enhanced and sharpened slightlly using photoshop but I promise you no colour added.

Used approx 15 sec exposure at ISO 800 on a cannon 450D attached to my SW200P (prime focus method) and as you can see there is colour there

Neil

post-25092-133877554936_thumb.jpg

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Great Pic.

can I ask what lenses if any were used for this ?

Im just wondering how many people like myself were a little dissapointed when first viewing a nebula through a scope to find it wasnt as big as a billboard advert and colourless. Come on be honest thats what we all wanted to see.

Kev.

Edited by Kevdan
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Kev no lenses were used. I used a ring adapter to attach the camera to the scope and set varying exposures between 8 and 20 secs. Used ISO 800 set on the camera. I had a remote trigger to avoid moving the scope but there are problems in the photo (i.e. star trails) which may be down to a) poor polar alignment :D scope to heavy for mount (eq5 synscan) and not balanced correctly with camera on. I will be trying out various changes in the future to rectify these.

Checked what I thought was a "reasonable" pictue and using photoshop adjusted brightness and contrast plus fiddled a bit with the "Unsharp Mask". Honestly that was all the processing that was done

Neil

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Most imagers do try very hard to achieve 'true' colour in thier normal RGB (red/gree/blue) images. We use these three filters to simulate the colour view our eyes detect in the daytime. Digital cameras work in this way, each light sensing pixel being covered by a red, green or blue filter with software to calculate the final blend.

However, what we also do is add layers taken in narrowband filters. These are highly selective. H alpha is a deep red, Oxygen111 is green, etc. They are good because they isolate particular features in a nebula and improve contrast, so showing structure that would normally be hard to see. This does change the colour but we try to keep it as close as possible to the pre-narrowband.

Then there are false colour images in which narrowband filters are combined in an artificial way known as colour mapping. This is always declared by the imager so you know what you are looking at.

Have a glance at this pair of images. First you see this bit of sky in a natural RGB image. Nothing there! Next to it a layer in an Ha filter is added and you can see the remains of an ancient supernova explosion spanning about three degrees of sky. That is the beauty of narrowband.

Olly

(Ex teacher trying to make up for earlier disappointments!!!)

1182344610_T6hNK-XL.jpg

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...Im just wondering how many people like myself were a little dissapointed when first viewing a nebula through a scope to find it wasnt as big as a billboard advert and colourless. Come on be honest thats what we all wanted to see.

Kev.

I was "bought up" on the Observers Book of Astronomy and such like - the majority of astro photos were black and white back then - CCD's etc had not been invented !.

So I had no expectation of colour in DSO's in fact I was suprised that my little 60 refractor could show any Messier objects at all :)

I guess, like in many things, later generations have higher expectations :D

Edited by John
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hi neil i am impressed you never got no trails with this 15 sc pic is the 200p goto ?what filters did you use and how did you avoid trails at 15secs is the scope a goto ? i have a 300p and any thing over 3/4 secs big trails so whats ya secret heres my rubbish attepmt at 3 secs

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hi kev did ya do any research befor ya brought ya scope or did ya see the glossy long expo pics or hubbles ?the grey black and white image is still mind blowing for me ? enjoy the view theres lots to see

I did see pics of the planets through a 150x750 scope and saw some good colour even though small planets, I just never gave it a thought that colour may not be there, Even though I still agree that the detail is more important than the colour, but both is prettier.

Kev

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Todd8137

No filters were used. This just happens to be an image where the trails did not appear as I had loads where there were trails. I used an eq5 Synscan mount which I believe is near the loading limit for the 200P. I believe to reduce the trails I will have to accurately polar align and balance the scope with the camera attached. I got hold of the WCS software (type of drift compensation I believe) to help with polar alignment 2 days ago but have not had any clear nights to try it out.

Your 3 sec doesnt look bad. I can assure you I had a lot of exposures that were rubbish with 1/4 " trails.

Neil

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thanks kev ,i have a goto to but nothing like your mount just the standard meade type i have the 300p which as the standard base i would love to some how get that mototrised but not sure but the battle for me goes on, a think the only way for me is wither to layer the pics up in Corel (10x 3secs) or try deep sky stacker cheers pat

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  • 3 months later...

I wondered about this myself. I built a 8" f8 newt in the early 80s and bought 8 and 15mm RKE Edmonds Scientific eye pieces. I lived in a neighborhood with sodium streetlights yet colors in M42 were bright. Since that time I have bought a 10" F10 Meade SCT and a Orion 120 ST. Neither of them allow me to see colors in M42 using TMB 6,9mm nor my Meade super plossels. Too many elements? Could the RKE's have been that good? M42 growing dimmer?:) I must admit that I was using 30years younger eyes.

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