Stacking visual RGB filters?!

[Kronos831]

Probably a stupid question...

Heyyy soo i am a begginer and about to buy my first telescope.A Skywatcher 200 

p. I ve just though of something , Since i know filters can be stacked i ve been wondering if i could take visual RGB filters and stack them.Specifically blue green and red in order to create a visual full colour image ,like photography. I know its probably a stupid question because people all over the world would have done this by now .But i m just curious. 

 

-Kronos

[Demonperformer]

Hi Kronos and welcome to SGL.

Nice first scope, you will see a lot with it.

Not a stupid question at all. (The only stupid question is the one you don't ask)

The way you do this is to take a monochrome image with each of the filters and then combine them in a program like Photoshop. If AP is where your passion lies, do yourself a favour and get yourself a copy of this book. It will save you time, trouble and heartache in the longrun.

Enjoy the journey.

[Kronos831]

First of all , thanks! Second of all i am talking about visual rgb filters i want to stack them in they eyepiece so i can get a full colour image(visually) it's probably not possible i just want to know why.I ll take a look at the book too thanks! Also whats the difference between getting rgb filters for photography and just processing the image in photoshop?

Thanks

 

-Kronos

[Cornelius Varley]

Just now, Kronos831 said:

First of all , thanks! Second of all i am talking about visual rgb filters i want to stack them in they eyepiece so i can get a full colour image(visually) it's probably not possible i just want to know why.I ll take a look at the book too thanks! Also whats the difference between getting rgb filters for photography and just processing the image in photoshop?

Thanks

 

-Kronos

What you are proposing won't work. Each colour filter blocks the other two colours so no light will reach he eyepiece if all three are stacked together. RGB imaging creates a colour image from three separate monochrome image files, one through the red filter, one through the blue and one through the green.  The monochrome images can then be combined in photoshop to create a colour image.

[Demonperformer]

Sorry, misunderstood what you were asking.

No that would not work. Each of the filters (red green & blue) only allow light of that colour through, blocking the other colours. So by the time you had stacked all three in the eyepiece, you would be blocking light in all three colours and would see nothing.

When you take a photograph with RGB filters, you take three photos of the same object, one with each filter, using a monochrome camera. You  now have three black and white photos, but to regain the colour, you need to combine them into one photo. Photoshop has "channels" for each colour, so you load the image taken with the red filter into the red channel and similarly with green and blue. When you combine them, this gives you the colour image.

The alternative for getting a colour image is to use a colour camera, when you don't need to use filters. There are advantages and disadvantages to each option.

[Demonperformer]

Just beat me to it, Peter, but at least we are both saying the same thing ?

[MarsG76]

That won't work either visual of photography since RGB Filters can only be used effectively one at a time. Each filter will block the light outside the actual color being transmitted, so by using all filters stacked you will get very little transmission of anything (in theory in a perfect world it would block every wavelength).

The difference between visual and photography filters is that the photography filters block all NIR wavelengths.

 

[Kronos831]

Good to know,and thank you for your fast replies guys!

[vlaiv]

Like pointed out, red, green and blue filters combined will cut out all light.

Reason why we see shades of gray and not color image when observing is not the same as with black and white photography (and use of filters to get color). We see black and white when observing is because light from nebulae and galaxies is very very dim, and it excites only cells in our eye responsible for "black and white" image and not color cells - not enough light to excite those cells. You might want to look up that on internet - there are two different type of receptor cells in eye called rod and cone cells and they work differently. So no amount of filtering will help there, but what will help is large telescope. Very large telescope . Some people reported seeing color in some nebulae when using 16 inch and above telescopes if nebula is strong.

[dannybgoode]

The other issue is that much of the detail you see in photographs of nebula etc consists of imaging very specific wavelengths that we cannot see with the naked eye and combining them with the colour data from the RGB frames that are captured.

Specialist astro cameras can 'see' well in to the infrared and ultraviolet parts of the spectrum which our eyes sadly cannot do so sadly there is not a way of seeing the detail and colour that you see in some of the outstanding images on here  

[Kronos831]

Yeah i know our eyes are more sensitive to grey-ish lights and am very aware that we cannot simply see  colorfull views with a telescope (dsos atleast)  i just wandered why i couldnt combine 3 filters to make a colorful image. That’s it

 

 

kronos