Light amplification... or something

[davidhorman]

I was thinking about telescopes and cameras the other day (I own at least two of each) and I got thinking about how much light pollution we have. I've only been able to really pick out the Milky Way on a few occasions, and only once was it exceptionally clear.

Then I got to thinking... could you build an arrangement of lenses and such (all optical, no electronics) that could collect light from a wider area and then present it to the eye so you'd see the same field of view, but much brighter?

Would such an arrangement also improve the eye's ability to distinguish colours? It's hard to see any variation of colour in the stars at night, but take a long exposure photo and it's pretty amazing...

David

 

[neutrino_cannon]

I was thinking about telescopes and cameras the other day (I own at least two of each) and I got thinking about how much light pollution we have. I've only been able to really pick out the Milky Way on a few occasions, and only once was it exceptionally clear.

Then I got to thinking... could you build an arrangement of lenses and such (all optical, no electronics) that could collect light from a wider area and then present it to the eye so you'd see the same field of view, but much brighter?

Would such an arrangement also improve the eye's ability to distinguish colours? It's hard to see any variation of colour in the stars at night, but take a long exposure photo and it's pretty amazing...

* picture removed to save bandwidth

David

Easy. Take a converging lense that's very wide, and take light from a wide area and focus it on a point.

Antbane, it's commonly called.

Seriously, an interesting idea. Perhpas if the signals processing was done digitally, light from the city could be ignored!

 

[wollery]

I was thinking about telescopes and cameras the other day (I own at least two of each) and I got thinking about how much light pollution we have. I've only been able to really pick out the Milky Way on a few occasions, and only once was it exceptionally clear.

Then I got to thinking... could you build an arrangement of lenses and such (all optical, no electronics) that could collect light from a wider area and then present it to the eye so you'd see the same field of view, but much brighter?

Would such an arrangement also improve the eye's ability to distinguish colours? It's hard to see any variation of colour in the stars at night, but take a long exposure photo and it's pretty amazing...

David

The problem with lenses is that they also act like prisms, and the larger the lens, the more pronounced this becomes. It's called chromatic aberration. You can get systems of lenses which correct for this, called achromatic lenses, but they are extremely expensive. Another problem is the weight of larger lenses. The solution is to use mirrors, currently there are several telescopes with 10 metre mirrors in operation. Of course that would be a little out of most peoples price range!

Another alternative is to purchase a sodium filter. Most UK street lights are Sodium vapour lamps, and emit light at only two narrow wavelength intervals. Do a search for "Neodymium filters", they cost about £30 for a 1.25" filter.

As for colour distinguishing it's all down to light levels. The light receptors in the eye which differentiate colour are less sensitive than the ones that just detect overall light levels (rods and cones, but I can never remember which is which). That's why things look almost black and white in low light situations.

 

[patnray]

AS woolery says, lenses are limited by chromatic abberation (also absorption of light and reflections between elements in achromatic lenses). BTW, the basic approach to achromatic design is to match every curved surface with an identical curve in the opposite direction...

In the simplest terms, just get a 'scope with a larger aperture. Or were you thinking of using an array of 'scopes and somehow combining the images?

I have used "light pollution" filters in my backyard here in San Jose. They do increase contrast with little loss in over all brightness. Especially good for faint objects such as nebulae.

Still, there is lots you can see with a decent 'scope, even in urban environments without filters. Enjoy!

 

[Zep]

Simpler solution: avoid haze. You will get light scatter from haze that is not necessarily the same frequencies as the light source. Haze acts as a variable and varying colour filter, as well as a light dispersant. Achromatic lenses and stuff will not compensate for this.

 

[TillEulenspiegel]

Even better solution if you have the$$$. Get an Hi-Res RGB output ccd camera (http://www.duncantech.com/MS4100_Data_Page.htm) and scab some software off the net or from your local NASA or University astronomy collage and bingo a tunable spectrum imaging system.

 

[davidhorman]

Or were you thinking of using an array of 'scopes and somehow combining the images?

I wasn't thinking of telescopes at all. I don't want to magnify the image (strictly speaking I don't want to do anything, it was just a thought experiment). I was thinking of some optical device that could show you just what you'd see with the naked eye, but with a greater light-gathering capacity, so what you get is an amplified view - as if you could dilate your pupils to a few inches across.

David

 

[epepke]

I wasn't thinking of telescopes at all. I don't want to magnify the image (strictly speaking I don't want to do anything, it was just a thought experiment). I was thinking of some optical device that could show you just what you'd see with the naked eye, but with a greater light-gathering capacity, so what you get is an amplified view - as if you could dilate your pupils to a few inches across.

A bug-eye would do it.