# What does the optical zoom in telescopes do?

How does the optical zoom works..

1. Does it brings the light closer to the object... Or
2. Does it just enlarges the picture of the object.

In other words... Suppose I have telescope with 1 light-year zoom capacity, could I see stars 1 year ahead of its light reaching earth...

Ps : I'm not physics graduate, but interested in physics. I joined here, to learn more... Please excuse me if my question is trivial or stupid.

• Your question is neither trivial nor stupid but I am not quite sure what you are asking for. Are you interested in general principles that make objects appear big when light is passed through some optical system (e.g. lens)? Or are you interested in some realization of a particular telescope (there e.g. refraction and reflection based telescopes)? Or do you want to know about general principles surrounding the travel of light from objects to receiver (we always see only the past of the objects, not their current state, because it always takes some time for light to reach us)? – Marek Dec 23 '10 at 14:09
• @Marek. When I zoom in at some distant object in my camera... It shows the object closer. I just want to understand whether the effect is brought by enlargement of the image or does it by some means capture the light before it travels the entire distance. – The King Dec 23 '10 at 15:18
• As I said its an elargement of the same image. Light alwayts travel to the camera, always. – TROLLHUNTER Dec 23 '10 at 15:30
• @King: you can't capture the light that hasn't traveled entire distance. All interactions in our world are local, so that means that to see something you need the light to travel all the way to you. The magnification is based purely on the properties of light beams being passed through the optical system of your camera. – Marek Dec 23 '10 at 15:35

The answer is 2. Zoom isnt measured in distance, it is more like a ratio of magnification. So it tells you how much you magnified something, ofcourse for lenses the zoom is slightly more technical.

A lightyear is a distance, its actually the distance travelled by light in 1 year, so when you see stars 1 ly. away, you see how they appeared 1 year ago.

the magnification is a property of diverging light. it really needs a diagram, but the further away the detector is from the focal spot, the bigger the image will appear

this is the best picture I could find

the picture is a bit sloppy because it implies the focal spot is in the lens, which is not usually true, but it gives you the concept

try this yourself with a magnifying glass - the further you hold your eye from the glass (not moving the object) the bigger the object should appear

the same is true if you move the magnifying glass away from the object, but for a slightly more complex reason about how far the lens can bend the light

• cheers mark. why did I not even think to use html? bizarre oversight! – SoulmanZ Dec 23 '10 at 23:11
• I think you need a minimum amount of site "reputation" to add images, so you wouldn't have been allowed. – Mark Eichenlaub Dec 24 '10 at 4:00

In the answer to you Question, light always travels directly, the zooming issue is comming from the lens, it means, the lens receives the light from the object and then based on the lens's physical nature it zooms the object, as per the model shown above.

I think the question hints towards a basic misunderstanding that most have regarding light, and respectfully offered to many: the way that light and information is passed is highly glossed over. Any device that can "see" can only interact with incident light, light that falls onto or into the device (including our eyes).

All possible information contained within the light can then be accessed, within the confines of the device. Kind of like a computer hard drive if you will. Depending on how you reach into that information will determine what information you read. Current discussion here relates to how the lease will change focal point, but that is one only one dimension to the information.

The changing foci redirects the peering into the incident light's store of information, and that is what zoom is doing.

I realize this may sound a tad bizarre to some, but one day the world will better understand light.