With the exception of the pinhole camera, every camera I’ve seen has had glass of some sort to direct light to the recording media.
Glass in cameras serves a number of purposes. Keeping dust out of the camera. Focus – focusing the light onto the recording media (be it film or CCDs). And also allowing the photographer or VJ to get closer or further away from the subject without having to move.
As mentioned in the post below (My Bag Over-runneth), I have two converter lenses. A wide angle adapter and a tele adapter. The former allows me to get an extremely wide view…maybe shoot in a small area and capture it all. The latter allows me to get a bit closer to the action without having to physically move closer.
That’s the simple explanation, which you can see in the photos above. Shot at about 15 feet away/from left to right:
Photo #1 – Canon HV20 with 2x Sony tele adapter/zoomed all of the way out
Photo #2 – Canon HV20 camera lens/no adapter/zoomed all of the way out
Photo #3 – Canon HV20 with Century .25 fisheye/zoomed all of the way out
Did I mention zoom above? Well, yes. Zoomed all of the way out is using the camera zoom to back off as far away from the subject as possible. Zoomed all of the way in is using the zoom to bring the subject as close as possible. Got it?
Then DON’T ZOOM! Check out this post to understand why (not).
Moving on…the other use of the lens to get the exact framing and focus and perspective you want.
Framing…why move the tripod if you can nudge the zoom a mite in or out? Saves time.
Focus (will have to follow up with photos and another post to explain this better) – if you understand depth of field, you can select your lens and distance and have certain elements of your shot in focus while others are out of focus. YOU choose – this isn’t luck.
Perspective – the look of the elements in the shot as related to each other. Look below. Two shots using the tele and wide angle adapters.
Notice in the first shot (using fisheye or wide angle) the elements seem far apart…there appears to be more space between the front element Lego anchorman at desk) and the rear element (TV truck). Then look at the third shot…the TV truck and anchorman appear closer together…there appears to be less space between the elements.
This is all relative. The first shot was taken inches away from the anchorman…the third shot was taken probably five feet away. So if you compare the distance from the camera to the closer element and the farther away one, it is LESS in the first shot and MORE in the second shot. To get a clearer idea, see the illustration below.
The top illustration shows the photographer close to the tree and the tree about an equal distance to the mountain.
The lower illustration shows the mountain the tree the same distance apart, but the photographer has moved back.
So the distance between the photographer relative to the distance between the tree and mountain has been altered.
From the photographer’s point of view, the objects in the upper illustration are far apart…in the lower illustration they are closer together.