Why not square lenses???

[Bifurcator]

Don't you think we should have round monitors too? Round print film, round paper, round picture frames, and round posters and post-cards?

We have the technology. We should do it!

No body better say triangles! >:{

--
PS: My eye glasses are square.

 

[Moglex]

Don't you think we should have round monitors too?

The earliest TV's had round CRT's that were masked off to provide a rectangular picture.

AFAIA oscilloscopes still do.

 

[Alex_B]

for laser optics you get rectangular lenses by the way ... but those have a curvature only in one direction, hence they do not have cylindrical symmetry. Outer shape always corresponds to the symmetry for reasons of better precision in manufacturing.

 

[Mike_E]

Light focuses in a circle (see circle of confusion for a hint) so anything outside of the circle's area needed to cover the sensor would be wasted and thus much more expensive to manufacture.

There may be aluminum lenses before too long though which should really excite everyone! (I'm not kidding)

 

[LWW]

The earliest TV's had round CRT's that were masked off to provide a rectangular picture.

AFAIA oscilloscopes still do.

And I'm thinking you are on the right track.

The film/sensor is making an image from the light which hits it and that light is a "sweet spot" out of the center of the lens.

Thinking it through further, if the front element were square and properly convex it would have to be cut from a round blank to begin with which, again, would make it more expensive to build.

Next problem, all of the inner elements would have to spin as they turned. Being they are not round this would induce numerous balance issues.

Lastly, the film nor the sensor are square, they are rectangular.

Now, if we had a rectangular lens front element it would have to remain in a fixed orientation with no front element rotation ... nor could any of the other elements rotate.

In reality, I assume this could all be worked out but we would be left with a lens which was much heavier, much more expensive, and much more problem prone.

I'm not a lens maker, but I do have some mechanical backgrounds and those are the issues I come up with as I think it through.

The modern lens is an elegantly simple design and I doubt that it can be easily improved upon at this point as far as the internal focus mechanisms go.

LWW

 

[Alex_B]

so LWW and I said almost the same... could be true then?

 

[Helen B]

As Garbz mentioned, a circular aperture (technically the aperture stop) helps with image quality. There are special process lenses for lithography that are designed to have shaped aperture stops. The shape of the aperture stop has no relation to the shape of the sensor or film (technically the field stop), but the lens designer must design the lens such that the aperture stop is evenly illuminated - therefore the shape of the rest of the elements must permit that. In practice that means that a rectangular lens would have to slowly transition from the shape of the aperture stop to the shape of the field stop. This would mean that the front element, for example, would be a rounded rectangle, not a true rectangle.

There may, therefore, be less 'wasted glass' in a round lens than you might imagine.

Some lenses, including a few of the Angenieux lenses I used to have for Leica and Nikon, have internal baffles at the front and back to reduce light outside the required frame. The best lens hoods, such as those used for large format cameras and for motion picture cameras, use mattes - a black mask cut out to the aspect ratio of the format in use. Sinar, for example, have an adjustable matte. 'Barn door' hoods can do a similar thing.

Best,
Helen

 

[NateS]

Wow.....I didn't expect to get such thourough and technical (and quantity) responses to this thread but great explanations. It all makes sense especially the aperture which I hadn't though about.

Next up, I'm making a round monitor to hang on my wall

 

[matt-l]

Next up, I'm making a round monitor to hang on my wall

send me a proto type!

 

[Alex_B]

There may be aluminum lenses before too long though which should really excite everyone! (I'm not kidding)

Are you certain you are not talking of aluminium oxide (e.g. sapphire), an oxide, not a metal?
Or some aluminium oxynitride, which belongs to the world of ceramics, not metals?

Both are nor aluminium, just like water is not oxygen.

 

[Jedo_03]

Now that we have FF sensors - eg Canon 5D - we find that even the best L lens cannot resolve the image (perhaps, maybe the 135 - but I dunno cos I'm not a Canon man) and this seems to be because the FF sensor cannot resolve the edges due to spherical aberation...
Now, I'm not a measureabater... at least not for Canon - cos I'm a Pentax man... but talk in other forums seems to be saying that the FF sensor has more resolution than the 'best' Canon lens...
If it is true - then why are Canon users paying $$$ for L lenses..??
Jedo

 

[Moglex]

Now that we have FF sensors - eg Canon 5D - we find that even the best L lens cannot resolve the image (perhaps, maybe the 135 - but I dunno cos I'm not a Canon man) and this seems to be because the FF sensor cannot resolve the edges due to spherical aberation...
Now, I'm not a measureabater... at least not for Canon - cos I'm a Pentax man... but talk in other forums seems to be saying that the FF sensor has more resolution than the 'best' Canon lens...
If it is true - then why are Canon users paying $$$ for L lenses..??
Jedo

The effective resolution of the system depends upon both the film/sensor and lens and is always less than the worse than the two.

Thus, if you are going for the highest system resolution you always go for the highest resolution of both lens and film/sesnor.

Of course, whether you should spend your money on a better sensor or a better lens (or somthing else entirely) is a much more complex question.

 

[Joves]

I wouldn't know why. Once they got the process down it shouldn't be any harder. If anything I'd almost think it would be easier. Maybe the bulk, but some of these pros don't care about bulk with their 6 foot long lenses.

You do understand how glass is ground? I sometimes still push glass for telescope optics and, Im here to tell you it would be a nightmare to get the optics to have the correct figure. Lenses are round because it is the shape that works. The others have been tried before and, still are being attempted. Square glass though does work for flats.

 

[VADER1775]

round lenses were made long before cameras; so why are the mirrors and sensors not round? could you imagine Galileo with a square telescope?

 

[Moglex]

round lenses were made long before cameras; so why are the mirrors and sensors round?

They're not in any of my cameras.