# Why not square lenses???



## NateS (Aug 7, 2008)

So I was just thinking.  The sensor and mirror on a camera are square/rectangular, the image comes out when viewed as a square/rectangle.........so why are lenses round?  Wouldn't it seem logical that a lens would be squared?  If so, I would think you could get ridiculously wide angle and you would have less problems with vigenetting.  

Any thoughts?


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## Steph (Aug 7, 2008)

NateS said:


> So I was just thinking. The sensor and mirror on a camera are square/rectangular, the image comes out when viewed as a square/rectangle.........so why are lenses round? Wouldn't it seem logical that a lens would be squared? If so, I would think you could get ridiculously wide angle and you would have less problems with vigenetting.
> 
> Any thoughts?


 
Round lenses are much easier to manufacture?


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## matt-l (Aug 7, 2008)

and use. how would you focus a square lens?   or hold it, it would not be comfy at all.


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## NateS (Aug 7, 2008)

Steph said:


> Round lenses are much easier to manufacture?


 
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.


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## NateS (Aug 7, 2008)

matt-l said:


> and use. how would you focus a square lens? or hold it, it would not be comfy at all.


 
Focus would be easy.  Use a push/pull focus mechanism like the older Nikon 80-200 f2.8's.


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## Garbz (Aug 7, 2008)

Missing a big point here. Think of how light bends, and then think of the aperture. Look specifically at 5 bladed lenses. Out of focus light sources are rendered as pentagons. The more blades, the more curve, the smoother the out of focus areas are.

The reason square lenses don't exist are the same reason that mirror reflex lenses are so unpopular. They would just produce a very crap image.

(Logical deduction here. I only assume it works like this. Wait for a Helen comment to see if I'm right)


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## Battou (Aug 7, 2008)

NateS said:


> 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.



I used to work in a steel mill, on the tube mill to be precice. Square tubing is a PITA to manufacture and is actually very low demand in comparison to standard round tubing. Any tube mill manufacturering the square tubing for a square lens would have to be conducting change over a lot. Change over from round tubing to square is a long time consuming task. Resulting in higher prices due to additional labor required to produce. It took our Senior mill opperator sixteen hours to cunduct change over for a thirty six hour run of square tubing where as a diameter change takes a matter of minuets in most cases. just not worth it.

and that is well before you even get to the optics part of it.


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## Steph (Aug 7, 2008)

NateS said:


> 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.


 
I don't know. My common sense tells me it is easier to spin a circular piece of glass to cut/grind/polish it into a lens element than to do the same with a rectangular one...


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## snowalker (Aug 7, 2008)

matt-l said:


> and use. how would you focus a square lens?   or hold it, it would not be comfy at all.



good point! I've been never thinking like this.


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## benp2k6 (Aug 7, 2008)

What shape is your eye?  Geometrically speaking a square lens is illogical


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## nynfortoo (Aug 7, 2008)

Isn't some of the glass in a lens concave/convex and almost parabolic?


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## Antithesis (Aug 7, 2008)

benp2k6 said:


> What shape is your eye?  Geometrically speaking a square lens is illogical



That's my exact thought on the subject, and also, the manfacturing would be far more difficult. Producing a perfect circle is far easier than producing a perfect square.


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## Bifurcator (Aug 7, 2008)

Garbz said:


> Missing a big point here. Think of how light bends, and then think of the aperture. Look specifically at 5 bladed lenses. Out of focus light sources are rendered as pentagons. The more blades, the more curve, the smoother the out of focus areas are.
> 
> The reason square lenses don't exist are the same reason that mirror reflex lenses are so unpopular. They would just produce a very crap image.
> 
> (Logical deduction here. I only assume it works like this. Wait for a Helen comment to see if I'm right)



Yeah, aperture apparatus is probably the reason it's not tried. View cameras and even some TLRs have square lenses for framing and stuff. There's the pentaprism too - which at least has corners.  I don't think it's the manufacturing that holds it back. I guess it's the function of light like you're suggesting.


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## tirediron (Aug 8, 2008)

Helen... you're needed!


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## Alex_B (Aug 8, 2008)

the aperture should best be round for all shapes of lenses 

There are cases of cameras which matte off a rectangle in front of the lens. Mainly to avoid flare resulting from unneeded glass surface i think.

But the lens behind is round again, why? because it is just way easier to produce a rotational symmetric glass object than a random shape with high precision. Rectangular lenses as used for those wearing glasses, are produced round and then cut after they got their curvature.

1. so it is always round first, rectangular cut afterwards -> higher cost

2. but then, if you had a round lens, no element would be allowed to rotate, not even the internal ones -> new lens designs and cumbersome mechanisms for zooming and focusing -> higher cost. potentially also higher weight.

3. then think of the lens barrel, rectangular? again much more cumbersome to produce. -> higher cost. also, a cylinder is much tougher to withstand mechanical forces, so you lose something here.

4. what would the gain be? the lens would not be that much smaller. It would probably not be lighter. But it would be more prone to asymmetrical stress/strain due to mechanical forces and heat expansion. It would be probably a pain to adjust. So image quality might suffer and the lens would be twice as expensive.

Now you decide, if this lens would be on your shopping list


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## Bifurcator (Aug 8, 2008)

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.


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## Moglex (Aug 8, 2008)

Bifurcator said:


> 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.


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## Alex_B (Aug 8, 2008)

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.


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## Mike_E (Aug 8, 2008)

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)


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## LWW (Aug 8, 2008)

Moglex said:


> 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


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## Alex_B (Aug 8, 2008)

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


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## Helen B (Aug 8, 2008)

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


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## NateS (Aug 8, 2008)

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


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## matt-l (Aug 8, 2008)

NateS said:


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




send me a proto type!


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## Alex_B (Aug 9, 2008)

Mike_E said:


> 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.


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## Jedo_03 (Aug 9, 2008)

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


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## Moglex (Aug 9, 2008)

Jedo_03 said:


> 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.


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## Joves (Aug 9, 2008)

NateS said:


> 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.


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## VADER1775 (Aug 10, 2008)

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


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## Moglex (Aug 10, 2008)

VADER1775 said:


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



They're not in any of my cameras.


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## Battou (Aug 10, 2008)

Moglex said:


> They're not in any of my cameras.



nor mine


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## Moglex (Aug 11, 2008)

Actually, looking at that again, I suspect Vader meant to ask why mirrors and sensors _aren't_ round.

The answer to that would presumably be that whilst making lenses round is the most sensible/efficient method of doing things for several reasons, we are far more likely to want a rectangular result than a circular one.

The point at which it becomes sensible to change format is at the mirror/film plane/sensor/focusing screen. There would be no advantage to making those circular and the design and manufacture would be a lot harder and lead to unnecessarily larger equipment.


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## nymtber (Aug 12, 2008)

Glass is ground and polished round. a typical (sperical) lens is just that, part of a perfect sphere. both grinding and polishing are much much easier with a round lens, and therefore thats the way most are done, ROUND. After polishing, the lenses can be shaped to darn near any shape needed for a job, square, star shaped (to a certain extent)...Ive been making optics for 8 months now, its an exciting and not so easy job. I make aspheres, which help with chromatic abbervation, and also cost quite a bit more!

I cant give away how I do stuff, but i will say since most of our polishing is done rotating, round objects kinda work better than square. Like I previoiusly said, we can shape the lens AFTER its polished to tolerance  Well, I cant, but other people in the shop can! 

hope that helps a bit too!


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## Mike_E (Aug 12, 2008)

Alex_B  here is a link to the aluminum story..  http://physicsworld.com/cws/article/news/20033

it's not new but gives cause to hope.  
mike


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## Thom K (Aug 12, 2008)

Optically it would not work, because the light is a cone. What I need to ask, is why not circular sensors?


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## Alex_B (Aug 12, 2008)

Thom K said:


> Optically it would not work, because the light is a cone. What I need to ask, is why not circular sensors?



because then we had circular images, which are hard to frame. 

a square lens would work by the way if the curvature would be rotational symmetric.


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## Alex_B (Aug 12, 2008)

Mike_E said:


> Alex_B  here is a link to the aluminum story..  http://physicsworld.com/cws/article/news/20033
> 
> it's not new but gives cause to hope.
> mike



But it is not alumin(i)um!!! transparent aluminum is a star trek invention and will never work since it is a metal.

that article is old, and the idea even older. they talk about *alumina*, which is *aluminium oxide*. aluminium oxide is not aluminium, just as sapphire is not aluminium, although it contains aluminium atoms.

the hardness of alumina has nothing to do with the properties of the metal known as alumin(i)um


(sorry I took this personal, but I have been working on alumina for the recent 4 years  )


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## VADER1775 (Aug 12, 2008)

Moglex said:


> Actually, looking at that again, I suspect Vader meant to ask why mirrors and sensors _aren't_ round.
> 
> The answer to that would presumably be that whilst making lenses round is the most sensible/efficient method of doing things for several reasons, we are far more likely to want a rectangular result than a circular one.
> 
> The point at which it becomes sensible to change format is at the mirror/film plane/sensor/focusing screen. There would be no advantage to making those circular and the design and manufacture would be a lot harder and lead to unnecessarily larger equipment.



You are right my friend.  That is what I meant, Why are they not round?  Thanks for pointing that out.


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## Mike_E (Aug 12, 2008)

Alex_B said:


> But it is not alumin(i)um!!! transparent aluminum is a star trek invention and will never work since it is a metal.
> 
> that article is old, and the idea even older. they talk about *alumina*, which is *aluminium oxide*. aluminium oxide is not aluminium, just as sapphire is not aluminium, although it contains aluminium atoms.
> 
> ...



Not a problem.  In what aspect may I ask?

Btw, I wouldn't have a problem with a clear sapphire lens.

It's sure that something needs to give in the materials department if the major companies are to keep driving the markets with higher resolving power.


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## Moglex (Aug 13, 2008)

Alex_B said:


> But it is not alumin(i)um!!! transparent aluminum is a star trek invention and will never work since it is a metal.
> 
> that article is old, and the idea even older. they talk about *alumina*, which is *aluminium oxide*. aluminium oxide is not aluminium, just as sapphire is not aluminium, although it contains aluminium atoms.
> 
> ...



I have a feeling that if they ever do start using glass made in part from aluminium we will indeed be talking about 'aluminium' and 'silicon' lenses.

And probably 'silicone' lenses to boot!


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## Alex_B (Aug 13, 2008)

Mike_E said:


> Not a problem.  In what aspect may I ask?



Simulating surface properties and adhesion properties of oxides.



Moglex said:


> I have a feeling that if they ever do start using glass made in part from aluminium we will indeed be talking about 'aluminium' and 'silicon' lenses.
> 
> And probably 'silicone' lenses to boot!



good comment  If we use improper terms, then we should do it with all consequences


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## abraxas (Aug 13, 2008)

Sheesh, I'm really high right now,... but I was just thinking, if there were square lenses, wouldn't we have to have square eyes?

nite-nite.


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## Thom K (Aug 13, 2008)

On the subject of circular sensors, take a rangefinder or a point-and-shoot for example. The issue is much simpler becuase there aren't mirrors and prisms to get in the way. With a circular sensor, you would maximize the capturable content, and then you could crop the circular image into a rectangle. The advantage would be that you could choose any size of crop, rotation would not matter, and you could get better composition with the extra content afforded by a sensor that captures more. It's hard to put into words, sorry.


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## John_05 (Aug 13, 2008)

NateS said:


> 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


 
Or,  just order one......


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## Garbz (Aug 14, 2008)

That's just dumb. The human eye has a larger horizontal field of view than a vertical. A circular monitor makes no sense.


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## Battou (Aug 14, 2008)

I lol'd




John, you should have hidden a link under that image

Like this:


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## Bifurcator (Aug 14, 2008)

Hahaha... That's awesome! I want 30" though!


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## John_05 (Aug 16, 2008)

Battou said:


> I lol'd
> 
> 
> 
> ...


 

I thought about it,  but I was in a hurry when I posted that,  and I couldn't think of a good link to put in.

BTW,  that's not a real monitor.  It's just a prank from Geeks.com from April Fool's day back in 2006 IIRC.

Still pretty funny though.  :lmao:


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## Battou (Aug 17, 2008)

John_05 said:


> I thought about it,  but I was in a hurry when I posted that,  and I couldn't think of a good link to put in.



I actually happened to have one in my history that I know would be broken to almost all users when I found your post, I could not help my self.


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