Do multiple lens cameras refract light differently to a single lens ones?

  • Thread starter ak33m98
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ak33m98
Why do high end camera modules have so many glass lenses, apart from the necessary lenses for focus and zoom why is it that in cameras like DSLR cameras there are so many low power lenses where a few high power ones would work do the same job, do the lenses diffract light differently when they're stacked together as small individual lenses than as one big one?
 

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  • #2
Danger
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I don't know. One component, though, is used to deflect part of the image to the viewfinder for a true "through-the-lense" preview of what the picture will be. That isn't necessary for a digital camera, as far as I know, but was for film models.
 
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What do you mean by "power"? Is it the zoom range?

High performance lenses are made of multiple elements to deal with various distortions that a single-element lens has.
 
  • #5
Drakkith
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The basic idea is that the more lenses, the more freedom the designers have to correct aberrations in the image. A single spherical lens suffers from just about every aberration there is: Axial and Lateral chromatic aberration, Spherical aberration, Coma, Astigmatism, Field curvature, and Image distortion. Adding lenses of different materials with differently curved surfaces enables the reductions/elimination of many of these aberrations. Also, the basic rule is that the more powerful a lens (or any optical element) is, the stronger the aberrations become, so using multiple low-power lenses is sometimes better than a single, more powerful lens.

http://en.wikipedia.org/wiki/Optical_aberration
 
  • #6
sophiecentaur
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There's another problem with SLR cameras and that is the fact that the mirror arrangement demands that the lens has to be further away from the image sensor / film than the effective focal length of the lens. That means you need 'relay optics'.
Also, a simple lens with a long focal length can be inconveniently long (Imagine a 500mm length of lens hanging on the front of your camera!) so they have to use telephoto lenses with a combination of extra lenses that behave like a physically long lens but may only be less than 150mm in actual length).
 
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Andy Resnick
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Just to add to Drakkith's reply- 'splitting' a single element into a doublet increases the degrees of freedom for the designer from 3 (two surfaces plus element thickness) to 7 (4 surfaces plus three spacings). Not all aberrations can be corrected in this way: chromatic aberrations require the use of different materials to correct the dispersion. Aspherical elements can be used to reduce the number of surfaces, and the location of the aperture stop provides an additional degree of freedom. The aberrations also depend on object distance: a lens may be well corrected for viewing distant objects, but horrible for viewing nearby objects. Similarly, correcting the aberrations over the entire field of view becomes more difficult as the field of view increases.

Even so, not all monochromatic aberrations can be fully corrected- the ideal design may require a zero-thickness or even negative thickness. Buchdal's and Kingslake's books are excellent resources. For example, Buchdal presents a detailed solution for a Cooke triplet: 6 surfaces and 5 spacings result in 5 dense pages of residual aberrations- only the primary and secondary monochromatic aberrations. This is why modern lens design is performed on a computer.
 
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Andy Resnick
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There's another problem with SLR cameras and that is the fact that the mirror arrangement demands that the lens has to be further away from the image sensor / film than the effective focal length of the lens. <snip>
This is also true- increasing the image distance can have the effect of making the lens asymmetric about the stop, greatly complicating the overall design:

http://kmp.bdimitrov.de/lenses/primes/_optics/15f3.5-i.gif
http://3zgehi1uaxi23dphbrgqa50r6z.wpengine.netdna-cdn.com/wp-content/uploads/2013/10/Nikkor_6mm_construction.jpg [Broken]
https://farm3.staticflickr.com/2889/13517837714_418ee3f9f5.jpg

Retrofocus lenses are very complex systems. Rangefinder cameras place the lens much closer to the image plane, resulting both in smaller lenses (easier to manufacture) and more symmetric designs (easier to correct):
 
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