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Why are sensors flat?

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As has been pointed out fabricating a curved sensor would be difficult. I can imagine a back illuminated CCD that has been thinned enough that it could be bent over a curved support after fabrication. If this is ever tried it would likely be for a (very expensive) extremely wide field telescope which wouldn't have a reflex mirror nor a focal-plane shutter. It could avoid the field flattener for infinity focus and reduce vignetting and aberrations at the image corners but I doubt it would be worth the trouble.
 
Oldvic said:
Something along the lines you propose was done, but as far as I can
tell only with film:
http://en.wikipedia.org/wiki/Schmidt_camera

Obviously, film is very easy to shape because it's thin and flexible.
Too easy, in fact: some cameras had vacuum systems designed to keep
the film flat against a back plate during the exposure (Contax, for
instance).
So, as you can see, even with film, the efforts were directed at
keeping the "sensor" flat rather than curving it to match a curved
focal plane from the lens.

Cheers
Click to expand...
Those Schmidt cameras which have been modified with CCD imagers have a field flattener added to correct the curved focal plane for the flat sensor array. Most telescopes used for serious imaging will be equipped with flatteners (even at the amateur level) and it's far easier to build the necessary lens than to mess around with trying to curve a sensor.
 
I think it will not be too long thill the adaptive optics will come to photography. The sensors will be adapive then. Adjusting to the lens as they have to to get the best out of them. Reducing the aberations and other problems. It is just a matter of time I think.
 
If you want to know more start looking for adaptive optics and e.g. Keck telescope. The sensors of the camera could even become cheaper that way. Why? Because you would have smaller sensor pieces, therefore less pixels that need do me working. You would have to sort out less costly pieces instead of the full sensor. You can get perfect images from lousy lenses...
 
totally agree

in the space of a couple of decades all our sensors
will become obsolete

quantum computers are also on the forefront and
will similarily render our computers obsolete

and in the space of a century I predict humanity
as whole will become obsolete... ;-)
 
Its RKM said:
Edward in Chicago said:
I posted this over in Leica talk but this one can be a bit more lively.

I'm not an engineer or optics designer but I've always wondered why
sensors are flat?
Click to expand...
To understand why sensors are flat you need to understand a little of
the silicon IC process.

Sensors are not made individually, many of them are made at the same
time on a single wafer of silicon, typically 8 or 12" in diameter,
depending on the manufacturer.

Sensors are flat because the silicon wafers are flat.

Silicon wafers are not made individually, they are cut from a single
crystal of silicon grown with the corresponding diameter and several
feet long - essentially a long cylinder that is sliced up into
individual wafers.

Silicon wafers are flat because that is the only way to cut the
silicon crystals.

It might be possible to cut the wafers into cap shaped domes, but
that would be extremely wasteful and only a few such wafers could be
cut from a single crystal, instead of many flat wafers. More
significantly though, the processing of the wafer in the IC foundry
usually depends critically on the crystal orientation at the surface.
With a flat wafer, this orientation can be defined precisely across
the entire surface of the wafer, resulting in uniform deposition of
the oxides, metals and dopants necessary to create the individual
sensors on the wafer. With a curved wafer surface, in addition to
requiring a completely unique (and therefore ultra-expensive, on the
scale of billions of dollars investment) wafer processing plant, the
crystal orientation would change across the surface of the wafer,
resulting in highly variable deposition and growth rates. Remember
growing salt or copper sulphate crystals in junior school? The end
result is something with flat surfaces - all crystals are like that,
so a curved wafer must have a variable crystal orientation and/or
have very high crystalline defects. Such defects cause growth and
deposition non-uniformity. Even if this problem could be solved
with limited trillions of dollars, which is unlikely, it would have
reduced yields compared to conventional flat wafer processing.

So there you have it:
Sensors are flat because silicon wafers are flat.
Silicon wafers are flat because they are cut from single silicon
crystals.
Single crystals have flat facets, so sensors are flat.

Any deviation from this basic rule requires the redevelopment of the
entire semiconductor industry and I don't think that the market for
photographic sensors could justify that let alone a single company,
such as Canon or Sony, afford it.
Click to expand...
--Well put.

-tyrants and cowards hide behind censorship-
 
Edward in Chicago said:
I think its the other way around. Lenses that focus on a curved
surface should be far, far easier to make. Achieving focus across a
flat plane is an essential compromise and focus precision
edge-to-edge is always a problem. Any optical engineers out there?
--
http://www.pbase.com/edward_in_chicago/root
Click to expand...
Look at it this way. Film was flat, lenses were designed to fit that paradigm. Now, if you change it all around, every lens on the market would have to be redesigned. Yeah, Canon and Minolta did that when they switched to AF film bodies, and there was a tremendous outcry. If any mfr were to do that, now, they would risk losing all of their customers in one fell swoop. There would have to be a compelling reason to stick with that mfr above all others. Then there's the R&D expense to figure in, since, with Canon's AF lens change, all the things they'e learned about lens design could be transferred to AF lenses. With your suggestion, they'd have to go back and rethink all the designs they'd done in the past. It could take years to replace all those lenses in the lineup, photographers would be abandoning the line to switch to something else with access to the lenses that particular photographer would need, cost would go up, profits would go down. Not a pretty scenario.
--
Skip M
http://www.shadowcatcherimagery.com
http://www.pbase.com/skipm
'Living in the heart of a dream, in the Promised Land!'
John Stewart
 
The demo video with the guy gesturing all over that large screen suggests another benefit to this type of GUI. You could wear wrist weights and get quite a workout while using the computer. Imagine a future where the computer nerds are the big guys you wouldn't want to mess with!
 
A paradigm has started...we just need to wait for it to come to market:

http://graphics.stanford.edu/papers/lfcamera/

As of now, RAW lets us adjust WB and Exposure after the shot is taken, but now imagine being able to adjust the...Depth of Field!
Edward in Chicago said:
Maybe I'm a bit nuts but the whole design of digital cameras seems to
be a bit like motorized horse carriages. Maybe a radical new design
paradigm is needed?

Opinions welcome.

--
http://www.pbase.com/edward_in_chicago/root
Click to expand...
 
Well,....anyone who has printed with curved negs or curved slides can vouch for the fact that they will do anything to keep them flat to makes prints with..

That being said, sometimes, a curved neg enabled special softening features for custom printing...but that was also hit or miss..

With digital, and use of post processing techniques,...I wouldn't want anything other than a flat sensor.

JP
--

http://www.Myspace.com/JPphotographer
 
Funkmasterta said:
As of now, RAW lets us adjust WB and Exposure after the shot is
taken, but now imagine being able to adjust the...Depth of Field!
Click to expand...
Maybe it will finally put the "RAW vs. JPEG" issue to rest: there will be even more tangible things that you can do only in RAW.
 
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