Why aren't cameras more sensitive to light?

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jmroberts70

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Maybe this is a stupid question or just one that's been answered a million times before but really, people... Why aren't cameras more sensitive to light than they currently are? Wouldn't it be better to build a camera so sensitive that you could practically take a shot in near darkness? Now I'm not talking about the normal "night vision" systems that emit their own light source that the human eye can't see and makes everyone look evil and possessed, I'm talking about making a sensor super-sensitive by default. You can always tone down the amount of light that comes in but you can't ever INCREASE the amount of light you have to work with. Now I know that if you're working with low light conditions, you have some problems: the photo can get grainy from increasing the ISO number, you have to use a tripod or the shot gets blurry because the sensor needs to be exposed for a longer period of time, etc... But why is this? Can't a manufacturer simply make a sensor that's overly-sensitive and then no-longer need to have longer exposure times or grainy, high ISO numbered shots? Can't they make a lens that takes in waaay more light than usual and compensate for the lack of light normally there?

Am I missing something here... like some law of physics?
 
I think the short answer would be that it's just not as easy as it sounds - or maybe way too expensive for production equipment.

The ISO rating and sensor quality of modern digital cameras are improving all the time - just have to be patient I guess. The Nikon D3 has, what, like 25.6k ISO on its sensor? The tech is out there; right now it's just really expensive to get a camera with that kind of sensor. I'm sure in another 10-20 years 102.4k or some other insane number will be standard ISO on all digital cameras. Who knows.

If anyone wants to chime in w/ some more technical info on what developments in sensor technology have to occur for much higher ISO's to be available, I'd be interested in knowing that as well...
 
It seams to me that sensor sensitivity could revolutionize photography --making it possible to take shots at dusk or near darkness in amazingly clear resolution, shots with a high degree of motion that look crisp and clear, etc...
 
Ya, i cant wait until i can take a picture indoors with out having to crank the ISO or use a tripod in a mid afternoon sun.,.
 
Think of all the crappy indoor shots that won't look nearly so bad because they won't be using indoor flashes head-on and casting shadows against the back walls and such. I HATE using built-in flashes!! I rarely see a good shot taken with them.
 
haha as soon as i have bought my camera's i get a flash (Canon XT, then a 20D, that was stolen and then a 40D)

all they need to do is allow you to tilt the built in flash up to reflect off the ceiling and that alone would make so many pics look better!
 
jmroberts70 said:
Can't a manufacturer simply make a sensor that's overly-sensitive and then no-longer need to have longer exposure times or grainy, high ISO numbered shots? Can't they make a lens that takes in waaay more light than usual and compensate for the lack of light normally there?

Am I missing something here... like some law of physics?
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That's what the higher ISO is; making the sensor more sensitive to light. ISO is a unit, so you can't make the sensor "overly sensitive" and still call it ISO 100. It's like asking, "why can't car companies make cars that are overly fast, so they don't need a high MPH to get somewhere quickly?"

As for the physics, in a given exposure, you have X number of photons hitting the sensor. The less you have, the higher your signal to noise ratio, and the more noise in your shot. One way to improve this is to make the sensor sites larger so more photons can be collected, but this drops the resolution of the photo.

As for the lenses, you need a wider aperture to take in more light. As the aperture widens, your depth of field decreases and the cost of the lens increases due to the size of the glass needed to make the lenses. At some point you hit a limit of what's useful when you have a lens that's expensive, heavy, and impossible to use because its depth of focus at maximum aperture is too thin.
 
ya, you got to spend money to get good lense for darker situations currently, hopefully that will change, as it more or less is already, look at the old say Canon XT vs todays XTi and see how much better they are in lower light with out needing to crank the ISo to 800 and get crappy grainy photo's.
 
MrGuvernment said:
ya, you got to spend money to get good lense for darker situations currently, hopefully that will change, as it more or less is already, look at the old say Canon XT vs todays XTi and see how much better they are in lower light with out needing to crank the ISo to 800 and get crappy grainy photo's.
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I beleive you still need to crank up the ISO but the newer cameras have less noise at the higher ISO.
My 40D at ISO 3200 blows away my old Canon D60 and 10D at ISO 1000.
 
fugu said:
That's what the higher ISO is; making the sensor more sensitive to light. ISO is a unit, so you can't make the sensor "overly sensitive" and still call it ISO 100. It's like asking, "why can't car companies make cars that are overly fast, so they don't need a high MPH to get somewhere quickly?"

As for the physics, in a given exposure, you have X number of photons hitting the sensor. The less you have, the higher your signal to noise ratio, and the more noise in your shot. One way to improve this is to make the sensor sites larger so more photons can be collected, but this drops the resolution of the photo.

As for the lenses, you need a wider aperture to take in more light. As the aperture widens, your depth of field decreases and the cost of the lens increases due to the size of the glass needed to make the lenses. At some point you hit a limit of what's useful when you have a lens that's expensive, heavy, and impossible to use because its depth of focus at maximum aperture is too thin.
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It would help to make the sensor elements larger while still maintaining resolution. Trying to fit 20 million pixels on an area the size of a pencil eraser doesn't help.
 
i think these few paragraphs from last years' DPP magazine can answer few questions:


the individual photodetectors in the Canon EOS 40D are about 5.7 micrometer across. by contrast, the width of a typical human hair is about 50 micrometers. for a sense of the downward trend in photodetector size, we can compare the EOS 40D to the EOS 10D that preceded it by just 4.5 years. the protodetectors on the EOS 10D were about 7.4 micrometers across, meaning in those 4.5 years they have decreased in size by about 23%. considering the tiny scale we're talking about, that's significant.

the number of electrons that can be held by an individual photodetector (which is measured as an electrical voltage) determines the definition of "full" in the context of the photodetector (this is referred to as a measure of "full well"). the larger the photodetector, the more electrons it can fit, and thus the stronger electrical charge it can record. the minimum charge (ostensibly, no charge at all) compared with the maximum charge provides a measure of the dynamic range of each individual photodetector - the darkest and brightest values each photodetector can measure.

this is where we start running into problems with the math. if we need the size of each photodetector to decrease as the number of megapixels increase, but we need bigger photodetectors to increase dynamic range, doesn't that mean with each jump in megapixels the dynamic range of the imaging sensor is decreasing? yes, it probably is. granted, there are other technological advances that mitigate this problem, but it's a clear example of how conventional wisdom can be dead wrong. ("i need more megapixels to produce a better image.")
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It would help to make the sensor elements larger while still maintaining resolution. Trying to fit 20 million pixels on an area the size of a pencil eraser doesn't help.
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i've got two words for you: Medium Format.

now, if you look at the prices of Hasselblad, PhaseOne, Leaf, Mamiya and others you'll quickly realize that having a larger size sensor, also means a large increase in price over the typical crop DSLR's. full-frame DSLR's however, become more and more popular.
 
Oh when I become a millionaire I'm going to get a Hasselblad take one shot and call it crap and toss it on the ground cause I'm just that awesome :)

Those are some pretty sweet camera's but they are more for Portraits then anything. So if your subject doesn't move and is well lit (like spotlights at 2ft away) then your good. So it doesn't seem like it would really work well in low light.
 
^pretty much. those medium format cameras are best used in studio settings. it's a cup of tea with its own set of problems.
 
P&S -> crop -> FF -> MF
for the same pixels, each jump in sensor size gets you better low light performance.

Basically, the limiting factor isn't sensitivity, its noise. At high sensitivity, the camera is having to guess "is that a photon? I don't know. We'll say...[yes/no]" at each minute change in voltage from the sensor.
 
I shoot a canon 5D MK11( full frame) and a 85L F1.2 lens when I shoot female nudes. This modern Pro-sumer level cameras ability to use low light is awesome. All I need is a nice window and I am all set.
 
Yeah that's low light though not pitch the extremely dark condition that we are talking about. Night vision means no light. Even a lens at f1.0 needs a light gracing the subject. It just needs less of it then other lens
 
I guess I'm still frustrated that my own eye seems to capture more light than the modern camera. But maybe it will just be a matter of time before that is no longer the case...
 
jmroberts70 said:
I guess I'm still frustrated that my own eye seems to capture more light than the modern camera. But maybe it will just be a matter of time before that is no longer the case...
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Well, your eye has had thousands of years to develop. Digital cameras have only been around a few decades. :D
 
ryan_975 said:
Well, your eye has had thousands of years to develop. Digital cameras have only been around a few decades. :D
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You need to think that through a bit. Given unlimited shutter time cameras have ALWAYS captured more light.

A F1.2 lens wide open and a ISO of 3200 is more sensitive than the human eye by several stops is my understanding.
 
lens pirate said:
You need to think that through a bit. Given unlimited shutter time cameras have ALWAYS captured more light.
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Now that's true. I can hear that

A F1.2 lens wide open and a ISO of 3200 is more sensitive than the human eye by several stops is my understanding.
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Now that's interesting. I guess I'm going to have to grab a DSLR and try that out...
 
lens pirate said:
You need to think that through a bit. Given unlimited shutter time cameras have ALWAYS captured more light.

A F1.2 lens wide open and a ISO of 3200 is more sensitive than the human eye by several stops is my understanding.
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It was a joke.
 
lens pirate said:
A F1.2 lens wide open and a ISO of 3200 is more sensitive than the human eye by several stops is my understanding.
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Sure, but its resolution and SNR are orders of magnitude worse than your eye. You're also going to blow out all the highlights in the image due to a comparatively limited dynamic range.
 
I've found that at f/1.4, ISO 800 or 1600, and 1/80s on my D40, I can take pictures without a flash in very low light which look about the same as the scene does in reality--if anything, a bit brighter. Nevertheless, this is an unfair and difficult-to-make comparison, because of the 1/80s shutter and the dynamic range issues as mentioned. The D40 is capturing far more detail in that time than my eyes ever could at 1/80s: just try blinking your eyes open/close and see how well you can perceive the scene. But, my eyes don't tend to "blow highlights" in that environment either, whereas the camera chokes on most point light sources at ISO 1600, e.g. light bulbs.

That doesn't mean I would object to having a sensor that does a solid ISO 6400 (or 25.6k if you're desperate) like that in the D700. But, it will have to wait until I have a kid or something :)
 
Well there is always the black silicon solution for low light but the probelm would be that it would be solely dedicated to low light. The ISOs would be in the 100K range so to make it work for daytime would give you high noise in the lower ISOs or, you would have to make shutter speeds in the milisecond range. Here is some stuff on the stuff. http://www.technologyreview.com/energy/21611/ And actually the newer sensors are very good at high ISOs like the D700/3. Back in the old days film of the speeds they operate at would be highly grainy/noisy, which is why many of us used to hypersensitize our film or, push it to shoot say from a 400 ISO to 1200 ISO.
 
Don't forget that as you make the device more sensitive it also becomes more sensitive to radiation like IR. Before you go and say, well just put an IR filter on it, you have to remember IR radiation is emitted by everything essentially, including the detector itself (which is why high resolution FTIR machines have an option to cool the CCD with liquid N2).
 
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