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#11
September 19th 04, 02:48 AM
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"Bob Alexander" wrote in message om... A short time ago, I was photographing a waterfall, fiddling with neutral density filters (screw them on, screw them off, be careful not to drop them, make sure they're clean, etc.) and I thought that life would be a lot easier if a digital camera had arbitrarily low ISO equivalent settings, e.g. ISO 50, 25, 12.5, 6.25, etc. We would all save the expense and trouble of buying and using ND filters. The Canon Powershot Pro1 does, effectively, have that feature with a built-in ND filter. Mark 
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#12
September 19th 04, 03:20 AM
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"Bob Alexander" wrote in message om... A short time ago, I was photographing a waterfall, fiddling with neutral density filters (screw them on, screw them off, be careful not to drop them, make sure they're clean, etc.) and I thought that life would be a lot easier if a digital camera had arbitrarily low ISO equivalent settings, e.g. ISO 50, 25, 12.5, 6.25, etc. We would all save the expense and trouble of buying and using ND filters. I know that high ISO equivalents introduce problems with noise, but is there any technological reason digital cameras don't have low ISO settings, or is it just that no one has thought of it yet? The basics of how a CCD works is that when a sensor element in the CCD is subjected to light, it generates a voltage which is then amplified, then converted to a digital value. To get the higher ISO equivalent, they increase the amount of amplification prior to converting to digital (the ISO 1600 & 3200 that is available as a custom function in some cameras is actually achieved by digital amplification but that's another matter). There is a certain amount of light that causes the CCD sensor to emit a 100% signal - the ISO rating of film that also saturates at that level is how the ISO equivalency is calculated. To achieve higher ISO equivalence, the amplification is increased, so to double the ISO, bright white is achieved if the sensor achieves 50% light, etc. To achieve a lower equivalent ISO would require lowering the amplification, but the sensor has already saturated, so all we would get is an image with the shadows having the eqivalent of the low ISO, but anything brighter than 50% grey would only appear as 50% grey. So the other alternative is to design the actual sensor so that is less sensitive to light so that the sensor itself is rated at ISO 25 for example. The problem here however is that to get the higher ISO's will still produce more noise. So while an ISO100 sensor will give acceptable results up to ISO800, an ISO25 sensor would only give acceptable results to ISO100. Obviously that wouldn't be acceptable to most users. Personally, the way I would like a DSLR to be designed, would be to have interchangeable sensors. That way we could put in a native ISO25 sensor, or a native ISO1600 sensor, or a B&W sensor, IR sensor etc, and make the DSLR truly as versatile as a cheap film body. I suspect however that the sensor probably makes up a big slice of the cost of a camera. Thanks, Bob Alexander
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#13
September 19th 04, 03:20 AM
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"Bob Alexander" wrote in message om... A short time ago, I was photographing a waterfall, fiddling with neutral density filters (screw them on, screw them off, be careful not to drop them, make sure they're clean, etc.) and I thought that life would be a lot easier if a digital camera had arbitrarily low ISO equivalent settings, e.g. ISO 50, 25, 12.5, 6.25, etc. We would all save the expense and trouble of buying and using ND filters. I know that high ISO equivalents introduce problems with noise, but is there any technological reason digital cameras don't have low ISO settings, or is it just that no one has thought of it yet? The basics of how a CCD works is that when a sensor element in the CCD is subjected to light, it generates a voltage which is then amplified, then converted to a digital value. To get the higher ISO equivalent, they increase the amount of amplification prior to converting to digital (the ISO 1600 & 3200 that is available as a custom function in some cameras is actually achieved by digital amplification but that's another matter). There is a certain amount of light that causes the CCD sensor to emit a 100% signal - the ISO rating of film that also saturates at that level is how the ISO equivalency is calculated. To achieve higher ISO equivalence, the amplification is increased, so to double the ISO, bright white is achieved if the sensor achieves 50% light, etc. To achieve a lower equivalent ISO would require lowering the amplification, but the sensor has already saturated, so all we would get is an image with the shadows having the eqivalent of the low ISO, but anything brighter than 50% grey would only appear as 50% grey. So the other alternative is to design the actual sensor so that is less sensitive to light so that the sensor itself is rated at ISO 25 for example. The problem here however is that to get the higher ISO's will still produce more noise. So while an ISO100 sensor will give acceptable results up to ISO800, an ISO25 sensor would only give acceptable results to ISO100. Obviously that wouldn't be acceptable to most users. Personally, the way I would like a DSLR to be designed, would be to have interchangeable sensors. That way we could put in a native ISO25 sensor, or a native ISO1600 sensor, or a B&W sensor, IR sensor etc, and make the DSLR truly as versatile as a cheap film body. I suspect however that the sensor probably makes up a big slice of the cost of a camera. Thanks, Bob Alexander
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#14
September 19th 04, 03:20 AM
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"Bob Alexander" wrote in message om... A short time ago, I was photographing a waterfall, fiddling with neutral density filters (screw them on, screw them off, be careful not to drop them, make sure they're clean, etc.) and I thought that life would be a lot easier if a digital camera had arbitrarily low ISO equivalent settings, e.g. ISO 50, 25, 12.5, 6.25, etc. We would all save the expense and trouble of buying and using ND filters. I know that high ISO equivalents introduce problems with noise, but is there any technological reason digital cameras don't have low ISO settings, or is it just that no one has thought of it yet? The basics of how a CCD works is that when a sensor element in the CCD is subjected to light, it generates a voltage which is then amplified, then converted to a digital value. To get the higher ISO equivalent, they increase the amount of amplification prior to converting to digital (the ISO 1600 & 3200 that is available as a custom function in some cameras is actually achieved by digital amplification but that's another matter). There is a certain amount of light that causes the CCD sensor to emit a 100% signal - the ISO rating of film that also saturates at that level is how the ISO equivalency is calculated. To achieve higher ISO equivalence, the amplification is increased, so to double the ISO, bright white is achieved if the sensor achieves 50% light, etc. To achieve a lower equivalent ISO would require lowering the amplification, but the sensor has already saturated, so all we would get is an image with the shadows having the eqivalent of the low ISO, but anything brighter than 50% grey would only appear as 50% grey. So the other alternative is to design the actual sensor so that is less sensitive to light so that the sensor itself is rated at ISO 25 for example. The problem here however is that to get the higher ISO's will still produce more noise. So while an ISO100 sensor will give acceptable results up to ISO800, an ISO25 sensor would only give acceptable results to ISO100. Obviously that wouldn't be acceptable to most users. Personally, the way I would like a DSLR to be designed, would be to have interchangeable sensors. That way we could put in a native ISO25 sensor, or a native ISO1600 sensor, or a B&W sensor, IR sensor etc, and make the DSLR truly as versatile as a cheap film body. I suspect however that the sensor probably makes up a big slice of the cost of a camera. Thanks, Bob Alexander
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#15
September 19th 04, 03:30 AM
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#16
September 19th 04, 03:30 AM
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#17
September 19th 04, 03:30 AM
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#19
September 19th 04, 03:35 AM
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The main reason would be that there isnt a large market for it.
On 18 Sep 2004 17:24:38 -0700, (Bob Alexander) wrote: A short time ago, I was photographing a waterfall, fiddling with neutral density filters (screw them on, screw them off, be careful not to drop them, make sure they're clean, etc.) and I thought that life would be a lot easier if a digital camera had arbitrarily low ISO equivalent settings, e.g. ISO 50, 25, 12.5, 6.25, etc. We would all save the expense and trouble of buying and using ND filters. I know that high ISO equivalents introduce problems with noise, but is there any technological reason digital cameras don't have low ISO settings, or is it just that no one has thought of it yet? Thanks, Bob Alexander
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#20
September 19th 04, 05:27 AM
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"Justin Thyme" writes:
"Bob Alexander" wrote in message om... A short time ago, I was photographing a waterfall, fiddling with neutral density filters (screw them on, screw them off, be careful not to drop them, make sure they're clean, etc.) and I thought that life would be a lot easier if a digital camera had arbitrarily low ISO equivalent settings, e.g. ISO 50, 25, 12.5, 6.25, etc. We would all save the expense and trouble of buying and using ND filters. I know that high ISO equivalents introduce problems with noise, but is there any technological reason digital cameras don't have low ISO settings, or is it just that no one has thought of it yet? The basics of how a CCD works is that when a sensor element in the CCD is subjected to light, it generates a voltage which is then amplified, then converted to a digital value. This is misleading. AS a CCD is exposed to light, photons coming in (mostly) generate electrons which are stored in the bin for each pixel. When reading it out, this stored charge is converted to a voltage and blah blah blah. However, these bins have a *finite size* and can only be increased in size by various material tricks (difficult) or physically increasing the size of the pixel/bin. Consequently, higher resolution sensors tend to have smaller bins. B
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