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#21
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How to measure ISO
In article , Tony Cooper
wrote: Not a big problem, but the question is which camera has the correct ISO setting, of if perhaps both cameras deviate from the true ISO 100. While you may have a point, it would not affect me to know that the ISO setting in my camera is 100 off or not. I know what I can expect from a setting, and set the camera accordingly. for one camera, perhaps, but that number may not be the same on other cameras. Trust you to argue by stating the bloody obvious. trust you to go on another rant, and i'm not arguing. If you routinely use two different cameras, you would soon learn to know what the result is for a particular setting. maybe so, but if the iso was correct, that would not be needed. |
#22
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How to measure ISO
In article , Alan Browne
says... You can do a standard candle test, if you like. Shoot a grey card in direct sunlight. Well, the sun light strength may differ depending on the day of the year and the geographical location. -- Alfred Molon Olympus E-series DSLRs and micro 4/3 forum at http://tech.groups.yahoo.com/group/MyOlympus/ http://myolympus.org/ photo sharing site |
#23
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How to measure ISO
On 2015-10-30, nospam wrote:
In article , Eric Stevens wrote: Not a big problem, but the question is which camera has the correct ISO setting, of if perhaps both cameras deviate from the true ISO 100. While you may have a point, it would not affect me to know that the ISO setting in my camera is 100 off or not. I know what I can expect from a setting, and set the camera accordingly. Things worked just as well in the days I set my exposure to the Weston scale. The numbers don't really matter but when you have more than one camera its nice if they share a common scale. exactly the point. Using film, you could use the same batch of the same brand in all your cameras - if you were worried enough about the actual 'speed' you'd shoot a test strip for each batch of film to determine the best 'speed' setting for that batch for you. You'd also be aware of differences between the cameras and lenses - and adjust shutter and aperture settings accordingly, or the film speed setting if the camera had its own 'automatic' exposure meter. Electronic sensors generally aren't interchanged between cameras, and their performance is remarkably stable over time, but they do vary one from another, and of course cameras and lenses still do so too. So you'll get to know that 'this camera tends to blow the highlights' or 'this lens is a bit dark at short focal lengths' or 'the fast shutter speeds tend to underexpose' and compensate to get the results you want. ISO 'speed' ratings are guides rather than absolute measurements. For electronic sensors there are at least three different methods of deciding what the 'speed' of a sensor is, and all allow for some subjective judgment. Wikipedia is a good place to start reading. -- -- ^^^^^^^^^^ -- Whiskers -- ~~~~~~~~~~ |
#24
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How to measure ISO
In article ,
Whiskers wrote: Not a big problem, but the question is which camera has the correct ISO setting, of if perhaps both cameras deviate from the true ISO 100. While you may have a point, it would not affect me to know that the ISO setting in my camera is 100 off or not. I know what I can expect from a setting, and set the camera accordingly. Things worked just as well in the days I set my exposure to the Weston scale. The numbers don't really matter but when you have more than one camera its nice if they share a common scale. exactly the point. Using film, you could use the same batch of the same brand in all your cameras - if you were worried enough about the actual 'speed' you'd shoot a test strip for each batch of film to determine the best 'speed' setting for that batch for you. You'd also be aware of differences between the cameras and lenses - and adjust shutter and aperture settings accordingly, or the film speed setting if the camera had its own 'automatic' exposure meter. one of the downsides of film is that every batch is different, one of numerous flaws that digital solves. because of that, many photographers bought film in large quantities so that they could calibrate their workflow for one batch. they had to freeze most of it so that it didn't expire before they had a chance to use it. crazy! they often took test shots, usually a macbeth chart or similar, so that they could adjust the exposure and colour balance to match their previous batch of film. fortunately that insanity is no more, as digital is consistent shot to shot for the life of the camera. Electronic sensors generally aren't interchanged between cameras, and their performance is remarkably stable over time, but they do vary one from another, and of course cameras and lenses still do so too. So you'll get to know that 'this camera tends to blow the highlights' or 'this lens is a bit dark at short focal lengths' or 'the fast shutter speeds tend to underexpose' and compensate to get the results you want. that's what having a standardized rating is supposed to solve. ISO 'speed' ratings are guides rather than absolute measurements. For electronic sensors there are at least three different methods of deciding what the 'speed' of a sensor is, and all allow for some subjective judgment. Wikipedia is a good place to start reading. the fact that there's more than one way to measure it makes the rating rather useless. it's at best, a rough guide. |
#25
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How to measure ISO
On 2015-10-30 03:10, Alfred Molon wrote:
In article , Alan Browne says... You can do a standard candle test, if you like. Shoot a grey card in direct sunlight. Well, the sun light strength may differ depending on the day of the year and the geographical location. That is true enough but it's also one of the sole independent tests you can do absent a lab with the right equipment. |
#26
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How to measure ISO
On 2015-10-30 12:38, Whisky-dave wrote:
On Friday, 30 October 2015 16:06:15 UTC, nospam wrote: In article , Whiskers wrote: Not a big problem, but the question is which camera has the correct ISO setting, of if perhaps both cameras deviate from the true ISO 100. While you may have a point, it would not affect me to know that the ISO setting in my camera is 100 off or not. I know what I can expect from a setting, and set the camera accordingly. Things worked just as well in the days I set my exposure to the Weston scale. The numbers don't really matter but when you have more than one camera its nice if they share a common scale. exactly the point. Using film, you could use the same batch of the same brand in all your cameras - if you were worried enough about the actual 'speed' you'd shoot a test strip for each batch of film to determine the best 'speed' setting for that batch for you. You'd also be aware of differences between the cameras and lenses - and adjust shutter and aperture settings accordingly, or the film speed setting if the camera had its own 'automatic' exposure meter. one of the downsides of film is that every batch is different, one of numerous flaws that digital solves. but batches of sensors are differnt too, which is whwere teh original Q came from in that two cameras set set to ISO 100 should expose at exactly the same level of brightness, but they don't. If they're the same model camera I'd expect them to be too close for casual measurement no matter what the batch. (Because I'd expect the manufacturer to store calibration data on the sensor). s fortunately that insanity is no more, as digital is consistent shot to shot for the life of the camera. doesn't help if you have more than one camera though. It's not so big a difference that you can't work them both. You have to know your cameras well. This is the same across my Hasselblad lenses .... on some the timer is a bit long (1/3 stop) which doesn't sound like much unless shooting E-6. Electronic sensors generally aren't interchanged between cameras, and their performance is remarkably stable over time, but they do vary one from another, and of course cameras and lenses still do so too. So you'll get to know that 'this camera tends to blow the highlights' or 'this lens is a bit dark at short focal lengths' or 'the fast shutter speeds tend to underexpose' and compensate to get the results you want. that's what having a standardized rating is supposed to solve. So hom come the OP was asking why his ISO one one camera is difernt from teh other. You'd have thopugh with 10 bit minium resolution they could get it right wouldn't you. For a given model they should be too close for casual measure. And in a precise test I'd assume far less than 1/3 stop. ISO 'speed' ratings are guides rather than absolute measurements. For electronic sensors there are at least three different methods of deciding what the 'speed' of a sensor is, and all allow for some subjective judgment. Wikipedia is a good place to start reading. the fact that there's more than one way to measure it makes the rating rather useless. So why have it ? Are you expecting the IOS to be measured at 5600k or 5400k or 3200k or anything else, or perhaps red, blue, green, or yellow magenta or cyan light would be best. Moonlight might be OK too for hi ISO. The standard sets an objective. Engineers at each co. interpret it as they see fit. it's at best, a rough guide. Yep. I remebr on boxes of film the sped was always given a s a guide rathe rthan a dead cert, a bit like setting a gues make or temerature on an oven. Yes I've even doen that and if I set my oven to 180C I can get temeratures of 165-200. Oven controllers are not very accurate - I agree with the range you show there. |
#27
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How to measure ISO
In article ,
Whisky-dave wrote: Not a big problem, but the question is which camera has the correct ISO setting, of if perhaps both cameras deviate from the true ISO 100. While you may have a point, it would not affect me to know that the ISO setting in my camera is 100 off or not. I know what I can expect from a setting, and set the camera accordingly. Things worked just as well in the days I set my exposure to the Weston scale. The numbers don't really matter but when you have more than one camera its nice if they share a common scale. exactly the point. Using film, you could use the same batch of the same brand in all your cameras - if you were worried enough about the actual 'speed' you'd shoot a test strip for each batch of film to determine the best 'speed' setting for that batch for you. You'd also be aware of differences between the cameras and lenses - and adjust shutter and aperture settings accordingly, or the film speed setting if the camera had its own 'automatic' exposure meter. one of the downsides of film is that every batch is different, one of numerous flaws that digital solves. but batches of sensors are differnt too, which is whwere teh original Q came from in that two cameras set set to ISO 100 should expose at exactly the same level of brightness, but they don't. different cameras have different sensors. two copies of the same camera will have the same sensor. you'd need lab instruments to find *any* difference, and if there is one, it would be much smaller than the manufacturing tolerances of the shutter and aperture. in other words, it can be ignored. because of that, many photographers bought film in large quantities so that they could calibrate their workflow for one batch. Some of that was to save money and always have film in stock. I used to buy 50ft reels of HP3 , 100ft reels of HP4. I still have the bulk film loader somewhere. I'm not to sure that had such a thing as workflows then. of course they did. they had to freeze most of it so that it didn't expire before they had a chance to use it. crazy! No most didn't freeze it they kept it cool in the fridge. that depends how long they're going to keep it. they often took test shots, usually a macbeth chart or similar, so that they could adjust the exposure and colour balance to match their previous batch of film. didn't need to as each was done individually and looked at. It was only when machines started bulk processing was that needed. it absolutely was needed. fortunately that insanity is no more, as digital is consistent shot to shot for the life of the camera. doesn't help if you have more than one camera though. that's the whole point. Electronic sensors generally aren't interchanged between cameras, and their performance is remarkably stable over time, but they do vary one from another, and of course cameras and lenses still do so too. So you'll get to know that 'this camera tends to blow the highlights' or 'this lens is a bit dark at short focal lengths' or 'the fast shutter speeds tend to underexpose' and compensate to get the results you want. that's what having a standardized rating is supposed to solve. So hom come the OP was asking why his ISO one one camera is difernt from teh other. You'd have thopugh with 10 bit minium resolution they could get it right wouldn't you. because there's no standardized rating system. ISO 'speed' ratings are guides rather than absolute measurements. For electronic sensors there are at least three different methods of deciding what the 'speed' of a sensor is, and all allow for some subjective judgment. Wikipedia is a good place to start reading. the fact that there's more than one way to measure it makes the rating rather useless. So why have it ? good question. Are you expecting the IOS to be measured at 5600k or 5400k or 3200k or anything else, or perhaps red, blue, green, or yellow magenta or cyan light would be best. Moonlight might be OK too for hi ISO. it should be standardized. it's at best, a rough guide. Yep. I remebr on boxes of film the sped was always given a s a guide rathe rthan a dead cert, a bit like setting a gues make or temerature on an oven. Yes I've even doen that and if I set my oven to 180C I can get temeratures of 165-200. that's because film is not as good as digital. technology advances. film is obsolete. |
#28
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How to measure ISO
On 28/10/2015 08:07, Alfred Molon wrote:
I have two cameras. At the same ISO, aperture and exposure time one takes brighter images than the other one. How to measure the real ISO values at which the cameras took the pictures? Sensorgen has some measured vs claimed ISO data. Some examples at set ISO 3200, calculated ISO is: EOS 7DII 2458 EOS 5DIII 2518 EOS 1DX 2423 D5300 2483 D750 2332 D810 2367 OMDEM5 1489 OMDEM10 1663 DMCGH2 2989 DMCGH4 1860 Phase One IQ180 990 A7R 2240 A7S 2627 The general trend seems to be that most overstate ISO by about 1/3 stop. That's probably sensible (blown highlight protection). Some are well over that 1/3 stop. Of course there's suspicion it's also done to "cheat" - to make the cameras look better than they really are in side by side high ISO comparisons. |
#29
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How to measure ISO
In article ,
Whisky-dave says... fortunately that insanity is no more, as digital is consistent shot to shot for the life of the camera. doesn't help if you have more than one camera though. The difference in ISO is actually not a problem, because the camera automatically sets the exposure and in manual mode you can determine the right exposure by judging the histogram. I was just curious how ISO could be measured. Got some feedback, but isn't there a scientific definition, e.g. "100 ISO is the camera sensitivity for which at an illumunance of ... lux the camera chooses an exposure of ..." - something like this. -- Alfred Molon Olympus E-series DSLRs and micro 4/3 forum at http://tech.groups.yahoo.com/group/MyOlympus/ http://myolympus.org/ photo sharing site |
#30
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How to measure ISO
In article , Me says...
Some examples at set ISO 3200, calculated ISO is: EOS 7DII 2458 EOS 5DIII 2518 EOS 1DX 2423 D5300 2483 D750 2332 D810 2367 OMDEM5 1489 OMDEM10 1663 DMCGH2 2989 DMCGH4 1860 Phase One IQ180 990 A7R 2240 A7S 2627 Hmmmm... isn't this cheating? Could be compared to the fuel consumption and pollution output levels which car manufacturers declare and what instead these values are in reality. -- Alfred Molon Olympus E-series DSLRs and micro 4/3 forum at http://tech.groups.yahoo.com/group/MyOlympus/ http://myolympus.org/ photo sharing site |
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