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03/13/2007 05:45:13 AM · #1 |
| on some camera reviews, there's a comparison chart that shows the camera's stated ISO, and the actual ISO sensitivity on the sensor. some cameras are at ISO150 when it states ISO100, or vice-versa. how does this impact the photographer? |
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03/13/2007 08:28:50 AM · #2 |
It really doesn't affect you at all. The manufacturer has the exposure function calibrated to the sensor, so the exposures will be fine. The image is what it is. We used to have to deal with this all the time with film, incidentally: we bought our film in bulk and tested each batch to determine the actual sensitivity of the emulsion batch, and made a note of it, and would set our light meters to the actual, tested ISO of the film rather than the nominal ISO. This was pretty critical when working with sheet film in the large-format camera.
Robt.
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03/13/2007 09:56:33 AM · #3 |
| From what I have read is that Canon dSLRs are slightly more sensitive than stated, ISO 100 is really ISO 125, Nikons however are rated correctly. |
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03/13/2007 10:20:44 AM · #4 |
| thanks. so lets say one guy using a camera-XXX (with actual ISO 125) at ISO100 can get away with faster shutter speeds as compared to a camera-YYY (with actual ISO100) at ISO100? assuming everything else is the same? |
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03/13/2007 10:26:44 AM · #5 |
Yes, Canons do tend to be a little more sensitive than the stated ISO speed (1/3 stop or less). The only ways that a misstatement of ISO speed affects you are:
- If the ISO speed is significantly overstated (camera is less sensitive than stated speed) then you're not getting what you paid ofr in low-light performance.
- If the camera is more than 1/3 stop off of stated speed, a well-calibrated external light mater will disagree with the camera's meter. This can be a problem if you're relying on the external meter and setting the camera accordingly.
I've never heard of a case where the actual ISO was significantly less than the stated ISO. That would be a marketing nightmare for the manufacturer. The second case is only really important in situations where exposure is absolutely critical. There are very few situations where exposure accuracy of less than 1/3 stop absolutely must be maintained, and I've never heard of deviations much larger than 1/3 stop, at least with quality equipment. |
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03/13/2007 10:27:31 AM · #6 |
Originally posted by crayon:
thanks. so lets say one guy using a camera-XXX (with actual ISO 125) at ISO100 can get away with faster shutter speeds as compared to a camera-YYY (with actual ISO100) at ISO100? assuming everything else is the same? |
Yes. Though the difference is very small. |
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03/13/2007 11:02:14 AM · #7 |
Originally posted by kirbic:
I've never heard of a case where the actual ISO was significantly less than the stated ISO. That would be a marketing nightmare for the manufacturer. The second case is only really important in situations where exposure is absolutely critical. There are very few situations where exposure accuracy of less than 1/3 stop absolutely must be maintained, and I've never heard of deviations much larger than 1/3 stop, at least with quality equipment. |
My Sony-W5 is about a stop less sensitive than rated for. Compared the exposure of a plain white wall with that from the Pentax film SLR (which gives well exposed slides), and it was off. |
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03/13/2007 12:01:21 PM · #8 |
The ISO is just another setting to control your camera. You can do all the math, and take measurements and figure our what the exact exposure should be. But that's a lot of work, and its easy to make a mistake. For most shooting, the ISO is close enough.
If exposure is important, use the histogram.
If exposure is critical, use the histogram and bracket the exposure. |
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03/13/2007 12:01:50 PM · #9 |
Originally posted by Raziel:
From what I have read is that Canon dSLRs are slightly more sensitive than stated, ISO 100 is really ISO 125, Nikons however are rated correctly. |
Perhaps Canon wants us to expose to the right? |
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03/13/2007 09:12:07 PM · #10 |
thanks again guys.
i guess the actual ISO isnt very important to most people after the introduction of TTL flash units. |
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