ISO ratings

[sorin_tps]

I found this tests on another site.

What can you understand from this? That Fuji ISO rating is fake?
And in fact ISO800 is only about ISO500?

[mattdm]

Okay, I'll bite. What makes you say that?

[Pave]

heh...what I see is display of photos made with different settings (shutter speed, apperture and ISO)...
I don't think it means that "ISO 800 is fake"...
I don't understand how you came to this conclusion...:)

[mattdm]

PS: data is from

http://www.imaging-resource.com/PRODS/G7/G7A7.HTM

http://www.imaging-resource.com/PRODS/F30/F30A7.HTM

in case those charts don't look familiar to you.

[John_Reed]

I found this tests on another site.

What can you understand from this? That Fuji ISO rating is fake?
And in fact ISO800 is only about ISO500?Not easy to follow those charts, as the ISOs don't line up. However, at ISO 800, you have the G7's shutterspeeds, 1/6, 0.3, 0.6, 1.2, 3.2, comparing to the F30's shutterspeeds of 1/5, 1/2, 1, 2, 4 at the same fc (footcandle) input parameters. (Assuming aperture differences are inconsequential) So you could conclude from that that the G7, at the same level of light input, takes less light to get the equivalent exposure to the F30. Is it because the F30 should be rated at 500, or could it be that the G7 should be rated at 1100 or so? Who knows what the absolute standard should be? This is only a relative comparison.

[Riley]

no surprise that the iso speeds are inaccurate
and they arnt the only ones, there is at least one canon thats the same

for those of you that believe in such bs, its not fake, or cheating
just like some cameras have it the other way
Leicas M8 is about 1/3 to 1/2 a stop out the other way
which means it shoots a lot higher than is claimed

what it relates too is metering across a range
just like speedometers, while they may be right at 10mph, they probably wont be at 100mph

[mattdm]

Well, it's not called "ISO" for nothing -- it actually is an ISO (http://www.iso.org/iso/en/ISOOnline.frontpage) standard (http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=11948 ). So there is an absolute correct answer. Without doing the calculations myself, though, the Imaging Resource site where these tests are from says: "a light level of one foot-candle corresponds to a normal exposure of two seconds at f/2.8 and ISO 100". That'd mean for the ISO 800 test in the first column the "correct" answer is 0.25 seconds.

The F30 picks 0.2 seconds, and the G7 picks 0.17 seconds -- so both cameras actually appear to error on the conservative side. (Note that they're that way at ISO 100, too.)

[John_Reed]

Well, it's not called "ISO" for nothing -- it actually is an ISO (http://www.iso.org/iso/en/ISOOnline.frontpage) standard (http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=11948 ). So there is an absolute correct answer. Without doing the calculations myself, though, the Imaging Resource site where these tests are from says: "a light level of one foot-candle corresponds to a normal exposure of two seconds at f/2.8 and ISO 100". That'd mean for the ISO 800 test in the first column the "correct" answer is 0.25 seconds.

The F30 picks 0.2 seconds, and the G7 picks 0.17 seconds -- so both cameras actually appear to error on the conservative side. (Note that they're that way at ISO 100, too.)Good stuff, Matt. Thanks for posting.

[Riley]

all it means is there are metering inaccuracies across the range
in that you can add/subtract with ev+(-) to get the right exposure
it is usually set at the top end of the scale where it is less troublesome
its not like people are lying or something

[Norm in Fujino]

Well, it's not called "ISO" for nothing -- it actually is an ISO (http://www.iso.org/iso/en/ISOOnline.frontpage) standard (http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=11948 ). So there is an absolute correct answer. Without doing the calculations myself, though, the Imaging Resource site where these tests are from says: "a light level of one foot-candle corresponds to a normal exposure of two seconds at f/2.8 and ISO 100".

I didn't realize that one foot-candle was equal to EV 2, but that's pretty correct. EV 1 is equivalent to 0.46 foot-candles.

One thing for the OP to remember is that all these figures relate to "absolute" levels of light on a scene. They are refer to different ways or combinations of settings that will produce the same absolute amount of light on the film (sensor).

[sorin_tps]

Well, it's not called "ISO" for nothing -- it actually is an ISO (http://www.iso.org/iso/en/ISOOnline.frontpage) standard (http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=11948 ). So there is an absolute correct answer. Without doing the calculations myself, though, the Imaging Resource site where these tests are from says: "a light level of one foot-candle corresponds to a normal exposure of two seconds at f/2.8 and ISO 100". That'd mean for the ISO 800 test in the first column the "correct" answer is 0.25 seconds.

The F30 picks 0.2 seconds, and the G7 picks 0.17 seconds -- so both cameras actually appear to error on the conservative side. (Note that they're that way at ISO 100, too.)

OK. Thanks! That was what I have looked for.
So, both cameras have an error on "good" side. Anyway is good to know that ISO800 on Fuji is about the same as ISO600 on Canon.

[mattdm]

OK. Thanks! That was what I have looked for.
So, both cameras have an error on "good" side. Anyway is good to know that ISO800 on Fuji is about the same as ISO600 on Canon.

I'm not sure we can be that precise, but yeah.