Is this true? (Technical question)

[Bigcrustyape]

If what he was saying is true than all hand-held light meters would be useless. You would need to input what camera, what lens, what focal length. Of course, this is not true. Light is light. A hand-held meter measures this light and gives a reading based on the photographer only inputting the ISO setting. Of course, all digital processors in each manufacturers camera will read this light slightly differently, but a difference of a stop (ISO200 - 400) seems very unlikely. You will certainly get a variance in the quality of the image between a kit lens and top end L series lens (barrel distortion, fringing etc) but not in exposure.

[AlphaBjerke]

Well, it looks like this has sparked quite a debate. I know I have learned a few things along the way.

Just for the record, I don't have his EXIF data because I have no way of contacting him. I am sure he was not shooting auto when it comes to ISO. I am not sure if he was in aperture mode or shutter priority.

Also, someone said his sensor is full size and more sensitive. ISO is a standard. If you follow the flickr conversation I linked earlier, there is a study that shows that DSLRs are not all the same when it comes to that standard, but it is a standard that has nothing to do with the quality of the sensor.

[autofocus]

Actually a saw a good article on "ISO standards" in one of my photo rags, and amazingly enough, ISO ratings on many brands and models of cameras were off...in some cases, nearly a full stop. One of my cameras (D300) was listed at 1/2 stop under what you thought it was. I was able to compensate for that in custom settings. It's like the days of muscle cars, for the sake of insurance premiums, many of the car manufacturers grossly under rated their cars horsepower...but don't ask me why the camera guys are so inaccurate

[candleman]

Originally Posted by auto-focus

Folks, Correct me if I'm wrong, but his $3000 camera has a bigger, better, and more light sensitive sensor than your camera...larger sensors have larger pixels, and can handle low light situations better than the smaller ones...and certainly handle digital noise better...that's one of the things your paying for when you buy a $3000 camera. All that said, his camera (body) may be able to properly expose an image better in the same conditions than your camera, and the particular lens should be much less of a factor.

hehe, sorry to say you're wrong.
OK, not "wrong",
sure, expensive cameras have better iso abilities, but in answering this question it does not apply.

the reason being that ISO is universal, it should be very close anyway.
iso 100 an camera "A" should in theory yeild the same sensitivity to photons (light) that any camera "B".
..because the sensitivities are modelled off of the sensitivities of film.
ISO stands for International Standards Organiisation (its actualluy IOS.. but we wont go there )

what you mentioned only comes into play when we crank up to higher iso's like 1250 or 1600. etc etc

[autofocus]

...but were not really comparing apples and apples. Sure, ISO 100 in camera "A" should theoretically be the same as ISO in camera "B." I know it's a standard. His question was why can one camera expose correctly at 100 ISO, and under all else the same conditions camera B needs to do it at 200 ISO. For starters, we really only have half the facts...was camera "B" a full frame sensor?...and if it was, full frame sensors have larger pixels jammed into their substrate making them more sensitive to capture available light.

[dcclark]

Sorry auto-focus -- as mentioned above, quite correctly, ISO 100 is ISO 100. A full-frame sensor, a cropped sensor, a tiny P&S sensor -- all are calibrated so that ISO 100 means the same thing. That's the point of ISO -- it's defined independently of the film or sensor that you are using.

You may be thinking of the idea that full-frame sensors do better at high ISOs. This is true -- ISO defines sensitivity to light, but on cameras with smaller sensors, high ISOs look grainier. On full-frame sensors, the high ISO photos look better. But my D40 at 1600 and someone else's D3 at 1600 both have the same sensitivity to light, even if mine will look terrible while the D3 will look great.

As some have mentioned, not all cameras are perfectly calibrated, which does mean that my ISO 100 might actually be truly ISO 150. That could account for a little variation, but even a full stop is pretty extreme to be miscalibrated.

[autofocus]

OK, I know that ISO 100 is ISO 100 regardless of the equipment...I'm not disputing that..all I'm saying is that one camera may be able to process/expose an image correctly at 100 ISO while another camera may need to do the same thing correctly at 200 ISO (just like the example given by the original post)..so why is that so?? It must be the difference in the equipment. Let's say pixels are analogous to the size of a window in a room..a large window lets more light in, whereas a small window in the same room lets less light in..agree? Most full frame sensors have larger pixels in the given space, this is documented. Further, larger pixels receive a greater flux of photons over a given exposure time (at the same aperture), so their light signal is much stronger. Can we then conclude that they let more usable light into the camera, therefore a lower ISO setting may be sufficient to properly expose the image, therefore they can shoot that same scene at 100 ISO. So when 200 ISO is required on one camera, the higher end camera because of better sensor sensitivity, and better DSP capabilities may be able to accomplish the same result at 100 ISO.

[dcclark]

Let's say a certain amount of light is entering the camera. The proper exposure is determined to be ISO 100, f/8, 1/200 sec. That represents a certain LV (light value). If we agree that it is the proper exposure, then any other camera which can take a decent photo will decide on something equivalent to this. It may be that the D40 (whose "native" ISO is 200) will choose to go with ISO 200, f/8, 1/400 sec, or perhaps ISO 200, f/9, 1/200 sec, but either way, those are all still equivalent to the same LV, and hence the same exposure. The ISO changed, yes -- some sensors have different minimum ISOs (which may have actually been the case here) -- but of course the aperture or shutter speed also changed, to allow the same amount of light in.

If a full-frame sensor (for example) is more efficient at collecting light, then its calibration (what exact level of sensor gain will correspond to "ISO 100") will be set so that ISO 100 is ISO 100 is ISO 100, as it is written on the stone tablets of the International Standards Organization.

I don't know what else to say -- the details of exact sensors have NOTHING to do with what ISO 100 is. Some sensors are better at collecting light, there is no doubt -- but then the cameras are calibrated to take this into account, so that there are no surprises about what exposures are appropriate in different circumstances.

[autofocus]

David, I'm not sure, but I think we're somewhat in agreement. If both cameras have the capability of ISO 100 available to them, and both shooting in the same ambient light conditions, but because of less high end electronics in one camera it may need to bump the ISO up to 200 in order to accomplish the correct end result. Whereas, the camera with higher end electronics can yield the same result at 100 ISO...and I know there will be some differences in the F/Stop and shutter speeds between the two. When I say higher end electronics, I'm speaking of improvements in CCD, or CMOS sensor technology, faster and higher resolution A/D processors, larger and higher speed buffers (RAM), and higher performing Digital Signal Processors. I sell this crap (industrial electronics) for a living, and like teaching for yourself, this is how I make my living.

[fletch]

Originally Posted by auto-focus

David, I'm not sure, but I think we're somewhat in agreement. If both cameras have the capability of ISO 100 available to them, and both shooting in the same ambient light conditions, but because of less high end electronics in one camera it may need to bump the ISO up to 200 in order to accomplish the correct end result. Whereas, the camera with higher end electronics can yield the same result at 100 ISO...and I know there will be some differences in the F/Stop and shutter speeds between the two. When I say higher end electronics, I'm speaking of improvements in CCD, or CMOS sensor technology, faster and higher resolution A/D processors, larger and higher speed buffers (RAM), and higher performing Digital Signal Processors. I sell this crap (industrial electronics) for a living, and like teaching for yourself, this is how I make my living.

No - No - No. If you tried to sell me some of this crap I'd be off like a shot.

ISO is ISO is ISO (Taking into account calibration) just like f/4 is f/4 is f/4

The most likely cause of the different ISOs used in the original question is that the OP and the other photographer ended up with different prictures. Either the ISO 200 shot was darker or the pictures had different compositions so the amount of light was different.

The size of the sensor of the cameras electornics won't affect the ISO you need to shoot at. All of the calibration will be done in camera. Sure a D3 can shoot higher ISOs than a D40 but if you shoot at ISO 200 with both cameras (with the same aperture and shutter speed) you will get the same exposure, it would even be the same if you went and tried a 5 year old Sony P&S camera. ISO 200 would still be ISO 200. End of, it really is that simple.

(Yes calibration may be off in some cameras but that is an unnecessary confusion IMO)