I am not sure ISO is ISO

[rpcrowe]

I have been reading a lot about one camera occasionally not matching another camera at the same ISO/exposure. One camera can possible under/over expose shooting at the same f/stop and shutter and with the same ISO while the first camera provides correct exposure.

I have noticed that my new (used) Canon 5D seems to underexpose about 1/3 to 1/2 stop compared to my 7D cameras. I am wondering if this is a factor of individual cameras or a factor of camera models/brands as a whole. In other words, would several 5D cameras expose differently from each other or would it just be that one model (like the 5D) be different from another model (like the 7D).

My 7D cameras both expose pretty well on the button (using the same exposure and ISO) and when I switched from a 40D to the 7D, I did not notice any difference in ISO.

This is no big problem in shooting still imagery but, could possible be a problem when shooting video with a two camera setup with plans to cut the shots together in the final production.

I have not done a test (just another thing on my to-do list)...

[Shadowman]

Would you do the experiment indoors or outdoors?

[Black Pearl]

How are you comparing the files?

Remember the dynamic range and gradation characteristics will be completely different between the two plus even RAW files have some processing at the sensor level which carries through plus ACR may handle them slightly differently.

[george013]

How are you comparing the files?

Remember the dynamic range and gradation characteristics will be completely different between the two plus even RAW files have some processing at the sensor level which carries through plus ACR may handle them slightly differently.

Even different lenses might give different results on the same F-number. In the DxO lens ratings the Tstop is mentioned.

George

[Adzman808]

There are different scales to measure ISO, and not all camera OEMs use the same one. Which gets some people up in arms, but really it's not a cheat.

However, I would expect Canon to use the same ISO measurement for all of its range...

The other thing is that digital cameras are effectively ISOless, when you crank the ISO you're not actually changing the sensitivity of the sensor, you merely changing the amount of analogue or digital gain that the internal software applies.

Typically, cameras start off adjusting the sensitivity with analogue gain, then swap to digital gain when analogue tops out, (FWIW this is at 1600 on my Sony sensored Fujis) as I Understand it... Analogue gain is preferable to digital

It MIGHT be that one of your Canons applies digital gain earlier than the other, so although the ISO value is the same, the way the cameras achieves it is different.

Something else that pops to mind is to ask if both your Canons have the same base ISO? If one is 100 and the other is 200, then at (say) iso400 one is adding 2 stops of gain, whilst the other is only adding one.

It might be something to do with this? But I'm not ofay with Canons to speak with any great authority.

[Mike Buckley]

could possible be a problem when shooting video

Video? What's video? Does my camera take video?

[rpcrowe]

Video? What's video? Does my camera take video?

I don't use my DSLR cameras for video, instead I use a dedicated Panasonic Prosumer video camera. However, a lot of folks use their DSLR cameras for video Often, since a capable DSLR + lens is a bit cheaper in cost than a professional video camera, DSLR's are used in multi-camera shoots.

If I were going to shoot professional video on a paying basic, I would very likely use a professional video camera. IMO they are a lot easier to handle for video than shooting with a DSLR.

How about this unit? Twenty grand for a body. Wow
http://www.bhphotovideo.com/bnh/cont...G&A=details&Q=

And that's not the most espensive knife in the drawer

[Rob Ekins]

If I were going to shoot professional video on a paying basic, I would very likely use a professional video camera. IMO they are a lot easier to handle for video than shooting with a DSLR.

Richard,
I have a friend that shoots high end corporate videos entirely on a 5diii and Mkii before that. so it can be done.


Here is a list of some movies and TV shows filmed with Canon and Nikon DSLR Cameras

[dje]

Hi Richard

I think it's fair to say that there is no definitive standard way of measuring ISO in a digital camera as discussed in this Wiki article on the relevant ISO standard. Don't be put off by the maths in the article, the initial summary says it all

"The Recommended Exposure Index (REI) technique, new in the 2006 version of the standard, allows the manufacturer to specify a camera model’s EI choices arbitrarily. The choices are based solely on the manufacturer’s opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings. This is the only technique available under the standard for output formats that are not in the sRGB color space. This is also the only technique available under the standard when multi-zone metering (also called pattern metering) is used.

The Standard Output Sensitivity (SOS) technique, also new in the 2006 version of the standard, effectively specifies that the average level in the sRGB image must be 18% gray plus or minus 1/3 stop when the exposure is controlled by an automatic exposure control system calibrated per ISO 2721 and set to the EI with no exposure compensation. Because the output level is measured in the sRGB output from the camera, it is only applicable to sRGB images—typically JPEG—and not to output files in raw image format. It is not applicable when multi-zone metering is used.

The CIPA DC-004 standard requires that Japanese manufacturers of digital still cameras use either the REI or SOS techniques, and DC-008[62] updates the Exif specification to differentiate between these values."

The transmission factor of the lens also comes into it as George has mentioned.

This is no big problem in shooting still imagery but, could possible be a problem when shooting video with a two camera setup with plans to cut the shots together in the final production.

Any decent video editor could fix this.

Dave

[loosecanon]

I find my 5D and 7D both expose too much to the right for my taste, so I use them with -1/3 exposure compensation, whilst I am more happy with the standard exposure of my 5D III. That said when highlights are important I still apply -1/3 or -2/3 exposure correction and then bring back correct exposure in lightroom as I like to keep detail in highlights. When shadows are critical then I bracket.
I suppose the correct exposure is the one that suits my style of photography.

[Manfred M]

Richard - this is an old "issue" as the marked ISO and the measured ISO may not be the same.

If you are interested, go to the DxOMark website where they have published actual versus quoted ISO ratings across the range for various camera bodies. For example:

http://www.dxomark.com/Cameras/Nikon...--Measurements.

Let's be frank, this is only one of three variables that could be causing "issues", as mechanical devices, we also know that the quoted shutter speeds and aperture settings could be off a tad (anything from design issues, manufacturing tolerances and wear and tear). I think the film / video industry is far more honest this way. Camera lenses f-stops are reported based on the entrance pupil / focal length ratio, where as video lenses are rated in t-stops, where the transmission of light is also factored in to the equation. This is what George was alluding to in his post.

This was a known issue even in the film camera days, where certain cameras tended to meter 1/3 stop lower because the negatives came out more saturated.

Bottom line for me is still the image I get out of the camera, and frankly to a very large extent that has a lot more to do with me than the accuracy of all these other parameters.