High ISO value display

[vAfotoriporter]

I just discovered something while checking high ISO sample images of the 5D mk3 on DPreview. It seems PM only displays ISO levels until 65535. This is the number that appears instead of 102400 that is the official value. I didn't check what is in the EXIF of the photos just used PM. Perhaps CameraBits didn't plan to have this high ISO levels when this variable has been created in the program - or there is some other bug.

[Sven]

Exiftool (mac, 10.7.3) shows also the value as follows:

ISO                             : 65535


BR
Sven

[vAfotoriporter]

Exiftool (mac, 10.7.3) shows also the value as follows:

ISO                             : 65535


BR
Sven

This means 102400 is off the official scale that is possible to display in the EXIF? Or Canon failed to display it correctly in the EXIF?
,-DDD

[Sven]

Hi!

65535 is the largest number that can be displayed with 16 bit...
(2^16 - 1)

BR
Sven

[vAfotoriporter]

Hi!

65535 is the largest number that can be displayed with 16 bit...
(2^16 - 1)

BR
Sven

Yes I know but it was not obvious that ISO value needs to be displayed in 16 bits....but completely understandable that the standard may not consider values will be higher than that when the standard was founded...

[FVlcek]

I believe the official EXIF standard allows only an unsigned short integer for ISO rating, that would indeed be 2 bytes with 65535 maximum value. At least that comes to my mind from remembering reading the specs (just lightly browsing them though).

Also, it's worth noting that all current high-ISO cameras only have "official" ISO up to 25600. All values after that are denoted as ISO Expansion, be it Low, High 1, High 2, etc. I guess the actual High-x is stored in the makernotes, and if the new Canon has a new format or changed makernote field for the "High" ISO expansion, it would of course be currently not viewable in current versions of PM/Exiftool.

[Sven]

The current value is listed in the "Base ISO"-Field.
Base ISO                        : 102400

It is also available in the "Recommended Exposure Index".

I have compared this to the sample with ISO of 25600 and it seems to be consistent...

But the samples are from a pre-production version... May be it changes to the production ones.