Nikon ISOInfo Tags

[rnwl]

Hi Everyone,

I have a question about the Nikon ISO Info Tags, I have a Nikon D300 and I have looked at the exif data, under the tag '0025' which says ISO info and directs you to Nikon ISOInfo Tags section of the page (http://www.exiftool.org/TagNames/Nikon.html#ISOInfo).

Just wondered if anyone knows how to work out this long number and what it means, how it relates to the ISO?

I have recorded my findings so far:

ISO        Hex

200      48, 01, 0C, 00, 00, 00, 48, 01, 0C, 00, 00, 00, 00, 00
250      4C, 01, 0C, 00, 00, 00, 4C, 01, 0C, 00, 00, 00, 00, 00
320      50, 01, 0C, 00, 00, 00, 50, 01, 0C, 00, 00, 00, 00, 00
400      54, 01, 0C, 00, 00, 00, 54, 01, 0C, 00, 00, 00, 00, 00
500      58, 01, 0C, 00, 00, 00, 58, 01, 0C, 00, 00, 00, 00, 00
640      5C, 01, 0C, 00, 00, 00, 5C, 01, 0C, 00, 00, 00, 00, 00
800      60, 01, 0C, 00, 00, 00, 60, 01, 0C, 00, 00, 00, 00, 00
1000    64, 01, 0C, 00, 00, 00, 64, 01, 0C, 00, 00, 00, 00, 00
1250    68, 01, 0C, 00, 00, 00, 68, 01, 0C, 00, 00, 00, 00, 00
1600    6C, 01, 0C, 00, 00, 00, 6C, 01, 0C, 00, 00, 00, 00, 00
2000    70, 01, 0C, 00, 00, 00, 70, 01, 0C, 00, 00, 00, 00, 00
2500    74, 01, 0C, 00, 00, 00, 74, 01, 0C, 00, 00, 00, 00, 00
3200    78, 01, 0C, 00, 00, 00, 78, 01, 0C, 00, 00, 00, 00, 00
4000    7C, 01, 0C, 00, 01, 01, 7C, 01, 0C, 00, 01, 01, 00, 00
5000    80, 01, 0C, 00, 01, 03, 80, 01, 0C, 00, 01, 03, 00, 00
6400    84, 01, 0C, 00, 01, 04, 84, 01, 0C, 00, 01, 04, 00, 00


There is a pattern there, but not sure what the pattern is, and how it relates to the ISO itself.

Thanks for any help 

Becky.

[Phil Harvey]

Hi Becky,

Your link provides all of the decoding information.  I'm not sure what else you want.  The first byte is the ISO, converted by the formula provided (val = 100 * 2**(raw/12-5)).  I don't know what the next 3 bytes are for (01 0c 00).  Then 2 bytes for ISOExpansion, etc...

- Phil

[rnwl]

Hi Phil,

Thank you very much for the quick reply. I want to know how these numbers relate to the ISO, that was all. I am just starting out in Software Development and have been given a camera issue to solve which involves working out these numbers.

Is there any chance you would be able to use one of the numbers (e.g. 48 for 200 ISO) in that formula provided so I can see how you're using it as I don't understand the formula.

Thank you,
Becky.

[Phil Harvey]

Hi Becky:

ISO = 100 * 2**(0x48/12-5)

where "**" is exponentiation.

- Phil

[rnwl]

Hi Phil,

Thanks very much, that has answered my question

Becky.