Author Topic: why do i have "funky" numbers in ss and f stop?  (Read 13167 times)

Offline Luiz Muzzi

  • Hero Member
  • *****
  • Posts: 704
    • View Profile
    • Luiz Muzzi Photography
Re: why do i have "funky" numbers in ss and f stop?
« Reply #15 on: November 07, 2013, 01:53:53 AM »
Okay just to throw a monkey wrench into this...

The newer Exif tags are APEX values and stored as such.  So if the aperture is f/5.6 then the corresponding APEX value that is stored is 5.0.  If the shutter speed is 1/60 (or really 1/64) then the corresponding APEX value is 6.0.

So, another option is to create new variables (I would choose {av} and {tv} mirroring the APEX definition) which show the actual APEX values, not translated to what a camera setting would be.

This is what some applications like Max OSX Preview displays.  This certainly distinguishes a "setting" versus the "actual APEX" value (well except for aperture of f/4 and APEX of 4 which are the same  :o).

If these new Exif values aren't present in a photo (case (a) above) then the {av} and {tv} variables would be empty (or I could convert old settings to APEX).  If the old Exif values aren't present (very rare case (b) above), then I would convert the APEX values from the new Exif fields to the equivalent "setting" value for the old variables.  And in this case you will get strange numbers like 1/99 for {ss}.

How does that sound?

And another thing to chew on: if you have a lens that has an aperture size larger than f/1.0 (there are some out there!) then apparently the APEX/Exif spec wouldn't be able to store the APEX value because it would be < 0.0 and the Exif tag for aperture value is supposed to be an "unsigned" value (i.e. zero or positive).  Guess we will worry about that when Canon and Nikon start making these lenses...

One more thing: if the Exif tag for APEX Brightness Value (0x9203) is present, then the {brightness} variable will show this directly rather than trying to compute it based on aperture, shutter, and ISO.  This variable has always been displayed as an APEX value.  I haven't seen this tag on Canon cameras but some Sony cameras (e.g. Alpha 7R) do indeed write this tag.

--dennis

Hi, Dennis
So, back to our original problem, if we get strange numbers with PM's present settings, what does that mean? That old exif tags are not present? That both new and old exif tags are present? But DPP does not show me those numbers. It still shows me the old familiar numbers (settings).
I am trying hard to understand what has changed with the new build of PM.
TIA,

-Luiz Muzzi

Offline dennis

  • President
  • Camera Bits Staff
  • Sr. Member
  • *****
  • Posts: 456
    • View Profile
    • Camera Bits, Inc.
Re: why do i have "funky" numbers in ss and f stop?
« Reply #16 on: November 08, 2013, 01:36:29 PM »
Hi, Dennis
So, back to our original problem, if we get strange numbers with PM's present settings, what does that mean? That old exif tags are not present? That both new and old exif tags are present? But DPP does not show me those numbers. It still shows me the old familiar numbers (settings).
I am trying hard to understand what has changed with the new build of PM.

Luiz,

The new build (coming shortly) will restore the same behavior for variables like {ss} and {f}.  They will continue to display the older Exif tags for Exposure Time and F Number camera settings so nobody will see "funky numbers" anymore.

To handle the newer Exif APEX tags, I've created new variables {tv} and {av} for shutter speed value and aperture value.  They will display the APEX values directly (e.g. 1/60 second is approx APEX 6, f/5.6 is approx APEX 5).  Additionally, I've added a variable {sv} which is the APEX value for the ISO (e.g. ISO 100 = APEX 5).  I've also added a new variable {bv} which is an alternate for {brightness} (which has always been an APEX value).

If a camera writes the {tv} and {av} and {bv} values (Exif 0x9201, 0x9202, 0x9203) then they will be displayed directly.  If a camera only writes the older Exif tags for Exposure Time and F Number, then PM will compute the {tv}, {av}, and {bv} APEX values from the camera settings.

The {sv} APEX value will always be computed based on ISO.

Hopefully this will work for everyone.

--dennis

Offline Luiz Muzzi

  • Hero Member
  • *****
  • Posts: 704
    • View Profile
    • Luiz Muzzi Photography
Re: why do i have "funky" numbers in ss and f stop?
« Reply #17 on: November 08, 2013, 04:12:07 PM »
Hi, Dennis
So, back to our original problem, if we get strange numbers with PM's present settings, what does that mean? That old exif tags are not present? That both new and old exif tags are present? But DPP does not show me those numbers. It still shows me the old familiar numbers (settings).
I am trying hard to understand what has changed with the new build of PM.

Luiz,

The new build (coming shortly) will restore the same behavior for variables like {ss} and {f}.  They will continue to display the older Exif tags for Exposure Time and F Number camera settings so nobody will see "funky numbers" anymore.

To handle the newer Exif APEX tags, I've created new variables {tv} and {av} for shutter speed value and aperture value.  They will display the APEX values directly (e.g. 1/60 second is approx APEX 6, f/5.6 is approx APEX 5).  Additionally, I've added a variable {sv} which is the APEX value for the ISO (e.g. ISO 100 = APEX 5).  I've also added a new variable {bv} which is an alternate for {brightness} (which has always been an APEX value).

If a camera writes the {tv} and {av} and {bv} values (Exif 0x9201, 0x9202, 0x9203) then they will be displayed directly.  If a camera only writes the older Exif tags for Exposure Time and F Number, then PM will compute the {tv}, {av}, and {bv} APEX values from the camera settings.

The {sv} APEX value will always be computed based on ISO.

Hopefully this will work for everyone.

--dennis

Hi, Dennis
I think that solution will be perfect.
Thanks for your understanding and quick reaction.
Regards,

-Luiz Muzzi

Offline jwvaughn

  • Full Member
  • ***
  • Posts: 140
  • Retired programmer
    • View Profile
Re: why do i have "funky" numbers in ss and f stop?
« Reply #18 on: November 08, 2013, 10:48:02 PM »
I agree with Luiz - Jerry