[KPhotoAlbum] "F Number" vs. "Aperture Value"

[Robert Krawitz]

On Mon, 02 Dec 2019 23:32:30 +0100, Johannes Zarl-Zierl wrote:
> Hi,
>
> Forgive me my technical illiteracy - I didn't realize that there are
> two almost identical measures at play here.
>
> The value called "Aperture Value" in the UI corresponds to
> Exif.Photo.ApertureValue, which is the APEX[1] value.  The value
> called "F Number" is Exif.Photo.FNumber, which is the focal ratio as
> commonly used.
>
> For better clarity, I propose we relabel the first entry to
> "Aperture Value (APEX)" and the second one to "Aperture Value (F
> Number)".  From what I've read about APEX though, I conclude that
> the APEX aperture value should have different values, i.e. the range
> is probably incorrect.

More useful than the individual APEX numbers would be the EV, which is
derived from the ApertureValue, ShutterSpeedValue, and ISO.  See this:
https://www.dpreview.com/forums/thread/447586#forum-post-4675324

I would definitely have use for finding all photos shot at a given EV
value (or range thereof).  That would, however, be an incompatible
change and would require rescanning EXIF data, so it's not something
we want to do lightly.  But it really isn't clear to me what use I'd
have for the APEX aperture value by itself.

> [1] https://de.wikipedia.org/wiki/Additive_System_of_Photographic_Exposure
>
> Am Sonntag, 1. Dezember 2019, 02:49:26 CET schrieb Johannes Zarl-Zierl:
>> Hi Robert,
>> 
>> Am Samstag, 30. November 2019, 03:41:28 CET schrieb Robert Krawitz:
>> > Why are there two separate controls in the search dialog?  They mean
>> > the same thing (but don't have the same effect -- one finds zero
>> > matches while the other finds the correct matches).
>> 
>> That's an interesting question. A casual glance at the source code doesn't
>> help, unfortunately: apparently both the aperture and the f-number were
>> added within a short amount of time (33cfb31cf vs 803e77395).
>> 
>> My best guess is that fnumber was first renamed to aperture, and then a
>> mistake was made when applying some patch, reintroducing fnumber...

-- 
Robert Krawitz                                     <rlk at alum.mit.edu>

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