Lense detected wrongly with Powershot G3 camera

[manutremo]

I'd just like to report a possible bug in EE1.5b3 with fix pack 1.

I have tested the sricpt with a photo taken with a G3 camera, obviously with its built-in lens.

Even with this non lens changeable camera, ee tries to guess the correct lens. In my case, even if EXIF says a focal of 7 mm, EE chooses my Canon EF 24-70. The camera is correctly guessed.

[Pekka]

manutremo wrote:
I'd just like to report a possible bug in EE1.5b3 with fix pack 1.

I have tested the sricpt with a photo taken with a G3 camera, obviously with its built-in lens.

Even with this non lens changeable camera, ee tries to guess the correct lens. In my case, even if EXIF says a focal of 7 mm, EE chooses my Canon EF 24-70. The camera is correctly guessed.



The lens guess system works by giving points to each "section" of data it finds a match for in database. I'll explain the flow as it is now:

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First it tries to see in manufacturer can be found from database (or as part of the manufacturer text). (1 point)

Then it checks the minimum aperture (does the EXIF aperture fit there?). (1 point)

Then it checks the maximum aperture (does the EXIF aperture fit there?). (1 point)

Then it checks if there is any lens that has that focal lenght available. (2 points)

If it finds a prime with perfect match to focal lenght used, it's given 3 points

Then it checks if you have photo for that lens (considered as more important) (1 point)

Then it checks if lens display name contains focal lenght found in EXIF (1 point)

If there are two or more identical scores, EE will use to one with lower id (older in database).

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As you can see, finding a lens with minimal real data from a database is not a very simple task. It can make errors and it will. If for example aperture from EXIF is not retrieved or it is wrong, the lens guess may be wrong.

Also, you may notice that it is important to have all the fields filled in lens editor for those lenses that you use.

The difference between EE and e.g. Breezebrowser is that Breeze just displays a line of text. EE will find a match in database which brings you lot of other data of the lens.

I will try to fine tune the system for better match for sure. Changing emphasis on different areas is one thing. One possibility to improve accuracy is to add a button to lens editor which would mark "my most used lenses", for cases where many lenses get equal score in guess algorithm.

[gillyworld]

Pekka,

Is this the method that programs like Brezebrowser , Zoombrowser, Yarcplus use? I have never seen the wrong values in these programs so is there a better way of calculating the values?

Alan

[Pekka]

gillyworld wrote:
Pekka,

Is this the method that programs like Brezebrowser , Zoombrowser, Yarcplus use? I have never seen the wrong values in these programs so is there a better way of calculating the values?

Alan

First of all Breeze displays a string of text, EE finds a certain lens id in database using scattered data. There is a BIG difference.

Secondly, there is some data in manufacturer specific part of EXIF data (MakerData) which can be used to improve guessing, like Canon EXIF which has a _possibility_ to display

(23) "long" focal length of lens (in "focal units")
(24) "short" focal length of lens (in "focal units")
(25) "focal units" per mm

And when these will be taken into account (and if they are saved by the camera) accuracy will be improved.

[Pekka]

Ok, I did some improvements to try out:
http://photography-on-the.net/forum/showthread.php?t=18319

[manutremo]

I agree with all that, but we are talking about a non-changeable lens camera.

Wouldn't it be easier that we have a switch in the camera record that says if the camera can switch lenses or not?

In the case that the camera doesn't have changeable lenses, you can skip the lens guessing, as for sure it will be the in-built lens.