exiftool is an incredibly powerful metadata editor /extractor it works on more than just photographs. It's a commandline tool
essentially the important options are
exiftool -s yourphoto.dng or jpeg or whatever.
This produces a list of all tags and values in the file. in its prefered name for the tag.
if you don't use the -s switch you get expanded names
so say
FOV :43.6 degrees
becomes
field of view : 43.6 degrees
to read a singletag
exiftool -FOV yourphoto.dng
would return just the one tag.
exiftool -AFPointsInFocus .
This is a useful one for pentax users but first lets explain the . it means current directory and exiftool will run on every file it finds that it knows how to get exif information from. so cd into a folder with photo's and type that and you will get the focus points used.
Now thats quite handy there are 11 focus points on most Pentax camera's and if you put a rule of thirds grid on top of your photo
there is 1 at each intersection the middle rectangle has 1 halfway along each side if you draw a cross between the intersections you get the centre focal point and the two outside ones are level with the centre point and in the mid point of the 2 rectangles left and right of the centre rectangle.
It helps to know where the camera thought it had focus.
The interesting value is none. So not in focus at any focus point of course its a plain of focus so something might be on that plain but it's likely this is a bad shot unless you focused and recomposed.
exiftool -AFPointsInFocus . > focus.txt
this redirects the output of exiftool to a text file 'focus.txt' this text file you can run a find on later and e.g find none and you might get told it occured 4 times and you can go to the list and there will be a photo filename associated with each case of 'none'.
Ok writing
exiftool -LensType yourphoto.dng
Lens Type : PENTAX-F 28-80mm F3.5-4.5 or Sigma or Tokina Lens
ok now that isn't supported by dx0 but what module might be close?
exiftool -LensType="Sigma 24-70mm F2.8 IF EX DG HSM" yourphoto.dng
and now that is written to the dng
its the sametag switch as for a read but ="new tag value is wriiten in quotes"
if a tag is read only or incorrect for whats required exiftool will tell you.
And as it happens thats enough to convince dx0 that you were using that lens on that body. You can find a list of all lenses that Pentax writes to the exif file and in dx0 module manager which lenses they have a supporting module for.
Ok but now i'm getting to where I am a little stuck.
Light Levels
On a DA 18-55 lens i took a series of shots at different apertures the results went something like
exiftool -LightValue
15 15 15.1 14.6 15 15 which is pretty much the same as you would expect
but with a km lens with green button metering i got no light value
AEMeteringSegments : 14.0 12.9 11.8 12.2 13.2 11.4 11.0 11.4 12.5 12.6 13.0 14.2 13.1 11.8 12.1 13.6 11.5 11.1 11.1 12.9 14.5 13.5 14.2 13.9 13.0 12.0 13.6 13.2 10.6 12.4 12.6 14.0 13.8 13.6 13.8 13.4 12.5 14.2 14.2 13.5 14.4 12.9 13.2 14.8 13.1 13.4 13.5 14.0 16.0 14.8 13.0 13.4 13.5 13.4 13.8 13.8 14.1 14.0 13.0 14.0 14.5 14.2 14.0 14.9 13.8 13.8 13.9 14.6 14.1 12.5 14.5 14.2 14.6 14.2 14.9 14.1 14.0
might have the answer if i knew where they were (the final light value is 15.0 )
I just did a series of shots. Effective LV Shutter Speed
======== ./_IGP3570.DNG F2.8
Effective LV : 2.5
Shutter Speed : 1/8000
======== ./_IGP3571.DNG F4
Effective LV : 2.5
Shutter Speed : 1/8000
======== ./_IGP3572.DNG F5.6
Effective LV : 1.0
Shutter Speed : 1/3000
======== ./_IGP3573.DNG F8
Effective LV : 0.0
Shutter Speed : 1/1500
======== ./_IGP3574.DNG F11
Effective LV : -1.5
Shutter Speed : 1/500
======== ./_IGP3575.DNG F16
Effective LV : -2.5
Shutter Speed : 1/250
======== ./_IGP3576.DNG F22
Effective LV : -3.5
Shutter Speed : 1/125
I think I may have cracked it Effective LV is exposure compensation!
AE Metering Segments is pretty much identical for each shot example below.
AE Metering Segments : 10.4 10.6 11.2 11.1 12.6 13.9 14.2 14.1 13.9 13.6 13.4 10.4 11.2 11.2 11.6 12.8 14.1 14.4 14.2 13.9 13.5 13.0 11.2 11.2 11.0 11.6 12.6 13.9 14.0 13.8 13.4 13.0 12.4 9.8 10.0 9.4 10.1 11.0 12.2 12.1 11.9 11.8 11.4 11.1 8.4 9.0 8.5 9.5 10.2 10.2 9.6 8.8 8.6 8.2 8.2 8.1 8.4 8.4 9.2 9.6 9.9 9.0 7.5 7.6 7.8 8.0 7.6 8.0 8.8 9.1 9.2 9.1 8.2 7.1 7.1 7.4 7.6
So the camera is measuring the light with the aperture wide open, then when the green button is pressed it calculates exposure compensation for the closed down aperture. It wasn't quite fair to the body because it's too bright outside. But i think based on this it should be possible to calculate the aperture used on a given lens
M42 lenses will be harder to figure if you take a shot at maximum aperture and record the light level then the following shots will probably stepping down 1 EV a stop.
What do you think