EXIF Reader -> Focus Distance

Telecorder

Came across a free EXIF reader that some might be interested in--
http://www.softpedia.com/progDownload/KUSO-Exif-Viewer-Download-52677.html
For Nikon D-lenses, it will give you the details for -->
Field of View in Degrees
Circle of Confusion
Depth of Field in meters
Focus Distance in meters
Hyperfocal Distance
as well as a lot more detail image/lens info...

Now one can have a bit better idea of just how far that subject was at the time of the image...

Its unclear, though, as to just how accurate the Focus Distance reading is to actual subject distance. I've checked the Focus Distance info on a number of images where I know the distance and it seems to be fairly accurate.

At the same time, though, I have other images where it doesn't make sense showing Focus Distance to a plane-in-flight's image as being at 74.99-meters and there's no way it was that close to me... Maybe I'm not understanding of how the Focal Distance vis a vis Hyperfocal distance is coming into play...
Perhaps others might enlighten me...

ziggy53

Good find! Thanks for sharing the link.

Telecorder

A poster in DPR indicated that--
"Different lenses have a different maximum distance beyond which the lens exif reports a fixed distance the longer the lens the greater the maximum distance reported.
For the AF-S 300mm f2.8G ED VR it is ~49metres, for my Sigma 800mm f5.6 it is 125m , within their working ranges the distances reported with these two lenses are very accurate. I've checked the Sigma against Digital OS GB maps and it is certainly within 20cm in 100m.
I test all my lenses using a test chart calibrated for 40 focal lengths and at this distance the two lenses above report the distance to an accuracy of a couple of cm."

This may well be as my 70-300VR maximum reported Focus Distance seems to be to 21.3-meters while my Bigma is 74.99-meters.

Mothman13 did a chart for a Nikon D80 with a 1.5X crop Factor for different FOV image sizes (18mm - 600mm)... Look at the vertical height of the field of view at each subject distance.

http://www.pbase.com/mothman13/image/74511515 (5 - 30 feet)
http://www.pbase.com/mothman13/image/74511517 (35 - 60 feet)

Using my D50/Bigma, I've derived the additional following relationship...
Subject Distance -- ~Vertical FOV (assuming 2,000 vertical pixels)
50-ft -- 20"
100-ft -- 40"
200-ft -- 72"
300-ft -- 110"
400-ft -- 140"
500-ft -- 175"
600-ft -- 210"

At least with the KUSO reader, it would appear the Focus Distance reported within the lens' setup is fairly accurate. I need to do some more controlled tests but this image was taped at 50-feet



And the KUSO EXIF indicates...
Standard Information
Make: NIKON CORPORATION
Model: NIKON D50
ImageSize: 3008x2000
CreateDate: 2007:01:02 14:48:25
ExposureTime: 1/1250"
Aperture: F6.3
MaxAperture: F6.3
DepthOfFocus: 0.25 m (15.73 - 15.97)
CircleOfConfusion: 0.020 mm
HyperfocalDistance: 1981.07 m
FocalLength: 500.0 mm
FocalLength35efl: 500.0 mm (35 mm equivalent: 750.0 mm)
LensSpec: 50-500mm f/4-6.3 D
FocusDistance: 15.85 m --> 51.9-feet....
FocusMode: Manual
MaxFocalLength: 508.0 mm
MinFocalLength: 50.4 mm


Perhaps not as much accuracy as I'd hope +3.8%

kithylin

I know it's bad forum etiquette to dig up old threads, but this is a great program, and thought i would add it also reads RAW NEF files from Nikon cameras.