DOF in Exif data

[ATJ]

I was scrolling through the Exif data for one of my images and I discovered that the camera (D300) records the depth of field which I thought would be quite useful. It also records the distance of the focal plane from the subject based on the focus information.

Here's the data from a group photo I took on the weekend with my 18-55mm lens:
Focus Distance : 2.66 m
Depth of Field : 5.45 m (1.64 - 7.09)

Quite useful I thought as it even tells you the front and the back of the sharp areas... that was until I looked at a macro shot at 1:1 with my 200mm lens at f/22:
Focus Distance : 0.50 m
Depth of Field : 0.00 m (0.50 - 0.50)

Um... a little more precision would have been helpful.

The Exif data does contain the hyperfocal distance which can be used with the focusing distance to determine distance to nearest and furthest points with acceptably sharp focus. For the same 1:1 image above:
Hyperfocal Distance : 90.77 m

According to my ILFORD Manual of Photography:

Distance to the nearest point of acceptable sharpness = (90.77 * 0.50)/(90.77+0.50) = 0.49726
Distance to the furthest point of acceptable sharpness = (90.77 * 0.50)/(90.77-0.50) = 0.50277

So the DOF is 5.51mm.

[colin_12]

Thanks for the calcs Andrew. They may come in handy.

[Glen]

Thanks Andrew for letting me know about a feature I didn't realise was there

[ATJ]

Here's a batch file I created to extract the DOF data from the Exif:

Code: Select all

@echo %1
@c:\programs\exiftool-7.06\exiftool -Focallength -Fnumber -FocusDistance -DOF -HyperfocalDistance %1
@pause

This uses exiftool and would need to be modified depending on where you place the code for exiftool

I then associated the batch file with .NEF files and so all I have to do is right click on the .NEF file and select Open with... DOF.bat and it displays the data, e.g.

Code: Select all

"D:\alTables\NikonD300\200810\DSC_5098.NEF"
Focal Length                    : 60.0mm
F Number                        : 16.0
Focus Distance                  : 0.21 m
Depth of Field                  : 0.01 m (0.21 - 0.21)
Hyperfocal Distance             : 11.23 m

That provides enough information to determine the DOF with more precision. Note that it is still only an approximation.

[ATJ]

oh, and the formulae for determining the distances are as follows:

Distance to nearest point in acceptably sharp focus = (h * u)/(h + u)
Distance to farthest point in acceptably sharp focus = (h * u)/(h - u)

where h is Hyperfocal Distance and u is Focus Distance.

You can extend the formulae to:

Distance in front of focus = u - ((h * u)/(h + u))
Distance behind of focus = ((h * u)/(h + u)) - u

[gstark]

That provides enough information to determine the DOF with more precision. Note that it is still only an approximation.

And there you have it, folks: another dslrusers.com first - the world's first precision approximation!

[ATJ]

the world's first precision approximation!

Precision says nothing about accuracy and so it makes perfect sense (mathematically) to have precision approximations and estimates.

And certainly not a world first: http://www.google.com.au/search?hl=en&q ... arch&meta=

[Mr Darcy]

Thanks Andrew you saved me from putting my Green Cardy on again. It's too hot for it at the moment

[ATJ]

Thanks Andrew you saved me from putting my Green Cardy on again.

You're welcome. I already had mine on for the DOF calculations.