Late night delima

Apr 5, 2005
Clarksville, IN
How to calculate the distance you were from your subject when you took the photo...if it is not in the exif file. Plus apparently the 200-500 nikkor doesn't report anything above 133 meters.

This is for the techy types. most may never even want to know!

I took some photos of a night heron a few weeks ago and when I was culling the images I wondered just how far away he was from me. I checked the exif but there was nothing listed. a quick on the internet found several reports of the 200-500 with d500 not reporting that value to the exif file.

the next best thing is to calculate it so started a couple hour exercise in finding the easiest way. The calculation is actually very simple;
The (actual object size times the focal length) all divided by the same images size on the sensor. All in mm.

here is what I came up with to make it as simple as possible. It seems like a lot but once you gather the information of the camera and change the ruler and image size in photoshop it's pretty simple. I have included a spread sheet screen grab at the end of the instructions.

I also proofed this by shooting a brick wall at 25 feet plus or minus a few inches. so I had easy access to actual measurements.

When your lens does not or is inconsistent with reporting the focus distance there is a way you can calculate it after the shot. The following is the information you need to have to do it.

Focal length of the lens when you took the picture,

The width of your sensor in mm

The width of your sensor in pixels

And most importantly, the length or height of the subject in mm

The width of the subject on the sensor after the photo was taken. your measurement should be made at the same distance at bove ends.
height of a person, a bird, length of a car, about the same distance as your subject or the subject itself. EX; if you took a photo of uncle Joe and you know about how tall uncle Joe is then that is all you need.

To make it even simpler I resized the image in photo shop
go to Edit / preferences / units and rulers
change ruler units to pixels
Click ok

Load your image, if raw, process and open
go to image/image size
set the width of your image to your sensor width in mm.
The height should be set automatically but it really isn’t needed for this.
I use a resolution of 300
Click ok

Place your cursor on one end of your object and write down the pixel number, do the same at the other end of the object, subtract the two, this is your object size in pixels. And goes in the spread sheet.
it's easiest if you build the spread sheet.

you can also easily calculate the size of something if your lens reports the distance.
spread sheet.jpg
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