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Thread started 30 Apr 2017 (Sunday) 11:53
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Is it possible to tell Subject Distance from EXIF data?

 
PCousins
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Post edited over 6 years ago by PCousins.
     
Apr 30, 2017 11:53 |  #1

The image below of a Song thrush is heavily cropped. The bird was a fair distance away and considering it was taken at 1/160s I did not expect it to be so sharp. I was interested in knowing how far the bird was from me, so I went to the exif data as there is so much information and there was no indication......So out of interest only does anyone know if at all possible can you tell distance to subject????

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Mark IV
EF500mm f/4L IS USM +1.4x
ƒ/6.3 700.0 mm 1/160 800 Flash (off, did not fire) Hide EXIF
Make - Canon
Orientation - Horizontal (normal)
X-Resolution - 350 dpi
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Software - Digital Photo Professional
Date and Time (Modified) - 2017:04:29 10:11:29
Artist - XXXXXXXXXXXXXXX
YCbCr Positioning - Centered
Copyright - Paul Cousins Photography
ISO Speed - 800
Exif Version - 0221
Date and Time (Original) - 2017:04:29 10:11:29
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Camera ID - 72157603810225532
Camera Type - Digital SLR
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BigAl007
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Apr 30, 2017 11:59 |  #2

Some lenses do seem to pass distance information to the body, as it is used by the ETTL flash system. This is then also recorded in the EXIF data, as part of the "Maker's notes" IIRC. The issue is that it seems as if the data is very unreliable, and is so of virtually no practical use. it may be of a little more use for images shot close in, but much over ten feet seems to result in almost random results.

Alan


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Wilt
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Apr 30, 2017 13:15 |  #3

I have a number of lenses that pass distance info that is recorded into the EXIF. I discovered, very rapidly, that distance info is PATHETIC!


I have done testing multiple times, using different lenses, and using a lot of distances. The consistency of EXIF distance is 'SELDOM RIGHT', although it might be consistent.

In this test, I put markers every 1' as measured with a tape out to about 25', took a photo, and checked the EXIF for all photos"
https://photography-on-the.net …showthread.php?​p=16743446

I also took a 70-200mm and shot photos at maybe 3m intervals...the distances only updated at intervals (without changed EXIF values for intermediate distances)!
https://photography-on-the.net …showthread.php?​p=16502870

EXPERIMENT to learn best for your lens! Measure, with your camera on tripod, to something the EXACT distance as the last number of the scale of your lens. My Canon 100mm has last distance 15', my Tamron 28-75 has last distance 7'.) AF at that point and see where it lands. Now put something 1' closer in front of your original target, and as you press the focus button note how much/little the scale shifts for a 1' change.


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Apr 30, 2017 13:45 |  #4

I'm guesstimating approximately 17 feet.

Very best,


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Wilt
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Post edited over 6 years ago by Wilt.
     
Apr 30, 2017 13:53 |  #5

Can you give us these two values?:


  1. what is the estimated length of bird (beak to tail) at life size?
  2. what is the estimated length of the bird as shot on sensor (size in mm?, or what percentage of the entire frame width?)


With both answers and knowing the FL of the lens used, it is indeed possible to compute the approximate distance.

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Post edited over 6 years ago by Archibald.
     
Apr 30, 2017 14:12 |  #6

I agree with Alan and Wilt that the distance info in the EXIF is very unreliable.

You could estimate the distance if you need to know it, from a simple formula based on similar triangles. It is

SubjSize/Distance = ImgSize/FocalLength. You can use feet on one side and mm on the other side of the equation.

Solving for distance gives Distance = SubjSize*FocalLength/I​mgSize.

So if the bird is 6" long and its image is 5mm on the sensor, then the Distance is 0.5Ft * 700mm / 5mm = 70 ft.

EDIT - sorry, Wilt, didn't see your post in time.


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May 01, 2017 03:53 |  #7

Thank you to all for your investigations/help...​.

You can see from my EXIF data that there is a hell of a lot of useless information there yet distance to subject comes down to a calculation.

I am not at all any good at estimating distances, I tend to think on the lines of I'm 6ft tall, something which is approx 10 of me away is 60ft. I would say that Archibald & Wilt's calculation is fairly accurate.

In this example the thrush is about 6" and looking at the photo on camera I have just checked it is 5 mm so Archibald was spot on.
Thanks Again




  
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May 01, 2017 05:06 |  #8

This might be useful here,

http://www.scantips.co​m/lights/subjectdistan​ce.html (external link)




  
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May 09, 2017 19:21 |  #9

Focus point plug-in in Lightroom.




  
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Wilt
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May 09, 2017 21:52 |  #10

SevenD2 wrote in post #18350458 (external link)
Focus point plug-in in Lightroom.

The focus point recorded in EXIF is horridly flawed and lacking in accuracy. In post 3 I reported two other posts of mine testing the focus distance precision vs. reality. And the scantips article linked in post 8 agrees with my testing:

"the DSLR Exif data may tell you Focus Distance, except you should realize that the focus distance reported is often seriously incorrect, especially for zoom lenses. "


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May 09, 2017 23:17 |  #11

Wilt wrote in post #18350576 (external link)
The focus point recorded in EXIF is horridly flawed and lacking in accuracy. In post 3 I reported two other posts of mine testing the focus distance precision vs. reality. And the scantips article linked in post 8 agrees with my testing:

"the DSLR Exif data may tell you Focus Distance, except you should realize that the focus distance reported is often seriously incorrect, especially for zoom lenses. "

This is my experience too.


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May 11, 2017 20:22 |  #12

.

SevenD2 wrote in post #18350458 (external link)
Focus point plug-in in Lightroom.

I thought that we had already dismissed that earlier in the thread, as being terribly inaccurate.


.


"Your" and "you're" are different words with completely different meanings - please use the correct one.
"They're", "their", and "there" are different words with completely different meanings - please use the correct one.
"Fare" and "fair" are different words with completely different meanings - please use the correct one. The proper expression is "moot point", NOT "mute point".

  
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Is it possible to tell Subject Distance from EXIF data?
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