Calculating subject distance from a photo

Hi guys and girls,

I am interested in those better at math than I working out how far away I was from the crab in this photo:

My estimation is that the crab is depicted at about 1:7 at 105 mm, which equates to about 96 cm distance to the sensor, so let's say 1 m.

HTH, kind regards, WIm

Thanks wimg, I won't argue with you, but I thought it was more. Oh well, there goes that theory

My analysis says about the same as WImg...I scaled the crab on my screen, I scaled the full photo width on my screen. Based upon your estimate of 2" crab body, the photo spans a 30" length. Assuming 105mm on 5D, that works out to about 95" shooting distance

Let's see if we can guess how close was I to this?

HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO

here is bigger pic:

and all the exif info:
Date/Time04-Mar-2007 13:19:49MakeCanonModel​Canon EOS 30DFlash UsedNoFocal Length70 mmExposure Time1/250 secAperturef/5.6ISO Equivalent200Exposure BiasWhite BalanceMetering Mode(-1)JPEG QualityExposure Programaperture priority (3)Focus Distance

HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO

Wilt wrote in post #3015889
My analysis says about the same as WImg...I scaled the crab on my screen, I scaled the full photo width on my screen. Based upon your estimate of 2" crab body, the photo spans a 30" length. Assuming 105mm on 5D, that works out to about 95" shooting distance

Thanks Wilt, I'll defer to you guys' calculations. I'll check next time I'm back there .

Simon....

grinchy wrote in post #3015904
Let's see if we can guess how close was I to this?

HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO

I would say in most circumstaces....too close! I don't trust those guys and their friends lurking near by. Do you have a rear view mirror on your camera?

SimonBl wrote in post #3015392
Thanks wimg, I won't argue with you, but I thought it was more. Oh well, there goes that theory

Sorry, just realized I took lifesize of crab, to compare magnification, so my calculations are off a factor of 2 or thereabouts.

Ok, again.

Crab is 2", or 50 mm. I took it that the legs were included in this, not just the shell. Crab is about 1/7 of total picture width. So the picture then has a size of about 14 ", or approx. 350 mm.

Sensor width is 24 mm, 350 mm / 24 mm = 14.6, let's say 15 to make things easier. This means that magnification is 1 : 15, not my earlier 1 : 7. This could actually be implied from the fact that the crab was about 2 inches, and the sensor is about 1 inch .

Anyway, this means the distance to the sensor was approximately 1792 or 1800 mm, or roughly 6 feet.

Sorry to have misled you. I do have to admit I was in a rush, on my way out, when I saw your post.

BTW, if the carapace only of the crab was 2 inch, it was even further away. In that case, the width of the picture is about 34 inches, and magnification about 1 : 70, which means at 105 mm a distance to the sensor of about 7.5 m, or 25 feet.

HTH, kind regards, Wim

grinchy wrote in post #3015910
here is bigger pic:
and all the exif info:
Date/Time04-Mar-2007 13:19:49MakeCanonModel​Canon EOS 30DFlash UsedNoFocal Length70 mmExposure Time1/250 secAperturef/5.6ISO Equivalent200Exposure BiasWhite BalanceMetering Mode(-1)JPEG QualityExposure Programaperture priority (3)Focus Distance

Sorry, Grinchy, can't help you here, as the Focus Distance has fallen away. Considering it was taken at 70 mm, I would agree with JMW: too close!

Kind regards, Wim

wimg wrote in post #3018369
BTW, if the carapace only of the crab was 2 inch, it was even further away. In that case, the width of the picture is about 34 inches, and magnification about 1 : 70, which means at 105 mm a distance to the sensor of about 7.5 m, or 25 feet.

Aha, I did mean the carapace only (but couldn't remember what it was called) and I am a LOT happier with that distance. It was a looong way down in a crevice. The snail was about 1" (25mm) in size (comapred to others around), so that feels good to me.

Many thanks for the 2nd look.

Regards,

Simon....

wimg wrote in post #3018390
Considering it was taken at 70 mm, I would agree with JMW: too close!

And I, for 3, agree!

I know it was WAY to close for my comfort....believe it or not that gator actually came out of the water and charged at me up the bank...I nearly jumped right out of my shoes and proceeded to run a 2.2 40 yd dash...