Puzzling EXIF Data (Page 2): Simple test: get a yardstick, lean it against a wall vertically, stand back 42 feet (14 paces) and just look at it at 500 mm in landscape mode. If it fills...

jcboy3

jerryc41 wrote:

This calls for several hours of experimentation and documentation. See, I just gave your day purpose.

Use different lenses and different focal lengths and see what the EXIF says. That will give you a base for comparison. You're comparing two things here - mechanical movement/setting of the lens, and electronic interpretation of the lens's position.

I can't wait for your report!

Simple test: get a yardstick, lean it against a wall vertically, stand back 42 feet (14 paces) and just look at it at 500 mm in landscape mode. If it fills the frame top to bottom, you are shooting at 500 mm no matter what the lens is reporting. If you are really only shooting at 300 mm, the image height is 5 feet so the yardstick will only appear to be 3/5's of the frame.

This should only take a few minutes (longest part is finding that darn yardstick). Use the remaining several hours to mow the yard because the grass is up to 6 inches on the yardstick.

Capture48 Loc: Arizona

I would check to be sure you have the latest firmware on your camera even though it seems to recognize the lens.

Picdude Loc: Ohio

jcboy3 wrote:

Simple test: get a yardstick, lean it against a w... (show quote)

Very interesting test. Please don't take this as me doubting you in any way, but how did you arrive at those numbers? I ask because I may want to use that formula with different lenses.

jcboy3

jcboy3 wrote:

Simple test: get a yardstick, lean it against a w... (show quote)

OOPS, this is for portrait mode, not landscape. For landscape mode, you need to be 63 feet back.

SonnyE Loc: Communist California, USA

jcboy3 wrote:

Simple test: get a yardstick, lean it against a w... (show quote)

What if the grass is freshly mowed? (The gardeners were just here.)

Can you post how you come to these distances? (Yardstick standing by.)

Sounds like a good shade tree mechanic way of checking. ;)

jcboy3

Picdude wrote:

Very interesting test. Please don't take this as me doubting you in any way, but how did you arrive at those numbers? I ask because I may want to use that formula with different lenses.

I made a mistake in the previous post; quoted numbers are for portrait orientation, not landscape. I usually use this relationship for portrait shooting, so...

At any rate, here is the formula:

Object Height related to focal length and distance

The relationship between object height and distance for a given lens and sensor is the following:

H / D = (S / F) * (Hp / Sp)

where

H = height of the object (unit of choice)
D = distance to the object (unit of choice)
S = sensor height (mm)
F = focal length of lens (mm)
Hp = height of the object in the image (pixels)
Sp = sensor height (pixels)

To solve for distance, we have

D = H * (F / S) * (Sp / Hp)

If the object fills the frame, then Hp=Sp.

For full frame, the sensor height is 24mm.

In this example, the object height is 3 feet, and the lens is 500mm

D = 3 feet * 500mm / 24mm

D = 62.5 feet

I shoot micro Four Thirds format, and use a simple rule of thumb for portrait mode:

With 45mm lens, 4 foot height, 10 foot distance.

For full frame, the rule is 90mm lens, 4 foot height, 10 foot distance.

jeep_daddy Loc: Prescott AZ

This is the second time I've read here on UHH about third party lenses reporting wrong EXIF info and images appearing to be about the same as a shorter native lens. It's really got me thinking that I'm glad that I've got all native lenses. I just watched a youtube video on focus breathing because I'd never heard of it. I had no idea that there was so much change in a lens being focused close and far. Now I know.

jcboy3

SonnyE wrote:

What if the grass is freshly mowed? (The gardeners were just here.)

Can you post how you come to these distances? (Yardstick standing by.)

Sounds like a good shade tree mechanic way of checking. ;)

Then I would kick back on the patio with a beer or glass of wine.

I've posted the equation in another response on this thread.

It's a useful way to check your lens for focus breathing (where close focus changes the focal length. Here's how to do it:

Put up the yardstick, step back 60 feet, put the lens at 500mm and focus. Yardstick should fill the frame.

Walk up to 20 feet and focus. You should only have a foot in the frame (1/3 distance, 1/3 height). If you see 15 inches, then the focus breathing has shortened the focal length to about 400mm.

You can take this right up to the minimum focal distance, and calculate the worst focus breathing.

Psergel Loc: New Mexico

jcboy3 wrote:

Then I would kick back on the patio with a beer or... (show quote)

Try the test after 3 or 4 beers. You may discover that focus breathing is no longer an issue.

SonnyE Loc: Communist California, USA

jcboy3 wrote:

Then I would kick back on the patio with a beer or... (show quote)

Excellent! Thank You for both explanations.
But it's too early for me to tip the wine box yet. I have a window I want to install. :lol:
When it's hot this afternoon though... ;)

Nikon_DonB Loc: Chicago

I called Sigma and they referred me to a company on the North side of town, Bigston Corp. who will upgrade the firmware while I wait. Still waiting to hear from their tech as to when.

Sigma stated that,"If the barrel reads 500mm, it is at 500mm." "There are firmware updates available."

I think it's time for the new 150-600 Tamron.

Psergel Loc: New Mexico

Nikon_DonB wrote:

I called Sigma and they referred me to a company on the North side of town, Bigston Corp. who will upgrade the firmware while I wait. Still waiting to hear from their tech as to when.

Sigma stated that,"If the barrel reads 500mm, it is at 500mm." "There are firmware updates available."

I think it's time for the new 150-600 Tamron.

The Tamron has already had at least one FW update

:lol:

Nikon_DonB Loc: Chicago

I just think it sucks how these big corporations rush this crap to market, to make the almighty dollar.

Then we have to run all over the place, like a bunch of idiots, to make it work correctly and get updates.

SonnyE Loc: Communist California, USA

Nikon_DonB wrote:

I just think it sucks how these big corporations rush this crap to market, to make the almighty dollar.

Then we have to run all over the place, like a bunch of idiots, to make it work correctly and get updates.

It's worse than that, Don.
They release this stuff, then take whatever feedback they can get from the victims (us) to fine tune their mistakes. (Haven't you ever seen the pop-up asking if you want to send a report to... )
Meanwhile, we get to work the bugs out for them.
John Q. Public is an awesome test bed, many folks in many countries. :roll: ;) :-P

Nikon_DonB Loc: Chicago

SonnyE wrote:

It's worse than that, Don.
They release this stuff, then take whatever feedback they can get from the victims (us) to fine tune their mistakes. (Haven't you ever seen the pop-up asking if you want to send a report to... )
Meanwhile, we get to work the bugs out for them.
John Q. Public is an awesome test bed, many folks in many countries. :roll: ;) :-P

I believe you are right Sonny