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01-11-2017, 12:41 PM   #1
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Determining Focal Length of a Photo

How does one determine the focal length used for a photo, if this information is not present? What focal length was used for this photo of a pleasing backyard pool in this web page?:

How Turf is Different From Astro Turf - This Little Light CD

I downloaded the jpg and none of the exif data was available, and also googled on the subject. Some information was available, but one had to know some dimensions of objects in the photo already, such as the height of a building, and the distance from the photographer to it. I don't know any dimensions in this photo, but might be able to estimate the height of the umbrella stand.

Have you attempted such a calculation before? How did you go about it?

Thanks for any help.

Glenn

01-11-2017, 12:52 PM - 1 Like   #2
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QuoteOriginally posted by GlennG Quote
How does one determine the focal length used for a photo, if this information is not present? What focal length was used for this photo of a pleasing backyard pool in this web page?:

How Turf is Different From Astro Turf - This Little Light CD

I downloaded the jpg and none of the exif data was available, and also googled on the subject. Some information was available, but one had to know some dimensions of objects in the photo already, such as the height of a building, and the distance from the photographer to it. I don't know any dimensions in this photo, but might be able to estimate the height of the umbrella stand.

Have you attempted such a calculation before? How did you go about it?

Thanks for any help.

Glenn
Its probably possible to work out the answer mathmatically, assuming the image hasn't been cropped, but its a lot easier to just estimate the focal length based off the image. For instance, it has almost the whole yard in the image and its taken from inside the yard, which means it has to be a fairly wide angle lens. The edges don't appear to be stretched and there is pretty minimal perspective distortion, so we can assume its not an ultrawide. I'd say something in the 24-35mm range (on a FF), likely closer to the 24. Something like the 15 or 21 on APS-C
01-11-2017, 01:01 PM   #3
Des
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QuoteOriginally posted by enoeske Quote
I'd say something in the 24-35mm range (on a FF), likely closer to the 24. Something like the 15 or 21 on APS-C
FWIW, my guess would be 14-18mm on APS-C or equivalent. The umbrella and potted plant look distorted to me (barrel distortion, typical of UWA).

It gets really hard if people have fixed distortions in PP or cropped a lot. Then you are left with trying to judge from perspective, subject/background differences etc.
01-11-2017, 01:16 PM   #4
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QuoteOriginally posted by enoeske Quote
Its probably possible to work out the answer mathmatically, assuming the image hasn't been cropped, but its a lot easier to just estimate the focal length based off the image. For instance, it has almost the whole yard in the image and its taken from inside the yard, which means it has to be a fairly wide angle lens. The edges don't appear to be stretched and there is pretty minimal perspective distortion, so we can assume its not an ultrawide. I'd say something in the 24-35mm range (on a FF), likely closer to the 24. Something like the 15 or 21 on APS-C
QuoteOriginally posted by Des Quote
FWIW, my guess would be 14-18mm on APS-C or equivalent. The umbrella and potted plant look distorted to me (barrel distortion, typical of UWA).

It gets really hard if people have fixed distortions in PP or cropped a lot. Then you are left with trying to judge from perspective, subject/background differences etc.
Thanks for your inputs here. Yes, my guess was also in the wide to ultra-wide region, based on similar thoughts. Just FYI, I was researching some potential home landscaping ideas. There are a number of photos that I've seen where I wondered about the focal length and have wondered just what are we looking at in the photos. Wide and ultra-wide lenses can make home interiors and exteriors look much different than they really look when viewed in person. I know that really wide photos are useful to get the scene all in one photo, but sometimes I think the result is actually a disservice if it distorts reality too much.

01-11-2017, 05:28 PM   #5
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QuoteOriginally posted by GlennG Quote
Wide and ultra-wide lenses can make home interiors and exteriors look much different than they really look when viewed in person. I know that really wide photos are useful to get the scene all in one photo, but sometimes I think the result is actually a disservice if it distorts reality too much.
If you are selling real estate you want the rooms to look big!

Ultrawide lenses can be a lot of fun. You can use the distortion of perspective for creative effect. It's true that, used badly, they make uninteresting photos (just trying to get everything in), but if you get close to a strong subject they can work really well. Wide lenses require particular attention to composition.

I think people have got used to wide angle shots because they are the default on smartphones. And there are countless bad photos taken with smartphones.

Last edited by Des; 01-12-2017 at 06:38 AM.
01-18-2017, 05:50 PM   #6
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You need to know or assume some things. First and foremost is the actual size and distance of an object and the format of the negative

Basically image size = subject size x focal length/ distance

This could be as basic as taking the width of the yard through the middle of the shot and the distance from shooting positio

The shot in the link was likely done with a 10-16 mm prime ( i M O)
01-18-2017, 06:44 PM - 1 Like   #7
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QuoteOriginally posted by Des Quote
If you are selling real estate you want the rooms to look big!

Ultrawide lenses can be a lot of fun. You can use the distortion of perspective for creative effect. It's true that, used badly, they make uninteresting photos (just trying to get everything in), but if you get close to a strong subject they can work really well. Wide lenses require particular attention to composition.

I think people have got used to wide angle shots because they are the default on smartphones. And there are countless bad photos taken with smartphones.
I love my 10-20mm. Most expensive lens I own, and it was worth every penny.






01-19-2017, 05:39 AM   #8
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Wonderful way to prove the creative potential of ultrawides @Sagitta. Superb shots.
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