"Zoom with Feet" using zoom lens

Not sure this is correct forum, but here goes: When using a zoom lens, why would a professional photographer choose to use min. and max. focal length on zoom lens the majority of the time, i.e., "Zoom with feet", and seldom use variable focal lengths as the zoom lens is designed for? I've been a photo hobbyist for some time, acquired the EOS Digital Rebel / 300D when it first came out, and after thous. of photo's, still learning. About a year ago, I purchased Bryan Peterson's "Understanding Exposure" -- very good book -- and just recently noticed that on maybe 90% of his zoom lens examples, he's either wide or long, very seldom in between. And when he does cite a variable focal length, it's usually an exact number. For one example, tho, on a 17 - 35mm, he did cite 24mm, one of a few. The subject matter of the book, of course, is exposure, but for each of his examples, he lists lens, focal length, f/stop, etc., and did not go into any detail on focal lengths. Seems to me that one is defeating a major purpose of zoom lenses when choosing min./max. focal, and seldom using variable focal capabilities.

Would optics possibly be a reason?

Tks for your comments.

Oh. Well, I'm not a pro, and I use pretty inexpensive lenses, so this probably doesn't apply to most pros. But sometimes I zoom with my feet because I'm in a really, really low-light situation and need as much light as I can get. At 18mm I can get f/3.5; if I zoomed in all the way to 55mm I would lose two stops of light. Once I get a better lens this practice will cease.

You're over-thinking it. You chose a focal length that provides the perspective you want & move your feet to frame the shot as desired. There's no conspiracy against odd focal lengths.

I have a question that sorta relates to this, too, if you shot a pic with say, a 20mm lens, then one with a 200mm, but way way way further back, so you got the same amount in the pic, would the image look the same?

No.

cdifoto wrote in post #6400415
You're over-thinking it. You chose a focal length that provides the perspective you want & move your feet to frame the shot as desired. There's no conspiracy against odd focal lengths.

Isn't that backwards? You move your feet to get teh right perspective then zoom to get the desired field of view, right?

Nope. I know what perspective I want before I know what framing I want.

stephen_g wrote in post #6400459
I have a question that sorta relates to this, too, if you shot a pic with say, a 20mm lens, then one with a 200mm, but way way way further back, so you got the same amount in the pic, would the image look the same?

There's a good sample of this somewhere around here but I can't seem to find it at the moment. The sample shows two people and a mountain in the background. The first shot is a wide lens and the photographer very close to the subjects. In this shot the people appear very large in the frame since they are so close to the camera. The second pic has the photographer moved back a ways and using a longer lens to get the same amount of the mountain in the frame. The mountain appears the same size but the people look much smaller because they are farther away from the lens.

cdifoto wrote in post #6400473
Nope. I know what perspective I want before I know what framing I want.

Exactly. So you move your feet to get into the position that gives the correct perspective then choose a lens/focal length that gives you the frame, right?

Longer focal lengths exaggerate depth of field creating more diffused bokeh. For portraiture and shooting more definitive subjects they require longer focal lengths to isolate themselves from the background, obviously. As for using shortest focal lengths to pull off the same look, you'd have to get very close and the subject would become distorted due to the wide field of view.

It's mostly about personal preference. I'd rather have a wide prime and a telephoto prime over a zoom because I too end up using 24mm or 105mm on my lens...

krb wrote in post #6400496
Exactly. So you move your feet to get into the position that gives the correct perspective then choose a lens/focal length that gives you the frame, right?

No.

Perspective is how things appear in relation to one another. Your own example of the mountain and the people is about perspective...due to focal length chosen.

I usually know how I want things to appear in relation to one another before I know how I want to actually frame the shot.

Take a portrait as an example. I want the sexy girl's features to be flattered, rather than distorted. So I'm not going to choose an ultra-wide lens, am I? No! I'm going to choose a short tele. 85mm for example. There. I've got my focal length chosen. I'm not even packed up for the shoot, but I already know what focal length I want to use. Now, when I get to the shoot and set up, THAT'S when I frame my shots...with my feet.

krb wrote in post #6400490
There's a good sample of this somewhere around here but I can't seem to find it at the moment. The sample shows two people and a mountain in the background. The first shot is a wide lens and the photographer very close to the subjects. In this shot the people appear very large in the frame since they are so close to the camera. The second pic has the photographer moved back a ways and using a longer lens to get the same amount of the mountain in the frame. The mountain appears the same size but the people look much smaller because they are farther away from the lens.

I saw another similar example in a book that I have (or, used to have), but I cannot think off-hand which book it is. It shows the difference clearly. This particular book had 3 or 4 different focal length shots, IIRC.

cdifoto wrote in post #6400566
Perspective is how things appear in relation to one another. Your own example of the mountain and the people is about perspective...due to focal length chosen.

Perspective (defined here as size relationship between objects near the camera and objects further from the camera) is totally controlled by distance between the camera and the various objects in the image. Focal length, in itself, has nothing to do with the perspective.

That said, experienced photographers often know what focal length they want to use (for a portrait, for example), because the focal length and the framing they want will force the photographer to be the proper distance from the primary subject to get the desired perspective.

The bottom line is, even if the photographer does not realize it, DISTANCE is what controls perspective, and NOT focal length.

Here's some proof: The two shots in this post from a previous thread were made with 20mm and 200mm lenses with the camera and subject in the same position. The 20mm shot was cropped to provide the same framing as the 200mm shot. If you examine the shots closely, you will find that the perspective (relationship of elements of the subject that are at different distances from the camera) is identical in both shots. Click on the thread name in the link to see the whole thread - good reading for the subject.

cdifoto wrote in post #6400566
No.

Perspective is how things appear in relation to one another. Your own example of the mountain and the people is about perspective...due to focal length chosen.

Okay, granted that high level decisions of "long vs short" happen first.

Working in a controlled environment gives you that luxury.

Now take sports as an example. You "move your feet" to select the perspective. Field level or up in the stands. Visitor's goal vs home goal vs somewhere along the sidelines. Then during the game you use the zoom to frame players to get the shots you want.

SkipD wrote in post #6400930
Perspective (defined here as size relationship between objects near the camera and objects further from the camera) is totally controlled by distance between the camera and the various objects in the image. Focal length, in itself, has nothing to do with the perspective.

That said, experienced photographers often know what focal length they want to use (for a portrait, for example), because the focal length and the framing they want will force the photographer to be the proper distance from the primary subject to get the desired perspective.

The bottom line is, even if the photographer does not realize it, DISTANCE is what controls perspective, and NOT focal length.

Here's some proof: The two shots in this post from a previous thread were made with 20mm and 200mm lenses with the camera and subject in the same position. The 20mm shot was cropped to provide the same framing as the 200mm shot. If you examine the shots closely, you will find that the perspective (relationship of elements of the subject that are at different distances from the camera) is identical in both shots. Click on the thread name in the link to see the whole thread - good reading for the subject.

Yeah I should have gotten into it a little deeper than that but...eh. I figured it's kind of a given. You're using a longer lens (focal length) because you want to be further away from the subject (distance) and still have tight framing (feet).