dpullum Loc: Tampa Florida

Better question is why UHH posts, give little information and why do people get bated to answer a vague question. Ballsafire has been around UHH long enough to know that it is not a "20 Questions" game. Big guy asked for further information and Ballsafire did not reply. ??????

Architect1776 Loc: In my mind

I believe that the question was crystal clear. One needs to look at the context and the stupid file compession responses are totally unrelated to DOF part of the question. Where visual compression of elements fits the context exactly. It is very simple to distinguish what is being asked and needed answer. If for some way out reason file compression was a part of the question the OP could clarify that it was not a comparative question as written but a two separate subjects that are unrelated question.

leftj Loc: Texas

Or in focus.

burkphoto Loc: High Point, NC

You may not realize that you are actually asking about (potentially) FOUR different things.

VISUAL or SCENE compression is the effect you get from a telephoto lens. As you increase the focal length beyond the "normal" lens perspective (which is the diagonal dimension of the sensor, often rounded up), you magnify a smaller and smaller portion of the scene that is recorded. Our perspective of distant objects makes them seem compressed. If you are five feet in front of two objects, one of which is 20 feet behind the other, you notice the relatively large distance between those objects. But if you are 100 feet from the first object, and the second is at 120 feet, when you use a telephoto to "bring things closer", you are not going to see much distance difference between those two objects.

Try it...

Conversely, if you put a wide angle lens on your camera and perform the same sort of exercise, at closer distances, the wide angle lens exaggerates the distance between the close and far objects, compared to a normal lens.

DEPTH OF FIELD is simply how much of a scene is in "acceptably sharp focus" in front of, and behind, the actual point of focus. As you stop down the aperture (set a higher f/number or smaller fraction), depth of field increases. When the lens is wide open (at its smallest f/number, or largest fraction), depth of field is very shallow.

Scene compression and depth of field are totally different concepts.

There are three other types of compression in digital photography. FILE compression is the use of various schemes to make an image file smaller, for faster transmission over slow networks, or to save more files in a smaller space. There is "lossy" compression (JPEG is the common example), and "lossless" compression (LZW and ZIP are common examples). Lossy compression throws away image data, which can be a good thing or a very bad thing, depending upon what you are trying to do. Lossless file compression doesn't "squash" your files as much, which avoids image deterioration, but leaves you with a need for higher bandwidth and more storage... Life is full of little trade-offs, and you have to decide what's more important for YOUR use.

Another type of compression is DYNAMIC RANGE compression. This is basically the use of a raw file to record more information from a scene than can be reproduced on a monitor or on paper. In post-production, the image is adjusted to reduce the dynamic range (brightness range, really) to something that can be displayed or printed. This is typically done by "pulling curves" in software.

Yet a third type of compression is found in digital cameras that record video — AUDIO compression (which may be called automatic gain control or limiting, depending on the brand and model of camera, and the exact characteristics of the circuitry used. Audio compression limits dynamic range (difference between loud and quiet sounds) to avoid distortion of loud sounds and to keep quieter sounds from getting lost in noise. Audio compression is probably THE single most important sound processing tool known to broadcasters, record producers, motion picture audio recordists, and advertisers. It creates that "larger than life" quality we hear on TV, on our car radios, at the movies... and yes, those commercials that are "louder" than the program we're watching.

Spirit Vision Photography Loc: Behind a Camera.

The attached snap is an example of compression. The longer lens used, brought (compressed) the objects in the scene together.

www.spiritvisionphotography.com

(Download)

Architect1776 Loc: In my mind

Excellent example.

ballsafire Loc: Lafayette, Louisiana

Architect has the question I asked "framed" correctly in the sense that I was inquiring. I was confusing compression with depth of field and wanted clarification in my own mind how these two concepts were different or alike. I, for a moment, thought that they were the same. That is why I capitalized both words in my question -- the administration gave me a warning about using capitals and I understood what he meant - "do not do that!" The answer is somewhat clearer although my mind can't fully grasp the answer yet. Yes, "visual compression" is exactly what I meant and I am trying to visualize the concept and how it is different from depth of field (dof).

camerapapi Loc: Miami, Fl.

You are talking about two different things. In digital photography compression usually refers to reducing the size of a file and in general that is typical of using JPEGs. RAW files can be also compressed to make the files smaller adding more storage to the memory card.
It is said that compression brings a reduction in quality. Perhaps that is a thing of the past because a high quality JPEG is an excellent file. Compressed RAW files also show excellent colors, details and contrast.
Depth of field has nothing to do with compression. In photography DOF refers to the plane of acceptable focus from foreground to background and usually it is associated with using small lens openings, like f16. I am sure that you know that large lens openings limit the sharpness of the photograph.
Compression, as has been already discussed also applies to teles. Teles tend to compress the background making distant subjects appear closer to the camera.

Rongnongno Loc: FL

Err..... OPTICAL compression, not size compression.

ballsafire Loc: Lafayette, Louisiana

Burkphoto -- you have done a great task of educating my knowledge of photography (and sound) -- I can "see" clearly now, Thank you!

ballsafire Loc: Lafayette, Louisiana

I enjoyed viewing all these photos and tried to visualize both "compression" and "depth of field." Very nice!

ballsafire Loc: Lafayette, Louisiana

Architect -- your concise answer was on the mark although I had to visualize what "The poles in the far distance if cropped out and enlarged would look the same as the telephoto shot" and I finally grasped the concept. Thanks for your help!

dpullum Loc: Tampa Florida

I knew what was meant, but that does not guarantee that others did. The addition of the words, prospective or visual distance, before the word compression would have made it clear to all. OR the question should have been a simple explanation of the effect after the poster had done a simple google search for "visual compression by telephoto lenses" Google would have responded using the words "prospective distortion." Perspective distortion is a bit more complicated than simple apparent distance between....see:
https://en.wikipedia.org/wiki/Perspective_distortion_(photography)

Looking at your contribution on Toilet Paper, you were brief and complete.... adding a smile regarding unruliness of cats. I am happy that I have been using the correct unroll direction except when I have had unruly cats.
http://www.uglyhedgehog.com/t-442836-1.html

fetzler Loc: North West PA

the question is really depth of field and perspective. If the magnification of the subject on the sensor is the same the depth of field is almost independent on lens focal length. Greater magnifications have less depth of field. A head shot on an 8 x 10 in camera is almost a 1:1 macro and as the magnification on the film is large depth of field is small. Lenses of different focal lengths should be used to change perspective. (Personal safety could be another reason). If one wishes the background to fall off quickly then choose wide angle. A great experiment is to take a portrait of a person with several focal lengths. In each of the photos the subjects head should be the same size on the sensor/viewfinder. Use one aperture . Background objects at different distances will also be helpful. On might choose 10mm, 20, 35mm, 70mm, 150mm and 300mm on a Dx camera. The subject to camera distance will vary considerably. You should find the depth of field to be the same but the perspective rather different.

fotografz

One of the coolest things demonstrating optical compression is the use of it as a motion picture technique ... where you can see it happen right before your eyes.

I believe it was Alfred Hitchcock that first used it in a major motion picture as a psychological effect in the film "Rebecca" ... when Rebecca suddenly realizes something terrifyingly profound, the lens zooms to a longer focal length while the camera dollies back to keep her the same size ... the visual result is that the background looms up behind her ... a very unsettling sort of effect. Can you imagine the precision required on the part of the camera operators?

Depth of Field can easily be demonstrated even without a lens. Sometimes when I forget my glasses and have to see something small ... I make small circle with my thumb and finger and look closely through it ... effectively "stopping down" my finger aperture to make the object I'm viewing sharper. You can do the same thing with a piece of cardboard and a nail hole. The smaller the hole the more Depth of Field. However, the smaller the hole the more light you need coming through it ... or in the case of photography the longer the shutter has to stay open to record the image.