[jsherman999]

But when people talk about telephotos compressing space, it is relative to a "normal" focal length taking the same shot while maintaining some subject in the frame at the same size. And that effect is very real -- the background will appear closer to the subject with the telephoto than with the wide angle. We've all probably seen those shots from the films Vertigo and Jaws that illustrate the concept.

...The fact is if an object is 12 feet in front of a brick wall.. and you take in image with an 18 mm lens and then count the number of bricks on each side of the object... then shoot it with a 200mm lens, moving back so the object is the same size.. and take another picture... you will count fewer bricks on either side of the subject with the 20mm lens...hence the back ground with the telephoto is considered to be compressed.

Yes, and it's part of the vernacular, it describes what's happening and attributes it to the focal length itself, when it has nothing to do with the focal length and has everything to do with distance to subject.

For example, after moving back to shoot your object 12 feet in front of the wall with the 200mm, if you were to put that 18mm lens back on the camera and shoot again from that same position, cropping to the same FOV as the 200mm shot, you would have exactly the same 'compression', be able to count exactly the same number of bricks behind the object. It's not some property of a telephoto lens that does that, it's distance to subject. A lot of people mistakingly think 'compression' is caused by some native property of long focal length lenses.

This has implications for the perspective discussion going on, which is why I highlighted it. Again, distance to subject is the key variable there, the focal length only has a correlative relationship with what we call compression.


.

.

---

Last edited by jsherman999; 01-15-2012 at 09:19 PM.

[bossa]

The place where your camera is when you take a picture.



I'm referring to where the camera is when the picture is taken, and how it relates to different frame/sensor sizes.

Those statements can mean anything depending upon your perspective. Sorry.. only kidding but I couldn't resist.

[vonBaloney]

Yes, and it's part of the vernacular, it describes what's happening and attributes it to the focal length itself, when it has nothing to do with the focal length and has everything to do with distance to subject.

For example, after moving back to shoot your object 12 feet in front of the wall with the 200mm, if you were to put that 18mm lens back on the camera and shoot again from that same position, cropping to the same FOV as the 200mm shot, you would have exactly the same 'compression', be able to count exactly the same number of bricks behind the object. It's not some property of a telephoto lens that does that, it's distance to subject. A lot of people mistakingly think 'compression' is caused by some native property of long focal lengths.

This has implications for the perspective discussion going on, which is why I highlighted it. Again, distance to subject is the key variable there, the focal length only has a correlative relationship with what we call compression.

Fair enough, but in practice using "equivalent crops" is generally not an option, so the lens is the thing. The focal length of the lens is the thing that ALLOWS you to be a different distance from the subject and have it appear the same size in the frame, and the focal length is a property of the lens. We talk about this compression relative to "normal" lenses, but a "normal" lens is that which is most like your ordinary experience. And looking through a telephoto or wide-angle lens DOES change your experience of the view in a way a normal lens does not no matter what you are looking at and how far away it is. And you haven't changed your distance to subject, merely put the camera to your eye. So to say the compression/expansion effects are ONLY about distance to subject is not really true. Not in real life. (You can't crop and enlarge a portion of what you are seeing with your own eyes, unless you are Steve Austin.)

[jsherman999]

... Perspective is something we learn to read and there are a few types of perspective to boot.

As I suspected, there are several different definitions of 'perspective' being used here.

Another example illustrating what I think most photographers are concerned with when they talk about "not wanting to move and use a different focal length to reframe, because it changes perspective"



In each of these shots, the photogapher moved forward to keep the subject (the sculpture) the same size in the frame. Note the radically changing relationship to the background:

100mm

70mm

50mm

28mm

[bossa]

The form of the 'subject' changes too as the 'subject' is only differentiated from the environment in the mind of the observer and not in reality. It's not just the relationship of the 'subject' to the background that has changed in these photographs. Everything in the longer focal length images is foreshortened, flattened or compressed more. Take your pick of the terminology.

[jsherman999]

The form of the 'subject' changes too as the 'subject' is only differentiated from the environment in the mind of the observer and not in reality. It's not just the relationship of the 'subject' to the background that has changed in these photographs. Everything in the longer focal length images is foreshortened, flattened or compressed more. Take your pick of the terminology.

Now you're losing perspective on the subject we're actually talking about. (sorry, couldn't resist either )

[jsherman999]

Here is one image with the cropped image next to it. It clearly shows the linear perspective, how fast the radial lines converge, are not the same. We will perceive the image on the left as having greater perspective or space or depth or whatever subjective term you would like..

.


The use of your phrase 'Greater perspective' here indeed tells me that you've been working on a different concept than what we were originally trying to describe. (FWIW, I wouldn't call that 'greater perspective', I'd call it 'greater convergence'.)


.

[mattdm]

.
50mm f/2.8 (on FF) left, 35mm f/2.8 (on aps-c) right,same exact distance to subject, vertical framing moved a bit:

Although there's more apparent depth of field, the bokeh on the "35mm f/2.8 (on aps-c)" shot is significantly nicer.

I guess that's the difference between a Limited lens wide open and a plastic nifty-fifty even stopped down a bit, and goes pretty far with me to the point that lenses are more important than sensor size, once you've reached a certain threshold.

[bossa]

Now you're losing perspective on the subject we're actually talking about. (sorry, couldn't resist either )

touché

[D4rknezz]

I bow to all your superior knowledge. For someone with relatively little understanding of the technical stuff behind pretty pictures - following this thread is like a roller coaster ride:
- X says something, I go....huh. That make sense.
- Y disagrees and says something, I go....aha. I see.
- Z disagrees with Y and adds something new X hasnt said, and I go....uhh...I guess X was right...to a degree?
- Y disagrees with Z, and explains more...and I...I....

I will persist! But uh...if I dont, someone need to pm me with the conclusion to this thread, complete with schematics and diagrams of what was agreed upon

[jsherman999]

Although there's more apparent depth of field, the bokeh on the "35mm f/2.8 (on aps-c)" shot is significantly nicer.

I guess that's the difference between a Limited lens wide open and a plastic nifty-fifty even stopped down a bit, and goes pretty far with me to the point that lenses are more important than sensor size, once you've reached a certain threshold.

I like the 35ltd macro bokeh also. Some people say they don't like it, I don't really understand why.

Incidentally, here's that same shot, but at 50mm wide-open on D700 (f/1.8) - that 50 get's a bit nervous with lined backgrounds at a certain distance:



But manage your distances just a bit and I think it performs just fine for a $110 lens:

f/1.8


Crop:


f/2


Maybe an interesting exercise: above was 50mm, what approx focal length is below (longer or shorter?)

[Laurentiu Cristofor]

Fair enough, but in practice using "equivalent crops" is generally not an option

It's very relevant in this thread because with a "cropped" apsc sensor, you get exactly such crop. And this makes a 50mm lens provide the same fov as well as the same perspective as a 75mm lens used on a FF camera in the same spot.

[vonBaloney]

It's very relevant in this thread because with a "cropped" apsc sensor, you get exactly such crop. And this makes a 50mm lens provide the same fov as well as the same perspective as a 75mm lens used on a FF camera in the same spot.

That's not an option in the field for a particular shot unless you have bodies of both formats, which is going to be a tiny percentage of people. In the field, you change lenses and walk around.

[alohadave]

that 50 get's a bit nervous with lined backgrounds at a certain distance:

The A50 f/2 gets what I call "Angry Bokeh" when there are leaves and branches in the background. Not a pretty sight.

[Yamanobori]

.


The use of your phrase 'Greater perspective' here indeed tells me that you've been working on a different concept than what we were originally trying to describe. (FWIW, I wouldn't call that 'greater perspective', I'd call it 'greater convergence'.)


.

I am sorry. I thought the argument was effect of cropping an image in regards to perspective--say, using a full-frame senor vs. a APC sensor with the same lens would not impact perspective.

The example I provided clearly shows Linear Perspective. It also shows the perspective is changing because of cropping or a change in focal length while maintaining the same object distance. And the more you crop, the less perspective the image will have until you you reach an infinitely small area where the image will have no perspective at all--or in common usage, space is being compressed. This is really basic stuff.

I am not really interested in your personal nomenclature. For your reference, here is the common definition of perspective from a standard source, The Focal Encyclopedia of Photography, Third Edition, page 548-55:

PERSPECTIVE Perspective refers to the appearance of depth when a three-dimensional object or scene is represented in a two-dimensional image, such as a photograph, or when the subject is viewed directly.

The article, as you can see, is quite long and thorough and never is you concept of "Convergence" mentioned. As far as perspective having no degree, you have hundreds of years of perspective drawing to contradict that. And before you claim that it has nothing to do with photography, the concepts on linear perspective in photography come directly from this work. The topic in photography has taken this work and expanded it to cover the problems that are unique to the medium.

The fact is, object distance is not the only factor in changing perspective in an image. I have provided the proof and explanation. Playing vocabulary games will not change that.