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05-07-2012, 09:53 AM   #31
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QuoteOriginally posted by Marc Sabatella Quote
And yet, we all agree the 28mm image shows no "compression effect" until you crop.
No, I wouldn't agree - the 28mm shot taken from the exact same position shows the exact same 'compression effect', it's just that the magnification provided by the telephoto lens makes it more obvious. The spacial relationships between the objects in the frame are dependent on distance to subject only.

This is an important thing to know, because the larger frame of reference that the wider lens provides that you mentioned is what's really capable of fooling you when you are trying to 'plan' your background effects. A lot of new shooters assume that they can get the exact same shot with a shorter focal length by just moving forward - and while the subject framing could be made the same by doing that, the background alters, the spacial relationship between objects in the background changes and grows less 'compressed', and the whole shot changes. If you try to make the case that 'FOV determines compression', then you are sort of mixing up cause and effect, and can confuse a lot of people... and frankly are just misleading. Distance to subject** is what determines perceived object distances relative to each other.

This knowledge has practical applications - for example, say you like the 'compression' you get behind your portrait subjects when you shoot from a certain distance using a certain lens. Maybe you don't have that lens that day, you have a shorter lens. If you move forward to frame the subject the same, your perspective and thus the compression alters unfavorably. However, if you are not severely megapixel-constrained, you can simply shoot from the same distance you would have with the longer lens, crop the result to the exact same FOV that the longer lens would have provided from that same distance, and your 'compression' is exactly the same as it would have been with the longer lens.

If you don't understand how distance really determines that relationship, and not FOV, you screw up that ^^ shot.


With regard to the OP's question about compression effects with lenses on FF vs. aps-c, I think I answered what he was asking with:

QuoteOriginally posted by jsherman:
"Now, as this relates to FF vs. aps-c:

1) if you shot the same lens on both formats from the same position (ie not moving forward with the FF shot to 'fill the frame',) the aps-c shot might seem more 'compressed' to you, but the level of compression would depend entirely on distance to subject.

2) If you cropped the FF shot to match the aps-c FOV, the compression would look the same.

3) If you moved forward with the FF shot to get the same framing/FOV as the aps-c shot, it would seem less compressed than the aps-c shot even though the framing was the same. "
The above can be demonstrated easily, and has, many times.


QuoteQuote:
It's really that simple.
It's really even simpler: distance to subject determines object compression.


** More precisely: The relative distance between foreground subject and background objects - because you can play compression games with small objects on a tabletop if you shoot close enough to the 'subject'.
.


Last edited by jsherman999; 05-07-2012 at 12:30 PM.
05-07-2012, 10:16 AM   #32
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QuoteQuote:
It's really even simpler: distance to subject determines object compression.
If you're going to learn one thing from jsherman, this should be it. Not saying there aren't more things you couldn't learn from him, but he's definitely made this one his "baby". It's a point worth emphasizing over and over. You can't change compression without moving your feet. It's not the same as zooming in and out. Magnification and compression are completely different effects and have different consequences when manipulating an image. If you don't know what you are trying to achieve, odds are, you won't accidentally find it.
05-07-2012, 10:18 AM   #33
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@jsherman i went on about this with Marc in another topic spanning over 3 pages but he still disagrees, saying that i can't understand what he is saying because i ain't a native english speaker.
So good luck with him
05-07-2012, 01:54 PM   #34
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@Marc "subtended": good word.

It's all about the angles. Wide angle is correctly named. Were "telephoto" called "narrow angle" there wouldn't be any confusion. You can make the angle narrower by extending the focal length, by reducing the size of the sensor or cropping a wider view. Apart from digital artefacts, the result is the same.

It's been (quite) a few years since I studied optics and I can't be bothered to dig out my university physics book but, as far as I can recall, the only physical quality of interest to us that derives from focal length independently of the size of the sensor is depth of field. Everything else that you see on your final print derives from the angle subtended by the subject on the sensor. I don't believe that there is a physical test that would enable you to distinguish an image taken with a 300mm lens on full frame from one taken by a 200mm lens on APS-C.

There is nothing inherently "wide" about the 28mm focal length, neither is there anything inherently "telephoto" about 200mm. It's all about the angle subtended on the sensor. That 28mm is at the far end of the telephoto range on a Fuji X10, for example. Neither is any form of distortion a consequence of focal length. Barrel distortion is simply a design compromise to achieve the intended angle of view on the intended sensor, which in the case of an old 28 was a frame of 35mm film. Leica will happily sell you a 28mm lens designed for full frame that has no measurable distortion for about two thousand quid. Given that, I'd be happy with the design compromise. If that 28mm were designed for APS-C instead it should be do-able with no distortion at all. Think about it: if a 10mm focal length inevitably made everyone look like their reflections in the back of a spoon, natural looking portraits with a compact digital camera would be physically impossible.

(On a related note, by selling us an extensive range of lenses specifically designed for the APS-C sensor rather than a range of repurposed full-frame glass, Pentax are actually doing most of us a service; it's both lighter on the wallet and lighter on the arms so stop complaining, folks).

As for that "compression", this an optical illusion produced by changing the field of view. We are able to perform the miracle of reverse projection (turning 2D into 3D) by making assumptions about the world. By presenting a different view to that of our eyes, these assumptions can be fooled. That is what makes us see distant objects being closer when viewed through a long lens: it's us making sense of what we see. We will interpret the 200mm / APS-C image in exactly the same way as the 300mm / FF one. Nothing to do with some imagined virtue of full-frame.

05-07-2012, 02:14 PM   #35
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QuoteOriginally posted by top-quark Quote
As for that "compression", this an optical illusion produced by changing the field of view.
And the objects common within both the original and the changed field of view will look equally 'compressed' if we have not changed positions.

QuoteQuote:
We are able to perform the miracle of reverse projection (turning 2D into 3D) by making assumptions about the world. By presenting a different view to that of our eyes, these assumptions can be fooled. That is what makes us see distant objects being closer when viewed through a long lens: it's us making sense of what we see. We will interpret the 200mm / APS-C image in exactly the same way as the 300mm / FF one. Nothing to do with some imagined virtue of full-frame.
I don't think anyone would argue that full frame brings more virtuous attributes to the subject of compression, and that's not (afaik) what the OP was asking about...

With regards to the 200mm (aps-c) vs 300mm (FF) having the same FOV from the same position, you are absolutely correct, as described in part by equivalence. It's also worth noting that objects behind the subject in both those shots will look equally 'compressed', since you have not changed positions (as they would if you took a shot from the same position with a 50mm lens.)


.

Last edited by jsherman999; 05-07-2012 at 08:02 PM.
05-07-2012, 06:19 PM   #36
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QuoteOriginally posted by jsherman999 Quote
No, I wouldn't agree - the 28mm shot taken from the exact same position shows the exact same 'compression effect', it's just that the magnification provided by the telephoto lens makes it more obvious.
It might seem to be that this is the case, but science and math show otherwise. It really is as simple as I put it before: if the AOV of the shot matches the angle subtended by the image, no illusion exists, but if they differ, then the illusion is created. There is no "compression effect" in the 28mm image because the angle match. Yes, objects appear are closer together than they would if the shot had been taken from closer, but that is *not* what is meant by "compression effect". That's just simple linear perspective. Indeed, that depends on position only, but this is *not* what we are talking about. Compression effect isn't just a term for the well known fact that distant objects appear closer together. There is more to it than that.

In the 28 image, the objects are not only close together but also small. Indeed, they appear exactly the same size they appear to the photographer's unaided eye from where he took the picture. We instantly and correctly perceive those objects are far away because of their small size, and we correctly gauge just how far away they are. We know from experience that distant objects look close together, so everything looks natural. The objects appear *exactly* as close together as their size imdicates they should. We understand the objects are not *really* only millimeters apart as they physically are in the print. We completely understand that they appear to be only millimeters in the print because it was taken from a distance, but they might really be a meter or more apart.

But in the 200 shot, the objects appear larger in the image than they appeared to the photographer. The larger size of the depicted objects *misleads* us into believing we are closer to the objects than the photographer actually was. After all, how would we know a telephoto lens was being used? All we have to go on is the size that objects appear in the print. And thus we mistakenly think we are closer than we are. In the 28 image, when we saw the pbjects only millimeters apart in the print, we understood this was oly because we are far away, and the objects might really be a meter or more apart. Now, since we don't realize we are so far from the objects, we see the objects only centimeters* apart in the image and mistakenly conclude they really are closer together than they actually were.

It is this disconnect that constitutes the "compression effect". Not the simple fact that objects appear closer together when viewed from a distance - that is true, but uninteresting, because it is completely obvious. The "compression effect" comes about when we *make incorrect judgements about the actual distance between the objects*, because *we are misled about the distance to the objects* and thus *don't correctly process the fact that the objects in the image are close together*.

*Objects that are millimeters apart in a 28mm image will be centimeters apart in a 200mm image. Either way, the actual onjets might have been a meter or more apart.

QuoteQuote:
The spacial relationships between the objects in the frame are dependent on distance to subject only.
This is of course true, but our *perception* of those relationships depends on whether the AOV depicted matches the angle subtended by the image itself or not. If so, all is well. If not, an optical illusion is created. That's all it is, of course - an illusion - but it is the nature of this illusion I am talking about, not the trivially true fact that distant objects appear closer together. Again, that is true, but so obviously true it is not worth discussing or putting a name to. The term "compression effect" refers to something far more subtle.

QuoteQuote:
This is an important thing to know, because the larger frame of reference that the wider lens provides that you mentioned is what's really capable of fooling you when you are trying to 'plan' your background effects.
While we've been talking here about telephoto compression effects, it is indeed true that wide angle lenses provide their own form of perspective distortion.

QuoteQuote:
If you try to make the case that 'FOV determines compression', then you are sort of mixing up cause and effect, and can confuse a lot of people... and frankly are just misleading. Distance to subject** is what determines perceived object distances relative to each other.
Yes, distance to subject determines perspective, ni doubt about that, and yes, many people completely misunderstand that. But you are incorrectly disregarding the effect that FOV does have, which is also real and measurable.
05-07-2012, 09:04 PM - 1 Like   #37
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.

QuoteOriginally posted by Marc Sabatella:
... Yes, objects appear are closer together than they would if the shot had been taken from closer, but that is *not* what is meant by "compression effect". That's just simple linear perspective. Indeed, that depends on position only, but this is *not* what we are talking about.
I think it is exactly what we (and the OP) were talking about. If you have another definition for compression, that would explain this disconnect, though.

"Compression", in the context of this thread (assuming I know in what context the OP was asking,) means "An effect of linear perspective distortion in which objects further away appear to be closer to each other, or compressed, and become more so the further the subject is from the viewer.... An effect that can be made more apparent through magnification of the 'compressed' area via the use of a telephoto lens, or by cropping."

Here is another description:

QuoteOriginally posted by Wikipedia - Perspective distortion (photography):
Compression, long-lens, or telephoto distortion can be seen in images shot from a distant using a long focus lens or the more common telephoto sub-type (with an angle of view narrower than a normal lens). Distant objects look approximately the same size – closer objects are abnormally small, and more distant objects are abnormally large, and hence the viewer cannot discern relative distances between distant objects – distances are compressed.

Note that perspective distortion is caused by distance, not by the lens per se – two shots of the same scene from the same distance will exhibit identical perspective distortion, regardless of lens used. However, since wide-angle lenses have a wider field of view, they are generally used from closer, while telephoto lenses have a narrower field of view and are generally used from farther away. For example, if standing at a distance so that a normal lens captures someone's face, a shot with a wide-angle lens or telephoto lens from the same distance will have exactly the same perspective on the face, though the wide-angle lens may fit the entire body into the shot, while the telephoto lens captures only the nose. However, crops of these three images with the same coverage will yield the same perspective distortion – the nose will look the same in all three. Conversely, if all three lenses are used from distances such that the face fills the field, the wide-angle will be used from closer, making the nose larger, and the telephoto will be used from farther, making the nose smaller.
I used to have a very succinct, but detailed and complete definition available that described exactly what we hear in common usage as 'compression'. Can't find it now, but the above should establish a working definition that fits the thread's OP.


QuoteOriginally posted by Marc Sabatella:
...In the 28 image, the objects are not only close together but also small. Indeed, they appear exactly the same size they appear to the photographer's unaided eye from where he took the picture. We instantly and correctly perceive those objects are far away because of their small size, and we correctly gauge just how far away they are. We know from experience that distant objects look close together, so everything looks natural. The objects appear *exactly* as close together as their size imdicates they should. We understand the objects are not *really* only millimeters apart as they physically are in the print. We completely understand that they appear to be only millimeters in the print because it was taken from a distance, but they might really be a meter or more apart.
Correct/agreed.

QuoteQuote:
But in the 200 shot, the objects appear larger in the image than they appeared to the photographer. The larger size of the depicted objects *misleads* us into believing we are closer to the objects than the photographer actually was. After all, how would we know a telephoto lens was being used? All we have to go on is the size that objects appear in the print. And thus we mistakenly think we are closer than we are. In the 28 image, when we saw the pbjects only millimeters apart in the print, we understood this was oly because we are far away, and the objects might really be a meter or more apart. Now, since we don't realize we are so far from the objects, we see the objects only centimeters* apart in the image and mistakenly conclude they really are closer together than they actually were.

It is this disconnect that constitutes the "compression effect". Not the simple fact that objects appear closer together when viewed from a distance - that is true, but uninteresting, because it is completely obvious. The "compression effect" comes about when we *make incorrect judgements about the actual distance between the objects*, because *we are misled about the distance to the objects* and thus *don't correctly process the fact that the objects in the image are close together*.
Also true, but none of this is contradictory to what I've been saying here - that the reason these objects appear closer together is directly attributable to distance from the viewer. In other words, as the subtended angle decreases (because the distance to subject is increasing!) the compression illusion increases. And: the exact same level and rate of object compression happens in every shot you take, regardless of focal length/FOV, if you take it from the same position. The telephoto lens (or cropping) just makes it more apparent, but it doesn't create anything that doesn't already exist in the image, were it taken with a wider-angle lens.

Example: (originally from Luminous landscape)

200mm, uncropped:



24mm, cropped to same FOV as the 200mm shot (smaller, because of a megapixel limitation):



Same level of 'compression' ^^

A 200mm vs. 24mm is an extreme example to show the effect more dramatically, but a more practical example would be to crop a 50mm shot taken from the same position an 85mm shot would usually be taken from, to preserve the relationship with the background, preserve the same 'compression' - similar to something a lot of working photographers do all the time.






.

Last edited by jsherman999; 05-07-2012 at 09:31 PM.
05-07-2012, 11:49 PM   #38
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QuoteOriginally posted by jsherman999 Quote
And the objects common within both the original and the changed field of view will look equally 'compressed' if we have not changed positions.
.
If you crop it, yes, otherwise that end of the green tunnel just looks like a far-away object. I'm with Marc. You keep saying the only thing that matters is distance to the subject, but then you proceed to making your case by cropping an image, thus delivering the best argument for why FOV does matter in the perception of compression.


Last edited by Ikarus; 05-08-2012 at 12:06 AM.
05-08-2012, 12:12 AM   #39
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QuoteOriginally posted by normhead Quote
You can't change compression without moving your feet. It's not the same as zooming in and out.
Hence the stupidity of the "zooming with your feet" concept in fact it's an oxymoron.

Cheers!

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05-08-2012, 01:52 AM   #40
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QuoteOriginally posted by Ikarus Quote
If you crop it, yes, otherwise that end of the green tunnel just looks like a far-away object. I'm with Marc. You keep saying the only thing that matters is distance to the subject, but then you proceed to making your case by cropping an image, thus delivering the best argument for why FOV does matter in the perception of compression.
Sure it matters in that it helps you to see the effects of the linear perspective distortion we call "compression" better, but it's not in any way the cause of that compression. Distance to that area and those objects are. And if you vary that distance, you vary that compression - that perceived distance between objects. If you simply vary the Fov, you do not.

You don't need to crop that image at all if you print it large enough to see that area clearly - the cropping is just useful to show you what's actually happening there, and is why the crop was shown on luminous landscape in the first place - to help illustrate the point I've been trying to make

Many folks mistakingly think that they can use a telephoto zoom to cause more "compression" by standing in place and zooming in to a subject, and they can't, because changing the FOV does not change the perspective. Many also feel that they can simply move forward with a shorter lens to get the same FOV as a longer lens, and thus the same shot, and they can't do that either - because maintainng FOV does not maintain the linear perspective distortion, or compression. Maintaining Distance does.


.
05-08-2012, 02:01 AM   #41
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QuoteOriginally posted by Abbazz Quote
Hence the stupidity of the "zooming with your feet" concept – in fact it's an oxymoron.

Cheers!

Abbazz
You can zoom with your feet if all that matters to the shot is FOV, not perspective or perceived compression. For a lot of shots, those things simply don't matter. But you're right, "zooming with your feet" never brings the exact same shot as standing in the same place and zooming would. If you had a zoom. If you don't, you do what you can do - move forward or backward and alter the perspective/compression, or crop it to keep the perspective the same.

Another thing you can do is use both zooming *and* a different distance/position to increase or decrease compression effects in neat ways. I can show you some of my own results from doing that tomorrow.

Last edited by jsherman999; 05-08-2012 at 02:37 AM.
05-08-2012, 06:02 AM   #42
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So would it be safe to say that if you took a picture of a tomato with a pineapple behind it at a distance of 1 metre, on the top of your dining table or something, no matter what focal length or FoV you use, as long as you are 1 metre away from the tomato, the relative size of the tomato and the pineapple will be exactly the same?

With a more narrow FoV you'd obviously fill the frame with more tomato, but it wouldn't make the pineapple look any bigger in comparison to the tomato. In that case FoV has no effect on compression, otherwise using a longer lens would make the pineapple look larger in comparison, or a 4x5 sheet of film rather than an APS-C sensor to get a wider view with the same focal length.

I can test this if you want, between the angles of 16 and 135mm at a distance of like a metre and a half or something.
05-08-2012, 07:16 AM   #43
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QuoteOriginally posted by Mareket Quote
So would it be safe to say that if you took a picture of a tomato with a pineapple behind it at a distance of 1 metre, on the top of your dining table or something, no matter what focal length or FoV you use, as long as you are 1 metre away from the tomato, the relative size of the tomato and the pineapple will be exactly the same?

With a more narrow FoV you'd obviously fill the frame with more tomato, but it wouldn't make the pineapple look any bigger in comparison to the tomato. In that case FoV has no effect on compression, otherwise using a longer lens would make the pineapple look larger in comparison, or a 4x5 sheet of film rather than an APS-C sensor to get a wider view with the same focal length.

I can test this if you want, between the angles of 16 and 135mm at a distance of like a metre and a half or something.
Yes so if the tomato and pineapple are the same size with your first example they will stay the same size relative to each other.
When you use wide angle lens the magnification is lower so you end up with more in your photo so your tomato and pineapple will appear smaller then with tele but they will both be equal of size as long as you dont move.
And thats what perspective is about the relative size to each other.


Now here comes a bit what Marc is talking about and that's the perspective of the viewer.
He also has a certain perspective when he stand at a distance away to look at your photo and that will effect if the perspective look natural or not. that's where the term "normal" lens comes into play. typically the viewer has 53 degrees AOV when looking at your photo so if you match the AOV the perspectives will be natural. If the viewer stands closer then you need to use a wider lens to get the natural perspective or stand closer to take the photograph

It's precisely the same for our eyes after all, when we stand far away it will look more compress then if we stand up close.

Last edited by Anvh; 05-08-2012 at 07:21 AM.
05-08-2012, 07:25 AM   #44
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QuoteOriginally posted by jsherman999 Quote
Sure it matters in that it helps you to see the effects of the linear perspective distortion we call "compression" better.
Limited FOV doesn't just help, it's essential for seeing the scene as 'compressed'. It's a function of two things - one is the image being taken far away from the subject, and two is not being given the visual context that tells us how far it was. We're essentially saying the same thing, and I appreciate you stressing the fact that distance is a key factor in this, but to me, going to the extreme of saying that it is the only factor is taking it too far. There is, after all, a reason why choosing longer focal lengths for a given FOV in the subject plane is the preferred method for creating the effect of perspective compression in photography. And yes, that does, of course, imply taking a walk away from the subject.

Last edited by Ikarus; 05-08-2012 at 08:14 AM.
05-08-2012, 09:07 AM   #45
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QuoteOriginally posted by Ikarus Quote
.... We're essentially saying the same thing, and I appreciate you stressing the fact that distance is a key factor in this, but to me, going to the extreme of saying that it is the only factor is taking it too far.
Distance is not the only factor involved to be certain, sorry if I gave the impression I was saying that. Without a presentation method that manipulates FOV, like telephoto or cropping to display the effect, it's not very useful. But distance is the key variable that needs to be manipulated to control 'compression'.

QuoteQuote:
There is, after all, a reason why choosing longer focal lengths for a given FOV in the subject plane is the preferred method for creating the effect of perspective compression in photography.
Agreed.

Last edited by jsherman999; 05-08-2012 at 09:16 AM.
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