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05-02-2012, 01:02 PM   #16
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In the simplest terms I can muster : The 'compression effect' is not really created by a lens or sensor format, it's created by distance to subject. The further from the subject you are, the more that objects in the frame will seem 'compressed' together. (this phenomenon also comes up in perspective discussions.)

Since telephoto lenses are usually used to take shots of faraway subjects, they are usually the lenses being used when 'compression' becomes apparent, and thus folks understandably think it's some inherent property of the lens, and it's really just about the subject distance.

In other words, if you were to take a photo of a subject (say a group of trees, 100 meters away) with a 28mm lens and a 200mm lens, standing in the same position, the 200mm shot would look more 'compressed' at first - but if you cropped that 28mm shot to cover the same frame/FOV that the 200mm shot did, the 'compression' would be exactly the same. The 28mm shot would look like crap, because it was so severely cropped , but it would show exactly the same 'compression'.

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.


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Last edited by jsherman999; 05-02-2012 at 01:08 PM.
05-02-2012, 04:34 PM   #17
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Agreed. That is exactly the correct way to explain it. It IS perspective related.

The further away from the observer are the subject/s the closer they appear to be to one another along a linear path in line with the observer and both objects appear flat relative to the space to the observer and each other when magnified via a telephoto lens. This is a result of linear perspective combined with the scale of the objects relative to distance from observer. The entire space in the line of sight between the observer with the telephoto and the subject must be fit into the picture whether it's in focus or not and as such all objects depth is scaled relative to the distance from the observer, magnification and the FOV. So in a sense there is compression but it is really only magnification of what is already there, and, whilst not an innate property of the lens itself, it is the lens or the size of the output print relative to the viewer that manifests that 'compression'.

PS: One should also take into account that light rays coming from infinity are parallel and so objects at infinity appear flat. When you zoom in on infinity with a telephoto lens you are seeing that flatness magnified.
PS2: Also, if you are using a telephoto lens to look at everything along a line of sight from a few feet to infinity then the you must be 'compressing' the view to fit everything into the space between the viewer and the distance. Otherwise there would be no magnification and the telephoto lens would have to physically move you forward in space.

Last edited by bossa; 05-02-2012 at 04:43 PM.
05-02-2012, 04:55 PM   #18
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QuoteOriginally posted by Marc Sabatella Quote
This is because the so-called compressin effects are not inherent to the lens or even to the recorded image, but are simply optical illusions caused if you take an image taken with a given angle of view and then print it and view it from a distance that yields a different angle of view.
What he said...

Make a crop of a scene from a wide angle lens and blow it up to illustrate the point. I posted a couple of examples several years ago showing this and will repost if I can find them.


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05-02-2012, 05:08 PM   #19
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QuoteOriginally posted by stevebrot Quote
What he said...

Make a crop of a scene from a wide angle lens and blow it up to illustrate the point. I posted a couple of examples several years ago showing this and will repost if I can find them.


Steve
Yes but you are still magnifying the image relative to the scale of the observer. Things aren't the same when when you need to alter something to make it visible.


Last edited by bossa; 05-02-2012 at 05:22 PM.
05-06-2012, 11:56 AM   #20
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QuoteOriginally posted by jsherman999 Quote
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In other words, if you were to take a photo of a subject (say a group of trees, 100 meters away) with a 28mm lens and a 200mm lens, standing in the same position, the 200mm shot would look more 'compressed' at first - but if you cropped that 28mm shot to cover the same frame/FOV that the 200mm shot did, the 'compression' would be exactly the same.
Yes, but the fact that the compression effect appeared different before the crop shows it isn't just about the distance. It is about the FOV of the image and how it compares to the angle subtended by the print itself. Cropping the 28 creates the same FOv as the 200, so indeed, same compression effect, but if the disance itself caused the effect, we'd see it in the 28 shot uncropped as well. This demonsrates very nicely it isn't really about distance but about FOV. The FOV of the 28 will never show any compression effect from any distance unless you crop; the 200 will always show the compression effect from any distance.
05-06-2012, 12:13 PM   #21
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In a Time Life series of books on photography printed in 1970 or so (the big grey ones) it took about 4 huge pages with a ton of diagrams to sort this concept out in my head and even then its hard to keep it all sorted due to the number of factors involved. This would be a good concept for a youtube video since its sorta critical to have visual aides when explaining it.
05-06-2012, 12:48 PM   #22
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QuoteOriginally posted by Marc Sabatella Quote
Yes, but the fact that the compression effect appeared different before the crop shows it isn't just about the distance. It is about the FOV of the image and how it compares to the angle subtended by the print itself. Cropping the 28 creates the same FOv as the 200, so indeed, same compression effect, but if the disance itself caused the effect, we'd see it in the 28 shot uncropped as well. This demonsrates very nicely it isn't really about distance but about FOV. The FOV of the 28 will never show any compression effect from any distance unless you crop; the 200 will always show the compression effect from any distance.

No, because the distance to the subject is what determines how close the objects in the frame seem to each other. This is one of the effects you get when you move - the 'perspective' changes, and the relationships of objects in the background to the foreground changes.

As in the example I gave, if you take a shot with the 200 and then moved forward so the FOV is the same at 28mm and shot with the 28, the 'compression' would be radically different, even though the FOV would be exactly the same. The distance to subject creates this 'compression' effect - the long telephotos only show it to you better without cropping.


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05-06-2012, 02:44 PM   #23
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QuoteOriginally posted by jsherman999 Quote
As in the example I gave, if you take a shot with the 200 and then moved forward so the FOV is the same at 28mm
Here it would be worth pointing out that the FOV can be made to match at a single distance only. The fact that it can never be made to match for more than one distance is precisely where the "compression effect" comes from. Beyond the chosen distance, the wider focal length will have a wider FOV than the longer lens, in front of it a narrower FOV. The easiest way to visualize this is by drawing two cones with different angles. They can be made to intersect at a single distance only.



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05-06-2012, 07:14 PM   #24
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QuoteOriginally posted by Ikarus Quote
Here it would be worth pointing out that the FOV can be made to match at a single distance only. The fact that it can never be made to match for more than one distance is precisely where the "compression effect" comes from. Beyond the chosen distance, the wider focal length will have a wider FOV than the longer lens, in front of it a narrower FOV. The easiest way to visualize this is by drawing two cones with different angles. They can be made to intersect at a single distance only.
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Unless I misunderstand your point, that's not true... you can move all you want while maintaining a constant FOV, you just need to alter focal length.

For example, shoot at 35mm, then at 50mm. The 50mm will have a tighter FOV. If you move forward a bit with the 35mm lens, you can match the original 50mm FOV precisely - but the perspective will have changed, and objects behind the subject would become slightly less 'compressed'.

The variable there, the thing that changed to alter 'compression', was distance to subject.


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Last edited by jsherman999; 05-06-2012 at 07:20 PM.
05-06-2012, 07:56 PM   #25
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QuoteOriginally posted by jsherman999 Quote
The 50mm will have a tighter FOV. If you move forward a bit with the 35mm lens, you can match the original 50mm FOV precisely - but the perspective will have changed, and objects behind the subject would become slightly less 'compressed'.
Yep, they are less compressed because the FOV behind the subject is wider with the 35. I guess my point is that one can explain the phenomenon in terms of FOV alone, without throwing the somewhat fuzzy term 'perspective' into the mix. See the illustration below, which hopefully explains it better.


Last edited by Ikarus; 05-06-2012 at 08:55 PM.
05-06-2012, 09:18 PM   #26
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QuoteOriginally posted by Ikarus Quote
Yep, they are less compressed because the FOV behind the subject is wider with the 35. I guess my point is that one can explain the phenomenon in terms of FOV alone, without throwing the somewhat fuzzy term 'perspective' into the mix.

You don't even need to use the term 'perspective' all here, if you don't want to. You can simply say: Distance to subject is what determines the level of 'compression' seen between objects in the frame. If you want to go further and explain why that's so, using common vernacular, you can mention perspective.

Since 'perspective' itself can be a fuzzy term and has at least two meanings even in the context of photography , we can stick to the Luminous Landscape usage:

QuoteOriginally posted by Luminous Landscape:

perspective: the appearance of objects relative to each other, determined by their distance from the viewer.

The important thing to remember about perspective is that as objects get further away, they appear smaller. This much is obvious. What's less obvious is that as objects get further away, the apparent distance between them decreases too.
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Last edited by jsherman999; 05-06-2012 at 09:49 PM.
05-07-2012, 06:10 AM   #27
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QuoteQuote:
the appearance of objects relative to each other, determined by their distance from the viewer.
And that's the most important part.
05-07-2012, 07:25 AM   #28
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OH boy...

Lenses are the same whether shot on APS-c or Full Frame, what's different is the size of the image.

"Normal" refers to the spatial relationships relative to each other in the frame compared to what you see with the human eye. So if you put a frame together and then blocked out most of the world and just looked through your 3x4 frame, the world you'd see would most resemble images taken with a 40mm lens. That is true whether taken with FF, 4/3 , MF or APS-c. It's the size of the sensor that changes, not the characteristics of the lens. In other words , you have the same DoF, "compression" etc. no matter what system you use. You merely have a bigger or smaller image.

Much has been made of the need for the bigger image. In many cases, you don't need a bigger image. If you had one you'd crop it. For example, shooting landscape at infinity with a 35 mm lens in APS-c is pretty much exactly the same as shooting with a 50 FF. You'd be hard pressed to quantify the difference between the two images, and there's no predicting which image you'd like more. FF folks tend to act like the FF image would be in some way preferable. IN fact, comparing larger and small sensor images, I've not found that to be true. Sometimes for whatever reason, our sensibilities judge the small frame image to be better. If you're talking landscape, you're talking field of view, or how much of the scene you're capturing from a given vantage point. It's only when discussing field of view that FF vs APS-c becomes an issue. FF gives you more FoV with a given lens. So you may want a slightly different set of lenses for an APS-c than with an FF camera. Instead of a 300 mm lens, you might want 200, instead of a 14 mm lens you might want an 8.

A 70-200 mm 2.8 zoom is a fraction the cost and probably equal the IQ of the equivalent 300mm 2.8 lens.

As has been pointed out many times, the compression of space within the frame and the apparent relationship of objects front to back increases with the distance from the subject. Again, this is the same for all systems. So as you move back depth seems to compress. This is important to the portrait photographer in that big noses need to be compressed, not exaggerated by being shot from close up. But again, this is not dependant on system. This is dependant on how far away you are. So whether you are shooting, with DA 77 on APS-c or 135 with FF, doesn't matter, it's the distance away from the subject that will flatten the image, not the lens used.

As a portrait photographer, you don't want people to look normal... you want them to look imperceptibly better than normal. Recognizable but "at their best". Most people need their faces flattened. A few may need a more close up treatment because their faces are flatter than the norm. Field of View for the most part doesn't matter in portraits, unless it's an environmental portrait. ( Like those shots you see in the news paper of an Architect standing beside a building he designed so you can see both the building and the person.)

Many of the assumptions that have been made concerning the advantages of FF over APS-c and APS-c over 4/3s don't stand up in real world situations. IN some situations, images may not be noticeably different. Other situations may favour larger or smaller crop sensors, but, it should never be assumed which system will produce the best image in a given situation. In some situations the smaller sensor with a wider angle lens will produce a more appealing image, in some situations the FF will. A huge proportion of the time, differences will be imperceptible, or only noticeable by people actually looking for those differences. Hence you have this whole group of FF photographers actually shooting to take advantage of small the small differences between APS-c and FF as if most people really care or even see a difference.

Then you have the MF people doing similar things. I actually quite like MF for portrait photography, the look is distinctive enough that people think they are getting something special. Of course 8x10 film is even better. But then, I have no desire to be a portrait photographer.

In the end however, getting out and taking pictures is what's important. As I look at our recent work, I become more and more aware of how irrelevant MTF numbers taken on flat surface are to 3 dimensional photography, and how irrelevant format and Mp are. !2 Mp is enough, and any camera will give you the best photograph available a percentage of the time. There will be times when the guy with the top of the line FF gets the best image. There will be times when a smaller sensor does better in the same situation. It's a trade-off. DIfferent results does not translate into one is better than the other, all the time. Image evaluation and what's pleasing to the human eye is just way more complicated than that.
05-07-2012, 08:28 AM   #29
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QuoteOriginally posted by jsherman999 Quote
No, because the distance to the subject is what determines how close the objects in the frame seem to each other.
And yet, we all agree the 28mm image shows no "compression effect" until you crop. Yes, pbjects appear closer together on the frame than they would if you were standing closer when you took the picutre - but then, the angle of view of the scene is such that it was obviously taken from a distance and hence our eyes *expect* things to look closer together. This creates no illusion; it matches our expectations perfectly. The illusion known as perspective distortion (with .telephoto compression" being one manifestation of this illusion) occurs only when our eyes are deceived - when our eyes perceive the objects being close together in the image but lack the frame of reference to realize that this is because we are far away. Leaving the 28mm image uncropped provides that frame of refeence - we see the people as small, and hence instantly realize they are far away. Crop it and magnify (or switch to the 200mm lens - anything that produces the narrow AOV), and now we don't realize the picture was taken from a distance, and our eyes are thus deceived into thinking the people are closer together.

QuoteQuote:
As in the example I gave, if you take a shot with the 200 and then moved forward so the FOV is the same at 28mm
As noted, that does not compute. Well, the term FOV (field of view) is imprecise, so let's be more specific - it is about *angle* of view. I don't care how far forward or backward you move, you will never change the angle of view of a lens. And again, that's what produces the optical illusion we know as perspective distortion - when the angle of view depicted in the scene does not match the angle subtended by the printed or displayed image itself.

It's really that simple. The eye sees a printed or displayed image and wants to assume that it is a "window" onto reality - the angle of view depicted in the image is the same as the angle subtended by the image itself. When this happens, objects in the image appear at the same size and relative position they would have to the photographer, and everything feels "right" in our perception of the imag. If the angle depicted in the image is narrower than that subtended by the image itself, objects will appear larger in the image than they appeared to the photographer. Assuming we recognize the objects and have a sense of how large they actually are, we will mistakenly perceive the larger size of the objects (created by the narrower AOV) as indicating we are closer to the pbjects than the photographer actually was, and this will then throw off our sense of perspective. The space between the objects is that which would be oberved by a distant observer, but we perceive we are closer than that, so we mistakenly think the objects are closer together than they are. Had the AOV depitced in the image matched that subtended by the image itself, we would instantly see we were far away and interpret the dostance between objects correctly.
05-07-2012, 08:46 AM   #30
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QuoteQuote:
The eye sees a printed or displayed image and wants to assume that it is a "window" onto reality - the angle of view depicted in the image is the same as the angle subtended by the image itself.
A good deal of the "art" of photography is in the manipulation of that window to create meaning that possibly is not present in the original scene. The artist manipulates reality to make a statement that has meaning. One of the ways of manipulating content is to use lens characteristics to emphasize or de-emphasize. If photography were all about accurately capturing a scene or event as the eye sees it, there would be a formula for creating the best visual accuracy and that would be that. But photography is not about visual accuracy. So there is no formula, and every scene demands it's own analysis and decisions about what the best way to shoot it might be. Up close with wide angle or further way with telephoto? Fish-eye or 21mm. 35mm or 50mm? 135mm or 250mm? Content is arranged differently and with different emphasis, with each of these decisions.

What's right is what makes the point you were making with your picture. The tools are only useful to help with the shot. if a 21mm lens on an APS-c gives you the exact perspective you want... any other piece of kit you have in your bag is a distraction, at least at that point in time and space.
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