APS-C lens mm are correct

[neuroanatomist]

Its just common to say "equivalent of blabla on APS-C". Maybe its just the wrong term used but so what? everybody knows what it supposed to mean.

You'd think so, but >80 posts here and many other threads on the topic suggest otherwise...

 

[PackLight]

Re. Perspective and focal length.

As a picture is worth a thousand words.

First comparison, 17mm lens and 200mm lens both on same camera from same place and both f8, these are the full images.

Second comparison, same images with the 17mm cropped to match the framing of the 200mm.

As you will see, whilst the dof is very different, the perspective (the size of the various elements within the frame with regards each other) stays constant. The woman, the trees and the jumps are the same size in both examples when the 17mm is cropped.

This is also a very graphic demonstration of why smaller sensors have deeper dof, the second image crop is effectively a small sensor shot with an 11 times crop factor, which still puts it way bigger than P&S's and phone cameras.

I have to disagree, your definition of perspective only relates to the size of things in the picture. Since the two pictures obviously have a different depth of field the one shot with the 200mm creates a different illusion of depth and therefore a different perspective. At best you can say the elements in the picture are the same size once cropped. You can say that the pictures were shot from the same perspective, your perspective. But the pictures do not have the same perspective.

 

[PackLight]

Its just common to say "equivalent of blabla on APS-C". Maybe its just the wrong term used but so what? everybody knows what it supposed to mean.

You'd think so, but >80 posts here and many other threads on the topic suggest otherwise...

What is amazing is that there are so many threads about it. Many people just use crop or ff not both. The reality of it is if you use a crop camera and do not own a FF, the ratios and comparisons are meaningless to you. If you own a FF and do not use a crop it is meaningless to you. Yet it is important to debate what does not matter.

But then again this thread went through 3 pages of perspective talk.

 

[neuroanatomist]

I have to disagree, your definition of perspective only relates to the size of things in the picture. Since the two pictures obviously have a different depth of field the one shot with the 200mm creates a different illusion of depth and therefore a different perspective. At best you can say the elements in the picture are the same size once cropped. You can say that the pictures were shot from the same perspective, your perspective. But the pictures do not have the same perspective.

Sorry, no. It's not his definition of perspective, it's THE definition of perspective.

But then again this thread went through 3 pages of perspective talk.

...and with apologies, unfortunately it seems the point is still not clear to some. ???

 

[ahab1372]

And while we are at it: compression is also not a feature of the lens, but of the distance. It is actually included in Neuro's THE definition of perspective.
If you are farther away, faces look flatter, no matter what lens you use.

 

[TexPhoto]

And while we are at it: compression is also not a feature of the lens, but of the distance. It is actually included in Neuro's I mean THE definition of perspective.
If you are father away, faces look flatter, no matter what lens you use.

Yes! You don't even need a lens. This effect can be seen with your eyes. Close one eye and put the other an inch from someones nose. (Maybe make sure this is a friend). Wow huge nose, fisheye perspective!

 

[PackLight]

Sorry, no. It's not his definition of perspective, it's THE definition of perspective.

How would this definition not apply, this is from a simple google search of perspective (it appears at the top);

"The art of drawing solid objects on a two-dimensional surface so as to give the right impression of their height, width, depth, and...
A picture drawn in such a way, esp. one appearing to enlarge or extend the actual space, or to give the effect of distance."

Granted we are not drawing in the literal sense of the word, but we are creating the image. Is our work "art" or are we just capturing an image relative to the viewer.

Personally if we are using the perspective as it relates to the content of the picture itself, I prefer this definition as it adds the element of depth.

This one is from the Free Farlex Dictionary online;
"4. The technique of representing three-dimensional objects and depth relationships on a two-dimensional surface."

 

[PackLight]

...and with apologies, unfortunately it seems the point is still not clear to some. ???

Crystal clear, I am just disagreeing with how we are using the word "perspective"
I think in a hobby we strive to create something that is considered art, we should use the definition that closely matches the one for art.

 

[neuroanatomist]

I suppose I should have indicated that's THE definition for photographic imagery.

The point of the definitions that pertain to drawing (which are the definitions you reference) is that for proper perspective, the size relationships of the rendered objects must be appropriate to one another and relative to the distance at which they are apparently rendered, so that 3D space is correctly represented as 2D. With a photograph, that's already a given due to the direct capture of the image, which faithfully preserves spatial relationships at the distance from which the image is captured, so those definitions are irrelevant to photography. I'm not arguing that photography isn't art, but the definitions you reference aren't any more relevant to a photographic image than they are to music as an art form.

You can choose to believe differently, and I'm sure many will agree. But then, many people think alot is a word, and that doesn't make it correct.

 

[PackLight]

From photonotes.org
Dictionary of Film and Digital Photography;

"Perspective.

Visual cues in a two-dimensional image which give the impression of three-dimensional space. Such cues include lines converging towards a vanishing point, aerial haze, different sizes of common objects, different zones of focus, etc."

I suppose there are alot of people that think this way. :

 

[neuroanatomist]

From photonotes.org
Dictionary of Film and Digital Photography;

"Perspective.

Visual cues in a two-dimensional image which give the impression of three-dimensional space. Such cues include lines converging towards a vanishing point, aerial haze, different sizes of common objects, different zones of focus, etc."

I suppose there are alot of people that think this way. :

I think you're still missing the point. The definition above is what perspective is, not what determines perspective. The point is that the only thing that determines perspective is distance. Not focal length. Not aperture. Not subjective blur. Distance, and only distance.

In the examples posted by privatebydesign, the perspective is identical. That is fact, and that is the point. Of course, the images have a perspective - in the images, the woman's left arm looks as large in diameter as the as the tree trunk in the background. Do you think her arm is really that big? No, because she is closer than the tree trunk. That's what perspective is. But what determines that perspective is how far both she and the tree trunk are from the camera. In both the cropped 17mm image and the 200mm image, her arm is the same relative size compared to the tree trunk. That's because the shots were taken from the same distance - thus, the perspective is the same, and the relative sizes of her arm and the tree trunk clearly demonstrate that fact. If privatebydesign had taken another shot at 17mm, this time matching the framing of 200mm without cropping, he'd have to be right next to her - and in that case, I'm sure you can envision that her arm would look much larger than the tree trunk. That would be because the distance had changed, which would change the perspective.

 

[neuroanatomist]

Here's an example from the wiki page on perspective distortion, an example that illustrates some of this confusion:

You see the different focal lengths printed on the images, and you see the relative sizes of the two water bottles changing, and you think that focal length is the reason. Even the text in the caption of that image suggests the effect is due to focal length. But consider...the pink bottle is the same height in all three images - therefore, as the focal length is reduced, the camera must have been moved closer to achieve the same framing. It's the movement of the camera, not the change in focal length, that results in the different perspectives.

Let me try to illustrate what I mean with a similar set of examples, but where I first vary just focal length but not distance, and then vary focal length and distance. Since I prefer beverages other than water, I selected a different pair of subjects for a similar test.

The two bottles are 18" apart, and the distances in the image below are measured from the sensor to the front bottle. All were shot at f/5.6. As described above, it's normal for the bottle in front to look larger, that's perspective - objects that are further away look smaller, even though we know they are the same size. Note that the bottle in front is the same height in all the images.

In the left column, the 50mm and 24mm shots were at the same distance as the 100mm images, and the images were cropped to match the framing of the 100mm image. As you can see, the relative size of the rear bottle is the same in all the images. The perspective is the same - the two bottles maintain the same relative size, despite the differing focal lengths. The distance is the same, so the perspective is the same.

In the right column, which is equivalent to the water bottle shots from the wiki page, the 50mm and 24mm shots were taken at successively closer distances to the bottles, matching the framing to the 100mm shot by moving the camera. As you can see, the relative size of the rear bottle gets smaller as the camera is moved closer. Different perspective, because the distance is changing. Comparing the side-by-side 50mm and 24mm images, you can see that with the same focal length but different subject distances, the perspective is different.

So, varying focal length alone, without changing distance, does not affect perspective. As stated above (by me and others), perspective is determined by distance, and distance alone.

As others pointed out above, 'telephoto' compression and 'wide angle' expansion distortion are the same phenomenon. The reference to 'telephoto' and 'wide angle' there is misleading - it has nothing to do with the focal lengths, only the distance. But longer lenses are usually used at longer distances, and wide lenses are usually used at closer distances (think of framing a person for a portrait), thus the erroneous association with a lens type when it's really the commonly used distances for those lenses that is the cause of both types of perspective distortion.

Regardless of whether or not this clarifies what determines perspective, I'm about to enjoy that bottle of Chocolate Stout. ;D

 

[PackLight]

Go enjoy, I just finished typing this and I saw you had posted so I modified it a bit.

I understand what you are saying, and perspective is determined by distance. (reading your last post, perspective distortion definitely is).

We were just using the term perspective, which by the definitions I have read means a few more things.

My point has been the final two pictures that were created. The perspective in those two pictures, the visual cues give a different impression of the three-deminsional space. That being the dof and field and focused areas.
There are many more sites offering similar or the same as I quoted, definition of what perspective "IS" as it relates to photography. I haven't found anything saying this definition is incorrect.

 

[ahab1372]

Regardless of whether or not this clarifies what determines perspective, I'm about to enjoy that bottle of Chocolate Stout. ;D

Enjoy, You've earned it.

 

[neuroanatomist]

We were just using the term perspective, which by the definitions I have read means a few more things.

Well, that's your viewpoint opinion perspective on the issue...

 

[ahab1372]

Go enjoy, I just finished typing this and I saw you had posted so I modified it a bit.

I understand what you are saying, and perspective is determined by distance. (reading your last post, perspective distortion definitely is).

We were just using the term perspective, which by the definitions I have read means a few more things.

My point has been the final two pictures that were created. The perspective in those two pictures, the visual cues give a different impression of the three-deminsional space. That being the dof and field and focused areas.
There are many more sites offering similar or the same as I quoted, definition of what perspective "IS" as it relates to photography.

which IMHO is not a good thing, because the term becomes ambiguous, and it is not clear any more what people are talking about.

I haven't found anything saying this definition is incorrect.

That still doesn't mean it is widely accepted, and even if it was, it is still not correct. I prefer the less ambiguous definitions

 

[PackLight]

That still doesn't mean it is widely accepted, and even if it was, it is still not correct. I prefer the less ambiguous definitions

Perhaps if we stuck with and used the term "perspective distortion" it would be less ambiguous and spot on, rather than a word that pulls up a half dozen different meanings when you word search. Kind of the point I was making, thanks.

 

[PackLight]

@privatebydesign

Perspective Distortion
Rectilinear Perspective
Vanishing Point Perspective
Height Perspective
Overlap Perspective
Dwindling Size Perspective
Atmospheric Perspective

A National Geographic photographers article on incorporating Perspective http://photography.nationalgeographic.com/photography/photo-tips/pbb-get-some-perspective/

Here is an interesting one, a photography gallery that named there gallery after the distance they were from an object when they took the picture;

http://www.perspectivegallery.org/about-perspective-gallery-

My only point is that using just the word "perspective" has a bit broader meaning to many people in photography than the one offered. You may not like that, but it is true.

 

[neuroanatomist]

My only point is that using just the word "perspective" has a bit broader meaning to many people in photography than the one offered. You may not like that, but it is true.

And alot of people use alot of words irregardless of they're proper meaning. That don't make them rite. That be true to, even if we doesn't like it muchly.

 

[Don Haines]

Focal length of the lens is the same no matter which camera it is mounted on. The basic difference between full frame lenses and APS-c lenses is the size of the image circle. If we assume no problems hitting mirrors, we get the following:
Put a full frame lens on either camera and the image circle covers the entire sensor. Put an APS-c lens on an APS-c camera and the image covers the entire sensor. Put an APS-c lens on a ff body and you get severe vignetting.

The difference in field of view (sometimes called reach or apparent focal length) between ff and aps-c comes from the sensor, not the lens. To try to explain this, imagine a camera body where you could slide in and out two different sensors, one a ff sensor, and the other a 4/3 sensor. ( I picked 4/3 because it is 1/2 the size and the math is easy) both sensors are 10 Mpixels and we use the same lens, which has a 20 degree field of view.

When you use the ff sensor, light from that 20 degree field of view hits the edge of the sensor and is captured as the edge of the image. When we slip in the 4/3 sensor, the same light as before enters the camera, but the smaller sensor only sees a portion of that light. The light that falls on the edge of the smaller sensor is now that light from the central part of the view, and what gets captured by the sensor is a 10 degree field of view. We look at the two images and we say that the 4/3 sensor image is like using twice the focal length because that's what the field of view looks like.

We are not cropping the image, what we are doing is sampling the view with a higher density of pixels for the central part of the image and ignoring the rest. If our ff sensor was 40Mpixels and we used just the center 10 Megapixels of the capture, the two resulting images would have been identical.

In the real world, things are not as clean. The smaller pixels, being smaller, are hit by less light, so the signal to noise level will be lower. That smaller pixel receives 1/4 the light as the FF pixel, so to give the same brightness in the output image, the gain of the sensor has to be turned up by a factor of 4 to compensate..... and this is where 2 stops of performance improvement of FF sensors comes from. It is harder (impossible?) to make a smaller pixel as good as a larger pixel so what you end up with is a series of trade offs.... And this is assuming our lens is perfect... Flaws in the glass will become more apparent with the higher sampling density.....

In ff vs APs-c you are trading pixel quality for pixel density. The real difference between the two is that the larger pixels of ff will always be better quality pixels than APS-c, given the same level of technology used on the sensor. The ff will perform better in low light, will have cleaner and higher images at higher ISO's, and cost more.