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Author Topic: APS-C lens mm are correct  (Read 23194 times)

neuroanatomist

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Re: APS-C lens mm are correct
« Reply #90 on: December 07, 2012, 09:52:15 PM »
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.
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Re: APS-C lens mm are correct
« Reply #90 on: December 07, 2012, 09:52:15 PM »

neuroanatomist

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Re: APS-C lens mm are correct
« Reply #91 on: December 07, 2012, 11:35:48 PM »
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
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PackLight

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Re: APS-C lens mm are correct
« Reply #92 on: December 07, 2012, 11:54:25 PM »
 :) 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

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Re: APS-C lens mm are correct
« Reply #93 on: December 07, 2012, 11:58:10 PM »

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

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Re: APS-C lens mm are correct
« Reply #94 on: December 08, 2012, 12:00:18 AM »
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...   :P :P :P
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ahab1372

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Re: APS-C lens mm are correct
« Reply #95 on: December 08, 2012, 12:04:55 AM »
:) 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.
Quote
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

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Re: APS-C lens mm are correct
« Reply #96 on: December 08, 2012, 12:56:50 AM »

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.

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Re: APS-C lens mm are correct
« Reply #96 on: December 08, 2012, 12:56:50 AM »

PackLight

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Re: APS-C lens mm are correct
« Reply #97 on: December 09, 2012, 12:33:19 AM »
@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

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Re: APS-C lens mm are correct
« Reply #98 on: December 09, 2012, 07:17:26 AM »
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.
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Don Haines

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Re: APS-C lens mm are correct
« Reply #99 on: December 09, 2012, 09:06:28 AM »
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.
« Last Edit: December 09, 2012, 09:43:35 AM by Don Haines »
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Don Haines

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Re: APS-C lens mm are correct
« Reply #100 on: December 09, 2012, 09:38:44 AM »
Don,

I agree with your summation but would change one word, "The difference in reach between ff and aps-c comes from the sensor,"

Should, for the sake of clarity, read "The difference in field of view between ff and aps-c comes from the sensor,"
Thanks! I edited my post to reflect your suggestion.
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Re: APS-C lens mm are correct
« Reply #101 on: December 09, 2012, 01:50:06 PM »
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.

("muchly", I found a new word to add to my vocabulary to frustarte my 5th grade english teacher  :D)

I have been thinking about this muchly and here is my thought;

Someone in reference to his photography asks about adding "perspective", changing the "perspective" or however they phrase the question.

His understanding may be in line with how you have defined it, or it may not.

The same person may have the understanding that "perspective" is the 3D illusion that some pictures have.
So do we tell the person they are incorrect when it comes to photography, do we tell this person that "the only thing that determines perspective is distance". I suppose we do, since that is the consensus of this thread.

I would hope if this person comes across an article that can take their photography to another level it doesn't hold that individual back from reading it because it is entitled "perspective" and the author has a different understanding of the definition. How can we have respect for this persons teachings if their understanding of the simple word "perspective" is different than ours. Just as in painting a photograph can have the illusion of depth by  altering colors, changing light intensity, shadows, changing the areas in focus  and altering the dimensional aspect and position and placement or location of objects. The difference is we have far less control on those aspects than someone painting. If someone describes these things as a way to control perspective in photography should we dismiss their teachings as they do not know what they are talking about?

I think explaining to someone that a 7D sensor does not have more "Reach" than a FF sensor, or that a EF-S lens at 100mm is not a 160mm in disguise, is a little more straight forward than describing "perspective". Again as you said "my opinion" thank ya muchly.  ;D


« Last Edit: December 09, 2012, 01:52:54 PM by PackLight »

Don Haines

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Re: APS-C lens mm are correct
« Reply #102 on: December 09, 2012, 03:10:08 PM »
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.

Neuro, you really made me smile here.....

"alot"

"they're"

regardless = without regard
irregardless - not a real word

"That don't make them rite"

"That be true to."

"muchly"

Either you are having way too much fun here, or you had more than one bottle of chocolate stout (possibly both).... Love it and keep up the good (bad?) work!
« Last Edit: December 09, 2012, 03:14:58 PM by Don Haines »
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Re: APS-C lens mm are correct
« Reply #102 on: December 09, 2012, 03:10:08 PM »

woollybear

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Re: APS-C lens mm are correct
« Reply #103 on: December 09, 2012, 03:39:48 PM »
Wow...I think I figured it out...

Put two photographers in a forum and you'll get three different opinions.

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Re: APS-C lens mm are correct
« Reply #104 on: December 09, 2012, 10:49:52 PM »
I guess my perspective on this is that someones point of view is distorted.  One thing about all of this is clear though --- neuro's shot of the beer - the file either lacks the resolution, or, the DOF of fields blurs it out too much, but I believe that from Neuro's perspective the chocolate stout is much nastier than whatever the one is behind it (IPA ?????).
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Re: APS-C lens mm are correct
« Reply #104 on: December 09, 2012, 10:49:52 PM »