APS-C lens mm are correct

[ahab1372]

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.

Yes, yes and yes. Distance only makes the perspective. The focal length and the sensor size determine the framing for a given distance from a subject.

As to the focal length equivalents: It is really a function of the sensor size, not of the lens. EF or EF-S doesn't matter. People/companies talk about the equivalent length to be able to compare how a lens on a certain camera feels in regards to the FOV, but they should really do so when talking about the camera, not the lens.

[KyleSTL]

The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.

So if I frame a photo the same with my 24mm lens and then with my 200 lens, the photos will have the same perspective?  Perspective, like the mm length, is part of the lens, not the sensor behind it.

No. Perspective is determined by the distance from the camera to the subject.  Focal length, sensor size, cropping - none affect perspective.

If you frame the same subject with a 24mm vs. a 200mm lens, you've changed the distance and that's what changes the perspective.  If you took the two shots from the same distance, the perspective would be the same, but the framing would be different. If you then cropped the 24mm shot to the framing of the 200mm shot, both the perspective and the framing would be the same.

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.
From a framing standpoint, so long as the camera and all objects within the frame have not moved, the images will have identical perspective, with different depths of field (assuming the same aperture).  EDIT: Although at macro-like distances, that may change.  Neuro might have to chime in on that.

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?
Yes, after applying distortion correction they will have identical perspective.

[PackLight]

The horse is dead but we go on;

As Perspective would apply to a picture;

"the technique or process of representing on a plane or curved surface the spatial relation of objects as they might appear to the eye; specifically : representation in a drawing or painting of parallel lines as converging in order to give the illusion of depth and distance"

Perspective as it would apply to you;

"the appearance to the eye of objects in respect to their relative distance and positions"

Thank you Merriam Webster

So would a picture taken at the same distance with two diffrent focal lengths have the same perspctive.
The wider lens would have contained in it, the ability to have the same perspective (illusion of depth and distance) as the long lens. However the picture with the long lens will not be able to give the same perspecitve (illusion of depth and distance) as the wide lens.

Choose your definitions and I believe most arugments so far can be made to fit.

[Daniel Flather]

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images.  The 35mm lens' subject will have a bigger nose.  So, an ef 50mm on a crop is different than an ef 80mm on FF.  Maybe something was lost in the ether, but 50mm is not 80mm.

[Sporgon]

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images.  The 35mm lens' subject will have a bigger nose.  So, an ef 50mm on a crop is different than an ef 80mm on FF.  Maybe something was lost in the ether, but 50mm is not 80mm.

In this example perspective would indeed be different because your distance would be (very) different. Take the shot with 35mm from the same position as your 200, then crop 35mm in post to the same framing - perspective will be identical.

[TexPhoto]

Noses are generally big in wide angle portraits, Because the camera is so much closer to the subject, not because of the use of a wide angle lens.  A headshot with an 85mm looks right, and a 28mm headshot looks wrong because you would not/could not take these photos at the same distance.

[Sporgon]

Noses are generally big in wide angle portraits, Because the camera is so much closer to the subject, not because of the use of a wide angle lens.  A headshot with an 85mm looks right, and a 28mm headshot looks wrong because you would not/could not take these photos at the same distance.

+1

[Chuck Alaimo]

Noses are generally big in wide angle portraits, Because the camera is so much closer to the subject, not because of the use of a wide angle lens.  A headshot with an 85mm looks right, and a 28mm headshot looks wrong because you would not/could not take these photos at the same distance.

doesn't lens curvature play into this too?  anything on the wide end has that bend to it, even if its at a distance right?  Isn't that due to the curvature of the lens, which is much more pronounced on wide angle lenses?  (also why wide angle tilt shifts are both specialized and pricey because they have comples systems inside to reduce curvature?)

[PackLight]

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images.  The 35mm lens' subject will have a bigger nose.  So, an ef 50mm on a crop is different than an ef 80mm on FF.  Maybe something was lost in the ether, but 50mm is not 80mm.

They would most likely be diffrent because of the depth of the background may appear diffrently, but maybe not. Since a picture is only creating an illusion of depth, if all things in the picture were of the same framing and the pictures were identical in appearance, then they would have the same perspective. Although you shot them from a diffrent perspective.
You are dealing with two diffrent things, what the picture shows and what your physical location is.
You can say your perspective changed, but it is still possible for the picture to have the same perspective.

[neuroanatomist]

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.

Yes and yes. So does a 1200mm lens. People incorrectly believe that the perspective is different because the distances at which such focal lengths are different. But it's the distance that determines the perspective.

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images. 

You changed the distance. Take the head shot with 200mm, then stay out and use the 35mm lens. Crop the latter to the same framing as at 200mm, you'll have the same perspective.

[PackLight]

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.

Yes and yes. So does a 1200mm lens. People incorrectly believe that the perspective is different because the distances at which such focal lengths are different. But it's the distance that determines the perspective.

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images. 

You changed the distance. Take the head shot with 200mm, then stay out and use the 35mm lens. Crop the latter to the same framing as at 200mm, you'll have the same perspective.

Or shoot a perfectly flat wall with the 35mm at 10', and the 200mm picture would have the exact same perspective at 57.14'. However you will not have the same perspective.

[Sporgon]

I think that to help clear this up a bit it is worth mentioning that in the practical application a 200mm does have a more compressed perspective than say a 20mm, because you have to be using the 200mm from much further away to achieve equal framing, that is assuming you are using the same sensor size !!

[PackLight]

I think that to help clear this up a bit it is worth mentioning that in the practical application a 200mm does have a more compressed perspective than say a 20mm, because you have to be using the 200mm from much further away to achieve equal framing, that is assuming you are using the same sensor size !!

Excellent 

Now we can start a discussion on compression and how it affects ff vs crop framing and crop factor. Really though it might just part of the explanation for the diffrence in perspective.

[Videoshooter]

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images.  The 35mm lens' subject will have a bigger nose.  So, an ef 50mm on a crop is different than an ef 80mm on FF.  Maybe something was lost in the ether, but 50mm is not 80mm.

That is because you changed the distance to subject in your example. If you stand in the same spot and take a photo of the same subject, the perspective will be identical with any lens, save for any distortion introduced by the lens (ie field curvature in a fisheye lens). Of course the framing will be very different, though cropping to the same framing will overcome this (though will not result in the best picture quality).

Apply this to a 50mm and 85mm lens, taking a portrait, and you get a perfect example of why we use equivalent FOV's. Put the 85mm lens on the FF camera, and take a photo. Now put your 50mm lens on that same camera and take another photo. The perspective will be exactly the same, but the framing is different - you have a whole bunch of extra area around the edges of the image. But, if you crop that 2nd photo to the same framing, it will have the exact same perspective as the first photo. Now, pair your 50mm lens with a APS-C camera. It will give the same photo (in terms of perspective and framing) as in photo 2, although it is already cropped straight out of the camera. The FOV will be the same (give or take a few mm), and the perspective will be the same, as the photo taken with the 85mm on the FF camera.

[Daniel Flather]

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.

Yes and yes. So does a 1200mm lens. People incorrectly believe that the perspective is different because the distances at which such focal lengths are different. But it's the distance that determines the perspective.

But an ef 35mm lens projects the  same image behind it regardless of the sensor behind it.  If I take a head shot with an ef 35mm lens, then change to a 200mm lens, back up to the same framing, they are different images. 

You changed the distance. Take the head shot with 200mm, then stay out and use the 35mm lens. Crop the latter to the same framing as at 200mm, you'll have the same perspective.

Backing up is the ether.