Canon lens choices for architecture.

[Guillermo Luijk]

What maths are we talking about here?
(...)
Everyone talks about the distance in front of the lens as the only thing that matters. I doubt that the distance to the front element makes much difference as I suspect the distance to the optical centre of the lens is what matters.
(...)
if we have an APS camera with a 50mm lens, a 35mm camera with an 80mm lens and a medium format camera with a 150mm lens all side by side looking at the same scene, lets say a person, then they will all fill the frame with the same image. However I say (as would many others) that each will have different look.
(...)
Long lenses compress distance and short images expand distance, so we use long lenses for portraits to reduce the size of the nose relative to the ears, and short lenses for landscapes to expand the vastne

Math equations that describe the 3D rectilinear projection over a 2D plane. There is plenty literature about that. All 3D video game engines implement these equations and the physics behind work pretty much the same as a camera.

What you call the optical centre, and many call wrongly the nodal point, is the entrance pupil of the lens.

The cameras and focal lengths in your examples will provide undistinguishable images in terms of perspective as long as the three entrance pupils are located at the same exact point. No different look, sorry.

What compresses distance is not long lenses but getting away from the subject. Focal length only affects field of view (FOV). Perspective depends only on distance from the entrance pupil to subject. Example:

Shot at 24mm:


Crop from that shot:


Shot at 85mm from the same camera location:


Identical perspective as the the 24mm shot. The 24mm shot just has a wider FOV. Of course in a practical situation focal length and distance to the subject are deeply related because we want to fill the frame, but it's important to know what variable influences in what, for example to understand what happens everytime you crop (reduce FOV) or stitch a linear panorama (increase FOV).

Regards

[drewaltizer]

I suppose that makes sense.  Im actual use, though, one does tend not to put the pupil in precisely the same place.  Further, to retain image quality most people would want to move the camera closet than would be ideal.  I think that better states why I prefer longer lenses to wider ones when possible.   I am generally not bothering to stitch an image for less information in my photo which I would get with 11 over 24 at a given pupil to subject distance.

[fdisilvestro]

Unfortunately i disagree with pretty much everything here.
Firstly the magnification is not the same. To make an A4 print (297 x210mm) from an APS camera (22x15.5mm) you magnify the image 182 times. For a 35mm camera (36x24mm) it's 72 times and for medium format (say 36x44mm or more) it's no more than 36 times. That's also digital magnification which is bad.

Magnification intended as the ratio between the printed/viewed image and the original physical object being photographed. E.g. a 1.7m tall person printed as a 10 cm figure in an A4 print.

DOF is definitely not the same if focal length varies. There is a mathematical formula but focal length is one of the key ingredients. Download any DOF app to see the relationship. The size of the entrance pupil may affect the maximum aperture available, but the aperture set affects DOF, not the maximum aperture available.

Do you know what the entrance pupil is?

A person shot with a short lens looks like a helicopter traffic reporter. Big nose and tiny ears. That definitely affects the look.

Not if you take the shot at the same distance as with a longer lens. See Guillermo post above

[BobShaw]

See Guillermo post above

All the shots are very similar, right down to the metadata.
Magnification is a combination of optical and digital. Digital is only 2 dimensional.

[aaronleitz]

Long lenses compress distance and short images expand distance, so we use long lenses for portraits to reduce the size of the nose relative to the ears, and short lenses for landscapes to expand the vastness. Short lenses basically distort. That is my observation. This to me is a big part of the medium format "look".

No. This is wrong. Focal length does not "compress" or "expand" distance. We use long lenses for portraits because they force us to step back and increase the distance between the camera and the human subject - thus rendering the size of the nose relative to the ears in a more pleasing way. See Guillermo's post.

Related to the OP: When I'm composing architectural shots choosing a focal length is the last thing I do. I usually start with a wide lens (because I know that focal length has nothing to do with "perspective" or "compression") and move around the scene keeping an eye on the relationships of objects to one another. Then once I figure out what I want to show and how all the elements fit together - I'll choose the appropriate focal length that results in the least amount of cropping away pixels. I choose the camera position before the focal length.

I think the 24mm T/S is a very useful lens. It's wide enough for most exterior architecture and overall interior shots. You can also add a 1.5 extender to make it a 36mm which is a very good focal length for interior shots.

[Guillermo Luijk]

A special highly "compressed" picture: even if the plane was roughly 200m far from the ground (just took off from a near airport), the satellite that got the picture was far more distant from the subject. That makes the scale of the plane nearly the same as that of the cars in the parking lot:



Shadow of the plane:


Regards


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