Really: I'll wait.
The closer you hold the hole, the more you can see of the scene, the further away, the less you see. So, short focal length means a wider angle view, long focal length means narrow angle view.
To illustrate the effect, I'll demonstrate why I do photography rather than drawing: on the left we have a pinhole very near the sensor, so the tree(!) only occupies a small part of the frame, on the right the pinhole is much further away, so the tree occupies lots of the frame.
So far so good?
Now, where this gets interesting is when you change the size of the sensor the light is falling on:
Three sensors indicated there, for a 60mm focal length: 35mm, the DX sensor in the Nikon digitals and most other digital SLRs and 6x6 film. Digital compacts have much smaller lenses.
If you trace the light you can see that the "house" (or "robot") is covering most of the 6x6 frame, that only a small part of it is visible to the 35mm sensor and even less to the DX sensor. A compact camera thinks that a 60mm lenses is a long telephoto while a 6x6 sensor sees it as a normal lens and a 4" x 5" would see it as an extreme wide-angle. Thus the 60mm lens on a 35mm is equivalent in angle of view to a 90mm on the DX sensor.
DId that help?
More seriously, great effort, you must have a scan nearby ! Next step: perspective (or the face you don't recognize with that big nose in the middle :-) )... Or why it is independent of the focal length but in direct relationship with the distance between the subject and the film plane (or captor, or CCD)...
The fact, as shown in Colman's drawings, that different focal lengths (i.e. the usual lens naming) gives you different viewing angles is often confused with the "perspective" effect (the too big nose). Most people think that with a wide angle you have a "bad" portrait, while with a mid-tele that's not a problem...
As in the drawings above, we tend to "fill" the frame for a portrait (just an example), so with a tele we are at some distance of the subject, while with a "wide-angle" we would be much nearer, thus accentuating the perspective effect.
It works with buildings too, when people want to get the whole church "in the frame" they often favor a great wide-angle lens increasing the weird feeling that parallels spires are meeting in some not too far points !
When you don't have the backing space for a "frame filling" shot (often the case in old cities) it is often easier (i didn't say better) to find a distant viewpoint (the hill outside the village ) and to use a big tele lens...
Or to use your ordinary lens (35m or 50mm) and frame part of the church in a way that conveys the feeling you had when seeing it (the church). :-) "What can I do, What can I write, Against the fall of Night". A.E. Housman
Or to use your ordinary lens (35m or 50mm) and frame part of the church in a way that conveys the feeling you had when seeing it (the church). :-)
As in gioele 's Prague picture below :-) "What can I do, What can I write, Against the fall of Night". A.E. Housman
Isn't that two separate issues? The face distortion is due to the way it's spread over the frame (compared to how we expect to see it - you can get the same effect by eye if you pay attention to what you're actually seeing), while the meeting spires is more to do with the sensor plane not being vertical - you point it up at the church and that causes distortion.
That's why view cameras can correct for it: you can set the back parallel to the subject and use the front movement to get the framing you want:
From Ansel Adam's The Camera.
The face distortion is about distance and as you say you can see it if you get near the subject's nostrils :-)
But for a given distance, a tele shot and a wide angle shot will generate the same perspective deformation if you superpose the two pictures (blowing one up or shrinking the other)... "What can I do, What can I write, Against the fall of Night". A.E. Housman
I just came back from a sudden trip from Finland; have I missed much? You have a normal feeling for a moment, then it passes. --More--
perspective (or the face you don't recognize with that big nose in the middle :-)
The folks I know who do portraits on a regular basis swear that 100mm to 135mm (35 mm cameras) lenses are the best for such work--just to avoid the problem you mention.
These lenses also mean that you can get detailed shots without getting too close to the subject. "Remember the I35W bridge--who needs terrorists when there are Republicans"
For portraits - in the sense of a depiction of a person - that include the environment you can use much wider lenses without making the person look too scary. It's all a matter of how much of the frame they're filling.
This is helpful, thanks. I will have to read over everything again when I am not supposed to be working! Ad astra per aspera
