Forums
New posts
Search forums
What's new
New posts
New media
New media comments
New profile posts
Latest activity
Media
New media
New comments
Search media
Members
Current visitors
New profile posts
Search profile posts
Log in
Register
What's new
Search
Search
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Forums
Learning
Education
How Sensor Size, Focal Length, Distance and Subject Size Relate to Each Other
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="WayneF" data-source="post: 336438" data-attributes="member: 12496"><p>All very well done, but this one sentence could be worded better (maybe "can be thought of as converging". Or maybe "is thought of", which is what you in fact are doing.) The sentence is true of a simple one element lens, like a magnifying glass. It could be assumed true of your hypothetical concept. Just not sure it should be said to be true. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /> Because our camera lenses are more complex and are built slightly differently. You shouldn't change your pictures, but maybe this one sentence could hedge about it. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></p><p></p><p>Lens designers can control the location of these "nodes" (using lens elements), and there are two nodes. The "triangle" from the subject plane is one (lets call its intersection node h), and the "triangle" from the sensor plane is a second node (let's call it h'... both shown in diagrams below). Those two fields of view are at equal opposing angles (as if they were the same one node), but the nodes are never in the same place. The lens elements sort of "relay" the signal between the internal nodes, from one to the other. I think same place is impossible in a multi-element lens. Except for macro distances, there is not much practical difference in the numbers of your examples.</p><p></p><p>But, it is a very big conceptual deal that they are different nodes, and there are strong advantages of two nodes NOT in the same location. For example, the definition of a telephoto lens is not necessarily a long focal length, but instead the actual definition of telephoto is a lens that that is shorter than its focal length. This specifically means point h' (focal length) is just outside the front lens element. So the lens is shorter (easier to carry and use). Your 200mm lens will not be as long as 200mm/25.4 = 7.87 inches from focal plane mark at rear of camera body. The word telephoto specifically refers to the moving of the node to a distant point (even if that meaning is about lost today).</p><p></p><p>A wide angle lens might be say 12mm focal length. But the FX frame is 24mm tall and the DX frame is 16mm tall, and both mirrors need room to be raised (mirror at 45 degrees is taller). A conventional 12mm lens would block the mirror (there were some very short fish eyes that did block it, mirror had to be locked up). So the typical WA lens instead puts point h' far behind the rear glass element, so the lens can be mounted well forward of the mirror, and the mirror is not blocked.</p><p></p><p>Here are diagrams which show this, from an old 1967 Nikon Handbook. I don't think the word Zoom is mentioned in this book yet. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /> </p><p></p><p><img src="http://www.scantips.com/g2/mike1.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p></blockquote><p></p>
[QUOTE="WayneF, post: 336438, member: 12496"] All very well done, but this one sentence could be worded better (maybe "can be thought of as converging". Or maybe "is thought of", which is what you in fact are doing.) The sentence is true of a simple one element lens, like a magnifying glass. It could be assumed true of your hypothetical concept. Just not sure it should be said to be true. :) Because our camera lenses are more complex and are built slightly differently. You shouldn't change your pictures, but maybe this one sentence could hedge about it. :) Lens designers can control the location of these "nodes" (using lens elements), and there are two nodes. The "triangle" from the subject plane is one (lets call its intersection node h), and the "triangle" from the sensor plane is a second node (let's call it h'... both shown in diagrams below). Those two fields of view are at equal opposing angles (as if they were the same one node), but the nodes are never in the same place. The lens elements sort of "relay" the signal between the internal nodes, from one to the other. I think same place is impossible in a multi-element lens. Except for macro distances, there is not much practical difference in the numbers of your examples. But, it is a very big conceptual deal that they are different nodes, and there are strong advantages of two nodes NOT in the same location. For example, the definition of a telephoto lens is not necessarily a long focal length, but instead the actual definition of telephoto is a lens that that is shorter than its focal length. This specifically means point h' (focal length) is just outside the front lens element. So the lens is shorter (easier to carry and use). Your 200mm lens will not be as long as 200mm/25.4 = 7.87 inches from focal plane mark at rear of camera body. The word telephoto specifically refers to the moving of the node to a distant point (even if that meaning is about lost today). A wide angle lens might be say 12mm focal length. But the FX frame is 24mm tall and the DX frame is 16mm tall, and both mirrors need room to be raised (mirror at 45 degrees is taller). A conventional 12mm lens would block the mirror (there were some very short fish eyes that did block it, mirror had to be locked up). So the typical WA lens instead puts point h' far behind the rear glass element, so the lens can be mounted well forward of the mirror, and the mirror is not blocked. Here are diagrams which show this, from an old 1967 Nikon Handbook. I don't think the word Zoom is mentioned in this book yet. :) [IMG]http://www.scantips.com/g2/mike1.jpg[/IMG] [/QUOTE]
Verification
Post reply
Forums
Learning
Education
How Sensor Size, Focal Length, Distance and Subject Size Relate to Each Other
Top