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How Sensor Size, Focal Length, Distance and Subject Size Relate to Each Other
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<blockquote data-quote="Eyelight" data-source="post: 336417" data-attributes="member: 24753"><p>Note: I think I have this worked out, but that does not mean it makes sense or that it is a perfect explanation. The diagrams are based on real numbers, but the math is absent to protect the innocent (keep it visual). I started fiddling with the diagrams the other day, but my Cadd software crashed and then Glen ran out of popcorn.</p><p></p><p>BIG NOTE: Let's leave specific cameras and pixels out of this thread. All we are dealing with is the four measurements and how they interact.</p><p></p><p><strong><u>Sensor Size, Focal Length, Distance and Subject Size</u></strong></p><p></p><p>These four measurements work together. Using any three you can determine the fourth. Changing one of the four will require changing at least one of the other three. Since we are mostly interested in FX and DX formats, we will use them, but the same applies to larger or smaller sensor sizes.</p><p></p><p>There is a point in a lens where light rays converge (it's more complicated than this, but thinking of it as a point will help with the basic ideas here presented). This point divides our measurements into two halves, before and after. It is the angle of view that ties the two halves together.</p><p></p><p>Sensor size and focal length determine angle of view. Angle of view and distance determine subject size (or view). This diagram shows how the four measurements come together using an FX sensor. The angle of view used is that of a 50mm lens.</p><p>[ATTACH]103245[/ATTACH]</p><p>What if we use a DX sensor with the same lens (same focal length) at the same subject distance? The DX / 50mm combo will see a smaller subject size.</p><p>[ATTACH]103246[/ATTACH]</p><p></p><p>What if we want to keep the same focal length and the same subject size? The DX / 50mm combo has to move to a greater distance.</p><p></p><p>[ATTACH]103248[/ATTACH]</p><p></p><p>What if we want to keep the same distance and the same view size? The DX sensor must use a shorter focal length lens to increase the angle of view to equal the angle of view of the FX / 50mm focal length combo.</p><p></p><p>[ATTACH]103257[/ATTACH]</p></blockquote><p></p>
[QUOTE="Eyelight, post: 336417, member: 24753"] Note: I think I have this worked out, but that does not mean it makes sense or that it is a perfect explanation. The diagrams are based on real numbers, but the math is absent to protect the innocent (keep it visual). I started fiddling with the diagrams the other day, but my Cadd software crashed and then Glen ran out of popcorn. BIG NOTE: Let's leave specific cameras and pixels out of this thread. All we are dealing with is the four measurements and how they interact. [B][U]Sensor Size, Focal Length, Distance and Subject Size[/U][/B] These four measurements work together. Using any three you can determine the fourth. Changing one of the four will require changing at least one of the other three. Since we are mostly interested in FX and DX formats, we will use them, but the same applies to larger or smaller sensor sizes. There is a point in a lens where light rays converge (it's more complicated than this, but thinking of it as a point will help with the basic ideas here presented). This point divides our measurements into two halves, before and after. It is the angle of view that ties the two halves together. Sensor size and focal length determine angle of view. Angle of view and distance determine subject size (or view). This diagram shows how the four measurements come together using an FX sensor. The angle of view used is that of a 50mm lens. [ATTACH=CONFIG]103245._xfImport[/ATTACH] What if we use a DX sensor with the same lens (same focal length) at the same subject distance? The DX / 50mm combo will see a smaller subject size. [ATTACH=CONFIG]103246._xfImport[/ATTACH] What if we want to keep the same focal length and the same subject size? The DX / 50mm combo has to move to a greater distance. [ATTACH=CONFIG]103248._xfImport[/ATTACH] What if we want to keep the same distance and the same view size? The DX sensor must use a shorter focal length lens to increase the angle of view to equal the angle of view of the FX / 50mm focal length combo. [ATTACH=CONFIG]103257._xfImport[/ATTACH] [/QUOTE]
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How Sensor Size, Focal Length, Distance and Subject Size Relate to Each Other
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