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General Photography
Macro
Focus distance.
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<blockquote data-quote="WayneF" data-source="post: 639169" data-attributes="member: 12496"><p>Then be glad you bought a 100mm lens, and got 4.5 inches at 1:1. If it had been a 55 or 60mm macro lens, it would have been more like 2 inches. This is simply the normal thing for macro lenses at 1:1.</p><p></p><p>Because, the meaning of 1:1 is that the distance in front of the lens is equal to the distance behind the lens. 1:1 means the image is same as real life size. So that is just a similar triangle, to be 1:1 means the subject height and distance must equal the focal length and image height, same triangles.</p><p></p><p>This is not measured from the exact front edge of the lens, but instead is measured to a principle point inside the lens somewhere. You have a 100mm lens (meaning, when focused at infinity, it is 100 mm). At 1:1 the lens is racked out some to focus closer, and the focal length is technically 2x longer at 1:1, or 200 mm. This also means the equivalent aperture will be 2 stops smaller then, actual maximum will be f/4 instead of f/2.8 (because f/stop is focal length / aperture diameter, and focal length is 2x longer at 1:1). Lenses and bodies today surely report the f/4 then, instead of f/2.8, but in old days, they didn't. Internal focusing lenses shift things inside, and can slightly vary this, maybe f/3.8 instead of f/4.</p><p></p><p>So at 1:1, the distance in front is necessarily equal to the focal length, let's say 200 mm. However, that is measured to the principle point inside the lens body, maybe an inch or two inside, so it is less distance to the actual front filter ring.</p><p></p><p></p><p>The 100 or 105 mm macro lens is often considered a plus due its slightly longer working distance. The difference between 2 and 4 inches is a lot. The closer camera can block the light, or it could scare the bug. <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>But the 55 and 60 mm has advantages too. For example, if you wanted to use 100mm for a table top scene, perhaps 18 or 20 inches wide, the 100 mm would have to stand back maybe 7 feet to get all of that in. The space in the room might not allow that. Similarly, copying documents on a copy stand would prefer the shorter lens, because its height column might not be that tall, and we couldn't reach the camera if it were. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /> The 55 or 60 mm lens is likely better suited for casual closeups (like 2 or 3 feet instead of 1:1), because they don't have to stand back so much farther.</p></blockquote><p></p>
[QUOTE="WayneF, post: 639169, member: 12496"] Then be glad you bought a 100mm lens, and got 4.5 inches at 1:1. If it had been a 55 or 60mm macro lens, it would have been more like 2 inches. This is simply the normal thing for macro lenses at 1:1. Because, the meaning of 1:1 is that the distance in front of the lens is equal to the distance behind the lens. 1:1 means the image is same as real life size. So that is just a similar triangle, to be 1:1 means the subject height and distance must equal the focal length and image height, same triangles. This is not measured from the exact front edge of the lens, but instead is measured to a principle point inside the lens somewhere. You have a 100mm lens (meaning, when focused at infinity, it is 100 mm). At 1:1 the lens is racked out some to focus closer, and the focal length is technically 2x longer at 1:1, or 200 mm. This also means the equivalent aperture will be 2 stops smaller then, actual maximum will be f/4 instead of f/2.8 (because f/stop is focal length / aperture diameter, and focal length is 2x longer at 1:1). Lenses and bodies today surely report the f/4 then, instead of f/2.8, but in old days, they didn't. Internal focusing lenses shift things inside, and can slightly vary this, maybe f/3.8 instead of f/4. So at 1:1, the distance in front is necessarily equal to the focal length, let's say 200 mm. However, that is measured to the principle point inside the lens body, maybe an inch or two inside, so it is less distance to the actual front filter ring. The 100 or 105 mm macro lens is often considered a plus due its slightly longer working distance. The difference between 2 and 4 inches is a lot. The closer camera can block the light, or it could scare the bug. :) But the 55 and 60 mm has advantages too. For example, if you wanted to use 100mm for a table top scene, perhaps 18 or 20 inches wide, the 100 mm would have to stand back maybe 7 feet to get all of that in. The space in the room might not allow that. Similarly, copying documents on a copy stand would prefer the shorter lens, because its height column might not be that tall, and we couldn't reach the camera if it were. :) The 55 or 60 mm lens is likely better suited for casual closeups (like 2 or 3 feet instead of 1:1), because they don't have to stand back so much farther. [/QUOTE]
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