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Max. magnification of lenses
Is there a way to calculate the max. magnification from the focal
length, sensor size and minimum focus distance? -- Alfred Molon Olympus E-series DSLRs and micro 4/3 forum at http://tech.groups.yahoo.com/group/MyOlympus/ http://myolympus.org/ photo sharing site |
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Max. magnification of lenses
On Thu, 17 Mar 2016 20:28:49 +0100, Alfred Molon
wrote: Is there a way to calculate the max. magnification from the focal length, sensor size and minimum focus distance? I don't think so. Theoretically you can in that the magnification is merely the image distance divided by the object distance so you can get any magnification you like by the suitable placement of the lens. The problem is that if the object or the image gets too close to the lens the performance of the lens degrades and no useful image is produced (unless you use a pinhole). These limits are inherent in the particular lens and there is no simple way of calculating them. -- Regards, Eric Stevens |
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Max. magnification of lenses
On 2016-03-17, Alfred Molon wrote:
Is there a way to calculate the max. magnification from the focal length, sensor size and minimum focus distance? You should take account of the amount of 'enlargement' in the final print or projection too. Few people use final images the same size as the sensor (unless you're talking medium or large format of course). As an approximation, given the height and width of the sensor, take the lens focal length as the distance from the lens to the sensor (it won't be in reality, this is just an approximation) and if you know or discover the nearest subject-to-lens distance that can be focussed, treat the lens as a single point through which all light rays pass and simple geometry shows you the subject height and width that will fit onto the sensor. The subject size will probably be in meters and the image in millimeters, so the 'magnification' is negative at this stage. Unless you use a real 'macro' lens set-up in which case you'll have to find the effective sensor-to-lens distance for your geometry. It will be substantially greater than the lens nominal focal length. As a rough indication, if you use extension tubes or a bellows extension, you can measure that extension (plus the distance from the camera lens mount to the sensor). That won't work if the 'macro' focus is achieved using fancy optics of course. Technically a 'macro' photo is at least as large on the sensor as the subject is in real life - but that isn't usually useful with small sensors. Then you print the image to something bigger than the sensor; a postcard perhaps, or A4, or something even bigger. How much of the entire image you print, and how big a 1mm square from the sensor ends up in the print is up to you (and your processing systems and the resolving abilities of the camera). You can short-circuit all the geometry just by taking a photo of a test card marked in mm at your closest focus point and see how big those mm are in an uncropped print ... or in a cropped print, or whatever form you want the final image in. -- -- ^^^^^^^^^^ -- Whiskers -- ~~~~~~~~~~ |
#4
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Max. magnification of lenses
In article ,
Whiskers wrote: Technically a 'macro' photo is at least as large on the sensor as the subject is in real life - but that isn't usually useful with small sensors. Nope, 'closeup' is good enough for them! -- teleportation kills |
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