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Max. magnification of lenses



 
 
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  #1  
Old March 17th 16, 08:28 PM posted to rec.photo.digital
Alfred Molon[_4_]
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Default Max. magnification of lenses

Is there a way to calculate the max. magnification from the focal
length, sensor size and minimum focus distance?
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Alfred Molon

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  #2  
Old March 17th 16, 09:38 PM posted to rec.photo.digital
Eric Stevens
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Default 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
  #3  
Old March 18th 16, 09:20 PM posted to rec.photo.digital
Whiskers
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Default 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  
Old March 20th 16, 05:50 AM posted to rec.photo.digital
android
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Posts: 3,854
Default 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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