Sharpest aperture?
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Phil V
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Check the mtf charts, but someone might already have done that.
As an aside though, Macro lenses are often recommended for copy work, can't remember the exact term (serves me right for trying to help when I'm half asleep) something to do with a flatter field of view?
As an aside though, Macro lenses are often recommended for copy work, can't remember the exact term (serves me right for trying to help when I'm half asleep) something to do with a flatter field of view?
Pookeyhead
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Thanks. Interesting, that's quite low(?).. People seem to suggest midway is usually the sharpest for most lens'? So setting it to say 5 would speed up the necessary shutter speed quite a bit when in a bright space for artwork photography, is that a good thing for detail etc? Thanks
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Pookeyhead
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Not really. A great many wide aperture primes perform best around f4. The 50mm Nikkor 1.4G has highest centre sharpness at f4... but a better balanced all round sharpness at f5.6. Between 4 and 5.6 is common for primes.
Blank_Canvas
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How accurate do they have to be ? For forensic work I used either a Nikon 50mm or 105mm on a copy stand with equal lighting. I would not use any wide angle lens for such work due to distortion etc. the term flat view lens is a bit of a misnomer. Any lens can be lined up perpendicular to a flat surface. It's just the some are more suitable than others.
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HoppyUK
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The sharper the lens, it will peak at a lower f/number (at least in the centre) as it hits the diffraction limit sooner - but at a higher level than less sharp lenses, that peak at higher f/numbers.
Most of the best quality lenses peak around f/5.6, a very sharp lens will peak at f/4, and the Sigma 50/1.4 Art, the sharpest lens I have tested, peaks at f/2.8 in the centre. Sharpness at the edges and corners is a different story however. They can continue to improve at higher f/numbers, even when sharpness in the centre is reducing. Take that Sigma 50/1.4 Art again - edge sharpness peaks at f/5.6.
Edit: Not sure how clear that is above! Basically, it is various lens aberrations that reduce sharpness - mainly chromatic aberration, spherical aberration, coma - and diffraction. Most aberrations reduce as the f/number is raised, but diffraction goes the other way and increases at higher f/numbers. Diffraction is directly related to the physical size of the lens aperture (as seen by the lens) and affects all lenses the same, regardless of quality. So sharpness peaks at the point where the reduction in the other aberrations crosses-over with the ever-increasing rise in diffraction.
The reason why edge and corner sharpness behave differently is, the further off-centre, the stronger most aberrations are, and harder to correct. So the lens has to be stopped down further and therefore the cross-over point with diffraction happens at a lower standard of sharpness.
Most of the best quality lenses peak around f/5.6, a very sharp lens will peak at f/4, and the Sigma 50/1.4 Art, the sharpest lens I have tested, peaks at f/2.8 in the centre. Sharpness at the edges and corners is a different story however. They can continue to improve at higher f/numbers, even when sharpness in the centre is reducing. Take that Sigma 50/1.4 Art again - edge sharpness peaks at f/5.6.
Edit: Not sure how clear that is above! Basically, it is various lens aberrations that reduce sharpness - mainly chromatic aberration, spherical aberration, coma - and diffraction. Most aberrations reduce as the f/number is raised, but diffraction goes the other way and increases at higher f/numbers. Diffraction is directly related to the physical size of the lens aperture (as seen by the lens) and affects all lenses the same, regardless of quality. So sharpness peaks at the point where the reduction in the other aberrations crosses-over with the ever-increasing rise in diffraction.
The reason why edge and corner sharpness behave differently is, the further off-centre, the stronger most aberrations are, and harder to correct. So the lens has to be stopped down further and therefore the cross-over point with diffraction happens at a lower standard of sharpness.
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