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Good link from Nat Geo... 
PostPosted: Thu Mar 31, 2011 4:51 pm Reply with quote
ivorfatarse
Joined: 12 Oct 2006
Posts: 795
http://www.nationalgeographic.com/ebooklets/e_ultimate_photo_guide.pdf?source=email_welcome2011

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PostPosted: Fri Apr 01, 2011 8:31 am Reply with quote
Humble Jim
Joined: 03 Jan 2005
Posts: 6185
Location: Leeds, UK
Yes, that's a very good document indeed. I hope they cover the creative potential of post processing one day.

The only technical issue I'd criticize it on is where it talks about use of f/16. The "sunny 16" rule was fine for film SLRs but if you ever use f/16 on a digital SLR you're unlikely to get sharp photos suitable for larger blowups, though small prints might be OK. Generally I stay off going beyond f/11 except when I really have no other choice.

The reason is a problem is called diffraction which affects image sharpness on DSLRs when lenses are fully stopped down (i.e. when they're made to 'squint' by closing the iris up a lot).

The amount the issue affects digital SLRs is down to the sensor size and the number of pixels packed into the sensor area. Generally the smaller the sensor and the more the number of megapixels the more intrusive diffraction will be. The issue has become more significant over recent years as manufacturers pack ever more megapixels into sensors.

The easiest way to avoid diffraction problems is to stay away from f/16 if you can and don't go past f/11. For some cameras, diffraction can start to intrude at f/8.

If you want the really nerdy explanation Smile, and to use a Diffraction Limited Aperture Calculator to work out your own camera's diffraction limits, then head over to THIS page.
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Good link from Nat Geo... 
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