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<blockquote data-quote="WayneF" data-source="post: 355513" data-attributes="member: 12496">That is pretty much how lenses are....&nbsp;&nbsp; It is not that they are so less sharp at f/4 (they are a little less sharp when wide open), but that the zone of sharpness is narrow.&nbsp;&nbsp; Just for an example...&nbsp; There are depth of field calculators, ( <a href="http://www.dofmaster.com/dofjs.html" target="_blank">Online Depth of Field Calculator</a>&nbsp; is one), and say at 75mm zoom, and focused at 20 feet, thenf/4 - the depth of field (zone of sharpness,&nbsp; acceptable maybe)&nbsp; is&nbsp; 18.4 feet to 21.9 feet.f/8 - the depth of field is 17.1 to 24.1 feet - a little wider range (about double) of perhaps acceptable sharpness.&nbsp;&nbsp; Called Depth of Field.These are approximations, not biblical numbers.&nbsp; There is no sharp dividing line at these numbers.The subject exactly at 20 feet is probably OK either way, but the background and foreground changes.</blockquote>

[QUOTE="WayneF, post: 355513, member: 12496"] That is pretty much how lenses are.... It is not that they are so less sharp at f/4 (they are a little less sharp when wide open), but that the zone of sharpness is narrow. Just for an example... There are depth of field calculators, ( [URL="http://www.dofmaster.com/dofjs.html"]Online Depth of Field Calculator[/URL] is one), and say at 75mm zoom, and [B]focused at 20 feet[/B], then f/4 - the depth of field (zone of sharpness, acceptable maybe) is 18.4 feet to 21.9 feet. f/8 - the depth of field is 17.1 to 24.1 feet - a little wider range (about double) of perhaps acceptable sharpness. Called Depth of Field. These are approximations, not biblical numbers. There is no sharp dividing line at these numbers. The subject exactly at 20 feet is probably OK either way, but the background and foreground changes. [/QUOTE]

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