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<blockquote data-quote="WayneF" data-source="post: 363001" data-attributes="member: 12496">? All images involve depth of field.&nbsp; But f/22 is a bigger story than that.&nbsp; Yes, it is pretty much about resolution.&nbsp; It&nbsp; is also pretty much about depth of field.&nbsp; And pretty much about focal&nbsp; length.fstop number = focal length / aperture diameter.f/22 on a 20mm lens has an aperture diameter of 20/22 = 0.9 mm.&nbsp; That is a pretty tiny hole, which causes trouble.&nbsp;&nbsp; f/4 is sharper.f/22 on a 60mm lens has an aperture diameter of 60/22 = 2.7 mm.&nbsp;&nbsp; This is borderline small, but certainly bearable when it helps DOF.f/22 on a 105mm lens has an aperture diameter of 105/22 = 4.8 mm, much more reasonable.&nbsp; f/22 might not always be a good plan for a short lens, but certainly a longer lens can usually benefit greatly.&nbsp; It's one advantage of the 105 and 200 mm macro lenses.&nbsp; But image SIZE is also a factor, and it can be the same.But f/22 is not necessarily always bad for short lenses.&nbsp; Let's consider 20mm and 100 mm, for round numbers.If you can think of your subject object image size as the count of so many line pairs, the subject object at 20mm covers 1/5 the size at 5x the resolution, and the subject object at 100mm covers 5x the size at 1/5 the resolution. This is the same number of line pairs (same detail) over the size extent of the subject object, and the detail in the objects can appear similar to us. So standing up up closer with the short lens, to magnify the subject image, will help f/22 at 20mm.&nbsp; It is not necessarily bad. But some situations are.Read the third equation down.&nbsp; Focal length magnifies it.&nbsp; The resolution factor depends directly on fstop number.</blockquote>

[QUOTE="WayneF, post: 363001, member: 12496"] ? All images involve depth of field. But f/22 is a bigger story than that. Yes, it is pretty much about resolution. It is also pretty much about depth of field. And pretty much about focal length. fstop number = focal length / aperture diameter. f/22 on a 20mm lens has an aperture diameter of 20/22 = 0.9 mm. That is a pretty tiny hole, which causes trouble. f/4 is sharper. f/22 on a 60mm lens has an aperture diameter of 60/22 = 2.7 mm. This is borderline small, but certainly bearable when it helps DOF. f/22 on a 105mm lens has an aperture diameter of 105/22 = 4.8 mm, much more reasonable. f/22 might not always be a good plan for a short lens, but certainly a longer lens can usually benefit greatly. It's one advantage of the 105 and 200 mm macro lenses. But image SIZE is also a factor, and it can be the same. But f/22 is not necessarily always bad for short lenses. Let's consider 20mm and 100 mm, for round numbers. If you can think of your subject object image [B]size[/B] as the count of so many line pairs, the subject object at 20mm covers 1/5 the size at 5x the resolution, and the subject object at 100mm covers 5x the size at 1/5 the resolution. This is the same number of line pairs (same detail) over the size extent of the subject object, and the detail in the objects can appear similar to us. So standing up up closer with the short lens, to magnify the subject image, will help f/22 at 20mm. It is not necessarily bad. But some situations are. Read the third equation down. Focal length magnifies it. The resolution factor depends directly on fstop number. [/QUOTE]

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