# Rethinking 4/3 Depth Of Field

Started Apr 11, 2013 | Discussions thread
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 Re: I'm not convinced... In reply to Anders W, Apr 13, 2013

Anders W wrote:

Great Bustard wrote:

Rriley wrote:

Ironically, I think shallow DOF with UWA is "da bomb":

24mm FF isnt UWA

I've always thought that 24mm (on FF) was the long end of UWA:

http://www.cambridgeincolour.com/tutorials/wide-angle-lenses.htm

The definition of ultra-wide is a little fuzzier, but most agree that this realm begins with focal lengths somewhere around 20-24 mm [on FF] and less.

If I'm in error on this point, I'd appreciate a link to a credible source with a "less fuzzy" definition.

I am not usually inclined to propose definite limits of anything, but 24 is to me precisely the border line between WA and UWA.

That's basically how I see it, too.  In fact, let me get nerdy (I know, I know -- too late!).  Let's think of focal lengths in terms of stops, with 0 stops being the sensor diagonal, and each stop increase/decrease doubles/halves the area of the scene on the focal plane.  Then, for FF, we have:

• -4 stops --> 11mm
• -3 2/3 stops --> 12mm
• -3 1/3 stops --> 14mm
• -3 stops --> 15mm
• -2 2/3 stops --> 17mm
• -2 1/3 stops --> 19mm
• -2 stops --> 22mm
• -1 2/3 stops --> 24mm
• -1 1/3 stops --> 27mm
• -1 stop --> 31mm
• -2/3 stops --> 34mm
• -1/3 stops --> 39mm
• 0 stops --> 43mm
• 1/3 stops --> 49mm
• 2/3 stops --> 55mm
• 1 stops --> 61mm
• 1 1/3 stops --> 69mm
• 1 2/3 stops --> 77mm
• 2 stops --> 87mm
• 2 1/3 stops --> 97mm
• 2 2/3 stops --> 109mm
• 3 stops --> 122mm
• 3 1/3 stops --> 137mm
• 3 2/3 stops --> 154mm
• 4 stops --> 173mm
• 4 1/3 stops --> 194mm
• 4 2/3 stops --> 218mm
• 5 stops --> 245mm
• 5 1/3 stops --> 275mm
• 5 2/3 stops --> 308mm
• 6 stops --> 346mm
• 6 1/3 stops --> 389mm
• 6 2/3 stops --> 436mm
• 7 stops --> 490mm
• 7 1/3 stops --> 549mm
• 7 2/3 stops --> 617mm
• 8 stops --> 692mm
• 8 1/3 stops --> 777mm
• 8 2/3 stops --> 872mm
• 9 stops --> 979mm

This thinking leads to the following classifications:

• Wider than -2 stops:  UWA
• Between -2 stops and 1 stop:  WA
• Between -1 stop and 1 stop:  Normal
• Between 1 stop and 2 stops:  Portrait
• Between 2 stops and 3 stops:  Short Telephoto
• Between 3 stops and 5 stops:  Long Telephoto
• Longer than 5 stops:  Super Telephoto

Thus, 24mm would just miss UWA, and 22mm would be the border.  I'm sure this is exactly what Rriley meant.

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