In article , Albert <olympus@xxxxxxxxxxx> writes
Today, I took a trip to the hot springs, and took a few pictures there,
followed by a few pictures at a very big and famous temple in Taiwan.
There was a small waterfall, and I wanted to take a good shot of it, and
so I shot it at F22 with a Polarizer on it, at about 1/8th of a second.
This is the first time I've shot at F22. Eager to see the results..
I'm bidding on a 24mm F2.8, and I just noticed that it only goes down to
F16 as compared to my 28mm, which goes down to F22. Am I really losing
that much, or no?
Most math tells me that F22's quality is not very good.. I'm wondering
if the DOF difference is that big between F16 and F22 that I'm really
missing out, or not by much.
Also, I'm wondering... if F16 on a 24mm is pretty much close to F22 on
a 28mm.
DOF roughly increases by 1.4 while the actual minimum blur spot at
optimum focus increases in size by 1.4. It depends what you are doing
with the image how significant this is, but it would be more noticeable
in large images.
It makes not a jot of difference what the focal length is for the blur
spot - its just the diffraction limited Airy disc radius of 1/22*W*f/#.
So F16 on a 24mm certainly isn't the same as f/22 on a 28mm - at the
negative. Since you could enlarge the 28mm image less to get the same
subject size as a 24mm image then you could argue that this increase in
blur spot is reduced by 7/6, which reduces the effect but does not
eliminate it. However, since reduced enlargement is not normally the
reason for choosing 28mm over 24mm it is a moot point.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers
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