I knew when I started on this that I'd get both myself and everybody else
confused. I'm good at that, I guess. Anyway, my final post on this subject:
Leaving out all the irrelevant bits, like that a 24mm lens on a half-frame
camera has a FOV equivalent to a 48mm lens on a full-frame camera, the original
question was whether or not the DOF scale on a 24mm lens still is accurate on a
half-frame camera.
It is, absolutely and unequivocally. The DOF scale is based on the size COC
the lens manufacturer deemed sufficiently small to be considered "in focus"
under normal circumstances. The diameter of the COC will be the same no matter
what format the lens projects an image onto.
If both the half-frame and full-frame images are enlarged to the same degree,
the COC will be identical. I think the confusion has come in when some folks
started talking about equal-size prints. Well, duh! To get equal size prints,
you have to enlarge the half frame twice as much, which makes the COC twice as
large. Assuming both full and half-frame photographs taken from the same place
and of the same scene and enlarged to the same degree, the half frame picture
is going to be exactly like that little 4x5 in. patch in the middle of the 8x10
in. print made from the full frame shot, with exactly the same DOF and COC.
Blowing the half frame up to 8x10 naturally makes the picture fuzzier.
Quoting from the National Geographic Photography Field Guide again, which I
recommend everyone have a copy of: "The zone of acceptably sharp focus will
seem more extensive in small prints than in enlargements. A foreground object
that appears sharp in a 4x6 print may look blurred in a 16x20 blowup and even
in an 8x10 when you view the picture closely."
So, that's been my basic point all along. The DOF scale is still accurate, but
when you begin with the handicap of a tiny image and have to blow it up more
and more, you've got the same problem you would have trying to make a good 8x10
print from an old Kodacolor 110 negative. It's that darned old silk purse and
sow's ear thing again.
Now, as Forrest Gump said, "That's all I have to say about that."
Walt, circling in confusion, maybe in a field with too much depth
--
"Anything more than 500 yards from
the car just isn't photogenic." --
Edward Weston
-------------- Original message ----------------------
From: "Piers Hemy" <piers@xxxxxxxx>
>
> Just for clarity's sake, that _isn't_ what _I_ was talking about, rather
> it's the converse (but it makes the good sense of what you were saying
> apparent, even if on this occasion not strictly relevant). :-)
>
> --
> Piers
>
> -----Original Message-----
> From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
> Of Walt Wayman
> Sent: 27 March 2005 22:54
> To: olympus@xxxxxxxxxx
> Subject: [OM] Re: Figuring out depth of field with 4/3 adaptor
>
> --snip
>
> I thought what we were talking about was photographs made with the same
> focal length lens, the difference being whether the full image was captured,
> as a full-frame camera would do, or just the center, as in a half-frame or
> 4:3 digital camera.
>
> --snip
>
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