Exaclty, so with the *ist you get greater DOF for the same focal length
or AOV. Which is fine if that is what you want but not gret if you like
shallow DOF without having to resort to a 300mm lens.
A.
On 19 Jul 2004, at 13:23, Don Sanderson wrote:
But with the smaller frame on the *ist D you get the same (subject)
image
size:
1.) From a Greater Distance with the same focal length.
2.) With a shorter Focal Length from the same distance.
Both of these conditions would INCREASE depth of field it seems to me.
Or is there some law of optics I'm not aware of at work here?
Don
-----Original Message-----
From: Tom Reese [mailto:[EMAIL PROTECTED]
Sent: Monday, July 19, 2004 6:39 AM
To: [EMAIL PROTECTED]
Subject: Re: Replacement for the FA 50 and 100 Macros? (Re: Pentax is
Dying)
Antonio wrote:
"Shorter lenses have greater DOF and because you are using shorter
lenses to get the same AOV as with 35mm you are therefore getting more
DOF."
It doesn't work that way. If you shoot a full length portrait with a
135mm
lens at f/8 and then you move much closer to the subject with a
50mm lens at
f/8 to get the exact same image size, the depth of field will be
identical.
What will change will be the angle of view. You will see much more
background behind the subject with the 50mm than you will with the
135mm.
Wide angle lenses give you more depth of field than longer lenses
when they
are set at identical points in the focusing range. A 20mm lens
focused at 10
feet will give you more depth of field than a 100mm lens focused
at 10 feet.
In your example, the wide angle lens will be focused at a much closer
distance than the longer lens. The DOF will be the same if the
subject image
size is the same.
Tom Reese
