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 > > >
