Thanks DagT >Both, depending on you priorities. If angle of view is important you say the first, if DOF is more important you say the >>>latter. In addition, as you say, the degree of enlargement also plays a part, along with resolution/diffraction limits etc.
I guess it matters who is asking (digital or 35mm enthusiasts) I have allways regarded DOF as sometihning like this: The speed of which sharpness is decreasing - from the focal point - to both sides of the focus point - further away towards infinity, and towards the camera. This "speed" is determined by the physical, optical laws rather than a subjective opinion about what is sharp and what isn't. All the best Jens Bladt mailto:[EMAIL PROTECTED] http://hjem.get2net.dk/bladt -----Oprindelig meddelelse----- Fra: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sendt: 22. marts 2004 10:33 Til: [EMAIL PROTECTED] Emne: Re: DOF and angle of view or focal length (long) > Fra: "Jens Bladt" <[EMAIL PROTECTED]> > Some of you people are very knowledgeable when it comes to optical science. > So, I would like to ask you this: > > On the internet there is an ongoing discussion about this subeject. > Some say, that smaller formats have greater DOF (Photonet). They say that in > order to get comparable images, I must use shorter focal length to go with > the smaller format, thus achieving greater DOF. They are using circle of > confusion (COF) theories to support their point of view. If you want the same field of view, that is correct. > I (and Photozone) say, that smaller formats only show a part of the image, > captured by a specific focal lenght. If I shoot the same scene twice with > the same camera, same lens (focal length( and same aperture and focus point, > you will get identical images on let's say APS and 35mm film - that is for > the part, that is covered by the smaller format (e.i. APS). I say that the > DOF of these two identical images - is exactly the same. I say that focal > length, aperure and focal distance determins the DOF. If field of view is unimportant, that is correct. The APS size sensor simply crops the image. > IMO COF theories are somewhat subjective, because the point to where a point > looks like a disc, depends on the degree of enlargement. I think that the > smaller image, captured by a shorter focal length needs more enlargement, > thus less appearing less sharp. > What is right and wrong here? Both, depending on you priorities. If angle of view is important you say the first, if DOF is more important you say the latter. In addition, as you say, the degree of enlargement also plays a part, along with resolution/diffraction limits etc. This image: http://foto.no/cgi-bin/bildekritikk/vis_bilde.cgi?id=13611 is impossible to make with an APS size sensor, because of the combination of shallow DOF and field of view. This was made using a 28mm @ 1:2.0. A corresponding 18mm will not be able to make the large difference between COF in focus and in the background. Compare images made with MF and APS formats and this is much more evident. DagT
