Thanks William, now I can sleep fimly again...:-) >In practice, I find that I have to stop down a bit more on 6x7 to get >similar DOF as I get with 35mm, presuming a similar angle of view is >being done on both cameras.
Exactly my point - if I want change angle of view I can do to things: 1. Change focal length, which changes DOF 2. Change ditance to subject (move the camera), wich also changes the conditions for DOF. All the best Jens Bladt mailto:[EMAIL PROTECTED] http://hjem.get2net.dk/bladt -----Oprindelig meddelelse----- Fra: William Robb [mailto:[EMAIL PROTECTED] Sendt: 22. marts 2004 07:35 Til: [EMAIL PROTECTED] Emne: Re: DOF and angle of view or focal length (long) ----- Original Message ----- From: "Jens Bladt" Subject: DOF and angle of view or focal length (long) > 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. > > 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. This part is true, to an extent. However, if you are going to use the same focal length, but change formats, then really, camera to subject distance pretty much has to change to be photographically useful. Or, if you are going to change formats, but not camera to subject distance, then you need to change lenses. In theory, I think you are correct. In practice, I find that I have to stop down a bit more on 6x7 to get similar DOF as I get with 35mm, presuming a similar angle of view is being done on both cameras. > > 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. Well, yes. Of course. William Robb
