I've thought about this too. I believe that a 50mm will require at least 1/75 sec to obtain the same amount of blurriness as 1/50 sec. om a 35mm camera, provided you enlarge the DSLR picture MORE to obtain the same, final picture size.
If a car moves at a certain speed, it will go from left to the right hand side of the frame in lets say 1 second when using a 50mm lens on a 35mm camera. That's 150mm/second on a 4x6" print. If the same car is photographed by a DSLR using a 33mm lense, the same thing happens - the car will move from left to right in 1 second. But, if you put the 50mm on the DSLR the car (driving at the sam actual speed) will move across the frame in just 0,67 seconds, causing an even more blurry picture. The car will travel at a speed of 225mm/second across the 4x6" print. This should prove that you must mulitiply the denominater of the usual "speed rule of thunb" by 1.5, when using an APS soize sensor. This means 1/75sec. for a 50mm on the *ist D/DS. I never reallty minded, because I really don't like to use slow speeds. How fast the speed should minimum be has something to do with how much movement/blurryness is acceptable for normal enlargments. It's the same kind of arguments that are used when we're talking about Circle of Confusion. There's no absolute truth, just a rule of thumb - or a matter of taste, if you like. Jens Bladt Arkitekt MAA http://hjem.get2net.dk/bladt -----Oprindelig meddelelse----- Fra: Juan Buhler [mailto:[EMAIL PROTECTED] Sendt: 2. september 2005 12:22 Til: [email protected] Emne: Auto-selected shutter speed on istD/s--wrong? I've been thinking about this for a while. Typically, in program modes with a FA lens, the camera will keep the shutter speed high enough to avoid blurry pictures when handheld. On a 35mm sized filmplane camera, this is roughly the inverse of the focal length, as we all know. So if you have a 50mm lens, 1/60 is the minimum the camera stays at (1/30 sometimes, but even that is acceptable.) It seems as if Pentax didn't update that part of its programs for the aps sized sensors. With a FA50mm on the istD, I keep getting 1/30s, even if the aperture is not full open (for example, I will get 1/30 at f:2.8 with the FA50/1.7, instead of the more acceptable 1/60 at f2). A 50mm on the istD is equivalent to roughly 75mm, so shouldn't 1/60 or 1/90 be the minimum speed the program chooses? Or am I very wrong? j -- Juan Buhler http://www.jbuhler.com photoblog at http://photoblog.jbuhler.com
