Hi Andy, Thanks for breaking it down so clearly. It helps a LOT! Happy New Year to you and all the others on the list. Deen At 2003-12-28, 08:49:00 you wrote: >Deen, > >>QUESTION: Say i want to shoot moving subjects, I realise the amount of >>background blur will depend on the subject movement, distance from the camera, >>focal length used, etc, but is there a nice rule of thumb to work out an >>optimal shutter speed? > >I don't know of a rule-of-thumb but I'll try to come up with something close. >First of all you need to determine how much blur you want - this is somewhat >subjective I would think. Using your camera's viewframe as the reference you'd >say that you want subjects in the background to blur a fraction of the size of >the frame. Let's say you decide you want blur to be something like 1/10th of >the frame's horizontal direction (which is also the direction along which you >are panning). Since the frame is 36mm wide this would mean you want the blur to >be about 3.6mm (or 4mm rounded off). > >Now you need to determine how long it takes subjects in the background to move >across your frame from edge to edge as you are panning. Estimating is OK. This >will obvioulsy vary depending on many of the factors you mentioned above plus >more. Let's say that given the subject you are planning to photograph this is >about 1/4 second. > >The implication of this is that images of subjects in the background move 36mm >in 1/4 second or that they are moving at a rate of about (36mm / 1/4 second) >150mm per second. > >To determine which exposure time will provide 4mm of blur when the image is >moving 150mm per second you divide the desired background blur by the rate of >movement of the background images and out comes the required exposure time. > >In this case it would be 4mm / 150mm per second or .0266 seconds which is about >1/3.75 or rounded off about 1/4 second. > >I hope this helps and is not too far off! > >Andy Davidhazy >andpph@rit.edu
