On Thu, 01 Nov 2007 13:49:37 -0500 photoforum@xxxxxxxxxxxxxxxxxx wrote:
I hate to disagree with so eminent and learned personage, Andy, but it was always my understanding that the design of a leaf shutter guaranteed that the center would receive more light than the edges. Just picture the way it works. It opens from the center to the edges and then reverses the process. The center has to receive more light. The difference in the amount is insignificant though for a properly functioning shutter. There is less difference at slow shutter speeds than high speeds. The blades moved at a constant rate; if they were able to move faster from the center and slow down toward the edges, the disparity could be resolved. It was virtually impossible to make a leaf shutter that would function at high speeds which was a reason for the development of the focal plane shutter. Or so I have been told many times in my early days in photography. Somebody correct me if I am wrong. Politely, please. Don ADavidhazy wrote: > Stephen, > > The center of a photograph is not any more exposed than the edges due > to the left shutter. > Lens design has a lot to do with the degree to which the non > uniformity of exposure > from edge to edge or corner to corner of a photograph is apparent. > Something called > the "cosine to the 4th power" is a factor at work. It has to do with > the angle at > which light rays arrive at the lens and the image surface ... and the > distance they have > to travel to get to the image plane. > > Some really wide angle cameras had a whirling fan installed in front > of the lens to > physically dodge the image forming rays allowing more to go to the > edges than the center > of the image. Others used a greyscale mask to try to accomplish the > same thing. Some > new lenses have included in their design a function that makes the > aperture appear to get > larger to light rays arriving at an angle than those that arrive more > from directly > in front of the lens. > > ... I think > > Andy > > > > > Stephen Ylvisaker wrote: > >> When shooting using a camera with a leaf shutter, do any of you have >> a way to counteract the leaf shutter effect? I mean, it's certainly >> not what I would call vignetting, but it is very apparent the center >> of the picture is the brightest point. And, I know it could be taken >> care of in the "printing" process by burning the center down a little >> bit. But, is there an "in-camera" method to counteract the effect? >> >> >> >> >> >> Stephen >> greyfell@xxxxxxxxxxx >> "...decide...whether or not the goal is worth the risks involved. If >> it is, stop worrying....", >> and "Worry retards reaction and makes clear-cut decisions >> impossible." - Amelia Earhart, aviatrix. >> > > >
Mr.Wizard was not just played by Don Herbert,
Don Herbert was a real wizard!
