So, would adding a filter to the front of the lens after focussing require adjustment as well? And, in the case of a Lee Gel, which is paper thin, would stopping down an extra stop take care of the difference? Everyone I know of focuses with the aperture wide open anyway unless doing close up work and even then might use use polaroid 55 or a sheet of tri-x developed in a hot soup to run a quick focus check to see if they are getting the DOF they need at a given aperture. If the only degradation from using the filter inside the camera comes from imprecise focus, I would say that using it inside offers benefits that far outweigh using it on the outside. We have always focused with the filters in place (unless we are talking about a polarizer which are difficult to use when inside the camera). I am referring to cc filters (mostly kodak) which we would leave on the camera as long as we are using a specific film emulsion. We have found problems in using stacks of them, though. if they aren't perfectly flat to each other, you CAN get reflections bouncing around between them which can show up on the film as any number of strange apparitions. r luis wrote: > > Karl wrote -- > > >hooroo Greg - maybe you have a local 'Lee' gel filter distributor >nearby, a theatre or lighting supply place should know. The stuff is >sold cheaply in thin sheet by the meter. I wouldn't ordinarily >recommend using a gel filter for taking pics but if you can mount it >flat and inside the camera instead of outside (to minimise reflections), >I shouldn't imagine you'd see much image degradation on a 4x5 > > I would not advise the use of inside, behind-the lens filters, specially for neophytes. It will result in out of focus negatives. l > Most photographers will never notice, and the rare few that do will attribute the degradation to the filter, but this is not the case. > > Almost no one realizes that using a filter behind the lens throws > the image out of focus. When using behind-the-lens filters, focusing > the camera is nearly impossible with these in place, so people > "logically" focus, then insert the filter -- throwing the image out of focus -- and then make the exposure. > > As Father Ansel clealy states in the Biblel...oops, I mean The Negative, one must compensate for this focus shift by focusing backwards 2/3 the thickness of the filter material. Who knows > how much that is ? Who can move the focusing knob precisely that > amount ? No one I know of. For all the trouble one goes to for sharpness with large format, I recommend keeping the filter up front, > and buying a decent shade for it. > > --- Luis > >
