Art, Well, we've sort of done that with digital cameras. They have also put my old Pentax cameras out of service, and after all the work I did fabricating a pressure plate that kept the film reasonably flat. At my age, I'm also an advocate of image stabilization - I'm taking sharp pictures, again - hand-held!
Jim Arthur Entlich wrote: > Hi James, > > Thanks for the formula. I guess we need to go back to glass plates ;-) > > Art > > > > James L. Sims wrote: > > >> Art, >> >> There was a depth of focus formula in the American Cinematographer >> Handbook that was gospel until proven wrong. The depth of focus, given >> a specific blur circle size, is a trig function of the cone angle Tan >> ½Angle = .5 x f# ÷ Lens Focal Length. Without special pressure plates >> or vacuum plates, the film bow in 35mm cameras is typically .003". 2¼ >> square format cameras have film sag that ranges from about .006" to >> .010". At large apertures, these dimensions can make a significant >> difference in image sharpness. >> >> The flatbed scanners that I'm familiar with have great depth of field, >> suggesting the lenses have very small apertures. However, image >> sharpness degrades as the lens aperture is reduced. I'm not sure what >> this effect is with flatbed scanners, because each lens is recording one >> element of the image per increment. >> >> Jim >> >> Arthur Entlich wrote: >> >> >> >>> There seems to be two main issues with depth of focus with film. One, >>> when the image is captured within the camera, and two, when it is then >>> reproduced, either as a print, or made into a digital file. >>> >>> With 35mm frames, in my experience, the second one is not that >>> significant as long as the digital scanner has a decent depth of focus, >>> which is determined by the aperture of the lens within the scanner. On >>> standard optical CCD film scanners, at least with 35mm frames, if the >>> light source is sufficient, it isn't a great issue, and is easy to test >>> for... either the grain (dye clouds) are evenly in focus or they >>> aren't. The places I have seen a real problem are with larger format >>> films, which may require special mounting, glass carriers, or some other >>> method of maintaining flatness and with film scanners that have >>> inadequate light sources which lead to needing to use a rather wide >>> open lens to capture the image, causing limited depth of focus. >>> >>> The CCD flat bed scanners I have used seem to have substantial depth of >>> focus. I have scanned 3d objects with very reasonable resolution and >>> sharpness. >>> >>> The in camera issue is another matter. I don't know the actual depth of >>> focus at film plane different apertures allow for in camera. Perhaps >>> someone has a chart that indicates the depth of focus relative to >>> aperture. It would be interesting to know. 35mm film is physically >>> small enough that I expect the deviation is of less significance, but I >>> can see how larger roll films or sheet film could end up problematical. >>> >>> Does anyone know if there is a chart which shows depth of focus at the >>> film plan versus aperture of lens used? That could be valuable to know. >>> >>> Art >>> >>> >>> >>> >>> >>> James L. Sims wrote: >>> >>> >>> >>> >>> >>>> All other arguments aside, flatness is much more important that some >>>> realize. Back in the eighties, I had a lengthy dialog with a well known >>>> research lab about depth of focus - it ain't exactly what the American >>>> Cinematographer's Handbook says it is. Film bows and sags. That's hard >>>> to control. >>>> >>>> Jim >>>> >>>> gary wrote: >>>> >>>> >>>> >>>> >>>> >>>> >>>>> One last point here. Film will probably never be as flat as a piece of >>>>> silicon. >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>> >>>> >>>> >>>> >>> ---------------------------------------------------------------------------------------- >>> Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' >>> or 'unsubscribe filmscanners_digest' (as appropriate) in the message title >>> or body >>> >>> >>> >>> >>> >>> >> ---------------------------------------------------------------------------------------- >> Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' >> or 'unsubscribe filmscanners_digest' (as appropriate) in the message title >> or body >> >> >> >> > > ---------------------------------------------------------------------------------------- > Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' > or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or > body > > > ---------------------------------------------------------------------------------------- Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
