Archived posting to the Leica Users Group, 2010/11/28
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Another issue with the digital sensor appears to be related to reflection of light from the rear element (reflecting back from the sensor surface). These now require multicoating. Jeffery On Nov 28, 2010, at 12:58 AM, afirkin at afirkin.com wrote: > Its the potential to cause problems with the photographic image and esp. > now with digital sensors which interests me. Not that many of my lenes > will stop down below f16/ f22 and mostly I'll use f8 or wider, but with > the creek shots etc I was using f22 to increase exposure. Perhaps I'd be > better with some ND filters. > > Cheers > > Alastair > >> Diffraction occurs on the edge of the iris diaphragm. Because the diameter >> of the aperture opening is determined by 2??r but the area of the aperture >> is determined by ??r??, the greater the radius, the greater the >> area:diameter ratio. Thus, the smaller the radius of the aperture, the >> greater the impact of diffraction. The shorter the wavelength, the less >> the diffraction, but it isn't much of a factor until you get to >> 1,000-power on a microscope. >> >> >> On Nov 27, 2010, at 6:11 PM, afirkin at afirkin.com wrote: >> >>> Diffraction Limits: >>> >>> The diffraction limit is dependent on the wavelength of the light and >>> the >>> f-stop. It is calculated as the size of an Airy disk (Sir George >>> Airy). >>> This describes the size of a circle from a point of light as it passes >>> the edges of the aperture. Fundamentally, as you decrease the aperture >>> size (increase the f-stop) the size of the Airy disks increases. An >>> Airy >>> disk can also be called a blur circle at the image plane similar to the >>> CoC for DOF. The simplified calculation (estimation) is 1500 divided >>> by >>> the aperture. Thus, f/8 yields .005 mm and f/64 yields .042 mm. The >>> relationship between the size of the Airy disk and resolution is known >>> as >>> the Rayleigh criteria. Since it takes two of these points of light to >>> define resolution the respective resolutions are 100 lp/mm for f/8 and >>> 12 >>> lp/mm for f/64. Obviously, stopping down the aperture to increase >>> depth >>> of field can lead to increased diffraction that blurs the entire image. >>> >>> Most photographers would agree that 35mm cameras become diffraction >>> limited at f/22. At smaller aperture sizes diffraction trumps depth of >>> field and the overall image loses resolution. For a typical digital >>> sensor size the diffraction limit is a factor at f/16. Diffraction >>> limits are less significant with medium and large format cameras. This >>> is only because there is less need for enlargement therefore the CoC >>> values can be relaxed. >>> >>> >>> _______________________________________________ >>> Leica Users Group. >>> See http://leica-users.org/mailman/listinfo/lug for more information >> >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information