Archived posting to the Leica Users Group, 2004/09/04
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Thanks Henning ! Is there any equivalent to reciprocity or Schwarzschild effect when shooting digitally ? I gather that noise can be a problem at high ASA/ISO and have read that lenses can be "too good" for a sensor, but nothing yet along these lines. It appears to me that the learning curve is shallow but does require quite a bit of new thinking. regards Douglas Henning Wulff schrieb: > At 9:08 AM +0200 9/3/04, Douglas M. Sharp wrote: > >> >> I was shooting in a very dim chapel of remembrance in Berlin and was >> getting shutter speeds >> too slow for hand holding and didn't have a tripod with me. Shooting in >> RAW mode at 400 ASA I deliberately underexposed in manual metering mode >> and then corrected the image >> in Canons File viewer Facility (which allows the pre-processing of RAW >> images) to get >> back to the shutter speed I would have had to use according to the >> automatic mode. >> The shot turned out IMO better than I expected (within limits) >> see >> http://gallery.leica-users.org/New-Old-Pictures/Ged_chtnis_1 >> >> I also read in a German photo publication that the ASA/ISO setting of >> 100 is not necessarily better than >> at 200, though I didn't quite understand why, they even suggest avoiding >> the lowest value. >> In addition, shooting with higher ASA values, at least with the Canon, >> seems to make the files larger - any ideas/explanations on this count? >> greetings from sunny Northern Germany. >> Douglas > > > If you shoot at higher ISO values, you produce more noise, or pixels > with values that have little to do with the scene values. In a > simplified sense, JPEG works by describing a value for an area with > similar values, so if there is a 'noise pixel', it has to be described > separately, taking up more space in the file. In some cameras, > shooting at the highest ISO can produce files that are 50% larger than > the slow speed, smooth toned low ISO files of the same scene. > > The 'underexpose' technique works just like pushing film. You're using > just the most sensitive part of the film or sensor, and then in > Photoshop you're 'overdeveloping'. With film this means that you get > higher contrast, more grain and generally poorer tonal quality. With > digital it means that you are getting more noise and getting poorer > tones through something called 'banding', as you are expanding your > finite number of digital levels that are useful to the total number of > levels your printer can handle. With the standard JPEG files, you get > 256 levels for each colour, and if you then only use the bottom 50 > (because the top 206 don't contain any useful info) and expand them > into the 256 level space, you might find that these are too large > 'steps' in some areas, resulting in a 'banded' look. > > With a DSLR, shooting in RAW and producing a 16bit file with millions > of values, this banding doesn't happen very easily because you might > wind up using 'only' the bottom 10,000 values, as 16bit has over > 65,000 values for each colour. When you then get the file ready for > printing, these 10,000 values easily get reduced to 256 that the > printer can deal with. -- Ihre bevorzugten Shops, hilfreiche Einkaufs-Hilfen und gro?artige Geschenk Ideen. Erleben Sie das Vergn?gen online einzukaufen mit Shop@Netscape! http://shopping.netscape.de/shopping/