As I said, I get far more noise "pushing" a shot two stops that was exposed at 800 than I do when shooting at 3200. In my experience, almost everything on dreview should be taken with a grain of salt. Pau ----- "Larry Colen" <l...@red4est.com> wrote:
> On Fri, Mar 27, 2009 at 05:58:13PM -0500, Nick Wright wrote: > > Would someone care to explain a little further about the 800 iso > thing? > > If you do some research on the dpreview pentax slr forum, Marc > Sabatelle pointed out that someone had written a raw converter (I > foreget his name, it's in my archives someplace) and he had > discovered > that above ISO 800 the circuitry doesn't change, the raw values are > just multipled by 2 or 4. > > > ISO real binary hex dec raw file values > 200 000000010110 0x016 22 000000010110 0x016 22 > 400 000000101100 0x02C 44 000000101100 0x02C 44 > 800 000001011001 0x059 89 000001011001 0x059 89 > 1600 000010110011 0x0B3 179 000010110010 0x0B2 178 > 3200 000101100111 0x167 359 000101100100 0x164 354 > > You'll see that at ISO 1600 and 3200 that data in the last bit, or > two > bits is just lost. Mind you, there's a lot of noise in the analog > signal anyways, so the actual information you're losing at the bottom > end isn't that much. > > The problem is if you have a pixel that is close to full scale at > 800: > 800 100000000000 0x800 > at 1600 and 3200 it just goes to > 111111111111 and clips > > So when you increase the ISO above 800, not only do you not get any > more information from the lowest bits on the darkest pixels, but you > clip the information on the brightest pixels. > > But, don't take my word as gospel, try shooting in some very low > light > situations, with the camera in manual exposure mode. Assume that at > 3200, the correct exposure is 1/10 second f/4.0. Shoot at f/4.0 at > ISO 800 1/2.5 1/5 1/10 > ISO 1600 1/5 1/10 > ISO 3200 1/10 > > And compare the quality of the shots. I've found that I get as good > of a shot at 1/10 f/4 in ISO 800 as I do ISO 1600 and ISO 3200. > > Given the choice, it's better to expose properly, but if you're > shooting dancers or musicians, people who are moving, you may get > better results trading noise for shutter speed. > > -- > The fastest way to get your question answered on the net is to post > the wrong answer. > Larry Colen l...@red4est.com > http://www.red4est.com/lrc > > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and > follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
