On 9/3/04 12:56 pm, "Bob Marchant" wrote: > David Kay wrote:- > >> adding more bits does influence the number of subject >> brightness levels in f-stops we can record. > > Err ....I don't think so. The chip has a level at which it can no longer > record shadow detail and a level at which it can no longer record > highlight detail. The difference in these two levels , the dynamic range > , is often referred to in f-stops . The range is of course defined by a > combination of the physical limitation of the chip and often additionally > imposed software limitations ( Noise suppression etc). The higher the > bit depth , the more recorded steps there are between the lowest amount > of light recordable to the highest amount recordable.Wither higher bit > depth , you are not achieving more f-stops , just putting more set > graduations between the f-stops.The graduations are the equivalent of > click stops as opposed to the constantly variable stops on some large > format lenses (These 'click stops' are of course necessary because of the > digitisation of an essentiallly analogue scene). > > I can see your thinking in the maths , but it's another one of those > conundrums. Bit depth is not related to f-stops in this way. If the Chip > has a dynamic range of two stops and a bit depth of 8 bits , then using > your logic there are four bits between each stop. By upping the bit rate > , I've now got 8 bits between each stop. I've not increased the dynamic > range , but I have smoothed out the digitisation of the image by having > more points of reference between stops. > > Speaking of conundrums, can anybody resolve this one ? If you do a a > series of time exposures say 2secs , 3 secs ,4secs then the 2second > exposure is logically one less stop than the 4 second exposure > (reciprocity ignored ), and the three second exposure is a half stop > between the two.If you want to increase the 4 sec exposure by half a stop > , then it should be 6 secs . However , by the same logic , if I want to > increase the exposure of the 3 sec exposure by a half stop , I end up > with an exposure of 4.5 seconds . Similarly , if I do the same with my 6 > second exposure I end up with 9seconds , but one stop over 4 secs is 8 > seconds ! > > Regards, > > Bob Marchant.
The answer is of course that 3 secs is not half a stop between 2 secs and 4 secs. Half a stop would be about 2.82 secs Paul > =============================================================== > GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
