PhotoRoy6@xxxxxxx: : : In a message dated 11/14/2007 9:46:21 A.M. Eastern Standard Time, : editor@xxxxxxxxxxxxxx writes:The good ones deliver 8-stops, the cheap digicams deliver : 6-stops. This so much depends on the algorithms the camera uses to write the image and the bit depth of the sensor. Many prosumer DSLR's use the same sensors as cheapie P&S's and each has its firmware writing differnt results for its different target audience. There was an instance I wrote of some time back where I shot a series of measured swatches and a sony DCS-f717 happily recorded 11 stops before it reached its limits. This was a test pertaining to claims that the P&S's camera limit was 8 stops - the claimant(s) were confusing the jpeg 8 bit (not the sensors bit depth of X) with 8 steps (2^8) with 8 stops.. (wrong!) Clarifying the above, looking at the results of 11 + stops taken in one shot saw the image clipped to under the 11+ stops (to like under 7 - I guess that was the limiting bit depth of the sensor coupled with the curve algorithm). However, shooting 2 exposures (setting the metered average -18% grey- and making two exposures at the *same settings* but for the first shot only shooting the lighter swatches, the other the darker swatches saw 11 stops of the range across the 2 exposures recorded accurately. The sensor can *see* a greater range than the bit depth permitted it to record.. I have also seen the algorithm expand the contast of tones too - it's all so hazy when it comes to digital (!) Even now I've had the chance to fiddle more with RAW format output from one particular camera I find curves being applied that are too arbitrary to categorise or understand :( :( the bit depth of the sensor is the big limiting factor though - Probably a good argument for HDR fans ;) : How many stops can a B&W negative hold? (At rated ASA) That depends on exposure and development - even at the rated film speed (or rather, the *standard* determined film speed) development reduction can result in an astonishing range of light levels captured. An oft stated 'average scene' has a luminance value of 2.23 (7 and a bit stops) - lens flare eats a bit of that and you end up under 7 stops. In parts of Australia where the light can be particularly harsh, 10 stops is not uncommon in an 'average' landscape scene. Shooting and developing as per the standard norm results in very contrasty prints so exposure/devolpment modifications are necessary. Shooting in those areas where the average is the norm and developing as per standard sees the tones represented realistically (which is what we're after ;) and 7 stops on the film in density goes nicely onto the paper as 7 stops of density which gives us a 'realistic' tonal range print where 7 stops = 7 stops. In reality normal tone b&w films can easily grab 14+ stops from a scene. (no bit depth limitations ;) : How many stops (max) can one print out with chemical development : of a print? (glossy? matte?) Matt appears lower than gloss to view, but the fact is the light levels under which it is treated contributes to this effect too. View a matt and a gloss print by transmitted light and you'll see they hold the same denity ranges, view them under an extremely bright light as reflective prints and again they'll exhibit the same tonal range. Measure it on a transmission densitometer and you'll find the densities are the same. The diffusion caused by viewing by low level reflected light cause the matt print to look as though it were lower contrast. There is however a Dmin and a Dmax for papers by reflected light, and that depends on a number of factors including wash times, silver content, printing techique etc.. on the whole the accepted Dmax is around 2.2 while the Dmin is often taken as 0.04 - so the paper has around 7 stops. In theory, photographing a gloss B&W print with B&W film under average lighting at the stated speed of the film, developing as normal and printing normal should reproduce the same toines as represented in the print (lens flare will muck this up though - anyone got a flare free lens? ;) : How many stops can a Color negative hold? (At rate ASA) **short answer, not as many as B&W but more than most chromes ;) Again we often heard the 'rule' that c41 films had a 'latitude' of 3-4 stops. In real terms this meant you had 3-4 stops clear of the 'average' scene to play with. Given the average scene was taken as 7-and-a-bit stops this suggests we can gather 10-11 stops plus a bit with colour neg (and then some). : How many stops of brightness can a slide hold? **Polaroids instant slide film held more than most chrome films so it looked 'muddier'.. :/ generally a lot less than a C41 film which is why cibas looked so contrasty compared to RA4 prints of the same scene.. Chrome shooters will tell you they had to be spot on with exposure to get the shot right. Still tones would fall below black and above white so again citing our average, we find chromes rounghly more or less represent the average scene of 7 stops with 7 stops-ish. Of course viewing by transmitted light, a chrome can and do display more than 7 stops of luminance (!), but that is an expansion of what was captured. **(the films characteristic curve from the respective data sheets give each individual films capacity to record scene luminance, which depend on the films dmax and dmin and the development curve, which is one of the reasons why people used different developers for different results.) Just stumbled across this rather nice explanation: http://www.dantestella.com/technical/dynamic.html funny though - I argued digital users hijacked and misused the term 'dynamic range' and here he is claiming the reverse ;) Another example of where 2 paths cross like photography and graphic design, except now we intersect with digital electronics as well. karl
