Archived posting to the Leica Users Group, 2008/03/04
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]"card at 1/60 @ f/2 and again at 1/125 @ f/1.4, the resulting pictures should look the same. I am not sure about that - 1.4 to 2.8 yes, 1.4 to 2 no stops are conventions anyway, not values per se Peter Klein wrote: > Richard: Thanks, this is what I expected. If you shoot a gray card > or an evenly-lit blank wall, out of focus, and convert the image to > grayscale, it's a little easier to interpret. I'm sure Photoshop has > some sort of eyedropper tool that measures the pixel values--most > editors do. > > Anyway, to clear up the questions others asked. . . > > If you shoot at several different f-stops, but adjust your shutter so > all exposures are the same EV, then all pictures should be the same > brightness. If I shoot a gray card at 1/60 @ f/2 and again at 1/125 @ > f/1.4, the resulting pictures should look the same. And with my film > OM-2 and 50/1.4 Zuiko, that's what happens. But put the same lens on > the E-1, and the picture taken at f/1.4 is much darker. I found that > I had to set the shutter 2/3 of a stop slower than the expected value > in order to get the same grayscale value as the f/2 picture (the E-1 > can adjust the shutter in 1/3 stop increments). > > f/2 and f/1.4 are one full stop apart. No see above - one click, not one stop hence your results > But on the E-1, when you open up from f/2 to f/1.4, the sensor doesn't > get a full stop more light. It only gets 1/3 stop more. The sensor > is somehow not receiving all the light that the lens is transmitting. > > I'm only detailing one test I did here. But the results were > confirmed by some practical available light photography. > > So no, we're not talking about a lens that's only transmitting 1/3 > stop more light when you open up the full stop from f/2 to f/1.4. > With film, the lens performs as it should. But when that same lens is > placed in front of a 4/3 sensor, something different happens. My > guess is that some of the rays get cut off by the pixel wells. It > must be a matter of angles, where the node is for this film lens vs. a > digital-specific lens that is more telecentric. The Leica 25/1.4 > Summilux does not have this problem. Somebody on dpreview tested it > the other day, and it behaves as it should. > > What it boils down to is that if you want a lens that truly delivers > f/1.4 on a 4/3 camera, you're not going to get it with an OM 50/1.4. > You have to buy the Leica lens, or the Sigma 30/1.4. Or maybe another > brand's "normal" f/1.4 lens > This you most certainly get right thanks again for the thread phx > --Peter > > At 07:15 PM 3/4/2008 -0800, Richard wrote: > >> Hi Peter, is there a way for Photoshop or something to give the >> average EV value or whatever so I don't have to eyeball the results? >> I ended up using something like >> ... >> 1/2500 @ F2.8 >> 1/5000 @ F2.0 >> 1/8000 @ F1.4 >> >> The shutter speed max out at 1/8000. So in theory, the F1.4 is >> overexposure by 25%? Eyeballing the resulting RAW ORF files, the 1.4 >> is actually darker, so it may support your theory that the difference >> is less than the one stop. >> >> All the other files look similar, except that *may be* at F11, it is >> brighter by a tad, but may be it's the cloud moving away :-) Not very >> dramatic though. F16 is fine again. >> >> So not very scientific, but may support your thesis... > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information >