thompsonkirk Posted May 17, 2015 Share #1 Posted May 17, 2015 Advertisement (gone after registration) I'm puzzled to find that when I use a 3-stop B+W ND filter on my Monochrom, I consistently get slightly underexposed files with more contrast and less shadow detail. In theory, this seems impossible – but I have no difficulty repeating the impossible, until I increase exposure compensation. Is there any explanation for this besides witchcraft? Kirk Link to post Share on other sites More sharing options...
Advertisement Posted May 17, 2015 Posted May 17, 2015 Hi thompsonkirk, Take a look here Monochrom and ND filters?. I'm sure you'll find what you were looking for!
Lenshacker Posted May 17, 2015 Share #2 Posted May 17, 2015 Are you comparing the images with the same F-Stop and only altering the shutter speed? Is the camera tripod mounted? Link to post Share on other sites More sharing options...
pop Posted May 17, 2015 Share #3 Posted May 17, 2015 How do you measure your exposure with and without the filter? Link to post Share on other sites More sharing options...
thompsonkirk Posted May 17, 2015 Author Share #4 Posted May 17, 2015 Yes, f stop consistently 1.4 or 1.8, with varying shutter speeds. Metering ordinarily by autoexposure, chimping a test shot to check highlights & using manual shutter if necessary/desirable. K Link to post Share on other sites More sharing options...
Lenshacker Posted May 17, 2015 Share #5 Posted May 17, 2015 Longer shutter speeds means that the "Dark Signal" will be higher, basically the number of electrons that creep into the image. Think of this as background noise, the longer the CCD is collecting the image, the higher the proportion of Dark Signal. The DNG file has a "TAG" to set the level for "Black". It is usually set to get rid of the background dark signal. I would need to have the DNG files to look at them, or you could try "RawDigger" to see if it reports the level for "Black" in use. Setting this value higher would increase contrast as it reduces the number of levels used to represent the image. Just a wild guess. Link to post Share on other sites More sharing options...
thompsonkirk Posted May 18, 2015 Author Share #6 Posted May 18, 2015 Thank you – a much better explanation than witchcraft! Kirk Link to post Share on other sites More sharing options...
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