I was practicing IR photography with a Singh-Ray I-Ray filter on a Canon 300mm f/4 IS and 5D Mark III body. Exposures were typically around ten minutes owing to an incoming storm, apertures f/5.6 - 7.1. On processing images tonight, I see that the IR photos have a consistent pattern of white dots when viewed and processed in DPP 4. When the images are completely desaturated they are quite obvious.
Initially I was worried I had a sensor problem: I had cleaned filter and lens immediately before use in the field, and would have expected any remaining dust from the filter to shift a little as I had to take off and put on the filter several times. I took ordinary color photos of the same shots and cannot find a trace of dots in the color shots even when desaturated.
I tried opening one of the images in Bridge, and I could see the white dots initially in the preview... and then they suddenly disappeared! I proceeded to open the file in Photoshop 6 and couldn't find a trace of them. Closed without saving, went back to DPP 4 and there are all the dots waving at me, pointing and laughing. I repeated this process a couple times with the same and different images. Once Bridge completes an initial preview of an image, it remembers any processing it does so future peeks in that session show no dots.
A sample crop of a desaturated image included as processed in DPP 4; yes, there are lots of dots, and they appear sharply focused as opposed to diffuse (as one might expect for lens dust).
Question: is this a software problem with DPP4, a hardware problem like sensor dust or sensor error, a common issue with IR by filter, or some combination thereof? I presume the dots are artifacts in the images since both software programs initially detect them, but if that is the case then why does Bridge clean them up even in its preview window?
Initially I was worried I had a sensor problem: I had cleaned filter and lens immediately before use in the field, and would have expected any remaining dust from the filter to shift a little as I had to take off and put on the filter several times. I took ordinary color photos of the same shots and cannot find a trace of dots in the color shots even when desaturated.
I tried opening one of the images in Bridge, and I could see the white dots initially in the preview... and then they suddenly disappeared! I proceeded to open the file in Photoshop 6 and couldn't find a trace of them. Closed without saving, went back to DPP 4 and there are all the dots waving at me, pointing and laughing. I repeated this process a couple times with the same and different images. Once Bridge completes an initial preview of an image, it remembers any processing it does so future peeks in that session show no dots.
A sample crop of a desaturated image included as processed in DPP 4; yes, there are lots of dots, and they appear sharply focused as opposed to diffuse (as one might expect for lens dust).
Question: is this a software problem with DPP4, a hardware problem like sensor dust or sensor error, a common issue with IR by filter, or some combination thereof? I presume the dots are artifacts in the images since both software programs initially detect them, but if that is the case then why does Bridge clean them up even in its preview window?