Andy Perrin Posted June 1, 2019 Share Posted June 1, 2019 This photo is with the Omega 340BP10 Excite FURA 20mm I tested back here. Photo subject is the Annisquam River in Gloucester, Massachusetts (my mother lives on the river, so it's convenient and pretty). We had some nice fog today. EL-Nikkor 80mm/5.6 metal, F/10 ISO160 10" + Omega340BP10Processing: lowered the saturation a lot, removed spots of sensor dust (urgh!), and corrected for vignetting. Sony FE 55mm/1.8 ZA, cropped, F/6.3 ISO50 1/1250" + BG38 2mm Link to comment
OlDoinyo Posted June 2, 2019 Share Posted June 2, 2019 That is a lot of chromaticity for a BP10 filter. I wonder if some out-of-band wavelengths are sneaking through. Link to comment
Andy Perrin Posted June 2, 2019 Author Share Posted June 2, 2019 OlDoinyo, that isn't very much chromaticity at all. It's only blue. Link to comment
dabateman Posted June 2, 2019 Share Posted June 2, 2019 That faint blue looks like IR leak to me. But still a good shot. My 340bp10 also leaks IR, for critical images I stack it with the Baader venus filter. But in many cases the IR leak adds some nice blue color, so I try to remember to use it unstacked first. Link to comment
Andy Perrin Posted June 2, 2019 Author Share Posted June 2, 2019 I was getting blue back here also?https://www.ultravio...ra-20mm-filter/ Okay, Andrea also got blue:Typically a sunflower can be white balanced on the UV-absorbing areas at the base of the rays. That gave a very strange result here. I'm not sure I consider it a successful WB, but I'm still thinking it over. Some local contrast sharpening was added after resizing.There is false yellow, blue, green or dark green-cyan and grey in this conversion and the next. That is rather remarkable for such a narrowband filter. Remember, we have all been supposing that there would not be much of a false colour range at all.https://www.ultravio...__fromsearch__1 I think that a white-balanced 340nm filter will show blue sometimes. Wait, are you guys being confused by the fact that I deliberately desaturated the yellow? Link to comment
dabateman Posted June 2, 2019 Share Posted June 2, 2019 I still think the highly IR reflective trees in the lower right of your image is showing the blue IR leak of the filter.If you have a baader venus filter, just stack it with that to prove me wrong. But I am sure you have an IR leak there.You could also stack with an S8612, if you don't have the venus U filter. But it will let through much less at 340nm. Link to comment
Andy Perrin Posted June 2, 2019 Author Share Posted June 2, 2019 Probably have to wait till Tuesday, I'm out of sunshine and going to be away tomorrow. Link to comment
Andy Perrin Posted June 4, 2019 Author Share Posted June 4, 2019 So, I did the suggested experiment and stacked with S8612. Pics later when I have a chance to process them, but the preliminary results were interesting. I could see blue in the image itself either way, but what was most informative is that there was a bright blue circular band around the edge of the image that looks like the putty I used to rear-mount the filter is either leaking light itself, or I just didn't fill all the gaps at every location around the filter and light is getting through that way. I think I need a better way to mount this filter. Update Here are the photos. The blue is obvious in both pics.Settings were F/5.6 2.5" ISO2000 for both. WB was redone for the second photo. Without S8612 1.75mm With S8612 1.75mm It gets worse in the second picture mainly because I changed the camera angle slightly and it seems very sensitive to the angle relative to the sun. Also the WB change may have affected it. Link to comment
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