Andy Perrin Posted January 8, 2021 Share Posted January 8, 2021 Could we see a B&W visible photo of the same scene? I don’t see the frost patterns but I’m probably not looking at the right thing. Link to comment
nfoto Posted January 8, 2021 Author Share Posted January 8, 2021 Look at the houses left and right. See the criss-crossing pattern on the facades? That is caused by heat transfer through the wall support structure. The visible impression of the dwellings is pretty much like what you can see in the previous IR picture (sans the IR "glow" of vegetation, of course). Link to comment
Andy Perrin Posted January 8, 2021 Share Posted January 8, 2021 I see some horizontal lines on the houses that might be what you are referring to? They remind me of what I see with the thermal camera. Link to comment
nfoto Posted January 8, 2021 Author Share Posted January 8, 2021 Yes. Those are the tell-tale signs of thermal transfer, which of course with an ambient temperature around -17C will generate frost patterns. The actual house paint colours are different (white-cream-greyish blue), but of course not manifested as such in monochrome. However, as UV "sees" the pigments most facades are UV "blue" due to TiO2 and other pigments, so are rendered quite bright in monochrome UV no matter what visible colour they represent. Link to comment
Andy Perrin Posted January 8, 2021 Share Posted January 8, 2021 TiO2 is a strong UV absorber (hence its use in sunscreens), so I'm not sure why it would be UV bright on houses. It could be responsible for the blue I guess by absorbing, but it would not act to brighten the reflectance, very much the opposite. Link to comment
nfoto Posted January 8, 2021 Author Share Posted January 8, 2021 Well, the house colours are white, pale cream, or grey blue, (one even brown, but not visible on all photos), and all look light grey in UV (monochrome). Link to comment
Stefano Posted January 8, 2021 Share Posted January 8, 2021 It may depend on how deep you are imaging in UV. UV-blue indicates increasing absorption at shorter wavelengths, and so such objects/surfaces appear lighter in the upper UV. Link to comment
JMC Posted January 8, 2021 Share Posted January 8, 2021 With TiO2 how it appears in UV depends on particle size and wavelength. Larger particles tend to scatter more UV, while smaller ones absorb more of it. I seem to recall as particle size decreases, the transition between scattering and absorption moves to shorter wavelengths, but would need to double check that. Link to comment
Andy Perrin Posted January 8, 2021 Share Posted January 8, 2021 Stefano, TiO2 is very strongly absorbing in UVA. While the exact spectrum depends on how it's annealed, typical curves look like this. 3.1eV = 400nm, 3.3eV = 375nm. Jonathan, good point about the scattering. I'm sure that must be why it's so light looking. The situation is analogous to the snow in my NIR/SWIR photos -- when the absorption coefficient was in the moderate range in the NIR pics (980nm), the snow appeared light due to scattering dominating, but as you push towards 1450nm, it went black eventually. Link to comment
nfoto Posted January 17, 2021 Author Share Posted January 17, 2021 Plenty of snow combined with bitter cold (down towards -20C) and recent health issues keep me indoors these days. Still one can manage a comparison of UV vs visible scene rendition, even shooting through triple-layer glazing. The monochrome version of the NEX-5N (courtesy Vivek Iyer) allows for hand-held UV although the outdoor scenery is a darkish white-out of frost fog and snow. Taken with the 3.5cm f/3.5 W-Nikkor (RF mount) on the NEX-5N, shooting through a triple-layer window that robs a lot of the image sharpness. UV needs about 6EV more exposure and alters scene reflectivity only in subtle manner for this winter scene. Link to comment
dabateman Posted January 17, 2021 Share Posted January 17, 2021 I hope you get better soon Birna. Even these monochrome images are interesting. Link to comment
Stefano Posted January 17, 2021 Share Posted January 17, 2021 Very interesting. There is indeed quite a difference in the wooden wall. Link to comment
Andy Perrin Posted January 17, 2021 Share Posted January 17, 2021 Yes, the horizontal lines of moisture are much more visible in the UV (now that I know what to look for). Feel better soon, Birna. Link to comment
Andrea B. Posted January 21, 2021 Share Posted January 21, 2021 This is like one of those kid puzzles where you are supposed to find the small differences between the two nearly identical pictures. I see the basketball backboard and the window frames. Link to comment
nfoto Posted January 21, 2021 Author Share Posted January 21, 2021 "Find Willy" -- my kids loved those large pictures. UV tonality can be very similar to visible in black-and-white, yet there are always clues present even when the (fake) colours are absent. In the spring or summer, differences would be more obvious. In this wintery scene, one has to be surprised there is any UV left to make a decent exposure!! (remember: hand-held camera). Link to comment
nfoto Posted February 12, 2021 Author Share Posted February 12, 2021 From today's experiments: experimenting with various old lenses and the Baader U on the NEX-5N. I was surprised by the UV output of my pendulum lamp ... it has 5 halogen LED lamps and 4 of them registered brightly in UV. The glowing spot in the lower left is my NEMO torch reflecting off stainless steel. A shutter speed around 1/6 to 1/13 sec at ISO 800 with the old lens, here the W-Nikkor 3,5cm f/2.5 from mid '50s, set to f/5.6 was surprising. Link to comment
dabateman Posted February 12, 2021 Share Posted February 12, 2021 Yes my newest halogen bulbs dip to 350nm. My older ones are blocked at 400nm.I quickly bought up a bunch of them pre COVID as they are great lights for IR and a full spectrum with the 1000 lines/mm film. I used that before I got a really spectrometer. Link to comment
KhanhDam Posted August 19, 2022 Share Posted August 19, 2022 Nice shots. How did your friend convert the Sony? There’s no ragged edges so I assume he did not scratch off the Bayer layer with wood stick? Link to comment
nfoto Posted August 19, 2022 Author Share Posted August 19, 2022 Vivek likely has access to laser equipment through his profession. Link to comment
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