FPL Posted April 24, 2018 Share Posted April 24, 2018 Most ND filters are quite transparent above 720nm, so I played with possibility to use stronger ND filter to create pictures with IR look but also with some normal colors preserved. This one was shot with Camdiox ND1000 filter: http://www.fpl.cz/uvp/nonir.jpg It needs scene where leafs are in direct sun light - - in shadow (even when there is lot of light) it delivers image close to result from unfiltered full spectrum camera.And is important to use as apochromatic lens as possible. Esp. wide lenses will produce heavy aberrations: http://www.fpl.cz/uvp/nonir2.jpg Some ND filters: http://www.fpl.cz/tst/ndir.jpgWould be nice to have their real transmission curves ... Link to comment
Andrea B. Posted April 24, 2018 Share Posted April 24, 2018 An interesting idea. I have some ND filters which have not been used for a very long time. Now I am enthused to find them and try this myself. That is quite some amount of color aberrations in the crop! It almost becomes an artistic abstraction. Readers, be sure to click Petr's link at the bottom to see the results from a wide range of ND filters. Link to comment
Cadmium Posted April 25, 2018 Share Posted April 25, 2018 I don't know the transmission of other ND filters, but the Schott NG filters don't seem to have much difference between visual and IR, so be aware of that."NG" filters are the Schott neutral density filters. Link to comment
OlDoinyo Posted April 25, 2018 Share Posted April 25, 2018 You might try playing around with crossed polarizers, as well--they don't attenuate much beyond 760 nm. Link to comment
FPL Posted April 25, 2018 Author Share Posted April 25, 2018 I don't know the transmission of other ND filters, but the Schott NG filters don't seem to have much difference between visual and IR, so be aware of that. Key is _difference_ between transmittance in visual and IR. You are using in your graph scale, on which it isn't so visible. When you display lower portion of transmittance graph for 2.2mm thick NG3 (what probably is base glass on which were build at least BW and VF ND1000 filters from above mentioned test), with linear scale on Y axis, then you can see quite significant difference: http://www.fpl.cz/uvp/ng3trans.jpg Link to comment
FPL Posted April 25, 2018 Author Share Posted April 25, 2018 You might try playing around with crossed polarizers, as well--they don't attenuate much beyond 760 nm.I don't believe that Vario ND filters based on crossed polarizers can produce enough difference in VIS/IR suppression, but I will try it! Link to comment
Cadmium Posted April 26, 2018 Share Posted April 26, 2018 Yes, ND filters are a mix of Visual and IR, and transmit a higher ratio of IR compared to to visual, and thus are a nice mix of visual and IR compared to a straight full spectrum, or a straight visual + IR wide open mix.However, I would not say that ND filters "are quite transparent above 720nm", in fact they will attenuate IR transmission, making the exposure longer.Above I was using 2.2mm thick as a typical filter thickness, but below I am using the 1mm thick example (as used in the Schott catalog) because it better shows the transmission of all their NG filters.The same ratio seen in the normalized graph can also be seen in either the diabatic of Linear graphs, however diabatic and linear graph versions also show the transmission attenuation applied to the exposure.Keeping in mind that this graph shows 1mm thick transmission, so 2mm thick will make exposure time even longer. When using ND filter for visual + IR mixing, you should experience some extended exposure time. Link to comment
Cadmium Posted April 26, 2018 Share Posted April 26, 2018 2.2mm thick version.Not all ND filters may be created equal, so I can't compare these graphs with your ND filter.The transmission of these Schott NG (ND) filters at even 1mm thick tend to attenuate the IR transmission quite a bit compared to a usual longpass filter.Notice how the normalized NG1 (black line) doesn't get to "1.00" until 1200nm, yet it isn't even up to 1E-03 at 1200nm.Also notice how NG11 and NG5 have slightly less transmission in IR than they do in visual (except between 690nm ~ 740nm).NG5 and NG11 would work for IR + Visual, but would actually reduce the IR more than the visual. One might use GG420 instead for a more flat Visual + IR curve mix.Notice how NG3 and NG4 (yellow and purple) would be the only two that would work practically for attenuating visual mixed with IR (depending on usual thicknesses),maybe ND9 (green) if it were very thin, but once again the overall attenuation is very strong, so it would require a long exposure time. Link to comment
Andy Perrin Posted April 26, 2018 Share Posted April 26, 2018 I guess I don't understand what the benefit of doing this is, given that IR filters are pretty cheap overall? Link to comment
Andrea B. Posted April 26, 2018 Share Posted April 26, 2018 If you already have them - which many of us do - then might as well use them for IR. I never thought of it myself. My NDs are all in some storage bin somewhere currently. I had those big rectangular (Lee or Cokin) filters from early digital days. When the camera dynamic range was smaller, it was useful to have a graduated ND filter for bright skies or sunsets. Link to comment
FPL Posted April 26, 2018 Author Share Posted April 26, 2018 I guess I don't understand what the benefit of doing this is, given that IR filters are pretty cheap overall?It's attempt to have visible IR effect but still at least some level of natural colors. It can't be achieved with any usuall IR filter. Link to comment
Cadmium Posted April 27, 2018 Share Posted April 27, 2018 Nice day out there so went out back and compared some IR filters and ND filters.Settings: F9, ISO 200, AP, Matrix, 0EV, Exposure times noted below. White balanced full frame marquee in NX2 (CNX2).The RG filters used here are 2mm thick, and the NG filters used here are 2.2mm thick. RG1000 1/20s RG850 1/100s RG9 1/400s RG695 1/400s NG3 1/25s NG4 1/25s Since the two NG (ND) filters looked dark, I added exposure compensation of 1 to them in post (NX2).ND3 1/25s +EC 1 post ND4 1/25s +EC 1 post Full Spectrum (no filter) 1/600s Link to comment
OlDoinyo Posted April 27, 2018 Share Posted April 27, 2018 I don't think the ND filters are terribly selective for IR in the last examples--we see IR effects just because the sensor is already very sensitive to IR, even with no filter. As I said before, experimenting with crossed polarizers will give more (and more controllable) selectivity. Link to comment
Cadmium Posted April 27, 2018 Share Posted April 27, 2018 I tend to think the ND3 example is somewhat pleasing and different, given no swap needed for blue sky, and red barn is a definite mix of visual.However, it does requite a longer exposure, especially if you don't want the brighter version out of the box.It works slightly like a UG1 or UG2A dual band IR shot, but not as strong of blue, and the addition of red in this case also from the visual mix,something you don't get with UG1/UG2A shots. Link to comment
FPL Posted May 1, 2018 Author Share Posted May 1, 2018 I have done few more test pictures with different OG/RG filters and with ND1000: http://www.fpl.cz/uvp/ogrgnd1.jpg http://www.fpl.cz/uvp/ogrgnd2.jpg http://www.fpl.cz/uvp/ogrgnd3.jpg Link to comment
Andrea B. Posted May 1, 2018 Share Posted May 1, 2018 These are cool comparison thumbnails!! Thank you for sharing them with us. Petr, if you have not already tried them, you might also enjoy the interesting false colors produced by the dual band-pass filters when used unblocked. For example, the BG3 (Blue + IR) or the U330 (UV+IR). The latter records mostly IR if used unblocked, but passes just enough UV/B/G to make things interesting in false color. Link to comment
FPL Posted May 1, 2018 Author Share Posted May 1, 2018 From those type of filters I like Hoya B410 (and also Schott UG5 give some interesting results).Only limiting factor is, that there are not available wide lenses apochromatic enough in such range. :-( Link to comment
Cadmium Posted May 1, 2018 Share Posted May 1, 2018 My compliments of the very nice comparisons! Excellent!By the way, someone was telling me the other day that the new LifePixel Hyper Color filter is a 470nm/475nm longpass, like a GG475 filter.I don't know other than what they told me, but the shots do look as such. Link to comment
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