Andy Perrin Posted February 10, 2017 Share Posted February 10, 2017 (Borrowed from the lime thread.) Andy, how was your SWIR image photographed? My understanding is that CMOS and CCD image sensors are photo blind above 1200 nM. You are correct. The cutoff is actually closer to 1125nm. So the SWIR is photographed using a fluorescent screen that upconverts SWIR photons into NIR photons. Physically, it is the anti-Stokes effect. The converter tube and screen are the CamIR Adapter, which is the same as the Edmund Optics version, which I obtained on eBay. I paid about 12% of Edmund's price! (I believe this to be the cheapest SWIR camera setup in existence! ...and it was still too damn expensive. :( ) This is with the Cine Velostigmat 25mm/F1.5 (20", F/1.5, ISO1600) With a Thorlabs 50mm SM1-mount lens (F/2) Link to comment
Andrea B. Posted February 10, 2017 Share Posted February 10, 2017 That certainly is an impressive looking rig! What investigations do you hope to make with this set-up?? Link to comment
Andy Perrin Posted February 10, 2017 Author Share Posted February 10, 2017 Just exploring! I have started already with the limes, as you saw. Anything with water in it seems to go dark, including humans. That's the overriding conclusion so far. I have no idea what else I'll find as I proceed. Link to comment
Hornblende Posted February 10, 2017 Share Posted February 10, 2017 You could try to demonstrate the transparency of a piece of sillicon metal in IR! Link to comment
Andy Perrin Posted February 10, 2017 Author Share Posted February 10, 2017 Heh, yes, if I had a piece of silicon! Link to comment
Andy Perrin Posted February 15, 2017 Author Share Posted February 15, 2017 Glass of water Link to comment
Hornblende Posted February 15, 2017 Share Posted February 15, 2017 This is so cool.We are drinking Coca-Cola without noticing it. Link to comment
Cadmium Posted February 16, 2017 Share Posted February 16, 2017 You can also use RG1000 stacked with S8612. I know this sounds crazy, but I have seen it done.I would not have thought it possible, because the sensor is limited to about 1200nm, and the stack transmission is very low,but with a long exposure I have seen this work the same way. Water is black (dark) with the stack.I have not tried this myself yet, but I will.Here is a graph I made showing 3mm thick RG1000, the test I saw used 2mm thick. Link to comment
Andy Perrin Posted February 16, 2017 Author Share Posted February 16, 2017 That's not possible (at least for the same reasons). Show it to me and I will try to find an explanation, but it's not shortwave infrared! Silicon goes transparent at 1125nm. Water darkens at 1400nm or so. Water has a number of dark regions other than SWIR, however. Link to comment
Hornblende Posted February 16, 2017 Share Posted February 16, 2017 With my Zwo astro-camera and an IR 850nm filter, water looks darker than usual.I will post a picture tomorow. Link to comment
Andy Perrin Posted February 16, 2017 Author Share Posted February 16, 2017 It does get a bit darker even in the NIR. This graph is from Wiki:https://upload.wikim...iquid_water.png But note that the graph is log-log, so it jumps by several orders of magnitude in SWIR. Uploader gave a link to a list of references, and it matches other plots I googled. (By the way, it is important to google LIQUID water...the vapor spectrum is not the same.) Edit: This link has an example with some "dark water" near the very bottom of the page. It does not go as dark as in SWIR, but it is certainly noticeable!http://www.randombio.com/d90infrared.html Link to comment
Cadmium Posted February 16, 2017 Share Posted February 16, 2017 Andy, you are complicating the issue by showing a false color IR image as an example of dark water. That always happens with false color IR water, you have to go higher to remove color from the water. Link to comment
Andy Perrin Posted February 16, 2017 Author Share Posted February 16, 2017 Cadmium you are looking at the wrong pic. See the pic that is two above that. Link to comment
Cadmium Posted February 16, 2017 Share Posted February 16, 2017 Yes, I see the correct pic now. Well, I never said it was possible, I only said I had seen it done. ;-)Here is my test of the same, using the same glass thicknesses as I had seen done, but I don't know the ISO and Aperture used on the test I saw.Suffice it to say it requires a lot of exposure time and ISO. Not much fun for me. But this shows what I had seen.This is a 1200nm+/- range, pushed to extremes, nothing more. I used RG1000 2mm thick + S8612 1mm thick (similar to the graph I posted above).What you are seeing here is upper transmission of the S8612, as much as I can push the sensor. The RG1000 is cutting off the lower transmission of the S8612. At least that's the idea.I am not endorsing it, I am just testing the idea.Shot using Kuribayashi 35mm lens, D7000 full spectrum camera, incandescent light, RO/DI water. Link to comment
colinbm Posted February 16, 2017 Share Posted February 16, 2017 What about S8612 by its self Steve ? Link to comment
Cadmium Posted February 16, 2017 Share Posted February 16, 2017 Col, S8612 alone would deliver a visual range photo. 300nm to 740nm using 1mm. Link to comment
colinbm Posted February 16, 2017 Share Posted February 16, 2017 What in the world was I thinking of ??? :-( Link to comment
Andy Perrin Posted February 16, 2017 Author Share Posted February 16, 2017 Well the spectra I found show the absorption does go up quickly past 1000nm, so it's not surprising in that light (no pun?) that it looks darker. But I don't believe that's really 1200, or if so, it's just BARELY. Like the last two photons in the bucket, so to speak! Link to comment
Cadmium Posted February 16, 2017 Share Posted February 16, 2017 Yep, and my hand is not dark when photographed with the RG1000 + S8612 stack. Link to comment
Andy Perrin Posted February 18, 2017 Author Share Posted February 18, 2017 Miso bottle Visible (iPhone 6S Plus), 1000nm LP filter (absorption glass from eBay, not sure which glass) SWIR using a modification of the above setup. I have now got an iris, a lens hood lined with Acktar Metal Velvet, and an SWIR BBAR-coated 50mm lens from Thorlabs. The latter increases the transmission quite a lot, enough that I can stop down to F4 now. Main difference seems to be that the miso bottle cap goes from light to dark. Link to comment
Andy Perrin Posted February 18, 2017 Author Share Posted February 18, 2017 As observed in the last pic, many plastics seem to go dark in SWIR. Look what happens to the plastic tensile test specimen (I think it was HDPE?) in the mug here: Link to comment
Andrea B. Posted February 22, 2017 Share Posted February 22, 2017 Heh, yes, if I had a piece of silicon! What about sand? Or a chunk of quartz SiO2? Gets you a bit closer to silicon. Link to comment
Andy Perrin Posted February 22, 2017 Author Share Posted February 22, 2017 Unfortunately, chemical compounds are nothing like their constituent elements. Here is what quartz looks like versus silicon (images from wiki): Silicon isn't that expensive, though, so I might just buy a chunk. Link to comment
Andrea B. Posted February 22, 2017 Share Posted February 22, 2017 http://www.ebay.it/itm/Silicon-element-14-sample-crystals-5-grams-99-99-in-labeled-glass-vial-/332007006478?hash=item4d4d28e10e:g:UwQAAOSwzaJYBpbM There you go! On Ebay for only US$8.80 + shipping US$5.15 = US$13.95.That's an Italian company. There is probably a US company somewhere who also sells samples of elements. Link to comment
Andy Perrin Posted February 22, 2017 Author Share Posted February 22, 2017 Yep, I'll probably get around to it! Link to comment
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