WEBVTT - Doubly Exposing Spirit Photography 0:00:04.480 --> 0:00:12.520 Welcome to tech Stuff, a production from iHeartRadio. Hey there, 0:00:12.720 --> 0:00:17.880 and welcome to this spooky episode of tech Stuff. I'm 0:00:18.040 --> 0:00:23.279 your ghost host Jonathan Strickland, executive producer with iHeart Podcasts 0:00:23.600 --> 0:00:27.240 and today, Well, first, I want to give a shout out. 0:00:27.400 --> 0:00:30.520 I was pondering what to cover on today's episode of 0:00:30.520 --> 0:00:34.200 tech Stuff, and I idly asked my best friend Shaye 0:00:34.360 --> 0:00:38.559 Lee what she thought I should do. Now. Shye is 0:00:38.600 --> 0:00:42.800 a podcaster herself, but she's also a guide on ghost tours. 0:00:43.200 --> 0:00:46.720 I've gone on her ghost tour before in Marietta, Georgia, 0:00:46.880 --> 0:00:50.400 and it was quite entertaining. She's also a tarot reader, 0:00:50.560 --> 0:00:54.080 she's an astrologer, and she's an all around witchy person. 0:00:54.520 --> 0:00:57.840 And the fact that we can be such good friends 0:00:58.000 --> 0:01:01.720 speaks very highly of her patients as well. Because I 0:01:01.760 --> 0:01:06.800 am notoriously not a believer in any of those things. 0:01:06.880 --> 0:01:09.319 But when I asked Shaye her opinion as to what 0:01:09.440 --> 0:01:13.640 I should talk about, her response was seasonally appropriate that 0:01:13.720 --> 0:01:16.959 I should do an episode about tech that folks have 0:01:17.160 --> 0:01:20.120 used in order to pull the wool over other people's 0:01:20.160 --> 0:01:24.440 eyes when it comes to stuff like ghosts and spirits. Now, 0:01:24.640 --> 0:01:28.479 in past episodes of tech Stuff, I have done episodes 0:01:28.520 --> 0:01:32.000 about ghost hunting equipment. I did a recent rerun of 0:01:32.000 --> 0:01:36.039 ghost hunting equipment episodes. So the short version of those episodes, 0:01:36.080 --> 0:01:38.200 if you haven't heard them, is that I do not 0:01:38.319 --> 0:01:42.160 believe in ghosts, and in my mind, the equipment falls 0:01:42.200 --> 0:01:45.759 between two extremes. And on one end you have tech 0:01:46.120 --> 0:01:49.880 that actually does do something, but it's completely unrelated to 0:01:49.880 --> 0:01:54.840 ghost hunting, like an EMF reader for example. These devices 0:01:55.040 --> 0:01:59.840 measure electromagnetic fields and they're important for folks like say, electricians. 0:02:00.240 --> 0:02:03.560 If a house has faulty wiring, an EMF meter can 0:02:03.600 --> 0:02:06.120 point an electrician in the right direction so that they 0:02:06.120 --> 0:02:08.600 can address the issue. Now, on the other end of 0:02:08.600 --> 0:02:11.239 the spectrum are tools that, as far as I can determine, 0:02:11.240 --> 0:02:15.760 have no real purpose, but they've been adopted and promoted 0:02:15.800 --> 0:02:19.000 by ghost hunter types. So an example of this category 0:02:19.360 --> 0:02:23.760 would be spirit boxes, which just scan through radio frequencies. 0:02:23.960 --> 0:02:27.560 So the idea is that spirits are somehow capable of 0:02:27.600 --> 0:02:32.360 sending messages by manipulating radio waves in an inexplicable way, 0:02:32.680 --> 0:02:35.280 and not just manipulating radio waves, right, It's not just 0:02:35.280 --> 0:02:39.240 that you tune a radio to a frequency that's unused, 0:02:39.280 --> 0:02:42.280 so you're just getting static. That's not what you're doing. Instead, 0:02:42.320 --> 0:02:46.960 the ghost is somehow able to communicate across different frequencies. 0:02:47.320 --> 0:02:50.160 So this would be like having a pair of walkie talkies, 0:02:50.200 --> 0:02:53.040 but in order to hear what your best friend is saying, 0:02:53.400 --> 0:02:56.160 you would have to change the frequency channel at just 0:02:56.240 --> 0:03:00.480 the right time and in sync with your friend. Otherwise 0:03:00.520 --> 0:03:02.120 you would just get a blip of what your friend 0:03:02.160 --> 0:03:04.880 was saying as they went through the different channels, and 0:03:04.919 --> 0:03:09.480 that's it. Now. Some spirit boxes flip through frequencies relatively slowly, 0:03:09.840 --> 0:03:13.240 and that means the occasional word or sound from an 0:03:13.320 --> 0:03:16.480 actual radio station will make its way through and that 0:03:16.520 --> 0:03:20.079 you'll hear it and you'll understand it. But obviously, if 0:03:20.080 --> 0:03:23.000 it's going that slowly, that means you could just hear 0:03:23.240 --> 0:03:26.320 a local radio program and you might just use some 0:03:26.400 --> 0:03:30.880 creative thinking to make whatever you heard fit whatever narrative 0:03:31.360 --> 0:03:34.640 you are searching for in your quest to support the 0:03:34.720 --> 0:03:39.400 existence of ghosts. Other spirit boxes are designed to rapidly 0:03:39.600 --> 0:03:42.920 scan through frequencies so that you're not likely to hear 0:03:43.040 --> 0:03:46.760 anything clearly. But how a ghost is supposed to communicate 0:03:46.800 --> 0:03:49.680 through that kind of method beats the heck out of me. 0:03:50.280 --> 0:03:52.880 Like a ghost has to be really determined to talk 0:03:52.920 --> 0:03:57.080 to you if they are going to manipulate radio waves 0:03:57.120 --> 0:04:00.840 in a cascade of frequencies. Unless the idea is that 0:04:00.920 --> 0:04:03.320 when you hit upon something, you stop and then you 0:04:03.600 --> 0:04:06.120 try to listen in, because that would be just like 0:04:06.200 --> 0:04:10.400 hitting the scanner button on a digital radio, where it's 0:04:10.520 --> 0:04:14.240 just going to seeking out, you know, strong radio frequencies 0:04:14.280 --> 0:04:16.560 one after the other, and that doesn't really seem like 0:04:16.600 --> 0:04:19.400 a useful tool to be either. Now, this is a 0:04:19.440 --> 0:04:22.760 really good point to drive home. So much of ghost 0:04:22.839 --> 0:04:26.720 hunting technology is based upon a very faulty premise, which 0:04:26.760 --> 0:04:30.800 is the presumption that ghosts can manipulate phenomena ranging from 0:04:30.920 --> 0:04:35.799 electromagnetic waves in general to radio waves specifically. Because here's 0:04:35.800 --> 0:04:38.400 the thing, y'all, ghosts haven't been proven to be a 0:04:38.440 --> 0:04:41.800 thing yet in the first place. So to me, that's 0:04:41.880 --> 0:04:44.480 like you're putting the cart before the horse. You know, 0:04:44.560 --> 0:04:47.880 if you say, if this meter goes beep, there's ghosts, 0:04:48.360 --> 0:04:51.320 that's a problem. If you haven't yet proven that ghosts 0:04:51.360 --> 0:04:53.920 are even a thing. You have to do that first. 0:04:54.000 --> 0:04:57.040 Then you have to establish that these ghosts, which are 0:04:57.080 --> 0:04:59.840 definitely a thing, can do whatever it is you're cl 0:05:00.400 --> 0:05:02.920 they can do. In short, the argument the ghosts can 0:05:02.960 --> 0:05:07.560 manipulate phenomena at all presupposes that ghosts exist. That's not 0:05:07.760 --> 0:05:11.240 the way science works. This is where I have to 0:05:11.640 --> 0:05:15.000 again hammer home the fact I am a skeptic. Do 0:05:15.160 --> 0:05:19.200 I think it's outside the realm of possibility that ghosts exist? Well, 0:05:19.240 --> 0:05:21.719 if I'm being honest, yeah, I do think that. I mean, 0:05:21.880 --> 0:05:25.440 I don't know everything though, right I do not know 0:05:25.600 --> 0:05:29.440 for sure, but I don't believe it, and I'm pretty 0:05:29.640 --> 0:05:32.880 I feel pretty confident it's not a thing. What I 0:05:32.920 --> 0:05:35.279 do know is that no one so far has produced 0:05:35.279 --> 0:05:39.560 evidence that satisfies me to suggest otherwise that I can 0:05:39.600 --> 0:05:43.320 say for sure, even if ultimately, if you put all 0:05:43.360 --> 0:05:47.120 the truth into a sieve, you would come up with 0:05:47.440 --> 0:05:50.760 I don't know for sure. I have, however, plenty of 0:05:50.800 --> 0:05:55.719 evidence of people using technology to fake the existence of ghosts. 0:05:55.960 --> 0:06:01.360 Hoaxsters and hucksters, snake oil salesmen and con artists. These 0:06:01.400 --> 0:06:04.560 folks have made use of technology to fool wishful thinkers 0:06:04.640 --> 0:06:07.359 and those saddened by the passing of loved ones that 0:06:07.440 --> 0:06:12.799 communication beyond the veil is indeed possible, and that spirits 0:06:12.920 --> 0:06:16.960 persist after earthly life. Has been extinguished. We don't have 0:06:17.000 --> 0:06:20.599 satisfactory evidence showing that ghosts are a thing, but we've 0:06:20.600 --> 0:06:24.640 got lots showing how unscrupulous people have tried to fool 0:06:25.240 --> 0:06:29.640 naive marks. Now, to be clear, you don't need technology 0:06:29.920 --> 0:06:32.680 to fool people. You know, some folks are just predisposed 0:06:32.680 --> 0:06:35.640 to believing in spirits for one reason or another. They've 0:06:35.680 --> 0:06:38.840 done most of the work for you, and a charismatic 0:06:39.000 --> 0:06:43.159 medium might convince an audience that the medium can converse 0:06:43.160 --> 0:06:47.039 with spirits simply through some routines that make little use 0:06:47.040 --> 0:06:50.520 of technology at all, from an audience plant, which could 0:06:50.520 --> 0:06:54.200 be very effective, to cold reading practices, which are a 0:06:54.320 --> 0:06:57.520 variable effectiveness. It all depends upon the skill of the 0:06:57.560 --> 0:07:00.920 medium doing the cold reading, but technology we certainly can 0:07:01.000 --> 0:07:04.000 help out. Now, in this episode, we're mainly going to 0:07:04.080 --> 0:07:08.760 focus pun intended on photography. Now, to do a full 0:07:08.920 --> 0:07:13.160 history of photography would take multiple episodes of tech stuff, 0:07:13.240 --> 0:07:16.880 So we're gonna hit some major highlights, and we're starting 0:07:16.960 --> 0:07:20.240 in the early nineteenth century because there was a French 0:07:20.360 --> 0:07:23.560 Smarty Pants who had the temerity to have the very 0:07:23.600 --> 0:07:28.160 French name of nisseephor Nips, and he came up with 0:07:28.280 --> 0:07:32.680 this mad idea of finding a means to make permanent 0:07:32.960 --> 0:07:38.200 the images that could be projected by a camera obscura. Now, 0:07:38.320 --> 0:07:43.559 my drugies. The camera obscura was typically a darkened room 0:07:43.840 --> 0:07:46.920 where you have no source of light other than a 0:07:47.160 --> 0:07:51.600 tiny pinhole cut through one wall. Light enters through the 0:07:51.640 --> 0:07:55.760 pinhole and then projects on the opposite wall from where 0:07:55.840 --> 0:07:58.240 the pinhole is. Right, that's how light works. It travels 0:07:58.240 --> 0:08:00.880 in a straight line. The remarkable thing thing is this 0:08:00.960 --> 0:08:04.240 light would actually project an image of the scene that 0:08:04.360 --> 0:08:07.320 was outside the darkened room on the opposite wall. So 0:08:07.320 --> 0:08:08.920 if you set one of these up and it was 0:08:08.960 --> 0:08:12.640 across from let's say a mountainscape, Like you're in a 0:08:12.760 --> 0:08:16.200 nice field and there's a mountain in the background, and 0:08:16.280 --> 0:08:18.480 you set up a camera obscura. So you've set up 0:08:18.520 --> 0:08:21.440 a room, a dark room that has just a pinhole 0:08:21.520 --> 0:08:24.080 in it on the opposite wall. You could see the 0:08:24.120 --> 0:08:28.920 scene of the mountain. It would be gorgeous, it'd be dim. Oh, 0:08:28.960 --> 0:08:32.120 also it would be upside down and reversed. Now how 0:08:32.200 --> 0:08:35.559 is that possible, Well, it's physics. It's a property known 0:08:35.600 --> 0:08:40.160 as the rectilinear propagation of light. But the phenomena opened 0:08:40.240 --> 0:08:44.079 up artistic opportunities. You could have a sketch artist or 0:08:44.280 --> 0:08:47.880 painter set up inside a camera obscura and they have 0:08:47.960 --> 0:08:51.400 a canvas on the wall where the image will be projected. 0:08:51.559 --> 0:08:54.080 They could then use the projected light to guide their 0:08:54.160 --> 0:08:57.040 hand as they painted a copy of the scene, and 0:08:57.080 --> 0:08:59.240 then you would just turn the canvas over and you 0:08:59.280 --> 0:09:01.680 could look at it side up, though it was still 0:09:01.720 --> 0:09:04.800 reversed right, so that was an issue. Plus, the light 0:09:05.080 --> 0:09:08.520 coming through the pinhole was not really that intense. It 0:09:08.559 --> 0:09:11.920 wasn't a very strong projection, so it's still pretty dim. However, 0:09:12.200 --> 0:09:16.040 through the use of things like optics like lenses and mirrors, 0:09:16.320 --> 0:09:19.880 it was possible to one gather more light so you 0:09:20.040 --> 0:09:23.120 get a brighter image projected. But you could also with 0:09:23.280 --> 0:09:26.320 the mirrors re reverse the image so that it was 0:09:26.440 --> 0:09:29.680 right side up and not reverse left or right. Even so, 0:09:29.840 --> 0:09:34.360 the effect was ephemeral, right, The image wasn't permanent. You 0:09:34.400 --> 0:09:37.559 could go into the room and see the image projected 0:09:37.600 --> 0:09:39.680 on the wall, which is pretty, but you could also 0:09:39.760 --> 0:09:43.480 just go outside and look at the landscape directly without 0:09:43.520 --> 0:09:45.760 looking at the projection. So the best you could hope 0:09:45.800 --> 0:09:49.800 for was to sketch and paint a copy of the image. 0:09:49.960 --> 0:09:52.920 Nipps wanted to find a way to really capture an 0:09:52.960 --> 0:09:56.520 image and then have it stay put. Now, about a 0:09:56.640 --> 0:10:01.320 century earlier, a German professor of a natic demonstrated that 0:10:01.360 --> 0:10:05.320 a solution of silver salts would darken when it was 0:10:05.400 --> 0:10:10.120 exposed to light. It was photoreactive, and further, he proved 0:10:10.400 --> 0:10:13.760 that it was light that caused the darkening process and 0:10:13.800 --> 0:10:17.280 not heat. That was something that some other people had 0:10:17.559 --> 0:10:22.240 put forward as a possible reason for this silver solution 0:10:22.400 --> 0:10:25.679 to turn dark. Nips decided he would coat a sheet 0:10:25.720 --> 0:10:29.080 of paper with silver salts and project an image with 0:10:29.120 --> 0:10:32.960 a camera obscura onto that sheet of paper, and he 0:10:33.040 --> 0:10:38.160 produced his first image this way in May of eighteen sixteen. However, 0:10:38.200 --> 0:10:42.520 the image was not permanent because once you brought this 0:10:43.120 --> 0:10:47.480 image out into the light, well, that light would cause 0:10:47.520 --> 0:10:49.280 the rest of the sheet to darken as well. It 0:10:49.720 --> 0:10:53.840 would cause the reaction on all the untouched silver salts 0:10:53.880 --> 0:10:56.360 that were coated on this piece of paper to also 0:10:56.440 --> 0:11:00.600 turn dark, so your image would fade and just turn 0:11:01.080 --> 0:11:04.960 dark across the entire canvas. Plus, the image he created 0:11:05.160 --> 0:11:07.560 was also a negative. The areas that were hit with 0:11:07.640 --> 0:11:10.280 the most light were the darkest, and the ones that 0:11:10.320 --> 0:11:13.120 were hit with the least light were the brightest, so 0:11:13.600 --> 0:11:15.920 that meant that the brightest lit parts of your image 0:11:15.920 --> 0:11:18.600 would end up being the darkest parts in what you 0:11:18.600 --> 0:11:22.679 would get a negative image. Now, Nips experimented with photochemical 0:11:22.720 --> 0:11:26.680 compounds that would bleach rather than darken when exposed to light. 0:11:27.000 --> 0:11:29.760 But still there was the issue of this resulting image 0:11:29.800 --> 0:11:33.280 disappearing once the whole thing got exposed. But yeah, you 0:11:33.280 --> 0:11:35.560 could bleach parts and then you don't have a negative 0:11:35.600 --> 0:11:37.880 image anymore. But once you take it out of the 0:11:37.920 --> 0:11:41.360 camera obscura and sunlight starts hitting it, the whole image 0:11:41.400 --> 0:11:45.200 begins to have this photochemical reaction. He also began to 0:11:45.240 --> 0:11:48.120 work with some chemical compounds that react to light, but 0:11:48.200 --> 0:11:51.920 they don't produce visible changes on their own unless they're 0:11:52.000 --> 0:11:56.760 later treated to a separate chemical process. He eventually lit 0:11:56.880 --> 0:12:00.960 upon using bitumen of judea, which is a kind of 0:12:01.320 --> 0:12:06.280 naturally occurring asphalt. It's a tar like substance, and when 0:12:06.320 --> 0:12:10.800 it is exposed to sunlight it becomes non soluble with 0:12:11.280 --> 0:12:15.960 certain chemicals like nitric acid also known as aquafortis. He 0:12:16.000 --> 0:12:19.760 would coat a plate, typically a copper or ten plate, 0:12:20.160 --> 0:12:23.800 with a varnish of this bitumen of Judea. Then he 0:12:23.840 --> 0:12:26.600 would take some translucent paper he would have like an 0:12:26.679 --> 0:12:29.800 etching on a piece of paper, treat that paper so 0:12:29.920 --> 0:12:32.800 that the paper would become translucent, and then lay that 0:12:32.880 --> 0:12:35.040 on top of one of these plates. Then he would 0:12:35.120 --> 0:12:38.520 expose the whole thing to sunlight for several hours, and 0:12:38.679 --> 0:12:41.280 enough light would pass through the translucent parts of the 0:12:41.280 --> 0:12:46.000 paper to cause a photochemical reaction to the exposed bitumen. 0:12:46.400 --> 0:12:51.080 The stuff that was shaded by etching would not react 0:12:51.080 --> 0:12:55.320 to sunlight, right because it's not getting hit. Then once 0:12:55.360 --> 0:12:57.960 he was finished, once he had done this for a 0:12:58.040 --> 0:13:01.880 while and had developed or exposed, I guess I should say, 0:13:01.880 --> 0:13:04.760 exposed the plate to sunlight for a few hours, he 0:13:04.800 --> 0:13:07.280 would give the plate a rent in a pretty darn 0:13:07.360 --> 0:13:12.040 aggressive solution, and it would dissolve the bittermen that wasn't 0:13:12.280 --> 0:13:16.160 exposed to the light, and it left the stuff that was. 0:13:16.280 --> 0:13:18.600 The stuff that wasn't exposed to the light would remain 0:13:19.200 --> 0:13:22.520 soluble and would dissolve. The stuff that had been exposed 0:13:22.559 --> 0:13:25.319 to light was insoluble and would stay on the plate. 0:13:25.720 --> 0:13:28.240 So what you would end up with is a negative 0:13:28.240 --> 0:13:32.280 image where the exposed plate would be the stuff that 0:13:32.840 --> 0:13:35.560 was the original etching, and then the stuff that still 0:13:35.600 --> 0:13:38.680 had Bittmen on it would be the parts where light 0:13:38.800 --> 0:13:41.240 was able to pass through. He took a similar approach 0:13:41.280 --> 0:13:44.920 to make this work with a camera obscura, using lithographic 0:13:45.320 --> 0:13:48.720 stones originally that were coded in bittermen of Judea. To 0:13:48.800 --> 0:13:52.560 capture a scene. It would take days of exposure to 0:13:53.240 --> 0:13:56.120 have enough of the photochemical reaction take place to a 0:13:56.120 --> 0:13:59.280 point where the exposed bittermen would not wash away when 0:13:59.280 --> 0:14:02.760 treated with these very abrasive chemicals. He would take that 0:14:02.840 --> 0:14:05.960 negative image, typically used on a plate of silver, and 0:14:05.960 --> 0:14:08.200 he would put that in a box that had crystals 0:14:08.240 --> 0:14:11.960 of iodine in it, and the crystals would evaporate, exposing 0:14:11.960 --> 0:14:15.360 the plate to iodine fumes, and this would cause the 0:14:15.559 --> 0:14:18.959 exposed silver, the bits that were not covered with the 0:14:19.200 --> 0:14:24.080 bitumen coating, to oxidize, and this oxidized silver would be 0:14:24.080 --> 0:14:27.920 a coating of silver iodide. He then would clear the 0:14:28.040 --> 0:14:30.520 varnish of bittermen off the rest of the image, so 0:14:30.560 --> 0:14:33.920 he'd take off the stuff that had been reactive with 0:14:34.000 --> 0:14:39.200 the sunlight and he would expose it to light, which 0:14:39.200 --> 0:14:43.920 would then cause the silver iodide sections to darken, while 0:14:44.120 --> 0:14:47.080 the stuff that had been exposed to bitumen or had 0:14:47.120 --> 0:14:50.040 been covered by bittermen doesn't. So essentially he used two 0:14:50.040 --> 0:14:54.040 separate instances of photochemical reactions to create a positive image, 0:14:54.080 --> 0:14:59.200 and photography, the early science of photography was born. We're 0:14:59.200 --> 0:15:01.360 going to take a quick when we come back, we'll 0:15:01.400 --> 0:15:06.800 talk about how developments to use another pun would change 0:15:07.080 --> 0:15:10.920 photography and open up the opportunity for the spirits to 0:15:11.000 --> 0:15:23.560 commune with us, or so we were told. All right, 0:15:24.200 --> 0:15:30.080 so we talked about nips and the invention of photography. Now, obviously, 0:15:30.200 --> 0:15:33.440 over the following years a lot of people would advance 0:15:34.000 --> 0:15:37.040 this technique, but the basic idea would remain the same. 0:15:37.120 --> 0:15:40.600 You would take a photoreactive surface, you would expose that 0:15:40.720 --> 0:15:44.640 surface to light under controlled conditions for an appropriate amount 0:15:44.640 --> 0:15:47.720 of time. Then you would process the negative image in 0:15:47.840 --> 0:15:51.920 order to create a positive image. But there was another 0:15:51.960 --> 0:15:58.120 intriguing possibility. You could expose a photoreactive surface more than once, 0:15:58.480 --> 0:16:01.520 and you could create really interesting effects that way. Whether 0:16:01.680 --> 0:16:04.600 it was a glass plate that had been coded in 0:16:04.600 --> 0:16:09.360 photoreactive chemicals or a film with a suspension of similar 0:16:09.440 --> 0:16:12.400 chemicals that are coding it, you could capture two images 0:16:12.640 --> 0:16:15.920 on a single surface and combine the two actually you 0:16:15.920 --> 0:16:18.560 could do it more than twice, although the more you did, 0:16:18.600 --> 0:16:21.400 the messier things would typically turn out, until you would 0:16:21.440 --> 0:16:24.920 just get a big blur. But we're going to skip 0:16:24.920 --> 0:16:26.680 ahead a little bit. You could also, by the way, 0:16:27.040 --> 0:16:31.280 combine two different negatives together. You didn't have to actually 0:16:31.320 --> 0:16:34.000 physically take a photograph with the same negative. You could 0:16:34.040 --> 0:16:37.720 take two different negatives and combine them through superposition and 0:16:37.800 --> 0:16:41.840 develop a single image from the combination. But let's talk 0:16:41.840 --> 0:16:45.400 about how modern film cameras work to kind of understand 0:16:45.760 --> 0:16:50.480 the science of double images on photography. Now, keep in 0:16:50.520 --> 0:16:54.440 mind the principles I'm talking about applied throughout the history 0:16:54.480 --> 0:16:57.600 of the development of this art. But let's kind of 0:16:57.640 --> 0:17:00.240 talk about the basic elements of a modern care camera. 0:17:00.560 --> 0:17:02.680 So with a modern camera, you've got your optics. You've 0:17:02.680 --> 0:17:06.160 got a lens. This lens focuses light onto the surface 0:17:06.280 --> 0:17:10.240 of photoreactive film or maybe an image sensor. If you're 0:17:10.240 --> 0:17:13.040 talking about a digital camera, you've got a shutter. The 0:17:13.080 --> 0:17:16.280 shutter's job is to block light from coming through the 0:17:16.359 --> 0:17:20.760 lens and hitting your film or sensor until the photographer 0:17:20.880 --> 0:17:24.480 actually wants to take a photo. And you typically have 0:17:24.560 --> 0:17:28.280 a mechanism in film cameras to advance and rewind the 0:17:28.320 --> 0:17:31.360 film so that you can take distinct images. So when 0:17:31.359 --> 0:17:34.800 a photographer pushes the button on a camera, the shutter 0:17:35.119 --> 0:17:38.760 opens for a precise amount of time. Now, professional cameras 0:17:38.800 --> 0:17:42.760 let photographers adjust how long the shutter exposes the film, 0:17:42.840 --> 0:17:46.359 also how much the shutter opens in order to expose 0:17:46.400 --> 0:17:49.920 the film. So faster shutter speeds are used to capture 0:17:50.080 --> 0:17:53.720 fast moving subjects because if the shutter's open longer, it's 0:17:53.760 --> 0:17:56.280 gathering more light. If something's moving, it's going to be 0:17:56.320 --> 0:17:59.000 a blurry image. Sometimes you might want that, that might 0:17:59.000 --> 0:18:01.400 be the effect you want. But in other cases, let's 0:18:01.400 --> 0:18:03.720 say you want to take a very precise photo of 0:18:03.760 --> 0:18:06.400 something that's moving very very fast, you need to have 0:18:06.520 --> 0:18:09.320 the shutter open and close in a fraction of a second. 0:18:09.640 --> 0:18:12.520 So this is why cameras that are used to film 0:18:12.680 --> 0:18:16.480 extremely high speed subjects in very slow motion, they need 0:18:16.520 --> 0:18:19.240 a whole lot of light to do it. Because that 0:18:19.280 --> 0:18:23.040 shutter is open for just the tiniest fraction of a second. 0:18:23.320 --> 0:18:25.080 It has to be able to gather as much light 0:18:25.119 --> 0:18:27.639 as possible in order to form an image. So you 0:18:27.760 --> 0:18:30.879 need more light to light these kinds of scenes. Now, 0:18:30.920 --> 0:18:33.640 if something isn't moving at all, then you can use 0:18:33.640 --> 0:18:36.199 a longer shutter speed and much less light. In the 0:18:36.240 --> 0:18:40.280 early days of photography, you often had people sitting still 0:18:40.320 --> 0:18:43.080 for minutes at a time in order for a camera 0:18:43.240 --> 0:18:45.560 to gather enough light so that you could get a 0:18:45.600 --> 0:18:48.880 decent photograph. This is one of the reasons you hear 0:18:49.240 --> 0:18:53.280 people in old pictures aren't smiling. It's not because they 0:18:53.280 --> 0:18:56.879 were all dour all the time. It's because they would 0:18:56.880 --> 0:18:59.240 have to sit for a photograph for minutes at a time, 0:18:59.320 --> 0:19:03.320 and holding a rictus grin for like five minutes is 0:19:03.359 --> 0:19:06.920 not the most fun experience. So instead you would sit 0:19:07.040 --> 0:19:11.000 still and patient, and you would wait until the photographer said, 0:19:11.000 --> 0:19:13.040 all right, that's enough time, and then you could go 0:19:13.320 --> 0:19:15.560 about your day. So you would have a more neutral 0:19:15.600 --> 0:19:18.320 expression on your face, and that would mean that you 0:19:18.320 --> 0:19:20.240 would be able to gather enough light, even in a 0:19:20.359 --> 0:19:26.399 dim interior setting, to be able to develop a decent photograph. Well. Typically, 0:19:26.760 --> 0:19:30.880 cameras advance the film after you take an image. Essentially, 0:19:30.880 --> 0:19:33.960 it pulls the film so that the next section of 0:19:34.160 --> 0:19:37.119 unexposed film is in place in order for you to 0:19:37.119 --> 0:19:40.200 take your next photo. To create a double exposure, you 0:19:40.200 --> 0:19:43.600 would need to either prevent the film from advancing, or 0:19:43.600 --> 0:19:46.280 you would need to rewind it back to its original 0:19:46.320 --> 0:19:50.360 frame that you had already exposed with your original photograph. 0:19:50.560 --> 0:19:53.119 Then you would take a second photograph, so you are 0:19:53.160 --> 0:19:56.919 shooting over your previous frame. When you develop the film 0:19:57.200 --> 0:20:01.200 to produce negatives and then ultimately insper these to create 0:20:01.240 --> 0:20:04.359 positive images, you end up with a combined photograph of 0:20:04.400 --> 0:20:07.960 those two shots, the second one on top of the 0:20:08.000 --> 0:20:11.400 first one. So for your standard photography, the second photo 0:20:11.440 --> 0:20:15.600 typically ends up being a background shot. For most uses 0:20:15.640 --> 0:20:19.880 of double images here like you might take a landscape 0:20:19.920 --> 0:20:23.240 shot as your second photograph that lets you place your 0:20:23.280 --> 0:20:26.400 first photographic subject pretty much wherever you would like them 0:20:26.480 --> 0:20:29.720 to be, or have them interact with some sort of 0:20:29.880 --> 0:20:34.119 environment that otherwise they aren't present for now. For it 0:20:34.160 --> 0:20:37.199 to work really well, you typically want your first image 0:20:37.200 --> 0:20:40.240 to have a lot of dark areas in it, because 0:20:40.520 --> 0:20:44.679 those dark areas are under exposed to light, meaning that 0:20:44.840 --> 0:20:48.719 you haven't created this photochemical reaction for that part of 0:20:48.840 --> 0:20:52.880 the film, and your second photograph, the under exposed part 0:20:52.920 --> 0:20:55.399 of the film from the first one, are going to 0:20:55.440 --> 0:20:58.400 receive more exposure to light, and the images you capture 0:20:58.560 --> 0:21:01.359 will show up in those areas that were dark in 0:21:01.359 --> 0:21:04.440 the first photograph. Let me explain by giving an example. 0:21:04.760 --> 0:21:07.760 Let's say you take a picture. You have a model, 0:21:07.960 --> 0:21:10.760 and your model is standing close to you, and you 0:21:10.760 --> 0:21:13.280 have your model in silhouette. You've got a source of 0:21:13.359 --> 0:21:17.639 light behind the model, so you've set your camera so 0:21:17.720 --> 0:21:21.640 that you're focusing on this model, but they are in silhouette. 0:21:21.720 --> 0:21:24.080 You know, it's a dark shape and the light is 0:21:24.080 --> 0:21:27.199 coming from behind them. You take that image, so now 0:21:27.280 --> 0:21:31.000 you've got a picture of someone. Where that someone is 0:21:31.240 --> 0:21:34.240 you can't really see them very well, they're a silhouette. 0:21:34.320 --> 0:21:37.080 But then you take a second picture. Let's say you know, 0:21:37.119 --> 0:21:39.359 you've rewound the film so that you're using the same 0:21:39.400 --> 0:21:42.320 frame again, and you go and take a photo of 0:21:42.320 --> 0:21:44.960 a city scape at night. So it's this brightly lit 0:21:45.280 --> 0:21:49.640 city scape. Well, the under exposed parts of film from 0:21:49.640 --> 0:21:52.040 the first picture are going to bring in that light 0:21:52.320 --> 0:21:54.639 from the second one. That's what's going to show up 0:21:54.640 --> 0:21:57.760 in the silhouette. So when you develop your photograph, you're 0:21:57.760 --> 0:22:00.920 going to have this silhouette of a but instead of 0:22:00.960 --> 0:22:03.840 it just being a dark silhouette, it's a city scape 0:22:04.160 --> 0:22:07.320 in the shape of a person. Silhouette. It's really a 0:22:07.480 --> 0:22:10.000 cool effect, and there's lots of different ways of playing 0:22:10.040 --> 0:22:12.480 with this. This is just a very basic example, but 0:22:12.560 --> 0:22:17.320 photographers have been using this double exposure technique for years 0:22:17.720 --> 0:22:21.719 to produce all sorts of interesting compositions. You can do 0:22:21.800 --> 0:22:24.120 similar things, by the way, with digital cameras. In fact, 0:22:24.160 --> 0:22:26.359 you can do things with digital cameras where they have 0:22:26.560 --> 0:22:30.280 apps that allow you to do this and they'll just 0:22:30.640 --> 0:22:33.880 handle the whole all the processing and give you the effect. 0:22:33.960 --> 0:22:36.800 But in the old days, you could achieve this effect 0:22:36.840 --> 0:22:40.639 in camera. You didn't have to do any special processing 0:22:40.760 --> 0:22:43.800 after the fact to get it. Now you could by 0:22:44.119 --> 0:22:47.399 taking two separate images and then just combining negatives together. 0:22:47.440 --> 0:22:50.040 You could do that as well with the superimposing one 0:22:50.080 --> 0:22:53.480 negative on top of another, but this method, you did 0:22:53.480 --> 0:22:55.959 it all in camera. Then you would go and develop 0:22:56.000 --> 0:22:59.439 your film and see the result. So the medium of 0:22:59.560 --> 0:23:03.560 choice in the old days of photography wasn't film because 0:23:03.560 --> 0:23:07.240 we weren't really into plastics yet. Instead, what was being 0:23:07.359 --> 0:23:11.360 used in say the mid to late nineteenth century were 0:23:11.440 --> 0:23:15.760 glass plates that had been coated with photoreactive chemicals, and 0:23:15.800 --> 0:23:19.400 you would slide the glass plate into a camera. Then 0:23:19.480 --> 0:23:22.840 you would take a photograph with the camera. This would 0:23:22.960 --> 0:23:25.800 expose the areas of the glass plate to light. You 0:23:25.840 --> 0:23:29.040 could then remove the glass plate, use some chemicals to 0:23:29.119 --> 0:23:33.320 develop the image, then transfer that image to a sheet 0:23:33.320 --> 0:23:36.440 of paper where you get your positive photograph. Then, best 0:23:36.520 --> 0:23:39.600 of all, if you're a photographer, you could clean the 0:23:39.640 --> 0:23:43.600 glass plate thoroughly and then use that same glass plate again. 0:23:43.680 --> 0:23:47.560 You would coat the glass plate with new photoreactive chemicals 0:23:47.760 --> 0:23:50.640 and use it again to take another image. Now, clearly 0:23:50.760 --> 0:23:54.560 doing that would destroy your negative in the process, like 0:23:54.680 --> 0:23:56.960 the negative that you took with the first picture, but 0:23:57.359 --> 0:23:59.480