Today's episode is sponsored by Squarespace. Yo, I wanted to do a super quick video about reciprocity and how I tame it like the angry beast out of hell that it kinda is. A lot of people have been sending me questions about film reciprocity so hopefully this silences you forever. So what is reciprocity? Honestly, it sounds kinda sexy. Well, it's not. To oversimplify for the sake of time, reciprocity is basically the fact that your film loses sensitivity to light the longer that it is exposed to light. It's okay to take a minute to try and wrap your head around that. I had a completely debilitating migraine the first time I tried to understand it, but then again, my IQ is lower than a bowl of stagnant mac and cheese. Resolpacity is just a consequence of the physical nature of film, so digital sensors do not need to worry about this. So if you're a digital photographer watching this, go ahead and pack up your Fuji Sex Pro 69 and get on out of here. Who does reciprocity apply to? It applies to everyone who shoots film, 35mm 120 large format 110 if you shoot that for some reason. I'm not hating, I just have a lot of questions. So why do we need to calculate reciprocity? Basically it's because if you're doing a long exposure and you don't correct for reciprocity, you'll likely get an under exposed image. When do we need to calculate for reciprocity? For a color negative film and black and white film, in most cases it's if your shutter time exceeds one second. For any shutter time is faster than one second. Generally, you don't need to worry about reciprocity. However, each film stock is different. I definitely recommend looking up your specific film stock's data sheet and finding the section on reciprocity. Slide film or color positive film has different rules regarding reciprocity, so you definitely need to look at the data sheets for those films because with a more crunch latitude, your metering needs to be spot on. However, the cool thing about color positive film is that it often has special reciprocity properties. For example, codex new Ectochrome doesn't require you to correct for reciprocity until your shutter time exceeds 10 seconds, which is pretty easy for me to remember because that's more than this channel's average watch time. Velvia 100, Rest in Peace, you were a real one. Doesn't actually require you to correct reciprocity until your shutter is over 2 minutes long. Fuji Provia 100 doesn't require any adjustments until after 128 seconds, and Velvia 50 doesn't require anything until after 4 seconds, which is just pathetic. Ugh, this already sounds exhausting. Is there just an easy way to deal with this? Yes. The fact that I stay so cool, common collected in the face of total reciprocity failure is by using something called the reciprocity factor, or the P factor. Most popular film stocks have a P factor readily available online. The P factor is basically just an exponential value that you plug into your shutter time. So how does it work? It's super easy. Basically, you take a normal light meter reading of your scene and note the shutter time. Let's say that we're shooting Ilford HP 5, and your light meter says the shutter time needs to be 5 seconds based on an aperture of F8 to get a correct exposure. Something that's kind of important to note here is that your light meter does not calculate reciprocity for you, because it doesn't know what film stock you're using, because it's not sentient, at least not yet. So because the shutter time is over 1 second long, we need to do a quick calculation to correct for reciprocity. So take your shutter time in seconds, and set it to the power of whatever your P factor is. So let's say that you're using the light meter for 5 seconds to the power of 1.33, 1.33, because that is the P factor for Ilford HP 5. It gives us a new shutter time of 8.5 seconds. So now if you use that shutter time instead of 5 seconds, you should get a correct exposure. If the light meter was telling me that shutter time needs to be 200 seconds long, I would do 200 again to the power of 1.33 for a correct exposure. But good luck with that. So that's it. It's really easy, and this approach hasn't failed me yet. Not every film stock has a reciprocity factor available online. When in doubt, I typically just use 1.3 and assume reciprocity kicks in after 1 second, because that seems to be a commonality with a lot of film stocks. For the record, that is the reciprocity factor that I use for a Sinistil 800T when I'm out doing questionable things at night, or also night photography. Here are all the P factors I've collected in my notebook for various film stocks if you want to copy them. But if you're tired already of hearing about P factors, how about the cool factor with today's sponsor Squarespace? 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And if you use the code grainydays, I check out, you can get 10% off your first purchase. Anyway, that's it. Sorry for the short episode this week. I'll try to do better next time, but I wouldn't count on it.