 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 kind of 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 kind of 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 Reciprocity 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 35 millimeter 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 underexposed 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 times 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 stocks 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 Kodak's 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 for reciprocity until your shutter is over two minutes long Fuji Provia 100 doesn't require any adjustments until after 128 seconds and Velvia 50 doesn't require anything until after four seconds, which is just pathetic. Ugh. This already sounds exhausting Is there just an easy way to deal with this? Yes, the way that I stay so cool calm and 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 five 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 one 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 in this case five for Five seconds to the power of one point three three one point three three because that is the p-factor for Ilford HP 5 It gives us a new shutter time of eight and a half seconds So now if you use that shutter time instead of five seconds You should get a correct exposure if the light meter was telling me the shutter time needs to be two hundred seconds long I would do two hundred again to the power of one point three three 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 one point three and assume reciprocity kicks in after one 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 Cynestal 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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You can start a free trial today at Squarespace comm slash grainy days and if you use the code grainy days at checkout 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