hi guys in one of my videos i have already showed you some sample photos i took using an nd filter but i guess some of you might still have questions about all the numbers on the filter like what does the number mean how many stops do you need so in this video i want to share with you some of the basic information about numbers on nd filters but before i start i just want to remind you if you hate math you might find this video a little boring but i promise it really helps sorting out the numbers on the filter package let's start from the simple ones one stop of light simply means an amount of light so if you increase or decrease one stop it means you double or cut the amount of light in half we all know that when you are using a camera there are three factors that decide how much light we let in that is shutter speed iso and aperture so one stop nd would mean cutting half of the light for shutter speed it equals from 1 100 to 1 200 and for iso it equals from 200 to 100 so just cut the numbers by half as for aperture it is more complicated we can take a look at this table i'm sure there is a calculation method behind it but you can just memorize these numbers and you can see the f-stop goes from 1 1.4 to 2.8 4 5.6 etc so there is an one stop difference between each f number all right i hope you are not too bored by all these numbers you might be wondering why do i have to understand all these numbers well it's because it can help you decide which stop you need when you buy an nd filter you might see the two to five stop or six to night stop this is just one way to express the amount of light and the second way to express is 0.3 0.6 0.9 etc this means how dark the glass is and the third way to express is nd4 and d8 and d16 like this this may look complicated but just remember each stop of exposure refers to half of light so one stop equals nd2 two stops equals nd4 three stops equals nd8 think of it this way and d4 because when you multiply 2 by 2 you get 4 and the 8 because when you multiply 2 by 2 for 3 times you get eight so it's two cubed and in this 16 is because when you multiply two by two for four times you get sixteen so take a look at the filter here it says nd2 to 2000 wow 2000 it looks like a large number right but it simply means 11 stops because if you multiply 2 by 2 for 11 times you get 2048 and the manufacturer just rounds it up to 2000 okay i hope it's clear enough now i'm going to show you how i can apply all these numbers to real life situations so before i put an nd filter on my lens i will just set my exposure my iso and shutter speed to exactly how i want it to be despite looking too bright and i will probably set the iso to a lower number so that i can get the best quality so now you can see my shutter speed is 1 200 f4 and iso 200 i can not lower it because of the picture profile so now obviously i am too bright and the meter here also tells me this is too bright as well so remember i am at one two hundreds now just to calculate i'm going to change the shutter speed to now one four hundredths so this is one stop and now 1 800 this is two stops and now three stops and here you can see the metering tells me this is the correct exposure so um remember we just counted three stops so this is the stops i need if i'm going to use an nd filter now let me give you a little quiz if your image is correctly exposed at 0.4 seconds but in order to create a very smooth water surface you would like to change the shutter speed to 30 seconds so how many stops of nd filter do you need you can pause the video to do some calculations to get the answer you should divide 30 by 0.4 and you get 75 and we know that 2 times 2 for 6 times equals 64. and 2 times 2 for 7 times equals 122. so 75 is in between right so the correct stop is somewhere between six and seven of course if you don't have the exact stop of the filter at hand you can always change the iso the aperture or the shutter speed in order to fit the filter that you have but i would suggest getting a variable nd filter because if you are new to filters you might not be sure how many stops you need in what kind of situation so you will have to do all kinds of calculations like i just did with a variable nd filter you can just turn the ring and experiment by yourself without having to change the filters all the time so i know some people say the variable nd filters can create vignettes sometimes i guess that's true for some cases but at least i don't notice anything with mine so i think it's all right especially when you are not using a super wide lens and of course you can do a lot more than just making things darker with an nd filter there are a lot of creative ways to use an nd filter but i'll just end the video here because i believe you have a lot to digest i hope this video is helpful for you remember to check out the previous video i made about nd filters the link is up there so if you like my videos please subscribe and give me a thumbs up i'll see you next time [Music]