So you are going to be setting your aperture according to what your desire is for the story you want to tell in your photograph, but from a technical standpoint you need to know about where your lenses most sharpest point is in setting the aperture, so we want to talk about the maximum sharpness now we're going to talk about lens design in another section here but there's a theory that when they design the lands the lens should be optically perfect when it's wide open so it's at its very best okay, it should be and the reality is they're not okay there's defects and there's problems with every single lens made even the most expensive ones and so the result is is that if you stop your damn lens down, you will disguise and hide the problems that you're len's house so it's a wave maybe your lands shows something called chromatic aberration we'll explain that later, but it shows chromatic aberration will if you stop your lens down from one four, two, two, two, two, eight, two, four it's go...
ing to hide that effect you're not going to see it as much in most of those problems situations and so stopping your lens down improves the quality but there's a problem if you take it too far and that is you hit a point of diffraction diffraction is light scatter as a result of passing through an opening and so in this example we have light coming through the lens and then the light's going to go through the aperture opening and let's say we're not closing our aperture very much what happens as light hits the edge of the aperture it scatters a little bit see how the top ray and the right rare just kind of moving off a little bit there not quite parallel they're diverging from where they would normally go and so this image is lightly affected by diffraction all right now let's try this again but this time we're going to force the light through a smaller opening and when we have less light going through there ah greater percentage of that light is heading the edges of those frame and diffraction and not going exactly to where it's supposed to go so the smaller we open the smaller we have this opening, the more diffraction we get and so if you're feeling confused and you're just simply asking ok what's the best aperture just tell me a number and I'll set that on my lands let's take a look at an example that I shot and I want you to judge the sharpness of these photos I shot these photos at different apertures and we want to look for what aperture results in the sharpest photos and we are looking at small portions of the middle of the frame and the corner of the frame and so let's, we'll do an audience protection patient pole just raise your hand. Who thinks one point force the sharpest aperture nobody in class. Okay, who thinks two point eight is the sharpest aperture? All right, how about five point six? Anybody think five point six is the sharpest aperture? How about f eleven? Okay, I'm seeing everyone's hand got there. Anybody think of twenty two? Okay? So what's going on is that our lens is supposed to be perfect at one point for but as we stopped down we start hiding the problems like this image down here of the close up of the cameras, the worst and the reason it's the worst because it's shot at one point for innit shows the problems of the lens and it's also taken from the side of the frame. Lenses are always sharper in the middle than they are off to the corners and sides. So as we move down the line, we're going to get sharper and sharper. But five point six is actually where I see the sharpest eleven is very close, but by the time we get to have twenty two, we definitely start seeing diffraction there and that's because we're stopping our aperture down too far and so the general rule of thumb and it varies from lands toe lens is that the sharpest apertures are going to be in the middle of the range so it depends on the lens that you have if you have a one four, two f twenty two, that might be of five six if your land starts at four, the sharpest point might be around f eleven, so it depends on the lens that you have is two where is the optimum sharpness on your lands? Forgetting for the moment that you might want mohr or less depth of field for artistic reasons in a photograph so let's just taken example of a full frame sensor with the lens that starts at one point four we're goingto have imperfections in the lens, and so if I'm shooting at one point four in the back of my mind, I know that there are imperfections with lands, but there is a maybe a maur compelling reason why I'm choosing one point for I really want that shallow depth of field or it's a really dark environment and I just really need to let in more light that's ok, I will shoot with lenses that have imperfections we all do now when you have that same lands on a cropped frame censor the exact same problems are visible all right chromatic aberration, flare, sharpness issues, it's the same lens it does thie exact same thing, but there is something that is different that happens depending on the cameras that you have so at a certain point as you close the aperture down, you're going to get into this diffraction zone in the diffraction is gonna get worse and worse and you like I will only shoot it f thirty two if I absolutely have to for depth of field raises what's different is that depending on your camera the diffraction zone will start sooner in some cameras than in other cameras and it has to do with their sensor and in particular it has to do with the size of the pixels and I used the full frame cropped frame here as an example just as a visual but the real difference is the pixels on there they typically are different, but what we want to know is because the diffraction is impacted by pixel size, not censor size. So let me give you an example so on top here we have nine pixels thatyou might have on a full frame sensor and down here we have twenty five pixels thatyou might have on a crop frame camera because crop frame cameras tend to have a lot of pixels packed into a smaller area, which means they have smaller size pixels. Now the circle represents a point of light that is coming through your lands and being cast onto your sensor on our full frame censor our little circle is well within one box, okay, so that is perfect, which means one little spot of light becomes one little pixel perfect but down here it's one pixel and it's starting to reach into the other areas now as our lens closes down to f to our circle grows a little bit but no big change at this point we go down to f twenty to our circle continues to grow but only ever so slightly at f four our lens continues to improve in quality because we're disguising these imperfections and we're getting to the sharpest point but notice what's happened down here on the bottom of the frame you'll notice that circle has starting to overlap the nearby pixels, which means that point of light is now being scattered onto nearby pixels, which means you're gonna get a little bit of blurriness in there if those neighboring pixels start picking up on that information. Five six is a great very sharp place to shoot on many lenses but with cameras that have smaller pixels by f ate if you look at the bottom of your screen you can see that circle is starting to encompass not only the one in the middle it has grown and is starting to cover its neighbors it's infecting its neighbors with this virus of slightly out of sharp areas and as we go into f eleven and sixteen you will see that this circle although it's the same size circle because it's the same lens it affects these picks the smaller pixels more than it does the large ones and so this is one of the reasons why large sensor cameras are preferred in some cases because they don't show diffraction quite the same amount at equivalent apertures and by the time you get down to thirty two you're going to have a lot of diffraction even in full frame sensor but it impacts the cameras that have smaller sensors typically because they have smaller pixels on and for anyone shooting a point and shoot camera that has manual capabilities the diffraction well it depends on a number of things but just as a real rough number you're going to start seeing that at f eleven sixteen in a full frame camera you might see it at eight or f eleven in a crop frame camera but on those little point shoots you might see it at half five, six or even lower it depends on the exact camera that you have and so that's a unique problem to be aware of and so by default I kind of like I'm in f ate guy okay faa and I'll change it winning where necessary I'm shooting a portrait I would rather have shallow depth of field by all means I'm going to use this I'm shooting a landscape and I need more depth of field by all means I'm going to use the f sixteen twenty to thirty two if I need to and so don't be afraid of using them. But be aware of the implications, because if you don't need to go here, you don't want to go here. Now. This actually dives into an area which about three percent of our audience is saying, go, john, go, go more of this. And we're going to kind of cut it off here because there's ah, whole different layer of complexity, it's, a whole dungeons and dragons thing that you get into, and we're not going to do it. But if you want to go, look up pixel size, airy disc and circle of confusion, just google and linc and surf to your heart's content, because there's a whole bunch more information that takes this to a whole nother level. But I think this gets the point across of actually where you need to set your lens and the implications of it, which is what my goal was for this section.