8 Key Points to Understanding ISO and Image Quality | Transcription

In this video we’re going to be talking about 8 key points to better understand ISO. In particular, how ISO relates to image quality. Lets start from the top.

Key Point #1

This is going to be a review for everybody because I expect that you’ve already understood and mastered this concept. You ISO is the cameras sensitivity to light. Okay, so you raise the ISO, your sensitivity increases. Now we basically use ISO in situations where the combination of shutter speed and your aperture doesn’t yield the correct exposure. You don’t get enough light. It could be because you need a close down aperture so that you get better depth of field, it could be because you need a faster shutter speed, or a combination of both. Either way, you’re not getting enough light so we’ve bumped up ISO to compensate, to increase that sensitivity to light. Now more specifically, it’s not actually the cameras sensitivity to light. It’s actually the cameras sensor, if we’re talking about a digital LSR, like this one. So we’re talking about the actual sensors sensitivity to light. But if we’re talking about a film camera, then we’re talking about the films sensitivity to light. So when you go out to purchase film, you’re looking at the films ISO rating, not the cameras. Cameras don’t have an ISO rating. Just the sensor or just the film. So, we know this, ISO is the digital or is the sensitivity to light either for a digital LSR’s sensor or for film.

Key Point #2

Number two is to understand that every bump up in ISO is going to basically introduce grain into your image. It’s going to do a couple other things as far as image quality, which we’re going to talk about in point three as well. That grain that it introduces is going to reduce image detail. I have the perfect little example set up here for you.

We’re here in Lightroom, what I want to show you basically is that we took this exact same image with a Canon 6D mounted on a tripod and we shot these cupcakes with different ISO settings. So lets look at these full screen, just so we can see each one of them. I’m going to hit I so we can see our information. We have our first image here at ISO 400 then we go up to ISO 1600 then we go up to ISO 6400 then we go up to ISO 12800. The differences between these images is actually relatively difficult to see but what we do notice if we zoom in is that we’re starting to introduce a little bit of grain. That grain is actually removing image detail. Lets say for example, if I were to select these two and I’m going to compare them side by side.

We have ISO 400 on the left and ISO 12800 on the right. Take a look at this, we have a lot more smooth and consistent detail within this image. Where-as the one on the right we can see we have this blotchiness. We have reduced over all detail in the image with that increase in ISO.

Now the great thing about cameras today is that you can step them up to 6400, 12000 ISO, and even beyond that – an A7S goes up to like 400,000 ISO, but that’s not necessarily usable. But at 12800, I’d still say that this image is usable, if you have to shoot with that ISO setting, it’s usable. Cameras are getting to the point where they can see in the dark basically. Just realize that every step up is going to introduce grain and that grain is going to reduce detail.

I have another extreme example I want to show you guys actually. This is on an A7S. Here you can see this is on ISO 1600 where we don’t even see hardly any noise which is really incredible because back in film in the early days of digital LSRs ISO 1600 was actually quite a bit and you would get a lot of noise. But look at this, it looks fantastic. But look at ISO 102,000. We can see a lot of that detail being destroyed and ISO 400,000 this yields… Basically at this point ISO 100,000 and 400,000 those are still unusable ISOs. At least in my opinion. Those really aren’t good enough quality. But on the Sony A7S you can go up to very high ISO numbers and still yield completely usable images which is absolutely fantastic.

Key Point #3

Moving on to key point number three is that raising your ISO is going to reduce overall color and dynamic range within your image as well. This is another effect that it has over the image quality. Now, what exactly does that mean? Here is one of the images that we captured actually during our shoots. I’m going to reset this now back to the original. This is one of those things where we talk about maximizing dynamic range within a single raw file. To do that, to maximize dynamic range, you need to shoot in raw and you need to shoot in your lowest possible, native ISO. We’ll talk about native ISO in a moment as well.

What we’re trying to do is if you look at the histogram, we’ve captured as much detail as possible from the shadows all the way up to the high lights. We’ve captured at least everything that the sensor can possibly capture within that range. If we raise the ISO, lets take a look at what this was shot at. This was shot at 100 ISO. If we raise the ISO to, say, 200 ISO, maybe the camera sensor is capturing 12 or 13 stomps of dynamic range within this image, we get all those shadows, we get all the highlights in that image. We take it and do basically this to it where we make our final adjustment where we pull up the shadows. We pull down the highlights. We get it nice and balanced and toned map image. But if I raise the ISO to say 200 then we’re going to leave off a little bit of that histogram. We may be clipping shadows, we may be clipping more highlights, because the camera may not be able to capture say 13 stops of dynamic range, it may be only capturing 12.7 stops. When we go up to ISO 400, we reduce again, maybe now its at 12 stops. ISO 800, now it’s at 10 stops. ISO 1600, now it’s at 8 stops. Every step up, we’re reducing the amount of dynamic range it can possibly capture within one single image.

That means if we’re trying to create a nice beautiful landscape with an amazing range of color and tone, we need to keep it at the lowest possible ISO. It’s also the reason when if you look at nighttime shots, where if you raise it up to say, ISO 3200 and ISO 6400, you kind of notice that the colors look a little bit dingy. They don’t pop the same way that they would, an image like this shot at ISO 100. Just remember that, again, stepping up not only produces grain, stepping up ISO will also decrease overall dynamic range.

All this talk about raising ISO, decreasing dynamic range, introducing grain, and so forth kind of might dissuade you guys from increasing you ISO, but it is absolutely necessary in many situations. This is what I would say for key tip number four.

Key Point #4

That is, that raising the ISO and getting your shutter speed up high enough where you get a sharp image is much, much better than keeping the ISO lower and getting a blurry image. For example, this image right here. This was shot at 1/160 of a second which gives us just enough sharpness to keep our couple sharp and in the shot. While also, introducing a tiny bit of motion, like kind of like these little petals that they’re throwing across the frame. We can even slow down a little bit more if you want to get more of that motion. But let’s say if I kept this at ISO 800 that would mean that I would need to reduce the shutter speed down from 3200 down to 1600 down to 800 we’d be going from shutter speed 1/60 down to 1/80 down to 1/40. At 1/40 of a second, yes, we might get better color. Yes, we might get better detail, but then we yield a blurry image. A blurry image that would be unusable.

This is my point, is that, our digital cameras, they’re fantastic. You can raise the ISO pretty high. Going up to 1600, 3200 is fine. Getting a sharp image, a usable image is always going to be more important than making sure you have perfect detail and absolutely perfect color, and dynamic range and so forth. Understand the situation and know when it’s totally appropriate and when you need to bump up the ISO.

Key Point #5

Key point number five that I wanted to bring up is that a lot of you will think that maybe it’s better for me to shoot at a lower ISO and then basically get a slightly darker image and raise it up in post rather than raise it up in-camera. That’s definitely a bad idea. I’m going to show you exactly why. In general, lets go back to, this hold b right here. I have two images that I want to demonstrate with. You can see here that one was shot at 30 seconds, F4, at ISO 400 and 30 seconds, F4, ISO 1600. Now this is a two-stop difference, going from 400 to 800 to 1600, that’s two stops. Yes, that is two stops.

What if I shoot it darker over here because I want to yield better dynamic range and better detail and so forth and I just brighten up in post to get a better look? Lets try that. You’re going to find out, that basically by doing this, you will actually get worse dynamic range, worse color, and especially worse detail by raising the exposure significantly in post.

In the left we have our image shot at 1600 ISO and on the right we have our image shot at 400 ISO. We raise the exposure by two stops to match in post production. Lets go lights out by hitting L, if you’re in light room. What we’re going to do now is zoom in now to this image and check this out, the image on the left, at the higher ISO in camera, yielded a better image than the one on the right where we shot at a lower ISO and then raised it digitally in post. So we have more grain over here. I see more color noise, where basically we have these kind of variations of color that don’t look good. Going into shadow we can see that we have more banding, more noise inside the shadows. We have all these problems, where as on the left shooting at the higher ISO in camera gave us a better image than basically trying to raise it in post.

That is key tip number five. Do not shoot at a lower ISO expecting to adjust it in post and get a better image by raising your exposure in post production. You’re always better off raising it in camera to the next native ISO that gives you a correct exposure than trying to do it in post.

Key Point #6

That leads me perfectly into key point number six which is what the heck is native ISO? I’ve said native ISO many times and I will probably say it many more times. So what is native ISO? Every camera, this is a Canon 5D Mark III, whether you’re on a Rebel, whether you’re on a 5D Mark III, whether you’re on a D800, whether you’re on a Sony camera, every single camera has as what’s known as a native ISO. For this camera, for the Canon 5D Mark III, the native ISO when shooting stills is ISO 100. This means that basically, every stop, every full stop from that native ISO is another native ISO number. What does that mean? If we go from 100 to 200 that’s a native ISO. 200 to 400 that’s a native ISO. 400 to 800 that’s a native ISO. 800 to 1600 and so forth. The inbetween numbers are not native ISO numbers. For example, ISO 160, ISO 320, ISO 4 – whatever. Those in-between numbers are not native ISOs. What’s essentially happening is that if you shoot at a number like that, the camera is actually shooting at ISO 100 and it’s digitally modifying it to shoot it at ISO 160 or whatever you’re shooting at. The camera is actually digitally brightening these images which will yield worse results than if you step it up to the next highest ISO.

For example, I would actually get a cleaner image shooting at ISO 200 and darkening it down a little bit versus ISO 160. Keep the camera … At least we recommend keeping the camera at the native ISO. For every camera it is going to differ. For example, on a lot of NIKON cameras, they start natively at ISO 200. So, ISO 200, 400, 800. Some cameras, are ISO 160 native. So it’d be ISO 160, 320, 480, and so forth. Just learn your particular camera and we recommend sticking with those native ISO numbers, just for best image quality.

Is it going to be a huge, massive difference? Well, no. But it will give a little bit of a difference in image quality and when you’re actually looking in and pixel peeping, it’s actually quite noticeable.

Key Point #7

Moving on to key point number seven, is that I would recommend leaving your ISO adjustment as the last step in the exposure equation. For example, you go into a scene and you choose a shutter speed that fits the type of action or whatever it is that you’re shooting or you pick an aperture that matches the type of compositional field that you want to have. At that point, then, decide what you need your ISO to be. So don’t rely on ISO, don’t just set ISO at 400 then go everywhere and start shooting because you really are kind of reducing image quality in a lot of situations that aren’t necessary. For example, I know a lot of shooters that will leave their cameras on ISO 400 and they’ll shoot outdoors the entire time, with it left on 400 because they’re worried about when they go into the shade the may not have enough light but when they go back into the day light they’ll have too much and they figure it doesn’t really matter. You’re better off adjusting in each scene that you need. So leave that as the last part of your equation because why would you want to reduce image quality just directly from the camera?

Key Point #8

Finally, key point number eight is that you can use ISO for creative effect but my guidance would be to be extremely careful. Let me show you exactly what I mean, lets go back to Ligor. I have to examples right here, I’m just going to bring them up in survey mode. These images were shot on a Rebel, they were shot during the course of this workshop. A lot of photographers when they go out into this kind of situation and more experienced photographers will say, I’m going to shoot this at ISO 400 or ISO 800 because it’s going to yield a less digital image. Digital cameras at 100 ISO, they can capture so much detail, so much dynamic range, that it almost looks digital in a sort of way and I one-hundred percent agree with that. So they’ll step it up to ISO 400 or ISO 800 and they’ll shoot a scene like this at a higher ISO which will reduce the dynamic range and add a little bit of grain and noise and reduce a little bit of color and it makes it look kind of like it did back on film. That’s great. It makes it look like a very natural, film-like effect. But what I would say is if you are an advanced photographer and you have a grasp on everything and you understand this, then fine, by all means go out and do it but there is a giant warning with that.

If you go out and shoot images like this in day light, if at a later point in time, you say oh man I really wish I had more detail in these shots, I really wish I had more color in these shots. You can never go back. If you shot these at ISO 400, whether you shot raw or JPEG, that’s not something that you can undo. It is always going to be at ISO 400 and the detail that you capture is going to be the detail that you have. If I want to introduce grain and kind of a film-like look in post, I can do that. I can do that with Lightroom, I can do it with Capture One, I can do it with Photoshop and I can do it and it’s fairly simple to do. There’s also pre-sets to help you do it as well but if you do it in camera and you further enhance it in post, whatever you’ve done in camera cannot be undone.

That’s my warning there and that’s kind of why I would say, I would recommend against doing it as a creative effect in camera because you always can add film-like effects later but you can’t take it away if you did it in camera. If you absolutely, one-hundred percent know that this is what you want and you’re okay with those images being that way forever, then by all means use ISO for creative effect. Otherwise, again, leave ISO as the last step in you’re creative exposure equation, and use it simply to get to the correct exposure.







Chapter 7: BONUS

Total Course Run Time: 6H 30M 21S