I was asked a question with the same title. When shooting in S-Log and lowering the ISO below the native ISO, you can consider what happens in such a situation. So, imagine shooting on a very sunny day outdoors. For example, when shooting with Sony S-Log3, the first native ISO is 640 for A7S3, and it would be 800 for A7M4 or FX3. Anyway, if you try to shoot at the first native ISO like this, it will be overexposed. But then, if you also forgot to bring an ND filter, in this case, the question is what happens when you lower the ISO to shoot. Most likely, especially those who have transitioned from photography to videography might think, Can't we just lower the ISO when it's too bright? You might think it's that simple, but in videography, it's not such a straightforward issue.

So, I'm going to explain based on Sony cameras. The content is the same for cameras of other brands anyway. First, let's look at the Sony exposure index chart. Now, if you look at ISO 800 here, you'll see a +6 at the top. This, in other words, indicates the dynamic range on the highlight side. However, looking at the graph, you can see that as the ISO decreases, the dynamic range on the highlight side also decreases. So, if you set it to 400, it becomes 5, and at 200, it becomes 4. In the end, at ISO lower than native, the highlights can easily be lost accordingly. Just looking at the graph now may not be easy to understand, so let's actually take some shots. Let's start by testing indoors. We have placed some lights at the back to easily see how the highlights are affected. And we will take shots while changing the ISO.

First of all, the exposure needs to remain consistent, so I will adjust the exposure to show the zebra on the gray card. Currently, the zebra level is set at 41%. This should be sufficient. Now, by starting from the native ISO 800, I will begin shooting. Then, I will decrease the ISO. If I lower it to 640, the exposure will change, so I will adjust the shutter speed. By slowing down the shutter speed, the exposure will be the same as before. Of course, when actually shooting video, I cannot keep the shutter speed slow all the time, but for now, the purpose is to adjust the exposure equally for testing. So, I will continue to adjust the exposure like this and shoot consistently. Therefore, starting with ISO 640, and then lowering the ISO to 500, I will continue to decrease the ISO down to 200 while shooting. Now, let's compare the shots that have been taken.

Currently, it's in S-Log3, so the entire screen is foggy, so I'll just convert it to Rec.709. With CST. The input is Sony S-Gamut3.Cine, and the input gamma is S-Log3, so this conversion should be fine. And I'll just copy the rest as is and convert it. Now, if we compare these, all the exposures are the same. They are all the same. ISO 800, ISO 400, ISO 200, all the same. However, the issue is with the highlight areas. If you look at the scope now, let's zoom in a bit. I'll switch it to a waveform. Now, looking at the waveform, this part is the highlight area, here and then here. Currently, the point that is clipping in the highlights is right here. This is the native ISO, so it's ISO 800. Now, what happens when we look at ISO 400? It goes down like this, right? The clipping point goes down. And if we go to ISO 200, it goes down even further like this.

Right? So, if we compare native ISO 800 and 200 like this, there is a significant difference. Therefore, ultimately, if you shoot at a lower ISO than the native ISO, the highlight side's dynamic range decreases, so clipping can occur more quickly, and eventually details are lost. Let's zoom in on the light part. Now, if we look here at ISO 800, which means it was shot with the native setting, you can see there is still some detail. However, when you go to 200, almost all of the highlights are clipped. So, the details disappear, right? Therefore, shooting at a lower ISO than the native ISO can easily cause highlights to be lost, creating this disadvantage. Of course, it's not just disadvantages. If we look at the noise on the shadow side and zoom in, looking at the noise on the shadow side...

When comparing ISO 200, the noise on the shadow side decreases compared to ISO 200. Due to YouTube compression, it may not be clearly visible, but there is a significant difference when looking at the original. So, if you look at the chart again, you can understand that as the ISO decreases, the dynamic range on the highlight side decreases but increases downwards, towards the black side. So, at ISO 800, it is 9, and at ISO 200, it becomes 11, increasing downwards. In conclusion, reducing the ISO does not change the sensor's entire dynamic range, but only shifts downwards like this. Do you understand? Now, let's see what was shot outdoors. Just like before, I exposed it to a gray card, starting from the native ISO 800, then lowering it to ISO 400, 200, like this. So, even though the exposure is all the same.

Highlight on the right side. If you look at the part, there's a big difference. So, ISO 400, ISO 200, it just disappears like this, right? So, as the ISO decreases, you can see that the highlights disappear faster. So now, if we summarize, when you use an ISO lower than the native ISO, the dynamic range on the highlight side decreases, so the probability of clipping increases. Therefore, as we confirmed earlier, when we think about whether we should lower the ISO in a bright environment, what is the best way? Using an appropriate ND filter to maintain the native ISO allows us to maintain the dynamic range ratio, so we can see that it is the best method. Does that mean we should never use a low ISO? Of course not. If there are no parts that are definitely clipped even when the ISO is lowered,

So, since the overall dynamic range remains the same. As I mentioned earlier, it just shifts downwards. So, even if there are no parts that become unpleasant to watch due to clipping, there won't be much to lose by shooting at a lower level. However, when you actually shoot in the field and lower the ISO, the highlights really fly away. So, it would be good to remember that you need to pay a lot of attention to this. I hope this information is helpful. I will see you again in the next video.

네이티브 ISO 보다 낮게 촬영하면???

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