20 19-06-06

? Hu Yiming

The concept of "ISO invariance" has been very popular in the technical circle in the past two years, but many ordinary photographers have never heard of it. So, what is ISO invariance?

? Increasing the ISO value of the sensor is equivalent to changing the big bucket into a small bucket, and the picture will be brighter, but the dynamic range will be significantly reduced.

? The above picture shows the relationship between ISO value and tolerance of Freescale IQ3 100 digital back and Pentax 645Z medium format camera. Other contemporary cameras behave very similarly.

? The following picture shows the same night scene taken in ISO 1250 for 30 seconds. We can see that the light is seriously overexposed (even though I have pulled the highlight to-100), the brightness of the whole scene is roughly appropriate:

? When we exposed the ISO 100, 3.7 30-second lens in the later stage, the highlights darkened, and we can see that the overall brightness is similar to the above picture (ISO 1250, 30 seconds), but the details under the light still remain.

? For a more convenient and intuitive contrast effect, I put two screenshots of 100% side by side (the one on the left is ISO 100 and the one on the right is ISO 1250). We can see that the noise on the left is still a little more than that on the right (but the difference is very small). Therefore, 5D Mark IV does not have true ISO invariance, but only approximate ISO invariance. However, according to the test of DPReview website, when the ISO value is above 400, 5D Mark IV begins to show true ISO invariance.

However, the dynamic range on the left is much larger, and the highlights are basically preserved.

The starry sky in this photo is ISO400, and then several files are highlighted in the back. The picture is very clean and sharp. In August, I was at a personal film exhibition in Beijing, and this work will print a high-definition light box nearly 2 meters in size.

? Below is the starry sky with 600 million pixels! This should be a record. At present, it is planned to print high-precision light boxes with a width of10m and a height of 6m. The degree of shock can be imagined, not to mention the difficulty of shooting itself. Just making and installing this huge work is a big project and challenge. We are still discussing the scheme and details with professional companies, hoping to achieve it.

Ok, let's call it a day. I hope it will help everyone, thank you!