Digital noise is not just the byproduct of a social media news feed. It’s also the byproduct of shooting pictures at a high ISO. Tanya Riseman gave a very good and thorough presentation about ISO at the December meeting of A Closer Focus. After her presentation the group discussed ways of mitigating noise and even embracing it as a form of grain from the film days. The best nugget of information cleared up the fallacy that raising ISO is raising the sensor’s sensitivity. The truth is raising ISO raises the sensor’s amplitude of the signal. In photography the signal is light and ISO is the sensor’s volume switch. In similar terms a radio signal containing music is amplified by the receiving radio with control of the volume switch. The radio doesn’t become more sensitive to the music, it just plays it louder with more distortion as the volume increases.
Due to time constraints, we couldn’t completely cover how to determine the amount of noise your particulate camera has at different ISO settings or how to determine the noise limit you are willing to accept in your pictures.
I recommend everyone read this article (lonelyspeck.com/how-to-find-the-best-iso-for-astrophotography-dynamic-range-and-noise) and go through the steps to determine the noise level for your camera. In summary, the steps to the testing is simple:
- Shoot in dark conditions: a dimly lit room or outdoors at night
- Shoot in RAW file format!
- Use (M) manual exposure mode
- Set “daylight” white balance (just so it doesn’t drift)
- Disable all forms of noise reduction (Long Exposure NR, High ISO NR)
- Shoot one exposure at each whole stop ISO (100, 200, 400, 800, etc.)
- Keep all other settings the same, change only ISO
- Match exposures in post processing and compare
Through my own testing I found that my Nikon D7000 operates at an acceptable ISO level of 3200. Of course this is subjective, someone else may decide the limit is 800 or even 6400. The point is, do your own testing and look at the pictures based on how you like to display them. The results will be different if you commonly print to 11×14 than if you only post to social media. Size and method of viewing matters a great deal when determining ISO acceptability thresholds.