I find I get marginal additional cooling on my QHY22 with 100% vs 75% cooling. Maybe 5C lower if it is a warm night, and 2C lower on a cold night. So I typically run my cooler at 75% as an optimum. On 5C nights here in Tassie, I typically cool the QHY22 to between -35C and -40C. Dark current is then virtually non-existent.
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