And what kind of exposures and iso are you using?
ISO100
Exposure 1/125…1/250
Aperture 4…8 - depending on first test. I making series of test shots with all aperture steps of my lens. Then select best results and use only this setting of aperture. For my lenses best result from 4 till 8 aperture steps.
I suppose a tripod is neccessary in absolute darkness, right?
No, I don’t use tripod.
Any idea about the temperature of the diffuser glass?
Don’t understand whats you about.