I used ND4 filter successfully for 200s long exposure of bright smartphone analog clock:
I placed ND4 filter over 5000lm led and light is still by far too bright for human eye.
I did smartphone photos through welding helmet safety glass before:
viewtopic.php?f=37&t=267999&p=1639428&h ... t#p1639428
Today I used HQ camera and "--focus" feature to bring 5000lm led in focus.
Then I placed welding helmet safety glass between camera and 5000lm led, and turned led on.
This is screenshot of camera preview with Field Of Merit display.
I am visible since safety glass does reflect.
I have no idea what ND? number welding safety glass has, must be a big number.
With reduced 200µs shutter time the 50 leds can be identified through safety glass:
Code: Select all
raspistill --focus -t 0 --shutter 200