When regulating flat field mask lighting for astronomical CCD cameras, fluctuation-free and extremely short exposure times in the (sub) millisecond range are required. Unfortunately, conventional dimmers cannot be used for this purpose, only a so-called PWM with a switch-on and switch-off frequency of 25 kHz or even faster!
Theoretically, it would be sufficient to reduce the voltage using an ohmic resistor if we wanted to dim incandescent lamps instead of LEDs. However, we absolutely need a dimmer with pulse width modulation, which regulates the time interval during which the full voltage is applied: The regulating instrument is switched on and off in quick succession.
Depending on the on/off frequency, various accessories can be operated: for a heating sleeve, switching on and off once per second, or even less frequently, would be sufficient because its inertia is very high. In everyday use for LED lights dimmed in this way (e.g. living room lighting), around a hundred cycles per second are sufficient, because the human eye can hardly perceive fluctuations above 25 Hz. For flat field masks, which were built for astronomical CCD cameras, at least 25kHz are required to guarantee an evenly illuminated surface even in a short lighting time.
- Input: RCA and 5.5/2.1 mm (note polarity: centre positive)
- Output: RCA and 5.5/2.1 mm (note polarity: centre positive)
- Frequency: over 30 kHz, typically 31-36 kHz (guaranteed to switch on and off more than 30,000 times per second)
