Kevin_A is the -25 gain for both 2600mc pro and 2600mc duo or just the duo?
By the way, "negative gain" is sort of a misnomer.
With ZWO and QHYCCD, "gain" is stated as a logatithm scale. ZWO uses log base 10, while QHY uses the more scienticic and mathematical log base e.
"Gain" is literally the gain of a linear DC amplifier that is placed between the sensor output and A/D converter input.
With log based 10 gain (measured as deciBels, where a Bel is named after Alexander Graham Bell) , it is defined as
log gain (in dB) = 20 x log10 (output voltage/ input voltage).
So, a linear gain of 1 (i.e., no amplification) will come out as 0 (zero) dB. A linear gain of 10 will give a log gain of 20 dB.
Now, ZWO further scales ther gain numbers by 0.1 dB gain per 1 unit of ZWO gain. I.e., log gain of 20 dB corresponds to a "gain" of 200 in ZWO's scale.
This gets us back to "negative" gain. Notice that a linear scale of 2 corresponds to a log scale of 6.02 dB or ZWO gain of 60.2.
A "gain of -25" is simply a "gain of -2.5 dB" and in turn is simply a linear gain of around 0.75. I.e., the sensor voltage is attenuated by a factor of 0.75 before it is given to the A/D converter to convert to ADU units.
Chen
