BSE Z imaging

[Probeman]

Can someone explain to me what exactly is the difference between the VS1 brightness and VS1 offset adjustments for the roller controls on the Sx100?

They both behave as brightness controls, but I'm sure I'm missing something.
john

[Mike Jercinovic]

As I recall, offset adjusts the input level of the video amplifier, and brightness adjusts the output level.  This is probably in the user guide docs somewhere (?)

[Probeman]

As I recall, offset adjusts the input level of the video amplifier, and brightness adjusts the output level.  This is probably in the user guide docs somewhere (?)

Hi Mike,
Ok, so what does that mean in practice?  That is, which one should be adjusted when?  What's your method for BSE Z image "brightness" adjustment?
john

[Mike Jercinovic]

The way I always thought about it (whether or not it's correct is another question), is that the offset subtracts (or adds) a dc level to the signal such that if you switch to high current, you adjust the offset to cut out a lot of the input signal that is just squeezing the contrast you want to see into the upper end of the range.  Then adjust brightness and contrast to effectively stretch (linear amplification) the visible signal to cover the dynamic range of the display.

[John Donovan]

The way I always thought about it (whether or not it's correct is another question), is that the offset subtracts (or adds) a dc level to the signal such that if you switch to high current, you adjust the offset to cut out a lot of the input signal that is just squeezing the contrast you want to see into the upper end of the range.  Then adjust brightness and contrast to effectively stretch (linear amplification) the visible signal to cover the dynamic range of the display.

Interesting.  So the offset adjustment is similar to a high pass (gain) filter?
john

[chenderson]

As I recall, offset adjusts the input level of the video amplifier, and brightness adjusts the output level.  This is probably in the user guide docs somewhere (?)

Yes.  Mike is correct.  See Sx100_Control_3.doc, Section 1-5-3-3-1.

In everyday use, keep the 'VS1 bright' around 600 (610 will usually come up after an automatic video "Adjust") and use the 'VS1 offset' and 'VS1 contrast' rollers to adjust the image to your liking.  If you can't scale the image brightness with offset and contrast, then go to the 'VS1 bright' adjustment (or adjust detector parameters such as gain, PM voltage, etc.).