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Hmm. I noticed from the day I started doing RGB imaging that the red channel was by far the easiest to focus, and had the greatest focus tolerance when compared to green and blue (green has less tolerance, and blue has the least tolerance).
I measure the tolerance by shifting the focus position either side of best focus until the image starts to break down. I can measure this shift in 0.02mm steps.
I'd assumed (perhaps wrongly) that the focus tolerance was some function of the wavelength, and so green had 533/633 as much, i.e. 0.84 and blue was 450/633 or 0.71.
That seemed to fit empirically with what I see, but maybe there's some other explanation for it? Fingers crossed for clear skies at lostock, you can see this first hand.
Bird
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