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I've got the Astronomik LRGB set as well, but find that each channel still focuses at a different point, even though they claim to be parfocal.
I believe it's due to the atmospheric dispertion, and the different wavelengths are being scattered by different amounts and so they'll focus at different points.
It appears to be more noticable at long focal lengths for planetary imaging, perhaps less noticeable at shorter focal lengths for deep-space/wide-field imaging.
I always [have to] refocus between each colour channel. Only a very slight amount, but it's definitely noticeable.
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