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Gents can i just raise the issue of "focusing" a filter that does not pass visual light. Astronomik comment on this in their literature, pointing out the 642mm IR Pass facilitates focusing as it has a component of visible spectrum. Since they claim these filters are parafocal one might assume if you can focus one that passes visible light then you might assume the 742 or 807 are also in focus. I would like to know how people shooting with the deep ir pass filters achieve focus, do you pick a bright object for focus then move to your target, assuming parafocus will be ok, or are test subs required to check?
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