Thread: Zwo 1600mm and sigma 135mm lens
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Old 10-05-2022, 02:52 PM
AdamJL
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Cool, thanks JA.

It could also be the thickness of the filter. Say your filter is 3mm (just a random number).. that means your backfocus is impacted by 1mm (usually 1/3 is the rule).

What filters are you using, Graham?
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