I am using a set of amazing set of combined ND and Circular polarising filters from SRP ND 8 & 16, had to get mine shipped from the states, but well worth the money.
They seem to keep the ISO at the desired level.
Review here
https://www.youtube.com/watch?v=zOetyiSC7kU
Also when not using Crystal Sky to monitor I use the IPad mini 4 with Osmo got a great holder adaptor from Dirty J designs again in the states. Works really well too.
You will need spacer if you want to use sun shade to prevent the gimbal hitting it when it does 360/180
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