Thanks for your comments guys, the other reason I used two cameras was that I was able to expose through one DSLR while taking darks with the other then swapping their roles and continue to expose
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Hi Andrew,
2 chips won't have the same noise pattern so this may not be working too well. The dark noise will only be the same for the same chip and will be different for the 2nd chip. Have a look at the darks from each camera and you should see they are not the same.
Greg.