Field Flattener / Image Train Assistance Please

[Wookie (Ryan)]

Hi All,

I was wondering if I could have some assistance with my optical train.

I have both an ED80 and ED120 and would like to use a William Optics AFR-IV Adjustable Flattener / 0.8x Reducer.

I have an SBIG ST4000xcm and AO-8 unit.

The ST4k is said to have 23mm optical path
The AO-8 is said to have 51.3mm optical path

The William Optics AFR-IV is adjustable between 66-86mm.

Am I right in thinking I can simply connect CCD-AO8-FF-SCOPE
and set the AFR-IV to approx. 74.3mm setting with no spacers?

Any assistance/confirmation appreciated.

Thanks