Hi All,

I'm researching the idea of going for Innovation Frontier's ONAG-SC (sensor size is right for my Atik383L+ Mono). I emailed Gaston Baudat asking out of all the product options which would best suit my imaging train:
Atik 383L+ Mono > EFW2 (loaded with Astrodon 36mm 5nm Ha OIII and SII + LRGB) > Stellarvue 102 FF/FR > Moonlite focuser > Explore Scientific 102mm Carbon Fiber APO

My guide scope is the Orian MMAG.

Gaston responded by pointing me at his spreadsheet back focus calculator and suggesting I go with a guide scope with large sensor size.
I downloaded the spreadsheet and spent a fair bit of time reading Innovation Frontier’s website to understand what all the acronyms mean and how it all comes together and eventually worked out what figures to plug in where on the spreadsheet.

That said, according to my measurements I still don't have enough scope port back focus.

I tried googling what the back focus for my scope is but most folks when asking in forums get "try spacers until it comes into focus," which didn't really help (I was looking for something like "the back focus for an ES102CF is xxx or calculated by xxx")

I measured the distance I wind the Moonlite focuser out to achieve focus in my current config and get 65mm, that's apparently 58.5 or so mm short:

Clearly, something is missing. Any thoughts?