I am on the wait list for a Takahashi e-130D. I ordered here in Japan from a company called K-ASTEC and it included tube rings, dovetail, and all the adapters to attach a camera, oag, EFW (see image below). While I wait I'm trying to get all of the accessories (i.e. Filters) ready for when the scope finally arrives.
I have, however, ran into some issues when trying to figure out backspacing from the corrector. In the white-papers Takahashi states that the backspacing should be 56.2mm from the corrector. Of course, you have to consider your filter thickness when calculating back spacing. The adapter that ships with the telescope allows me to rotate the camera, EFW, OAG, without moving the focuser itself. However, K-ASTEC, has made the adapter to have 57.2mm -0.2mm/+0.8mm of backspacing. That means they assume that you will be using filters with 3mm of thickness.
I'd like to avoid Chroma/Astrodon at the moment and I don't really want to go with Baader (bad experiences with them in the past). I've considered Antlia 50mm (3mm thick) filters, but their QC is not the best and I got burned by them on my last purchase.
I really want to go with Astronomik filters, especially their MaxFR filters for fast optics. But the filters are 1.1mm thick, as are all Astronomik filters.
How critical is this backspacing for these scopes? I know most correctors have a tolerance of -1mm/+1mm, but I want to make sure before I actually make a purchase.