Not sure why I haven't tried this before, but I've just checked out my Baader Mark IVs in the Tak without any barlow or GPC element and they do come to focus no problem. For full disclosure I'm using a FT2025-BCR focuser and an A20-302 adaptor, can check exactly what length that is. Also, a T2 BBHS diagonal with the Binoviewer connected directly via a T2 quick changer ring to keep the light path short. Lovely views of the DC, with 25mm 50 degree eyepieces the field of view felt plenty