[avandonk]

Andrew here is a pic of the modded 100ED. I cut 100mm off the main tube and then fitted an Astro Physics 2.7 inch focuser with an Astro Physics Focal Reducer (0.67) first slotted thing. Then an AP 2 inch adapter (second slotted thing) followed by a Borg rotator (allows rotation without losing focus) and two Borg filter boxes and then a Borg Canon T-ring. This gives me a versatile experimental platform for filter and multiple filter exposures. This setup only very slightly vignettes the full frame 5DH. The only things that actually vignette are the 48mm filters.
You can see how well the AP FR flattens the field by checking out the corners of the image. The focal reduction and field flattening is controlled by adjusting the distance between the sensor and the FR. Borg bits are really good for this.

Bert