Rolling your own field reducer?

[Macavity]

I am currently assembling a photographic (video!) "back end" for my skywatcher MAK150. The standard T2 diagonal holder threads directly to a filter wheel, then onwards to a Borg helical focusser. But I am now wondering quite WHERE to insert a field reducer... In the optical sense.

Experiments suggest, even a humble ATIK (simple achromat?) 0.5X (f=80mm) reducer works well in a variety of places. The video chip is but 1/2", so Fields do not seem to be unduly non-flat, even right down to F4/5. But physically, the reducer might more conveniently reside on the end of the video camera, than the end of the scope? A shorter focal length would be better for a faster system and wider, un-vignetted, field perhaps...

Just wondering if anyone has attempted to MAKE a custom field reducer. Commercial, f~40mm, bi-convex, achromats seem to be readily available in 1 inch (25.4mm) diameter for £30-50? But, where might one obtain standard 1.25" diameter threaded cells and lens retaining rings? Cannibalising (supplier default) eyepieces, might be a possible solution, I guess...

P.S. I sense I'm not looking for conventional wide chip, flat-field, perfection, just a brighter image, with wider fields, for DSO's...