I've been reading about PD 170 owners complaining that their lenses have become slightly "askew" at the rear, causing focus distortion. I'd like to know if using a matte box (in particular, a Chroszeil 4 X 4) without the rods will put undue strain on the front of the lens causing the rear of the lens to pull away from the camera body.

I think the fact that you are asking, answers the question.

The lens is largely plastic and even if it were all metal, if you hang a large weight on the front, yes, you can distort the lens. Probably permanently (in the case of plastic) if you leave the load on it.

Thanks for your prompt reply. So then, if, at some time in the future I want to use filters with the matte box, I should get the rods?

I wouldn't put the matte box on there if it weighs more than a few ounces without the rods.

The other consideration is what happens if you bumpt the matte box when you don't have rods installed. The force applied to the lens and lens mount is increased because of the longer lever arm represented by the lens and matte box.

If you notice, the film-camera folks are very careful of their lens setups and they, for the most part, have all-metal lens bodies.

Props for this thread, convinced me even more to add the Century Optics Mattebox onto my wishlist, even tho its really expensive over here (around $800 !).