Thanks, at least Agena Astro seems to have relevant information on field stops, I'll keep that in mind.
Yes Dave, 13mm is certainly on the high side, especially on TV85, which is 600 mm. On my NP101 at 540mm I rarely use more than 17mm, then there has to be VERY little disturbance at least.
Orion (Telescope.com) lists field stops for their eyepieces and Explore Scientific does too. They are with the individual eyepieces.