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Sorry guys but I updated the article in post #1 with a final test that turned out interesting enough that I felt it worth the update. Basically the following is added:
Finally, the rectilinear distortion in the Modified Erfle is extremely low. When placed in a daytime spotter scope straight lines in the off-axis, even right up to the field stop, stayed straight. I then wondered how the true field of view (TFOV) might differ in this eyepiece compared to something like an Explore Scientific 24mm 68° or a Tele Vue 24mm Panoptic, both of which have a significant amount of rectilinear distortion. Having an Explore Scientific 24mm 68° on hand I compared it to the Burgess 24mm Modified Erfle and discovered that the TFOV of both the 61° Modified Erfle and the 68° Explore Scientific were almost exactly identical! So although the Modified Erfle visually shows a smaller AFOV, its TFOV is almost exactly the same as the wider Explore Scientific 68° with its added rectilinear distortion to maintain more controlled off-axis star points.
Also added comment about how the elements and groups of the Ultra Mono with Barlow is still on par with other planetary eyepieces like the XO. Your comments here on that I felt were important points to add. Thx!
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