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I played a bit more with original Opteka and Rokinon FF doublet in Opteka assembly..
The difference is obvious... (first attached image).
Also, the experiment with Meade 2x Barlow indicated the barlow is not well corrected for CA (second image).
In the process, I rediscovered the old issue - problem with helical thread (focus mechanism). Due to a lots of play, the whole front end can be tilted for +/- 0.3mm out of axis, and the lens would go out of colimation.
Earlier I sorted this out with 3 springs, that force the front end towards the back, thus removing the play. I will have to modify the bracket a bit to fit those springs (at least 2 of them)...
Saga continues...
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