Hello everyone,
I find the original prototype test:
http://www.astro-foren.de/showthread.php?t=9585
I not understand German (and have trouble with Eanglish...
)
but, what I understand is the triplet is ok on Red, but just 1/3 wave
on the green, where the eye is most sensitive.
Now this is a triplet, and I can't see any small shim to separate the elements to a proper gap in a air spaced design. Which mean, I guess
is the gap is made with plastic rings. So my theory is, the manufacturer
not spending the money, time to fine tune each assembly for best spherical
aberration at green. It's about luck what you get. I had a 5" achro before,
and play with it a lot, try to get the best correction with different gaps.
Well, unfortunately one of the surface had a zone, at 70% dia. Actually it was a different radius from there. It was impossible to optimize.
With the triplet it would be daunting task without proper gear to get the
right settings between the elements.
But after all it's still a good deal, especially for wide field photo.