Quote:

---

Explains exactly what I have seen with some of the ED
doublets out there. They tend to not handle the red well
so that they can be well corrected in the blue/violet. My
Orion 80ED fell out in the red, and worked better with a
prism diagonal.
My 80mm triplet and 127mm triplet are well
corrected in the red, but fall out a bit in the blue/violet.
I tried a prism diagonal in my 80mm triplet, and the color
correction got noticeably worse on a white fencepost with
the prism. Just a bare trace of violet at 160X with a
mirror diagonal, that went to clearly evident blue/violet
with the prism and same eyepiece. No magic, just a shift
back to a standard correction on the ED scopes that seem
so well corrected in the blue/violet. Too many fail to
understand the effect of poorer red correction on the view
of certain double stars (such as Izar) and the planets.
Shifting the color correction does seem to sell scopes
though.

As to the Chromacor, yes, definite, real improvement. I
still remember the experience I had testing you first
prototype on my 120mm and 150mm achromats. The improvement
in planetary detail was immediately evident. The Chromacor
provided a real improvement in color correction, I can
vouch for that from experience.


Tom

---

Hi Tom.
Your observations seem to support what I've suggested.
I certainly wouldn't imply that using a prism will improve the correction of an ED triplet (or doublet) which has already been optimized for visual observing.

The marketplace is now flooding with ED doublets and many (most) of them appear to display the red defocus you and others have mentioned. If a relatively inexpensive prism-type diagonal can neatly solve that issue, I think there's a great potential for owners of these scopes to realize improved image quality for a small additional investment.

Post Extras