History of the ED/APO refractor?

With the aparent history being made by the Orion ED80 as a cheap but
effective near-apo refractor, I've been very curious about the history
of ED and APO refractors but I can hardly find anything on Google or
Yahoo. Just general stuff about the refractor and reflector (jeesh,
not even a metion of Schmidt or Ritchey-Chretien?).

Who first figured out these methods to reduce chromatic abberation?
What different designs are used (I've seen references to triplets,
air-spaced doublets, oil-spaced triplets, etc.)? What materials are
used? Special glass/fluorite combinations? Special coatings to realign
the different colours?

Any info appreciated,

Drew

Who first figured out these methods to reduce chromatic abberation?
What different designs are used (I've seen references to triplets,
air-spaced doublets, oil-spaced triplets, etc.)? What materials are
used? Special glass/fluorite combinations? Special coatings to realign

Fully color corrected lenses have been around for a long time, at least since
the 1960s. It is no special trick to design one, neither does it require fancy
computer optimization.

Materials that can correct color are different types of ED glass and CaF2
combined with various types of short flint or even crown glasses.

Special coatings do absolutely nothing to change the color correction of a
lens. All they do is to reduce the air to glass light loss which amounts to
approx 3% per surface for high grade ED/Fluorite and 5% for crown/flint
glasses. Hard coated oxide type multi-coatings can also help protect the
fragile ED/Fluorite materials from abrasion if they are applied with an ion
beam machine.

Roland Christen

"Drew32" wrote in message
...
With the aparent history being made by the Orion ED80 as a cheap but
effective near-apo refractor, I've been very curious about the history
of ED and APO refractors but I can hardly find anything on Google or
Yahoo. Just general stuff about the refractor and reflector (jeesh,
not even a metion of Schmidt or Ritchey-Chretien?).

Who first figured out these methods to reduce chromatic abberation?
What different designs are used (I've seen references to triplets,
air-spaced doublets, oil-spaced triplets, etc.)? What materials are
used? Special glass/fluorite combinations? Special coatings to realign
the different colours?

Any info appreciated,
The coatings, have nothing really to do with it.
The concept of the achromat, was worked out within a few years of light
refraction being partially understood. The basic idea (that you use one
refraction to split the spectrum, and another to put it back together), was
demonstrated by Newton, with his original 'prism' demonstration. The key
'breakthrough', was the idea of using glasses with different degrees of
dispersion, so that you could still have useful optical 'work' being done,
yet put the light pretty closely together again. Using a simple pair of
glasses (traditionally crown/flint), a fairly good result could be obtained,
but the light would only be properly re-assembled at two frequencies. Many
people then went on to try more complex glass combinations, and to
reconstruct the light at multiple colours. The idea of the 'APO', was
developed for microscope lenses, not telescopes, where it was realised that
the light could be accurately reconstructed at three frequencies, and the
combination could also be corrected for spherical aberrations at two of
these frequencies. Within only a few years flourite was tried as one of the
glasses (by Carl Zeiss), and the 'flourite apochromat' was born.
The term 'APO', has been 'diluted' since, with scopes that only display a
lack of chromatic aberrations at three frequencies, being called in some
cases "APO's", despite failing to meet the full definition of the term.
You'd have probably had better luck, looking for 'apochromat', rather than
'APO'.
http://www.microscopy-uk.org.uk/mag/...jachromat.html
The coatings, reduce the losses at the surfaces, but don't affect the actual
refraction.

Best Wishes

Maybe this is what you are looking for:
http://alice.as.arizona.edu/~rogerc/

Maybe this is what you are looking for:
http://alice.as.arizona.edu/~rogerc/

A great page. Thanks for point this out.

jon

Drew32 wrote in message . ..
With the aparent history being made by the Orion ED80 as a cheap but
effective near-apo refractor, I've been very curious about the history
of ED and APO refractors but I can hardly find anything on Google or
Yahoo. Just general stuff about the refractor and reflector (jeesh,
not even a metion of Schmidt or Ritchey-Chretien?).

Who first figured out these methods to reduce chromatic abberation?
What different designs are used (I've seen references to triplets,
air-spaced doublets, oil-spaced triplets, etc.)? What materials are
used? Special glass/fluorite combinations? Special coatings to realign
the different colours?

Any info appreciated,

Drew

I just came upon this while searching for info on flourite and found
it interesting.

http://voltaire.csun.edu/tmb/tmb1.html

Joe