Generally these are all marketing terms.
Not quite the same thing."apochromatic", which means much the same thing as "achromatic",
No.technically, the terms refer to different levels of the same feature (achromat, apochromat, superachromat, in that order).
The terms "ED", "FL", "HD", etc., are also marketing terms generally relating to the specific proprietary type of optical glass used that has specific dispersion characteristics which that manufacturer has developed in order to provide as much chromatic aberration correction as possible.
HD: high definition. A pure marketing term. Can mean about anything. Meaningless.
That's what I have been saying.Although HD doesn't tell the buyer anything specific about the glass type used in a binocular or scope, ....
In practice, the labels ED, FL, HD, LD, XD and others such labels are ways that manufacturers signal to buyers that they are using some kind of exotic glass or fluorite (and perhaps other aspects of design) ...
-that might suggest to the original poster or others new to the sports optics scene reading this thread that ...
That's what I've been saying: mostly meaningless.-there is no way to rank HD, LD, ED, FL, XD etc according to which is superior based on the label alone----AP
... although we still haven't had anyone post a definitive description of the Leica HD Ultravids versus the non HD! ...
--AP
That's what I've been saying: mostly meaningless.
...Thank you for confirming my statements.
... From your description, I'd guess you aren't generally very aware of (i.e. bothered by) CA ...
--AP
You're correct that we agree on these points, but given the way they asked the question, I just wanted the original poster or others reading this thread to know that these labels _do_ indicate the use of special optical materials or other designs to significantly reduce chromatic aberration in comparison to similar models, and are in that sense not meaningless labels. Granted, the differences aren't as large as with scopes, but in my experience, the use of these materials in binoculars improves performance.
--AP