Carl1024 Loc: Kaneohe, HI 96744

what does it mean?
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Ysarex Loc: St. Louis

Apochromatic.

A lens that focuses all color wavelengths to the same plane.
Here's a recreation of a famous APO lens: https://www.bhphotovideo.com/c/product/1526146-REG/voigtlander_apo_lanthar50_apo_lanthar_50mm_f_2_aspherical.html

Note the three color stripes R, G, B on the lens.

rmalarz Loc: Tempe, Arizona

"APO" stands for "Army Post Office". It is normally followed by a number which serves as a code for a particular military unit or installation. ... Military addresses must show the grade, full name with middle name or initial, and PSC number, unit number, or ship name.
--Bob

Don W-37 Loc: Bangkok, Thailand

Simple: APO = Army Post Office!
😁😁😁

ecobin Loc: Paoli, PA

APO stands for After Pandemic Opportunity

User ID

Army Post Office.

Juy Loc: Delaware

LOL

D-5008 Loc: Raleigh, North Carolina

camerapapi Loc: Miami, Fl.

Everybody is wrong on this one. The true meaning of APO is "Advanced Photographic Opportunities."

TRSquared Loc: South Carolina

The term apochromatic is applied to an optic that brings 3 different wavelengths of light (colors) to the same focus as opposed to only 2 wavelengths for achromatic optics. With this design approach, the focus vs. wavelength plot can bed made nearly flat across the visible range of colors, thereby reducing chromatic aberration to a minimum. This result is something that is not possible with an achromatic design.

PhotogHobbyist Loc: Bradford, PA

Requirements in military addresses are flexible, depending on the service person's assignment. My son and daughter in law have been active duty for over 20 years and their addresses DO NOT require full name, grade (or rank) or any service number or other identifying number.

rmalarz Loc: Tempe, Arizona

My source was https://www.defense.gov/

YMMV
--Bob

JBRIII

The best refractor telescopes are now APOs using 3 lens as the objective and new low dispersion glass for at least one of these. As stated allows much better color correction and shorter focal lengths. I recently saw a 180 mm refractor advertized, for old style objective it would be F12 or even F15, that's a tube of 84 to 105 inches. Unlike a reflector eyepiece other end so image the tripod needed. To get a feeling go see the 24" at Lowell observatory. The largest operational refractor ever made was 40" due at least partially to mount flexture from what I have read. Canon uses these new glasses in at least some lenses.

Abbreviations are becoming a pain, one is suppose to do this, "use first time (UFT)" , but many, maybe most now just spell out the phrase once and then use the abbreviation after that, sometimes paragraphs or pages latter. Journals can have a list of common abbreviations which can be used, but are shown at start of journal.

Government is great at using them so much you often don't realize what they really mean. All scientists were SYs. No y in scientist, at least in English, stood for "Scientist Year", our projects were called a CRIS, which stood for the system defining projects, Current Research Information System". So we were time units performing a system??

SalvageDiver Loc: Huntington Beach CA

TRSquared Loc: South Carolina

There are even APO optics with more than 3 lenses such as some of the TeleVue telescopes (such as the NP101) which are of the Petzval design. Joseph Petzval invented the design around 1840 after he learned of the problems of long exposures with the slow photo materials of the day. So ironically one of the earliest lens designs, the Petzval, is now used by TeleVue to produce several of the finest scopes in the world. TeleVue's design has 4 elements arranged in 2 groups with considerable separation between the groups. The second group is at the back of the telescope close to the eyepiece or camera.