shropshirelad63
Well-known member
I was just wondering what made the old apo 77 a great scope as it doesnt have the ed glass? is it worth buying one 2nd hand or how does it compare with a modern but cheaper scope with ed?
I have had the 77 APO with the 32 mm & 20-60mm eyepieces for many years now & have always found it a superlative instrument producing bright contrasty images without a trace of CA. In the unlikely event that I should ever to replace it, it would only be for the extra reach afforded by a really big scope, 90-100mm or more.
Perhaps a silly question; but is not "APO" just Leicas own designation for what other manufacturers call ED, HD, XD, etc..??
Basically It's just some sort of indication that the optics in question counteract color fringing / chromatic aberration. At least that's what I thought...
'APO' is short for apochromat (as opposed to achromat). This is because an apochromatic objective is used in the four scope models with the 'APO' designation. As far as I'm aware - and according to the Leica brochure of the time - 'ED'/fluorite glass was also used in the APO62/77 objectives as it is in the newer 65/82models. I have an 'old' APO62 which absolutely amazes me for its effective control of chromatic aberration; it still punches way above its weight against more recent models from other big brands.
Yeah, but that's as far as I know It's the same thing: APO/Apochromat = ED/Extra low Dispersion optics.
https://en.wikipedia.org/wiki/Apochromat
This page seems to support it as well: http://www.overgaard.dk/leica_definitions.html
Etienne, forgive my pedantry but, as I read them, neither of these sources supports your statement that these terms have the same meaning. 'ED', 'HD' etc refers to the composition of the glass from which the lenses are made. Apochromat describes the construction of the lens itself. The Leica scopes used cemented triplets in the objectives as I recall. This means that the lens is actually a composite of three separate lenses cemented together, one or more of which is made from flourite (ie 'ED'/'HD") glass. This serves to bring the so-called 'secondary spectrum' to a common focus resulting in a sharper, more accurate image with reduced chromatic aberration.