Aspheric lenses / elements - REALLY ?

[semilog]

Likewise with my old Canon FD 55mm F1.2 aspherical. Much, much better than the non-aspherical version.

Jim B.

Even Erwin Puts acknowledges that the FD 1.2 shows that Leica should have adopted aspherical elements (especially in the Noctilux) sooner than they actually did. That FD was *way* ahead if its time.

 

[semilog]

Yes, there are good and bad lenses, but Leica non-ASPH still qualify as good for any application I can think of.

Ask yourself, then, why the 50/1.4 ASPH is head and shoulders above *any* comparable lens ever made by any other manufacturer. That lens, and the new Noctilux 0.95, are by all accounts peerless.

Aspherical elements are of course just another tool in the optical bag — but an important tool, like low-dispersion glass. They can solve design problems that are not easily solved in any other way.

 

[ampguy]

wow, what a bunch of great explanations. No wonder my Lumix FZ3 with Leica Aspherical zoom lens cost so much 😉

 

[HenningW]

Tele lenses need less elements, so ASPH is not as important. However, APO glass is more important to correct for chromatic aberrations. Adding complexity, as well.

Both 50 Lux and 90 cron ASPH have APO elements.

Roland.

There is no such thing as 'APO glass' or 'APO elements'. Apochromatic correction refers to the system as a whole, meaning that a lens will focus three colours at the same plane (for a specific focussing distance).

The number of elements does not dictate whether a lens can benefit from aspheric elements. Aspheric elements are more useful, generally, in lenses with wide apertures and wider angles of view where the elements have stronger curvature, but in the end residual spherical aberration determines whether aspheric elements are useful.

Henning

 

[Gabriel M.A.]

Just like "sugar free", "asph" doesn't mean "better". Like everything, if well-applied or understood, aspherical elements can both improve image rendering efficiency (if you can call it that) and reduce costs.

In the early days, aspherical elements had to be ground my hand by very very very very skilled workers, at a high reject rate, which is why the early Noctiluxes (Noctilae? Noctili??) were so effin' expensive. Now, most manufacturers use a "mold" process. The catchiness of "asph" to mean "better" and "expensive" still lives on in this second- second- second-hand a-friend-of-mine-told-me-that-a-friend-of-his intertubes cross-posting misquoting era. 😀

 

[Roger Hicks]

Ask yourself, then, why the 50/1.4 ASPH is head and shoulders above *any* comparable lens ever made by any other manufacturer. That lens, and the new Noctilux 0.95, are by all accounts peerless.

Well, depending on your criteria for "head and shoulders above" and "comparable". That was my point about "the right application".

Sorry for the delayed reply; I'd not checked the thread for, well, yes, about 3 weeks.

Cheers,

R.

 

[xwhatsit]

Optical engineers dreamed of aspherics decades before the ability to manufacture them was available. And the first was made in 1955, the Elgeet 12mm f/1.2 Cine Navitar Wide.

Actually, some of the oldest lenses around are aspheric. The rock crystal Visby lenses, built by some unknown Vikings 1000 years ago in Gotland, used aspheric surfaces, and according to the linked Wikipedia article, "They are so well produced that even computer optimisation has not been able to improve their performance". 😕

 

[KenR]

Does this help other than at the widest apertures?

 

[semilog]

I think we generally agree, Roger. It *always* comes down to what one's photographic goals are, and how to best use the tools at hand.

 

[Roger Hicks]

Does this help other than at the widest apertures?

The advantage diminishes with aperture, so a lot depends on (a) what you mean by 'the widest apertures' and (b) how much difference you're looking for. By f/5.6, differences between most good lenses of 35mm and above (for 24x36mm) are trivial. At wider apertures, yes, there should be a difference.

Also, usually, fewer surfaces = more contrast, so using the above rule of thumb that 1 aspheric suface = 2 cylindrical surfaces (for correction) there's an advantage there too.

Cheers,

R.

 

[Sonnar Brian]

Typically Low Dispersion Glass has been used in most modern Apochromats. The term applies to the lens as a whole, but since the 1970s many manufacturers refer to the Low Dispersion elements as "APO Elements". Perhaps marketing, but the LD elements are usually highlighted when showing off the optical block diagram.

My Pentax 85/4.5 uses Calcium Fluorite for all of the elements.

 

[ferider]

There is no such thing as 'APO glass' or 'APO elements'.

Yes there is, Henning. By Dr. Z\"ugge, Zeiss (http://www.dantestella.com/zeiss/achromat.html):

Hence, the next step required by the optical designer is to also correct the secondary spectrum in these cases. The result is the apochromat. The only aid available for this purpose is the use of very special optical materials: long-crown glass (fluor crown glass and calcium fluoride) and special short flint glass. These can therefore be justifiably called extreme types of glass, since they not only display an unusual behavior with regard to the relative partial dispersion, but are also extremely expensive and difficult to process.

See also Brian's post.