Now I know a bit about lenses, but this kinda smelt funny to me and I never
encountered any plausible explanation until I came across the links below.

Which makes me wonder if the 'digital lenses' photographers are  buying are
indeed telecentric and producing collimated light at the back end, or
whether they're just a scam by the camera companies selling ordinary lenses
and obfuscating things with a fine sounding term. (as many of us old buggers
believe)

For a start it seems that telecentric lenses are considerably bigger than
normal lenses, with a lot more glass - and I mean BIGGER  (the cited
example below would suggest that the aperture needs to be significantly
larger than the object or image height!)

Secondly, the disadvantages of telecentric lenses - has anyone using a
'digital lens' noticed that Aunty Mary looks the same height whether she's
5 feet away of 100?  Apparently a telecentric lens would have her the same
height..

Apparently it's relatively easy to check if digital lenses do as they
claim, and that's the bit I've been looking for! - all you need to do is
look through them .. if the apparent aperture looks to be a REALLY long way
away then you may be peering through a telecentric lens (or a wide angle
and confusing distant with small ;)

Not having any 'digital' lenses I can't check, but I'd be keen to hear any
ones observations

more on the matter:

"What is Telecentricity?

Telecentricity is a special property of certain multi-element lens designs
in which the chief rays for all points across the object or image are
collimated. For example, telecentricity occurs when the chief rays are
parallel to the optical axis, in object and/or image space. Another way of
describing telecentricity is to state that the entrance pupil and/or exit
pupil of the system is located at infinity"

"In a system with object space telecentricity, movement of the object
toward or away from the lens will not result in the image getting bigger or
smaller, " so there is no magnification based on distance from the lens /
subject (!)

http://en.wikipedia.org/wiki/Telecentric_lens

http://www.edmundoptics.com/technical-support/imaging/what-is-telecen...

of course there are other explanations

http://www.dpmag.com/buyers-guide/lenses.html?start=1

"Every manufacturer has its own terminology to describe the top-notch
optical qualities of the best glass and coatings of its lenses. These
terms, like SD, LD, ED and APO, describe low-dispersion characteristics."

that's what i'm talking about!  an apo lens is neither new, nor a glass or
coating.. it's as we all know, a lens shape

"Benefit: Low-dispersion glass and coatings minimize aberrations—the kinds
of color and sharpness problems that appear dramatically amplified when
images are enlarged. Internal coated elements help stop flare, and front
element coatings make the glass more scratch- and dust-resistant."

uh-huh.. ore 'nothing-new-here' too :/  In fact, where are the thorium
elements of yesteryear?

and on it goes, crapping on about various rubbish

sigh

k

The only two things that are somewhat unique in these lenses are:

1- they have extra light baffling and flocking on the rear section to avoid any
possibility of light reflected off the digital sensor bouncing back to said sensor.
2- they have extra coating in the internal and back elements to stop any
possibility of flare caused by light reflected back from the sensor.

Digital camera sensors are highly reflective, unlike film was.  If care is not
taken in the making of the lenses, there can be introduced flare and/or
reflections affecting the sensor and lenses from the light bounced back from the
sensor surface.

And that is just about all there is on "digital" lenses.  The rest is pure,
unadulterated marketing bullshit reinvented to make it sound like "science".
Just like most "climate change" arguments, really...