'Digital lenses"

[karl shah-jenner]

Here and elsewhere I've heard reference to lenses being 'digital lenses' -
translation, the light exiting the rear of the lens is designed to hit the
sensor plane collimated or straight on.

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.

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, this 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-telecentricity/

karl

[David Dyer-Bennet]

On Wed, October 14, 2009 06:22, karl shah-jenner wrote:
> Here and elsewhere I've heard reference to lenses being 'digital lenses' -
> translation, the light exiting the rear of the lens is designed to hit the
> sensor plane collimated or straight on.

That, plus more attention to anti-reflection coating on the back of the lens.

I think I'd have noticed, and people would notice in photos, if the
distance to the subject didn't affect the image size.  In fact, I think
that must be some sort of error in the description.
--
David Dyer-Bennet, dd-b@...; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info

[Bob W8IMO]

I just received the November 2009 issue of Digital Photo, formerly PC Photo, and AKA dpmag.com.

Here is the link to what they say about digital lenses......

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

Bob

karl shah-jenner wrote:

Here and elsewhere I've heard reference to lenses being 'digital lenses' -
translation, the light exiting the rear of the lens is designed to hit the
sensor plane collimated or straight on.

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.

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, this 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-telecentricity/

karl



  

[karl shah-jenner]

Bob lenses"


: I just received the November 2009 issue of Digital Photo, formerly PC
: Photo, and AKA dpmag.com.
:
: Here is the link to what they say about digital lenses......
:
: 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?


"ASPHERICAL AND RECTILINEAR
Aspherical lenses offer several advantages. First, they reduce spherical
aberration as light passes through the lens, resulting in sharper images
and reducing linear distortion in wide-angle lenses. The use of aspherical
elements also allows lens designers to use fewer glass elements than they
otherwise could for a given lens, making smaller and lighter lens designs
possible. Rectilinear lens design makes wide angles appear more natural
(and less distorted) by keeping straight lines from curving quite so
noticeably." (..or at all in the case of some older lenses)

again - nothing special :(

k

[karl shah-jenner]

http://www.antiyawn.com/photography.html

interesting to see things from a customers perspective.. and he's not happy
at someones efforts at photography!

k

[David Dyer-Bennet]

On Wed, October 14, 2009 13:53, karl shah-jenner wrote:
> http://www.antiyawn.com/photography.html
>
> interesting to see things from a customers perspective.. and he's not
> happy
> at someones efforts at photography!

Interesting; thanks!

I wonder how much doing what the young man (who I largely agree with)
wanted would have ended up not making the mother happy?  Because one
important point is that the actual customer here was his mother, who he
says was happy.

I haven't done senior picture for highschool or in large volumes (I did a
number of college senior pictures as portrait sessions for friends back
when I was around that age); but the question of what you do when a kid
shows up with fairly serious stubble must be somewhat tough.  The amount
left by the skin treatment the professional used, and the amount showing
in the picture the guy took of himself later, suggests that it might have
been considerable.  And it sounds like he hadn't thought about it when he
showed up for the session.  Just showing the stubble as it was is likely
to upset parents, who are mostly the real customers, right?  It must be a
bit of an interesting balancing act in many ways.

--
David Dyer-Bennet, dd-b@...; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info

[herschel-9]

OMG... what a load of crap

As far as I know, "digital" lenses mostly are lower quality lenses with an image circle only big enough to cover the smaller chips.

h


David Dyer-Bennet wrote:

On Wed, October 14, 2009 06:22, karl shah-jenner wrote:
  

Here and elsewhere I've heard reference to lenses being 'digital lenses' -
translation, the light exiting the rear of the lens is designed to hit the
sensor plane collimated or straight on.
    

That, plus more attention to anti-reflection coating on the back of the lens.

I think I'd have noticed, and people would notice in photos, if the
distance to the subject didn't affect the image size.  In fact, I think
that must be some sort of error in the description.
  

[PhotoRoy6]

My understanding is similar to Hershel's. A digital lens is a lens that is designed for the "half frame" DSLR APS-C camera. Since it only needs to cover a smaller sensor it can be made smaller and cheaper thus providing a lighter camera to carry.

Roy

[karl shah-jenner]

Roy

: My understanding is similar to Hershel's. A digital lens is a lens that
is
: designed for the "half frame" DSLR APS-C camera. Since it only needs to
: cover a  smaller sensor it can be made smaller and cheaper thus providing
a
: lighter  camera to carry.


well like I said, i've seen explanations here on PF saying that digital
lenses produced collimated image forming light..

and I still find it hard to swallow.  The explanation of telecentric lenses
goes some way to explaining how this might work, but the claim by non
specialty camera manufacturers that their lenses are telecentric is
something I doubt (they often seem to avoid using the word and instead
describe how their 'digital' lenses creat a non-converging parallel ray
induced image)

much as Olympus does here
http://www.olympus-europa.com/consumer/dslr_7045.htm

though they use the term 'near-telecentric'

haha

right



As to a lens being called digital because it's designed for a smaller
frame, that's just weird (probably marketing hype, but weird nonetheless).
The little Pentax 110 of yesteryear - a fine camera by the way - managed by
labelling it's lenses in mm, same as everyone else did for so so long.. and
I really don't think too many people got confused and assumed that the 24mm
was a wide angle ;)

it's almost as weird as the concept of a '4/3 lens system' - another odd
term i've seen floating about lately


Has no one else has encountered the claim that digital lenses output
parallel rays of light to the sensor?


k

[Pablo Coronel-3]

Thus 17mm lenses are the normal low end of a zoom, just like the 28mm of yesteryear
Now, a good 10 or 14mm is as expensive as its counterpart in normal lenses, and very few are available.

On Thu, Oct 15, 2009 at 5:19 AM, <PhotoRoy6@...> wrote:

My understanding is similar to Hershel's. A digital lens is a lens that is designed for the "half frame" DSLR APS-C camera. Since it only needs to cover a smaller sensor it can be made smaller and cheaper thus providing a lighter camera to carry.

Roy

[James B. Davis]

On Wed, 14 Oct 2009 23:19:47 -0400 (EDT), PhotoRoy6@... wrote/replied to:

>My understanding is similar to Hershel's. A digital lens is a lens that is  
>designed for the "half frame" DSLR APS-C camera. Since it only needs to
>cover a  smaller sensor it can be made smaller and cheaper thus providing a
>lighter  camera to carry.
>Roy

This all reminds me of a pair of speakers I bought way back when digital music
was coming out, on the box they'd printer 'digital ready'. Basically they were
just speakers and cheap ones at that, always regretted buying them.

Nikon has a whole lineup of digital lenses now, pity that they've gone full
frame, hehehehe

Not that there's anything wrong with smaller sensors, still like my 10d.

--
Jim Davis, Owner, Eastern Beaver Company:
http://easternbeaver.com/ - Motorcycle Electrics
Check out my incredible fuse panel - the PC-8 is a hit!
1990 Honda VFR750, 1988 Honda Africa Twin 650

[David Dyer-Bennet]

On Thu, October 15, 2009 02:18, James B. Davis wrote:

> Nikon has a whole lineup of digital lenses now, pity that they've gone
> full frame, hehehehe

Nikon just released a new DX macro lens this week, in fact.  They seem to
think both DX and FX will be around for a while.  They probably know at
least as much about it as I do!

Were it not for my uses for extreme high ISOs, I would have stayed with
DX.  It's easy to get 15mm-e for DX on the wide end, which is wider than
I'd ever had before on film, and I think of myself as mostly a telephoto
guy anyway, where DX is a clear-cut win.  But I did want the extreme ISOs,
and so ended up with a D700, FX, and had to change out some lenses in a
hurry.  As compensation I'm playing with a full-circle fisheye, and I've
got out to 12mm wide which I've had some fun with, but those are all new
areas, not my primary photographic goals.

--
David Dyer-Bennet, dd-b@...; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info

[David Dyer-Bennet]

On Thu, October 15, 2009 02:02, Pablo Coronel wrote:
> Thus 17mm lenses are the normal low end of a zoom, just like the 28mm of
> yesteryear
> Now, a good 10 or 14mm is as expensive as its counterpart in normal
> lenses, and very few are available.

Ultra-wide zooms for DX are surprisingly affordable, going out to 12mm,
11mm, even 10mm.  My 12-24/4 Tokina was only $600 new (a few years ago),
less than half what the standalone 14mm lenses cost, even the Sigma.

I'm currently shooting the Sigma 12-24mm full-frame lens, which is quite
remarkable for a bit over $800 (I got it just before it went up, but I
think that's where it is these days).

--
David Dyer-Bennet, dd-b@...; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info

[David Dyer-Bennet]

On Thu, October 15, 2009 01:38, karl shah-jenner wrote:

> Has no one else has encountered the claim that digital lenses output
> parallel rays of light to the sensor?

Yes, that's a standard claim.  And I've read a number of articles on
micro-lens configurations over the sensor designed to make, for example,
the Leica M8 and M9 bodies work better with existing lenses (film accepts
light at an angle much better than digital sensor do, since the grains are
actual three-dimensional structures).  I regard all this as well-accepted,
uncontroversial.  But I admit to not having attempted to dig into it, or
understand the detailed implications for lens design.

Is it possible that you've latched onto "telecentric" when they're
actually using different techniques, with different side-effects?  There
are usually several ways to accomplish a given goal.
--
David Dyer-Bennet, dd-b@...; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info

[David Dyer-Bennet]

On Wed, October 14, 2009 16:22, Herschel wrote:
>         OMG... what a load of crap

Um, can we maybe discuss this like civilized people?  Instead of reacting
to a simple statement of what's widely reported (note I don't claim it's
TRUE) in all the print media and web sites by calling it "a load of crap"?
If it's not true, despite being pretty much universally accepted, you're
going to have to present evidence and make arguments, not just sling
around insults.

>  As far as I know, "digital" lenses mostly are lower quality lenses with
> an image circle only big enough to cover the smaller chips.

Don't try to tell anybody using Nikon's 17-55/2.8 DX that it's a "lower
quality lens"; they will laugh at you, probably not very politely.  Or the
35/1.8 DX.  Or Canon's EF-S macro lens.

I won't for a moment disagree that the designation "digital" on lenses has
been thrown around somewhat randomly and hasn't always meant anything, and
that it has no very specific definition.  However, I do think that as
we've learned more about digital photography, we've found some issues with
how image-forming light coming out a lens interacts with film vs. digital
sensors, and that some changes to lenses and some changes to sensors (or
the microlens arrays over the sensors) have been made to make things work
better.  These issues include how the sensor reacts to light at shallow
angles (considerably differently from film), and the fact that the sensor
is shiny and thus can make sharp reflections, in addition to the fact that
many DSLR cameras use smaller-size sensors than 24x36mm

--
David Dyer-Bennet, dd-b@...; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info

[herschel-9]

Ok,  so maybe not lower optical quality... just smaller image circles and of course, here's the con, with smaller image circle there's narrower angles of view thus with narrower angles of view you get more "Parallel" light rays...

It's a lens-makers joke.... get it?  The jokes on us.

Herschel


a result of

David Dyer-Bennet wrote:

On Wed, October 14, 2009 16:22, Herschel wrote:
  

        OMG... what a load of crap
    

Um, can we maybe discuss this like civilized people?  Instead of reacting
to a simple statement of what's widely reported (note I don't claim it's
TRUE) in all the print media and web sites by calling it "a load of crap"?
If it's not true, despite being pretty much universally accepted, you're
going to have to present evidence and make arguments, not just sling
around insults.

  

 As far as I know, "digital" lenses mostly are lower quality lenses with
an image circle only big enough to cover the smaller chips.
    

Don't try to tell anybody using Nikon's 17-55/2.8 DX that it's a "lower
quality lens"; they will laugh at you, probably not very politely.  Or the
35/1.8 DX.  Or Canon's EF-S macro lens.

I won't for a moment disagree that the designation "digital" on lenses has
been thrown around somewhat randomly and hasn't always meant anything, and
that it has no very specific definition.  However, I do think that as
we've learned more about digital photography, we've found some issues with
how image-forming light coming out a lens interacts with film vs. digital
sensors, and that some changes to lenses and some changes to sensors (or
the microlens arrays over the sensors) have been made to make things work
better.  These issues include how the sensor reacts to light at shallow
angles (considerably differently from film), and the fact that the sensor
is shiny and thus can make sharp reflections, in addition to the fact that
many DSLR cameras use smaller-size sensors than 24x36mm

  

[karl shah-jenner]

David:


On Thu, October 15, 2009 01:38, karl shah-jenner wrote:

> Has no one else has encountered the claim that digital lenses output
> parallel rays of light to the sensor?

>Is it possible that you've latched onto "telecentric" when they're
actually using different techniques, with different side-effects?  There
are usually several ways to accomplish a given goal.



it's the description often used - that of light playing on the sensor
running parallel to the optical axis I've latched onto, something that to
me, never made sense knowing what I do of lenses.  Then the term
'telecentric' started popping up (or "near-telecentric") in descriptions
and manufacturers explanations.

So I dug and found an explanation of what telecentric lenses actually are,
and while they do as described - they do not in any way appear to be used
for standard photography.   These are the only lenses I have ever heard of
which produce image forming light parallel to the optical axis.  There may
be others I don't know, but telecentric lenses are a whole world of
different for me and I cannot imagine (nor have I found) anything to
suggest another lens configuration that can pull off this magic


What I suspect is the manufacturers were having the marketing guys write up
whatever they liked to convince buyers that they needed new lenses - aside
from the obvious problems of using lenses designed for 35mm on what is
often essentially a competitor to 110 - and this is no different from the
issues one would experience using a Pentax MF lens on a 35mm camera.

Of course the cameras are different and an adapter is needed -

The tricky bit is they've manufactured the cameras to integrate to a small
extent with the 35mm systems available.  I'm again guessing, but this was
to make it easy for people to make the switch .. marketing telling us that
the transition is almost seamless - "hey people, they even LOOK the same!".
The fact being it's really not.  "Not only have you bought a whole new
camera body, you now need to buy new lenses (!)  You can still use some of
the old ones, but there will be problems"

But how to make people buy the new lens range?  Spin some story about how
the light behaves differently..





>I won't for a moment disagree that the designation "digital" on lenses has
been thrown around somewhat randomly and hasn't always meant anything, and
that it has no very specific definition.  However, I do think that as
we've learned more about digital photography, we've found some issues with
how image-forming light coming out a lens interacts with film vs. digital
sensors, and that some changes to lenses and some changes to sensors (or
the microlens arrays over the sensors) have been made to make things work
better.  These issues include how the sensor reacts to light at shallow
angles (considerably differently from film), and the fact that the sensor
is shiny and thus can make sharp reflections, in addition to the fact that
many DSLR cameras use smaller-size sensors than 24x36mm


Shiny is another one that gets me.  Some film surfaces have been *very*
shiny, and atop that, some very pale - reflecting a *lot* of light around
inside cameras.

If you recall many years back me describing here how I built an
infrared-lit film changing cabinet with a CCD camera inside?  it made
loading troublesome cameras, spools and sheet film holders very easy and
was extra handy if I wasn't sure if a double dark was loaded or not ;)

As I was doing a lot of IR photography I popped a bunch of cameras and
lenses under the IR to have a peek and see how reflective the inner
workings of the cameras were.. which is when I discovered deep black
anodised aluminium reflects IR light like chromework   - at the end of the
day I found old British lenses with black painted interiors reflected the
least and mirrored what I had been experiencing when using various lenses -
a much sharper, contrasty image than with any other lenses.  And another
surprise was the cameras - the Canon T70 ( a dog by anyone's definition)
was by far and away the darkest camera internally for IR light.  It was
also the *only* camera with a dark film pressure plate.  Since Kodak
weren't using an antihalation layer in their IR film, the T70 was the best
camera to use for IR if one didn't want the dreamy, flared results we were
used to seeing in pictorial photography.  - Adding black paper from 120
roll film to cover the pressure plate of other cameras helped to a degree,
but the internal reflections were still there..  My point - reflections
occurred and most people didn't notice a jot.

The Olympus cameras equipped with off the film metering were a lovely
design, and for 90% of users performed faultlessly - but there were still
that 10% who found a niggling problem - and for those using photography for
critical applications, they came to realise the levels of light reflected
from differing films caused differing exposures.  Again, few people noticed
anything.



Another gadget I built was intended for testing film speeds - a panel of ND
squares I could photograph ensuring a full range of exposures in 1 stop
intervals across a single frame of film :)  Except it didn't work.  The
reason as I reported here was that different lenses produced quite
different contrasts.  What I didn't report was that when using the same
lens and switching films, different films had different contrasts.  This
was not just a development issue as one would expect, as I had controlled
for that by establishing reference development times from direct exposed
and developed film.  This again suggested refection of the film surface
played some part.  mhey - I gave all this experimenting up and worked with
what I had  ( I decided while it was a nice mental exercise,  *I* didn't
really care either ;)



Digital sensors - there is some interesting mechanics at play there!

microlenses.  Firstly we know it's not a straight sensor by sensor
conversion to image.  We don't *need* super highly resolved light falling
on each individual sensor, in fact it's undesirable as it causes all manner
of problems like moiré - subsequently an antialiasing filter is added to
'blur' the light.  We use 3 or more sensors to determine the colour of the
light then we interpolate that back into three separate pixel colours and
locations.  Microlenses are needed though to gather the light hitting that
part of the sensor and focus it tightly onto the phototransistor it's self.

Now we all know a bit about lenses, and we all know how a dome shaped
hemispherical lens sitting above something will work - pretty much whatever
angle the light strikes the hemisphere will be focussed pretty much dead
centre - where the phototransistor sits ..just as it's designed to do to
prevent the light falloff from reflection that would occur if the dome were
not there and the surface were in fact flat.  ..(if you didn't know this,
think how a wide angle works)

So we have microlenses and a fuzzing filter, we have algorithms playing
with the data collected from the photosites - we even know now that
fringing is correctable by firmware (the Sony F828 was widely criticized as
having poor optics due to purple fringing - the fact is such fringing was a
reality even for film but few people ever enlarged film images to the
extent they do when simply viewing digital pictures and subsequently never
saw it)

When we have all this, what need is there for anything faintly resembling a
requirement for light rays to be collimated, even partially?

 Maybe an argument could be presented for such a thing but then where are
the real world examples?

I'd imagine that in its infancy when DSLRs were first hitting the market
and sensors were still being refined we'd have seen an uproar from people
buying into these systems who used their old film camera lenses only to
find vignetted dark corners, blurry images and colour fringing.  It didn't
happen.

So what the heck is all this in the manufacturers blurb about telecentric
or near telecentric lenses, parallel light, etc?


Again, I'd love to hear from anyone who owns a 'digital' lens made by a
manufacturer who claims any such thing who can look through the lens and
see if the aperture look *really* far away (like infinity?)

I suspect it's all bunk.  Always did, I just never had a firm grip on what
it was they were claiming before..

karl

[karl shah-jenner]

this is doing my head in..

http://www.lhup.edu/~dsimanek/scenario/labman3/telecen.htm


you have *got* to see the image on this page using a real telecentric
lens - the distant part of the object appears larger than the close part !



"When this experiment was written, back in 1972, telecentric lens systems
were considered somewhat "exotic". But now (2006) they are finding new
applications in astronomy, machine imaging applications and industrial
quality control measurements. Imaging arrays are generally small compared
to the area of photographic film images, and their performance is very much
improved when all light rays impinge normally (perpendicular to) the array
surface. This is due to the three dimensional nature of the sensor
elements, and the fact that some incorporate tiny color filters above each
sensor element. The entire sensor array is smaller than the diameter of the
typical film camera lens. So it is quite practical to use a system
telecentric on the image side to ensure that condition of normal incidence.
Now such a system is even used in digital cameras (for example the Nikon
Coolpix)."

I wonder if the author is swallowing the Nikon marketing or whether this is
truly the case - has anyone noticed the effect described and clearly
visible in the image?



especially when taking this into account
"Q: Why don't you state the focal lengths of your lenses?

A: Unlike other telecentric lenses that have real focal lengths, such as
55mm for one popular model, Double Telecentric lenses have infinite focal
lengths. Optical engineers call this being afocal. It's why the Double
Telecentric design can have much larger Magnification Depth of Field." from
http://www.lw4u.com/mvh-machine-vision-FAQ.htm


there's also this
http://www.edmundoptics.com/TechSupport/DisplayArticle.cfm?articleid=239

[James B. Davis]

On Fri, 16 Oct 2009 17:19:29 +0800, karl shah-jenner <shahjen@...>
wrote/replied to:

>this is doing my head in..
>
>http://www.lhup.edu/~dsimanek/scenario/labman3/telecen.htm

I like just pointing and shooting, easier on the head. I let the Canon engineers
worry about the lens on my G10. It has a great range, has some distortion,
doesn't cost too much, get pretty pictures from it...

Mind you I'm liking the Manual mode more and more.

--
Jim Davis, Owner, Eastern Beaver Company:
http://easternbeaver.com/ - Motorcycle Electrics
Check out my incredible fuse panel - the PC-8 is a hit!
1990 Honda VFR750, 1988 Honda Africa Twin 650

[lookaround360]

Jim,

Thanks for the authoritative URL. Its salient point for all below:

QUOTE

Application

When this experiment was written, back in 1972, telecentric lens systems
were considered somewhat "exotic". But now (2006) they are finding new
applications in astronomy, machine imaging applications and industrial
quality control measurements. Imaging arrays are generally small
compared to the area of photographic film images, and their performance
is very much improved when all light rays impinge normally
(perpendicular to) the array surface. This is due to the three
dimensional nature of the sensor elements, and the fact that some
incorporate tiny color filters above each sensor element. The entire
sensor array is smaller than the diameter of the typical film camera
lens. So it is quite practical to use a system telecentric on the image
side to ensure that condition of normal incidence. Now such a system is
even used in digital cameras (for example the Nikon Coolpix).

END QUOTE

Most likely all digital camera systems also use non-glass optical
correctives to great advantage. One would suppose that the glass and the
correctives correspond in some way to make the "digital" lens unlike a
standard lens. No point in being reflexively cynical about marketing
trade names and claims.

AZ

LOOKAROUND - Since 1978
Build a 120/35mm Lookaround!
The Lookaround E-Book 5ed.
http://www.panoramacamera.us

> -------- Original Message --------
> Subject: [SPAM] Re: 'Digital lenses"
> From: "James B. Davis" <jim@...>
> Date: Fri, October 16, 2009 6:53 am
> To: List for Photo/Imaging Educators - Professionals - Students
> <photoforum@...>
> On Fri, 16 Oct 2009 17:19:29 +0800, karl shah-jenner <shahjen@...>
> wrote/replied to:
> >this is doing my head in..
> >
> >http://www.lhup.edu/~dsimanek/scenario/labman3/telecen.htm
> I like just pointing and shooting, easier on the head. I let the Canon engineers
> worry about the lens on my G10. It has a great range, has some distortion,
> doesn't cost too much, get pretty pictures from it...
> Mind you I'm liking the Manual mode more and more.
> --
> Jim Davis, Owner, Eastern Beaver Company:
> http://easternbeaver.com/ - Motorcycle Electrics
> Check out my incredible fuse panel - the PC-8 is a hit!
> 1990 Honda VFR750, 1988 Honda Africa Twin 650