----- Original Message -----
From: "Randy Little" <randyslittle@xxxxxxxxx>
To: "PhotoForum educational network" <photoforum@xxxxxxxxxxxxx>
Sent: Sunday, April 05, 2015 7:19 AM
Subject: telecentric design in digital camera lens design all
the FACTS
The links are as follows. first the the HP Patent that is used at part
of
the Micro 43 standard and also used by other lens manufacturers as needed
depending in lens and camera pairings.
http://patents.com/us-6535249.html
In this link you will notice that the lens graphic shown matches up pretty
much exactly to those in the the HP patent. (HP being part of the m43
consortium)
http://four-thirds.org/en/fourthirds/index.html
That patent is used again as part of the spec for m43
This page shows the use of that patent in the m43 spec
Scroll down to item 3, you will see 2 graphics. Not the start button in
the top left of each graphics. clicking play does exactly what one would
expect from a play button. :-)
http://www.four-thirds.org/en/special/microftmerit/merit2.html
I though the techies who didn't realise this type of lens design was
happening might enjoy seeing this.
The design is not required for all lenses but it is put into practice by
more then m43 as needed.
Companies like Sony (and kodak at one point) have gone to great lengths to
optimize the microlens on the sensor to help with occlusion. In some cases
it works just fine but it can still have issues with shorter focal length
lenses. m43 olympus and HP wanted a solution was more ideal. Why, is a
question only they can answer and probably won't. We do know that
Olympus
designs lens for Sony and has a history with other manufactures like
Nikon.
So since we know for a fact that telecentric design is used for some
digital lenses then that also means by definition that those lenses
collimate the light.
this can very easily be checked. See below.
Edmunds optics definition of telecentric.
*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.
The easiest way to tell if a lens is telecentric (collimated to parallel or,
described another way, light is parallel to the optical axis) is to look
through the back of the lens from right up close (comparable to the film
plane distance) or at arms length , the lens should present an image that
your eye can see very easily. It should do this just as easily as looking
at a distant object, where the approaching light rays are also nearly
parallel. No difference, if the light rays are in fact parallel or nearly
so.
As folks would know from looking through the back of a conventional lens,
you can't focus an image - it's all just a blur as the light is
converging/diverging - this is what conventional lenses do. Like I said -
very easy to see whether a lens is telecentric or not.
I also believe there are other parts to what they define a telecentric lens
as being, not covered at this moment.
Does one need a digital lens? no.
Is the above the only design principle applied to making a lens more
optimized for digital sensors? No.
Do none digital lens work fine in a whole lot of cases, yup
Can optical shortcomings be corrected in post? Yup
there are lens profiles for most of the most common lenses new to old for
lots of optical shortcomings.
Randy, I've just never seen any self-described digital lens as doing
anything any differently to a conventional lens when I've examined them -
the descriptions of them producing light parallel to the optical axis got me
very excited back in the early days which is why I poured over so many
lenses trying to find this trait.. and I never did... and why I came to be
disillusioned by the claims.
It was only in labs and the like where I found those expensive (and really
limited )telecentric lenses. It also led me to dig through my microscopes
and find I already owned set of 3 telecentric lenses, those attached to my
old school 100 kilo (200 lb) 'profile projector' . Profile projectors
are/were kind of monstrous microscope-y looking things used as comparators
that demand precision and accuracy in measurement
http://profileprojectors.com/ and telecentric lenses were often fitted to
such beasts as you needed to be able to tell sizes extremely accurately
irrespective of the distances - and looking through the back of these
lenses, whatever the observers distance from the lens, the image can be seen
clearly.. the eye focuses it by converging the parallel light. press your
eye against the back of the lens or hold it at arms length - the image
through these lenses remains the same *because* the light exiting the back
of the lens is parallel to the optical axis.
it's really kinda cool.. but as I said before, of limited use.
k
