The myth of the "smaller" 4/3rds lens

That is only by making lens surfaces more curved (to increase
magnification or reduce it more) in a given space. Also, extensive
and expensive use of ED and other exotic glasses helps allow this. But
people have to remember that lenses cannot "shrink" beyond a certain
point and it has NOTHING to do with sensor size. A 200mm f2 lens STILL
needs a 100mm wide front element to claim it is 200mm f2 (200/100 =
2). The REASON it seems that Olympus can make "smaller" lenses is
because a 200mm lens on a Full frame or 1.3-1.6 cropped sensor
provides a wider angle of view than the 2x Olympus that in-turn allows
Olympus to put more pixels into a given area of a scene, and resolve
more detail for a given lens focal length (provided both the Olympus
and the other brand have the same pixel count). So the proverbial
300mm lens on the 2x sensor functions like a 400mm lens on a FF
camera. The reciprocal being that you cannot get as wide a view with
an Olympus sensor as with a larger sensor because it would require
making lenses with shorter focal lengths. The shortest lens I've ever
seen was Nikon's 6mm which on a FF SLR has twice the field of view as
a 4/3rds camera.

But, if someone is thinking Olympus can produce a 300mm f2.8 lens any
smaller than Canon, they would be dead wrong. The lens STILL needs a
107mm of clear front aperture to meet it's speed claim.

 

There is ongoing research into ways to focus light for photographic use that
does not totally rely on glass/plastic as we know it particularly for use
with very small sensors.
The technology of imaging is evolving in ways that will not rely on
traditional materials just as digital sensors have replaced film for most
uses.
Bigger is not better even at this point in the development of digital
photography and will come to be seen as the liability it has always been
when better technical solutions become available.

 

The flaw in this logic is number of photons. A smaller
camera with a smaller aperture lens collects fewer photons.
The signal-to-noise ratio in digital camera images is directly
related to the square root of the number of photons collected
in each pixel. Smaller pixels with smaller photons collected
also results in smaller dynamic range.

http://www.clarkvision.com/imagedetail/does.pixel.size.matter

Roger

 

You can't simply "get smaller" without reaching a point that bumps up
against limitations rooted in the properties of light itself. Others here
have discussed this at length (Think Roger and David Littleboy).

 

Why would you make such a point of this.. and then go about telling us
the opposite? Of course sensor size makes a difference, *for a given
angle of view*! And if you don't hold the angle of view constant for
comparing whether a given camera/lens combination is bulkier than
another, then what is the point?? Yes, we know about sensor noise
issues, but this was about lens size/bulk.

Umm. Forgive my pickiness - I'm a bit rusty on lens design. But is it
the *front element* that gives the aperture calculation???? I mean I
realise it has to be a certain size to allow the lens to operate to
it's full 'f' capability, but isn't it the APERTURE that is used for
calculating the f-ratio? Ie the IRIS opening, not the front element.
I humbly apologise if I'm wrong, and I realise they are of course
related, but let's be *accurate* here...

As per my initial comment - DUUUH!

Am I missing something here as well? It's a 2x multiplication factor,
and yet Rich says a 300 goes to ..400? Umm, yeah right...

Sigh. Never looked at a video camera or a compact?

Err, say what? I missed the point of that line.. Yes, to match that
6mm lens, Oly would have to create a 3mm. Challenging? Yes indeed.
But how many 6mm (35 equiv) owners are there around here? (That 6mm
lens, if mounted on the Oly, would act like a 12mm (35 equiv) extreme
w/a, and I doubt *many* folks would be agonising that they couldn't go
wider...

But they *can* create a 150mm f2.8 that is smaller and is the
EQUIVALENT lens in terms of field of view. Sigh.

Now it's 'front aperture'? See comment above. Happy to be corrected...

 

While it is in principle possible to make a flat camera that from a
magnification viewpont has a very long lens or one that from a depth of
field and sharpness viewpoint has a very wide aperture using techniques
developed for long-baseline interferometry, the difficulty with these
techniques is that you don't get the sensitivity normally associated with
those large apertures. I can't see this approach as being other than a
niche solution.

 

Roger,
I don't think anybody implied a smaller aperture here. Yes, you'll
always need a large area to collect photons from (the "front element"),
but the rest of the "lens" (length etc) is not fixed by physical
considerations.

Take a look at this:
http://prola.aps.org/abstract/PRL/v85/i18/p3966_1

Cheers!

 

Mark,
When it comes to lenses, the only physical limitation is the
relationship of the area from which light is collected ("front element")
to the magnification of the image on the sensor. The rest is only
determined by what we use to make the lenses (currently, glass).

 

hmmm <scratching head>
http://physicsweb.org/articles/news/9/4/12

 

If it could be scaled to the dimensions required for photographic lenses
(the uses described seem to be on a very short distance scale) then it might
yield a lens sharper than current technology, but photographic lenses are
seldom diffraction-limited at large apertures anyway, so it would seem to be
a nonstarter.

 

So when will we get these portable gravitic lenses?
And will we need a huge truck for the power requirements, or
will there be a hip-pocket fusion plant to go with it?

That must be why the APS films were such a rage and outsold
everything else. Oh, no, wait, that's the reason every
self-respecting photographer uses a Minox instead of small, medium
or large format, and why all the digital cameras are modelled
after the Minox cameras ... instead of these large rectangles,
which you can hardly put into a small pocket or up your sleeve.

-Wolfgang

 

The idea is that it's a nontraditional way to focus light.

 

"negative refractive index material" means that the speed of light is
higher than c within that material, while this is not strictly
impossible, it can only be obtained by quantum effects. And those
usually have a major statistical behavior, which supposedly imposes noise.

-Michael

 

c>1 is, in fact, strictly impossible (for the group velocity of light,
which is what is of interest here). What "negative refractive index"
means in this context is a bit more technical, and in Pendry's paper he
actually considers a material for which the dielectric constant and the
magnetic permeability (which describe the response of the material to
applied electric and magnetic fields, eg light) are negative. Their
product is still positive, and so the speed of light is not different
from free space. Of course, this is an approximation, in actual
experimental realisations it'll be slower.

And reasoning that quantum effects always induce noise is simply
untrue: Consider solids, which only exist because of quantum mechanical
effects. Or, to take a more obvious example, a Bose-Einstein
condensate: a purely quantum effect in which all the particles behave
in an identical way even at finite temperature. Quite the opposite of
what you'd expect!

 

I don't think this "holy grail" of refraction has been used across the
visible spectrum yet.

 

The general rule in lens design is you never use more aperture than you
have to.
Which means the front lens diameter (what isn't cut off by any
retaining rings) is the aperture. However, it is possible that some
lens designs have been made using a larger size than true aperture once
internal body "stop downs" have been used. This would be used in a
case where CA or some other aberration could be controlled in no other
way, but it's rarely used because the cost of lens fabrication and
materials rises exponentially with element diameter. The iris opening
does dictate the aperture, but the iris in most lenses should open
nearly as or as wide as the element's front aperture. Waste not....

No, the angle of view is 1/2 of that in a FF camera, so the 300mm on an
FF = 600mm on the 2x.

You'd be amazed how many FF Canon shooters regularly use 17mm or wider
lenses.
I'd venture very few 4/3rds owners will have a 8-9mm lens available.

That is true, but it is NOT the same as making a 300mm smaller than
another 300mm. I was talking about lenses of the same f.l., not lenses
that were equivalent in action on the two different sensors.

As I said, in most lenses the front aperture IS the full aperture and
determines the focal ratio. However, we are talking about normal and
tele lenses and NOT wide angle lenses that have completely different
characteristics. Which is why Olympus's old 8mm fisheye has a front
element about 120mm wide. If you compare the old OM 8mm with the new
one,
the new one (made to support 4/3rds instead of FF) is substantially
smaller.

 

I was merely trying to point out that various "physical limits" aren't
as hard as they would appear. Others are, of course.

 

Hmm.... The beginning of my reply disappeared, somehow. It should have
read something like:

The refractive index n is usually defined as the ratio of the speed of
light in vacuo and in a material; thus, what you say would refer to n<1
rather than n<0. At any rate,
c>1 is, in fact,.......


Apologies.

 

The accurate answer is the entrance pupil determines the true
aperture. The front element must be at least the true aperture,
or you don't get the full amount of photons. Typically, the
front element is larger than the entrance pupil. The iris
diaphragm may be much smaller as the lenses in front of the
iris usually focus the light into a smaller cone. The entrance
pupil is not necessarily a physical aperture. It gets
quite complex in the many element lens designs for modern cameras.

The problem with reducing the lens aperture is that it collects
fewer photons. So in the equivalent field of view same
megapixel count camera scaling, the 300 f/2.8 collects
4 times the number of photons as the 150 mm f/2.8.
So the two cameras may produce the same resolution images,
but the smaller camera image is 2x noisier for the same exposure
time.

Roger

 

You *do* seem to be fixated on photon noise. (O;

In my response, I said:

I thought that was sufficient, given the topic.

Roger:

But hang on - first up, we are talking about two completely different
camera formats, and noise may or may not be an issue. Is noise an
issue on a Hassy back? On a Canon 1DS MkII? On a Nikon D2X? On a P&S?
Yes, of course at some point it becomes an issue, but you can't just
blithely say it is 2x noisier and seemingly dismiss the concept.

Given possible improvements in sensor design (- I seem to recall that
when pushed you admit that there is probably at least another factor of
30% or so left for improvements in processing, more efficient sensor
packing, different designs of wells, microlenses etc), and the fact
that already many sensors *somehow* perform well beyond their weight
(eg the Fuji sensor designs, the F30, the larger canon CMOSes) - I
don't believe that 4/3 is too small to ever have a really good
low-noise sensor, which is the implication..

In other words, it may indeed be "2x noisier", but if the noise is so
low that a 2-fold increase is still very low-noise, who cares? In
theory you could shrink the best Canon FF CMOS to 4/3... and it would
be 2x noisier... Do you think anyone would be complaining much about
those noise levels?

Like I said, this post was about the alleged "myth of smaller 4/3
lenses". There is no myth. You can make a smaller lens, given a
smaller sensor. *At some point* sensor noise may/will become an issue,
but to say that 4/3 is that point reminds me of some Arthur C Clarke
quotes:

Any sufficiently advanced technology is indistinguishable from magic.

Every revolutionary idea seems to evoke three stages of reaction. They
may be summed up by the phrases: (1) It's completely impossible. (2)
It's possible, but it's not worth doing. (3) I said it was a good idea
all along.

If an elderly but distinguished scientist says that something is
possible, he is almost certainly right; but if he says that it is
impossible, he is very probably wrong.