For the cost of today's lenses, should they be diffraction-limited, wide open?

$1800 for an 85mm f1.4 from Nikon. That's about 2x what the old one cost.
Is the lens $1000 better or should it be as good at f/1.4 as f/4? I'm not
sure. I know that some optics made as f/4.0 have been diffraction limited.
Pentax had some, but they weren't camera lenses. Some have claimed certain
telephotos in the pro bracket have been diffraction-limited at f/2.8, but
I've never seen it demonstrated. So, the question is, is it possible to
make say a 35mm, 85mm diffraction-limited at f/1.4 and if so, at what
price? Likely it is, but they haven't done it.

On 8/11/2012 1:48 p.m., Anthony Polson wrote:
Rich wrote:
$1800 for an 85mm f1.4 from Nikon. That's about 2x what the old one cost.
Is the lens $1000 better or should it be as good at f/1.4 as f/4? I'm not
sure. I know that some optics made as f/4.0 have been diffraction limited.
Pentax had some, but they weren't camera lenses. Some have claimed certain
telephotos in the pro bracket have been diffraction-limited at f/2.8, but
I've never seen it demonstrated. So, the question is, is it possible to
make say a 35mm, 85mm diffraction-limited at f/1.4 and if so, at what
price? Likely it is, but they haven't done it.


It might be better if, instead of using the term "diffraction
limited", you described your requirement as "a lens that gives its
sharpest results when wide open". That is what you mean after all.

Only Leica makes lenses that do that, and Leica lens prices are
self-evidently very high indeed. Ridiculously high, even for Leica
users.
Which Leica lenses?
http://www.photozone.de/canon-eos/20...report?start=1

Summilux R 50mm f1.4 is pretty good, but peaks at f5.6 here, much the
same as any of the ( /much/ cheaper) 50mm lenses.



I'm considering replacing two of my Leica lenses in the next year
before signs of wear mean their used values begin to fall. I'm
looking hard at Carl Zeiss ZM and Voigtländer lenses, both made in
Japan by Cosina and costing a fraction of Leica prices. However, they
don't perform at their best wide open.

On 08/11/2012 00:27, Rich wrote:
$1800 for an 85mm f1.4 from Nikon. That's about 2x what the old one cost.
Is the lens $1000 better or should it be as good at f/1.4 as f/4? I'm not
sure. I know that some optics made as f/4.0 have been diffraction limited.
Pentax had some, but they weren't camera lenses. Some have claimed certain
telephotos in the pro bracket have been diffraction-limited at f/2.8, but
I've never seen it demonstrated. So, the question is, is it possible to
make say a 35mm, 85mm diffraction-limited at f/1.4 and if so, at what
price? Likely it is, but they haven't done it.

f1.6 and full achromatic mirror telescope has been done by Cambridge
University.

http://www.ast.cam.ac.uk/about/three-mirror.telescope

20" aperture prototype was built. That is one of the fastest diffraction
limited wide field instruments I know of.

You are hampered in real cameras by simultaneously wanting diffraction
limited and a flat film plane when the lens is fast and the small angle
approximations no longer hold. There is always a trade off.

Anything can be done in principle but the cost to manufacture it and
difficulties in assembly make it prohibitive. You could get the on axis
sharpness truly diffraction limited by sacrificing edge resolution but
never all at the same time and a flat film plane. Something has to give.

At around f4 or f5 things are a lot easier. Most real lenses tend to
have their resolution sweet spot at about that working aperture.

--
Regards,
Martin Brown

On 08/11/2012 00:48, Anthony Polson wrote:

(...)
"a lens that gives its
sharpest results when wide open".

Only Leica makes lenses that do that,

That's a ridiculous claim.

http://www.cookeoptics.co.uk/
and
http://lenses.zeiss.com/camera-lenses/carl-zeiss-camera-lenses/cine_lenses.html
would be 2 examples of lens manufacturers other than Leica that are
sharp wide open.

And I have a hunch that these qualify as well:
http://www.canon.co.uk/For_Home/Product_Finder/Digital_Cinema/Cine_Lenses/
http://www.fujifilm.com/products/optical_devices/cine/



--
audentes fortuna iuvat

On 08/11/2012 16:53, Anthony Polson wrote:
Joe Kotroczo wrote:

On 08/11/2012 00:48, Anthony Polson wrote:

(...)
"a lens that gives its
sharpest results when wide open".

Only Leica makes lenses that do that,

That's a ridiculous claim.

http://www.cookeoptics.co.uk/
and
http://lenses.zeiss.com/camera-lenses/carl-zeiss-camera-lenses/cine_lenses.html
would be 2 examples of lens manufacturers other than Leica that are
sharp wide open.

And I have a hunch that these qualify as well:
http://www.canon.co.uk/For_Home/Product_Finder/Digital_Cinema/Cine_Lenses/
http://www.fujifilm.com/products/optical_devices/cine/


With respect, I believe you have missed the point here.

First, I was talking about still photography, not cine. I have no
interest in, or specialist knowledge of, the latter. Neither is it
on-topic for this newsgroup.

A lens is a lens. Nothing stops you from taking stills with a cine lens.

Second, I was not talking about lenses that are merely *sharp* wide
open but lenses that give *their sharpest results* when used wide
open. There is a difference.

So was I. Cine lenses must be of equal sharpness along the full range of
stops, so they should be equally sharp wide open as they are stopped down.

In fact, shouldn't a lens that is less sharp stopped down than it is
fully open be considered defective?


Perhaps, given the confusion I appear to have caused, I should have
stayed with Rich's term "diffraction limited". ;-)

There is a difference between "diffraction limited" and "sharpest at
full aperture" too... A lens that is sharpest at full aperture is not
necessarily diffraction limited.


--
audentes fortuna iuvat

On 08/11/2012 23:32, RichA wrote:
On Nov 8, 12:24 pm, Joe Kotroczo wrote:
On 08/11/2012 16:53, Anthony Polson wrote:









Joe Kotroczo wrote:

On 08/11/2012 00:48, Anthony Polson wrote:

(...)
"a lens that gives its
sharpest results when wide open".

Only Leica makes lenses that do that,

That's a ridiculous claim.

http://www.cookeoptics.co.uk/
and
http://lenses.zeiss.com/camera-lenses/carl-zeiss-camera-lenses/cine_l...
would be 2 examples of lens manufacturers other than Leica that are
sharp wide open.

And I have a hunch that these qualify as well:
http://www.canon.co.uk/For_Home/Product_Finder/Digital_Cinema/Cine_Le...
http://www.fujifilm.com/products/optical_devices/cine/

With respect, I believe you have missed the point here.

First, I was talking about still photography, not cine. I have no
interest in, or specialist knowledge of, the latter. Neither is it
on-topic for this newsgroup.

A lens is a lens. Nothing stops you from taking stills with a cine lens.

Second, I was not talking about lenses that are merely *sharp* wide
open but lenses that give *their sharpest results* when used wide
open. There is a difference.

So was I. Cine lenses must be of equal sharpness along the full range of
stops, so they should be equally sharp wide open as they are stopped down.

In fact, shouldn't a lens that is less sharp stopped down than it is
fully open be considered defective?



Perhaps, given the confusion I appear to have caused, I should have
stayed with Rich's term "diffraction limited". ;-)

There is a difference between "diffraction limited" and "sharpest at
full aperture" too... A lens that is sharpest at full aperture is not
necessarily diffraction limited.

What difference? What would cause a lens wide open and diffraction
limited (across the visual spectrum) to not be sharpest when wide
open? Resolution laws would argue otherwise.

But you can still make a lens that is at its sharpest when wide open but
whose sharpness is not significantly improved by stopping down. Such
lenses are usually designed to avoid vignetting at the corners of the
field of view. They are not diffraction limited at full aperture but
they hold their sharpness at some particular nominal diameter.

--
Regards,
Martin Brown

On 08/11/2012 23:32, RichA wrote:

(...)
There is a difference between "diffraction limited" and "sharpest at
full aperture" too... A lens that is sharpest at full aperture is not
necessarily diffraction limited.

What difference? What would cause a lens wide open and diffraction
limited (across the visual spectrum) to not be sharpest when wide
open? Resolution laws would argue otherwise.

Who says that a lens has to reach it's diffraction limit wide open? Can
it not be diffraction limited at f/11 or something, and less sharp at
any other stop, smaller or larger?

And who says that a lens which is sharpest wide open has also reached
it's diffraction limit? Can it not be sharpest wide open, but still a
long way off it's diffraction limit?

After all, what "diffraction limited" really means is "reaching it's
theoretical maximum resolution".

--
audentes fortuna iuvat

Joe Kotroczo wrote:
On 08/11/2012 23:32, RichA wrote:

There is a difference between "diffraction limited" and "sharpest at
full aperture" too... A lens that is sharpest at full aperture is not
necessarily diffraction limited.

What difference? What would cause a lens wide open and diffraction
limited (across the visual spectrum) to not be sharpest when wide
open? Resolution laws would argue otherwise.

Who says that a lens has to reach it's diffraction limit wide open? Can
it not be diffraction limited at f/11 or something, and less sharp at
any other stop, smaller or larger?

And who says that a lens which is sharpest wide open has also reached
it's diffraction limit? Can it not be sharpest wide open, but still a
long way off it's diffraction limit?

After all, what "diffraction limited" really means is "reaching it's
theoretical maximum resolution".

And what is meant by "sharpest"? Sharpest in the centre? Sharpest at
the edges? Those are often two different apertures.

--
Chris Malcolm

On 09/11/2012 17:58, Chris Malcolm wrote:
Joe Kotroczo wrote:
On 08/11/2012 23:32, RichA wrote:

There is a difference between "diffraction limited" and "sharpest at
full aperture" too... A lens that is sharpest at full aperture is not
necessarily diffraction limited.

What difference? What would cause a lens wide open and diffraction
limited (across the visual spectrum) to not be sharpest when wide
open? Resolution laws would argue otherwise.

Who says that a lens has to reach it's diffraction limit wide open? Can
it not be diffraction limited at f/11 or something, and less sharp at
any other stop, smaller or larger?

And who says that a lens which is sharpest wide open has also reached
it's diffraction limit? Can it not be sharpest wide open, but still a
long way off it's diffraction limit?

After all, what "diffraction limited" really means is "reaching it's
theoretical maximum resolution".

And what is meant by "sharpest"? Sharpest in the centre? Sharpest at
the edges? Those are often two different apertures.

If you want to pick nits the problem is that to be "sharpest" as a true
fully optimised glass based apochromat requires that the red image be
truly diffraction limited and the green and blue images be very slightly
geometrically degraded. I don't think anybody does this in practice. You
end up with slight purple haloes on point sources.

resolution is 1.22D/lambda

Varies by a factor of two from deep red 680nm to violet 340nm.

Astronomical instruments are optimised to diffraction limited for object
at infinity and a realisable (not not always flat) focal plane.

Camera lenses have to cope with a wider range of object distances.
Mostly the marketing dept stick APO on to fleece wannabbees like RichA.

The RichA troll just likes to **** and moan.

--
Regards,
Martin Brown

RichA wrote:
On Nov 8, 5:49*am, Martin Brown
wrote:
On 08/11/2012 00:27, Rich wrote:

$1800 for an 85mm f1.4 from Nikon. *That's about 2x what the old one cost.
Is the lens $1000 better or should it be as good at f/1.4 as f/4? *I'm not
sure. *I know that some optics made as f/4.0 have been diffraction limited.
Pentax had some, but they weren't camera lenses. *Some have claimed certain
telephotos in the pro bracket have been diffraction-limited at f/2.8, but
I've never seen it demonstrated. So, the question is, is it possible to
make say a 35mm, 85mm diffraction-limited at f/1.4 and if so, at what
price? *Likely it is, but they haven't done it.

f1.6 and full achromatic mirror telescope has been done by Cambridge
University.

http://www.ast.cam.ac.uk/about/three-mirror.telescope

20" aperture prototype was built. That is one of the fastest diffraction
limited wide field instruments I know of.

You are hampered in real cameras by simultaneously wanting diffraction
limited and a flat film plane when the lens is fast and the small angle
approximations no longer hold. There is always a trade off.

Anything can be done in principle but the cost to manufacture it and
difficulties in assembly make it prohibitive. You could get the on axis
sharpness truly diffraction limited by sacrificing edge resolution but
never all at the same time and a flat film plane. Something has to give.

At around f4 or f5 things are a lot easier. Most real lenses tend to
have their resolution sweet spot at about that working aperture.

--
Regards,
Martin Brown

Only problem, with a central obstruction like it has, contrast would
suffer.

It should be possible with today's lens and mirror making technology
to devise a mirror which instead of reflecting straight back, offset
the folded beam offset to one side, thus avoiding the need for the
obstruction.

--
Chris Malcolm