what a lens design sacrifices for sharpness

[roberto_watson_garc_a]

when designing a lens, caracteristics are put in a level to valance a design (a way to say it)

 

<p>

 

so what most be sacrifice in order to gain sharpness.

[john_chan2]

I think the distinction of sharpness in modern optics is really

limited to the discussion of edge-to-edge sharpness. The advances in

the inplementation of aspherical surfaces (especially with the Leica

lenses) has really done wonders for corner to corner sharpness and

lower levels of light falloff at maximum aperture. I think what gets

sacrificed is the subjective term "bokeh".

 

<p>

 

To get the kind of sharpness from the newer 35 Cron Leica had to

correct more for spherical abberations (hence the aspherical surface)

and when spherical abberation is neutral to over-corrected

the "bokeh" suffers. This is why in my humble opinion the older 35

Cron and the 35 Lux ASPH have a more pleasing "bokeh" (both are

sharpest in the center and taper off at the edges) than the newer 35

Cron or 28 Cron (which are uniformally sharp across the field).

 

<p>

 

Of course this is all subjective and one can also argue for the bokeh

of the newer lenses but "to each his own".

 

<p>

 

Then again, one can also point to the Nikkor lenses which are over-

corrected for spherical aberrations and aren't really designed

with "bokeh" in mind. That is what you pay for in Leica glass.

Somehow, Leica is able to design their ASPH surfaces so that they

approach total correction of spherical aberrations on the low side.

So there's always a touch of residual spherical abberation in the

glass to give the pleasing OOF effects (as witnessed by the 24

Elmarit... an outstanding lens in my arsenal). But for the 35 mm

focal length I felt that Leica's approach to perfection was an

exercise in compromise.

 

<p>

 

Cheers,

[MTC Photography]

Field curvature

[steve_rasmussen]

I have never heard of bokeh being an aberration and I am doubtful that

designers actually consider it as a characteristic of a lens. If

anyone has data to prove otherwise, I'd like to hear it. BTW,

spherical aberration can be corrected out nearly as well with

spherical surfaces as with aspherics by traditional means such as

using super high index glass and lens bending.

[Rob F.]

Lens bending? So Leica has flexible glass now? What'll they think

of next? Bokeh isn't an abberation of course. But it's a

characteristic Leica must have been aware of for many years. The

good bokeh of so many Leica lenses over the years can't be a

coincidence. Surely it has been intentional.

[MTC Photography]

Bob, your are right.

<p> The design of lens is much an art as science. It is not possible

to correct all and every high order abberations, hence, the the blend

of residue abberations makes up the characteristics of Leica lenses.

<p> Just like different brands of wine, has different taste and favour

even though the main components are water and alcohol.

<p> Like violins, the sound of an Antonio Stradivarius is

differernt from Nicolo Amati.

<p> The lens designers of Wetzlar, Midland and Solms are the

equivalent of masters of Cremona

[nesrani]

What must be sacrificed in order to gain sharpness?

 

<p>

 

Mostly, your bank account balance.

[budc]

Wade through Erwin Put's various treatise (links below) and you'll

know a lot more and probably be more confused in the process. At

least Erwin clears up a lot of misconceptions.

 

<p>

 

http://www.imx.nl/photosite/leica/technics/optics01/lensdesign01.html

 

<p>

 

http://www.imx.nl/photosite/leica/magazine/threegen.html

 

<p>

 

http://www.imx.nl/photosite/leica/technics/faq.html

[steve_rasmussen]

Bob: Lens bending is a very real technique used by designers to help

correct coma and spherical aberration. Maybe Martin will explain it to

you.

[ray_moth]

One thing that I have heard is that highly corrected Leica lenses can

suffer from some slight vignetting at wide aperture, although this

can be overcome by stopping down by one or two f-stops.

[roberto_watson_garc_a]

I also belive vignetting can be easily corrected in printing than an

aberation.

[peter_hughes1]

The cult of sharpness came about, I believe, because of the needs of

commercial photographers to have snappy, contrasty, razor sharp

images. But there is much more to the character of a lens than

sharpness, which is why many photographers--especially the ones who

have recovered from the "latest is greatest" fever--prefer older

lenses. But, as I have said elsewhere, trying to discuss the

character of a lens with most photographers would be like trying to

discuss the character of acoustic pianos with pop keyboard players.

The nuances have long been lost in the noise.

[Rob F.]

I'm waiting to hear how lens bending works. Can this be done at

home?

[paul_chefurka]

Well, my wife once discovered a 135/3.4 I hadn't told her about.

When she was through, the lens barrel had acquired a substantial

curvature. Maybe that's what this was about. Fortunately I had full

passport coverage, because I needed it to go and live in another

country till she cooled down...

[roberto_watson_garc_a]

Don´t let cool down too much Paul, remember the temperature of color.

Keep it 3.4...

[steve_rasmussen]

OK Bob: It was discovered many years ago that a lens element had more

spherical aberration when both surfaces had the same radius of

curvature as opposed to having different curvatures. Designers found

that a ratio in curvature between the two sides of around 6 to 1

nearly eliminated spherical. This bending of the lens away from a

symmetrical shape is known as lens bending. No, they don't actually

bend the lens, it is ground to the designed shape.

[roberto_watson_garc_a]

Well Steve, lens designing can be as fascinating as making pictures.

I confess my self as a frustrated mathematic.

[david_bellamy]

Some bokeh stuff I found recently:

 

<p>

 

Tamron 90/2.8 bokeh pictures. I like my 90/2.5 bokeh a bit better I

think, although I dont think the pics on this link were taken wide

open:

http://www.geocities.com/SoHo/Workshop/8827/TamronBokeh.html

 

<p>

 

Links:

http://www.kenrockwell.com/tech/bokeh.htm

http://www.imx.nl/photosite/leica/technics/optics01/lensdesign01.html

http://www.imx.nl/photosite/leica/technics/faq.html

http://www.imx.nl/photosite/leica/magazine/threegen.html

http://www.canon.com/do-info/

http://www.foto.no/nikon/lens_surv.html

http://nemeng.com/leica/

 

<p>

 

"Bokeh" by Peter Zimmerman.

http://www.slonet.org/~dkrehbie/bokeh/bokeh.htm

 

<p>

 

A Technical View of Bokeh:

http://fox.nstn.ca/~hmmerk/HMArtls.html#anchor26001

http://fox.nstn.ca/~hmmerk/HMBooks.pdf

http://fox.nstn.ca/~hmmerk/DOFR.html

http://fox.nstn.ca/~hmmerk/

 

<p>

 

 

Minox Historical Society: Bokeh:

http://www.minox.org/bokeh.html

 

<p>

 

Bokeh-Shmokeh?

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=005rYD

 

<p>

 

Bokeh: Various Questions:

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=000fFO

 

<p>

 

Le*ca Test vs Trial part 2 and Re [Le*ca] Diffraction limited; bo-ke:

http://mejac.palo-alto.ca.us/leica-users/v18/msg09754.html

http://mejac.palo-alto.ca.us/leica-users/v17/msg11954.html

 

<p>

 

Re: "If it ain't bokeh, don't fix it!" or "So Confused I'm going in

Circles.

http://www.lynnfarmerphoto.net/35MMBoard/messages/2dqtr99/3896.html

 

<p>

 

Other messages:

http://www.lynnfarmerphoto.net/35MMBoard/messages/3dqtr99/5343.html

http://digistar.com/rollei/1999-09/0629.html

 

<p>

 

*YAWN* Time for bed, methinks. More pictures to take tomorrow!

 

<p>

 

Dave Bellamy.

[david_bellamy]

Some pretty good stuff on those links Bud, - better than most I have

found on the web. I was looking for some good lens design

information, or some things referring to camera lens 'quality',

resolution, MTF?, SQF?, bokeh etc. Any more ideas for websites or

books on those?

 

<p>

 

I was particularly fascinated by how the designers manage to get the

out of focus image to be 'centre-weighted' on both sides of focus,

giving good bokeh, or if that is indeed possible - it seems to be

according to some things I have read lately.

 

<p>

 

It is good to know that some designers at least consider the

aesthetics of the image as well as the technical issues such as

sharpness of resolution.

 

<p>

 

Kind regards,

 

<p>

 

Dave Bellamy.

[brian_harvey]

I think the best "BOKEH", is the adjustable kind. Sometimes, I also

like some auto focus, and maybe I'll have about 6 frames a second.

Oh, you'll need a Nikon 105, or 135 F2 DC to adjust your "BOKEH".

Leica does'nt make one. What am I thinking? No one else does either!!

[peter_hughes1]

Here someone has attempted to simulate bokeh with a rendering

program. I wonder how it compares to the real thing.<p>

<a href="http://www.flarg.com/bokeh.html">Simulated Bokeh

Rendering</a>