En CLB41 Nasse LensNames Distagon

7/24/2019 En CLB41 Nasse LensNames Distagon

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Carl Zeiss AG Camera Lens Division Dezember 2011

From the series of articles on lens names:

Distagon, Biogon and Hologon

by

H. H. Nasse


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Carl Zeiss AG Camera Lens Division 2/15

Retrofocus lenses and why they were invented

In this third part of our series of articles onZEISS lens names, I would like to presentthree different lens types. All share the

final syllable gon in their name, whichindicates that the lens has a large fieldangle. This part of the name is derived

from the Greek word gonia () whichmeans angle and was also used bymany other manufacturers of wide-anglelenses. One of the earliest examples is thefamous Hypergon with its 130 fieldangle, which the Berlin firm Goerzintroduced to the market around 1900.

However, the three lens types Distagon,Biogon and Hologon also display major

differences along with this commonfeature. Examining these differences isparticularly helpful to understanding theparticular lens properties. Thus it seemedappropriate to discuss them in the samearticle.

In photography, the term standard lensis

usually understood to mean a lens with afocal length about as long as the diagonalof the image field. The 24x36 mm imageformat has a diagonal of 43.3 mm, APS-Cformat 28.4 mm, the analog medium

format is between 70 and 90 mm with itsdifferent versions and the digital between55 and 60 mm.

With a wide-angle lens, the focal length issignificantly shorter than the diagonal ofthe picture format. If it is about the sameas the long side of the format, the lens isconsidered to be a moderate wide-anglelens. Super wide-angle lenses are thosewith focal lengths between the length ofthe short side of the format and half thediagonal. Those with even shorter focal

lengths are often referred to as extremewide-angle lenses, though the delineationbetween super and extreme is fluid, ofcourse, and to some extent a matter oftaste.

A lens with a shorter focal length can bederived from an existing one by reducingall its dimensions accordingly. This issimilar to the principle of model railroads.Thus many small and medium format

lenses look very similar, differing just insize. Of course, with this scaling of

optical designs, a reduction of the image

circle and of the distance of the lensesfrom the image plane is achieved, which isnot always desired. Thus a usable wide-angle lens is not automatically obtained,and if the focal length and image circle arereduced by the same factor, the fieldangle remains the same.

In fact, moderate wide-angle lenses havebeen made with the design structure ofthe conventional lens types like Tessarand Planar. However, if the field anglecontinues to be increased and good

correction for the increasingly obliqueincident rays of light is desired, thesedesigns reach their limits. Wide-anglelenses have always required new ideasand are among the most difficultchallenges in optics.

A particular problem of many cameras isthat the distance of the last element inthe camera lens from the image planemust not be less than a particular value,because some technical function stillrequires space between the lens and the

image sensor. With an SLR camera that isthe reflex mirror which redirects the imageonto the focusing screen before thepicture is taken. Also a beam splittingprism in cameras with three sensors forthe primary colors or just the function forTTL light metering can require a largeback focal length for the lens. In the1930s, cine cameras often had a lensturret for changing the field angle quickly.This function also required that the lenswas not extended too deeply into thecamera.


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In 1917, the Technicolor process for colormotion pictures was introduced in the filmindustry. From 1932 on it was verysuccessful, and in 1939 the film epic Gonewith the Wind used it. The Technicolorcamera used a splitter prism to produce first

two, later three color partial imagesadjacent to one another on the strips of film.This prism required so much spacebetween the lens and the film that the focallength of normally constructed lenses couldnot be shorter than 50 mm. Nonetheless, tofilm with this camera with larger field angle,despite these constraints, a new lens typewas developed in those days, with a largenegative element arranged in front of astandard lens.

In 1950, Pierre Angnieux in Paris andHarry Zoellnerat Carl Zeiss Jena appliedalmost at the same time for a patent forthe first lens for 35 mm reflex camerasbased on this principle of the invertedtelelens. The Jena lens was given the

brand name Flektogon, and Angnieuxnamed his lens Retrofocus to indicatethat the focus was shifted backward.

This term originally introduced as a brandname ultimately became a generic namefor all these lenses, known better todaythan the expression inverted telelens.

The principle of the inverted telelens, imaging of an object from left to right. A lens with negativerefractive power in front of the positive refractive power of the base lens produces a greater fieldangle on the object side while increasing the back focal length, i.e. the distance of the last lens vertexfrom the image plane.

The diverging effect of this lens increasesthe field angle while slightly reducing theconverging effect of the positive refractivepower behind it, so that the rays do notintersect until a greater distance is reached.Thus the negative power front lens reducesthe focal length and increases the backfocal length. Because this arrangement ofrefractive powers is exactly the opposite ofthe telelens design principle, such a lens isalso called an inverted telelens.

There were already certain predecessors ofthis at the beginning of the 20th century,where such negative elements were placedin front of projection lenses to produce largeprojected images in small rooms. Such frontconverters are still available today forpermanently integrated lenses.

From the end of 1952, such wide-anglelenses were also developed at Carl Zeissin Oberkochen, initially a 5,6/60mm for theHasselblad 1000F. These have borne thebrand name Distagon ever since,

derived from distance and the previouslymentioned Greek word for angle. Thus aDistagon is a wide-angle lens with alarge distance to the image.


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Lens cross-section of the first retrofocus lensfrom Carl Zeiss Oberkochen, the Distagon 5,6/60for the Hasselblad 1000F (1954).

An improved version of the Distagon 5,6/60 fromthe year 1956. This optical calculation wasscaled and produced as the Distagon 4/35 forthe CONTAREX 35 mm camera starting in 1958.Since the spherical aberration increases as thefourth power of the aperture, for example, onecan make the same lens design faster forsmaller image formats.

The lens cross-sections show that thesewide-angle lenses were not excessivelycomplex in design with six or sevenelements. And they were an example ofmodesty with respect to speed. Today, thethought of a maximum aperture of f/4 wouldprovoke an amused smile, but at that timethis was a wise limitation to ensure that themoderate wide-angle lenses offered morethan just moderate quality.

f-number k = 8

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Contrast transfer of the Distagon 4/35 at an

aperture of f/8. In its day it was among the bestof this focal length.

As simple as the basic idea of theretrofocus lens is, the calculation of theoptics initially faced new challenges. Thisis because the strongly asymmetric designwith respect to the distribution of therefractive power led to the occurrence of

some aberrations to a far greater extentthan with an approximately symmetricallens, where the contributions from thefront and back half of the lens compensateeach other.

The problems which occur to a greaterextent are primarily coma, distortion andlateral chromatic aberration. It was firstnecessary to learn how best to managethese aberrations. And because the earlyDistagon types were designed in the1950s with little computer support, this set

limits to the complexity of the opticaldesigns.

Thus the advancement of the Distagon inthe 1960s and 1970s was inextricablylinked with the enhancement of theoptical calculation which occurred at thattime due to increasingly fast computersand improvements in programs, whichgradually enabled automated optimizationof a design. In Oberkochen, ErhardGlatzel was a primary force in theapplication of this new tool, which resulted

in many excellent Distagon designs.

By the mid-1970s, this progress,supported by new optical glass types withproperties not previously available,enabled such good, complex lenses suchas a 3,5/15, 1,4/35 or 1,4/25 to be built forthe 35 mm SLR.

Today the Distagon type is one of themost important and best performingprinciples of design for our camera lenses,

particularly if large field angles and a highmaximum aperture are both required. Ofcourse, the lens is then somewhat largerand more complex and thus also notcheap. But its good definition and imagefield illumination characteristics are worththe effort involved.


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If the design conditions require extremeasymmetry such as in the 3-chip camera inthe 2/3 format in which a color splitterprism with 48 mm length occupies thespace between lens and sensors, Distagondesigns have to be rather long compared to

the focal length:

With the extreme wide-angle DigiWideDistagon 1.7/3.9mm (focal length is aboutone third of the format diagonal, i.e.corresponding to about 14 mm in the 35mmformat), the overall length of the lens isabout 60 times as large as the focal length.

With this camera, a Distagon also isntnecessarily a wide-angle lens: theDigiPrime Distagon 1.5/70mm has the

field angle of a 280 mm lens for the 35 mm

format, yet it is a retrofocus lens due to thelarge back focal length demanded by theprism and the telecentric design but thetopic of beam angle will be discussed later.

Modern high-performance lenses of theDistagon type can be quite complex; 12 to16 elements are not uncommon. OurUltraprime Distagon 2.8/8mm for 35 mm

motion picture with a 130 field angle isconstructed with 24 elements. A fewexamples can illustrate what a long roadthis was from the very beginning to this

complexity:

f-number k = 4 f = 24 mm

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Contrast transfer of a retrofocus lens 4/24mmfrom the 1950s, here measured fully open. Thecurves nicely illustrate the typical difficulties to

make a good wide-angle lens: only a small areain the middle shows good image quality, butalready at 5 cm distance from the centre thecontrast drops to values, which are typical forvery fast lenses in the old days. Edge andcorners are overall very poor.

Since a wide-angle lens often shows awealth of details rather small in an image,the natural tendency is for the eye to haverather high expectations for the imagequality of the lens. At the very least, thislens would have to be stopped down

enough to increase its performance:


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4/24 mm at an aperture of f8; the contrast andsharpness are relatively good for sagittalstructures up to 15 mm image height but thenstill drop abruptly. The well-corrected imagecircle is actually too small, edge and cornersremain to look poor. Most of all, however, it isevident that the dashed curves for tangentialstructures fall sharply in the middle from highvalues. The cause of this is the large lateral

chromatic aberration.

Microscope photographs of the tangential lineimage of three camera lenses at 10 mm imageheight and f/8 aperture, from left to right:the 4/24 above, the Distagon T* 2,8/21 for theContax and the Biogon T* 2,8/21 ZM.

With the 24 mm lens from the 1950s, thetangential line image is 30 to 40 m wide,i.e. somewhat more than the circle ofconfusion (CoC) limit for lowenlargements. Thus particularly well-defined images could not be expected

from this lens, and at edges with greatdifferences in brightness it showed colorfringes. The two line images to the right of


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that are examples of perfect imagedefinition, which are achieved byparticularly high glass complexity in case ofthe Distagon T* 2,8/21, while the BiogonT* 2,8/21 relies on its symmetric design.

However, these two 21s are reallyexceptional lenses. The followingperformance curves are typical of themajority of the retrofocus super wide-anglesfor SLR cameras, clearly illustrating theefforts required to solve the problems ofasymmetry:

f-number k = 5.6 f = 20 mm

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MTF curves of the Flektogon 2,8/20 from CarlZeiss Jena at aperture f/5.6


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MTF curves of an otherwise excellent 4/21 whichalso shows the low tangential values toward theedge of the image due to lateral chromaticaberration.

In 1992, Karl-Heinz Schusterat Carl Zeissdeveloped the Distagon T* 2,8/21 for theContax/Yashica system, a retrofocussuperwide-angle lens which was at least as

good as the best symmetric types withrespect to image sharpness. The 2.8/21

even had a related lens, the PCApodistagon 3,5/25, with a larger imagecircle, which unfortunately was neverproduced in series due to its highmanufacturing costs.

Lens cross-section of the Distagon 2.8/21 forthe Contax SLR, a relatively complex lens with15 elements in 13 groups. However, it had noaspherical surfaces. Its performance,

particularly the perfect correction of lateralchromatic aberration, was achieved solely bythe combination of very special (andexpensive) high-index glass types with glasstypes displaying extremely high anomalous

partial dispersion.

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Already at aperture f/4, the Distagon T* 2,8/21achieved superb image quality; thus it is nowonder that its price on the pre-owned market

often exceeded the original price after it was nolonger produced.

The Distagon T* 2/25 ZE orZF.2is a newwide-angle lens for SLR cameras whichalso offers excellent overall performance.To achieve compactness despite thehigher maximum aperture, the design ofthis lens is not quite so complex,consisting of 11 elements in 10 groups.However, these also include threeelements made of glass types with a highanomalous partial dispersion, achievingchromatic correction which is not quite asgood as with the legendary 2.8/21, but


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which produces almost no visible colorfringes in most cases.

What is partial dispersion? Thismysterious-sounding technical term isappearing with increasing frequency in

brochures. If, for example, a negative andpositive lens are combined to correctchromatic aberration, then the element withthe lower refractive power must have thehigher dispersion so that the colordispersing effects of both lensescompensate for each other without alsocanceling the refractive powers of bothelements.

But Nature works in such a way that therefractive index of glass does not changeuniformly with wavelength, but the variation

becomes greater and greater at shorterwavelengths. Thus the graph of thesedispersions over wavelength is not linear; itis curved. Normally, the dispersion curvesfor glass types of higher dispersion showgreater curvature. This is why thecompensation of the color dispersion effectsdescribed above does not work perfectly. Asmall chromatic aberration remainsbecause the curvatures do not match.

Glass types with anomalous partialdispersion deviate from the normal

relationship between dispersion and thecurvature of the dispersion curve. For them,the ratio of the change in refractive indexbetween blue and green to the changebetween green and red differs from that ofnormal glass, allowing better chromaticcorrection with these glass types.

Optical design of the new Distagon T* 2/25 ZF.2

The next to the last element of the lens hastwo aspherical surfaces. These contribute tobetter correction of the spherical aberrationsand coma caused by the higher maximumaperture, and they have a favorableinfluence on distortion. Thus the 2/25 no

longer displays the wavy distortionsometimes criticized in the 2.8/21.

In focusing, the front and back part of thelens are moved differently (using floatingelements) to maintain high image qualityeven at close range.

In particular, it is a general characteristic ofasymmetric lenses that they are moresensitive to changes in scale if no particularcountermeasures are taken. The olderDistagon T* 2,8/25 focuses by means of an

overall movement without variable airspaces, and therefore it cannot be seen inany way as a macro lens despite its verynear short focus.

Image corner (500 x 500 pixels from 24 MP) withthe Distagon T* 2,8/25 at a distance of 25 cm,stopped to aperture f/8.

Image corner (500 x 500 pixels from 24 MP) with

the new Distagon T* 2/25 at a distance of 25 cm,stopped to aperture f/8.


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MTF data for a Distagon T* 2/25 ZF.2 at fullaperture. A large part of the image area displayshigh, uniform quality, a brilliant picture with

excellent reproduction of details. Stopping downis only necessary if the outer edges areimportant or greater depth of focus is desired.


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The Distagon T* 2/25, stopped down slightly.


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Comparison with the Distagon T* 2/28 for theContax from 1974 shows the improvement

achieved.


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The other approach to outstanding picture quality:symmetrical wide-angle lenses

If the design of the camera permitselements of the lens to be placed also fairly

close to the image, i.e. if a short back focallength is possible, then image qualityequaling the best Distagon lenses can alsobe achieved at much lower effort byconstructing an approximately symmetricallens.

In 1946 the first patent for a new kind of

symmetrical wide-angle lens was applied forby the Russian lens designer MichailRoossinov. It looked as if two retrofocus

lenses had been combined with the rearelements together and thus had a

symmetrical arrangement of positiverefractive powers close to the aperture,surrounded at the front and back by stronglynegative menisci.

As of 1951, Ludwig Bertele carried thisidea further and designed the legendaryBiogon on behalf of Zeiss. At that time, italways had a maximum aperture of 4.5 andwas built with various focal lengths for aseries of image formats: 21 mm for the 35mm format, 38 mm for the 6x6 mediumformat, 45 mm for the 6x7 format, 53 mm

for 6x9 and 75 mm for the 9x12 largeformat. There was also a 2.8/38 testprototype for the medium format and aBiogon 5.6/60 for photogrammetry, whichwas developed for NASA.

The cameras used with these lenses wererangefinder cameras such as the Contaxfrom Zeiss Ikon or special housings in thesystem such as the Hasselblad Superwideor flat-bed cameras or special technicalcameras.

Optical design of the Biogon lens f/4.5

The name Biogonwas used for the firsttime in 1936 for a 2.8/35 mm lens for the

Contax rangefinder camera, also designedby Ludwig Bertele. Its name also includesthe final syllable gon, referring to theangle. Of course, the syllable bio had adifferent meaning than today, which isoften associated with foodstuffs inGermany and elsewhere. At that time itwas often used to express the possibilityof very dynamic photography and referredto quite different technical properties of thelens. We are already familiar with theBiotar, with a high speed which madedynamic photography possible.

A super wide-angle lens with a 90 fieldangle makes one think more of a camerawhich captures the subject with aperspective which, with appropriately highfinal magnification, gives the viewer theimpression of being in the middle of theaction.

The image quality of the Biogon wassensational in the 1950s, and itscombination of a large field angle andnonetheless perfect definition up to thecorners led to a real boom in wide-angle

photography. Even today, these lensesoffer credible performance:

Blendenzahl k = 4.5 f = 21 mm

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MTF curves of a Biogon 4,5/21 from 1956,measured at full aperture.


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In addition to excellent contrast anddefinition properties, these lenses alsooffered perfect image geometry with almostno distortion. For the Biogon 4.5/21, themaximum radial deviation was 40 m. Thatis less than 0.1%, i.e. nothing compared to

the 2 to 4% typical of retrofocus lenses withthe same field angle.

Thus it is understandable that these lensesalso continued to be used for a time in SLRcameras with a flipped-up mirror andattachable viewfinder. Convenience wasdeliberately sacrificed in the interest ofimage quality, because composing animage on the viewing screen is of coursesimpler and better than with a conventionalviewfinder.

This comparison of a Distagon 2,8/25 (right) witha Biogon 4,5/21 (left), both mounted for theContarex from Zeiss Ikon, demonstrates onceagain the great differences in the two designs.The Biogon is nearly as long, but disappears forthe most part into the camera; this of coursebrings its mirror to rest.

The new Biogon lenses designed in recenttimes have a somewhat larger back focal

length to facilitate exposure meteringthrough the lens with modern cameras aswell. A lens mount extending to directly infront of the focal plane shutter couldconceal the measurement cells to be usedto meter the exposure from the lightreflected by the shutter. Whereas the backfocal length of the Biogon 4.5/21 was only 9mm, in the Biogon 21 for the Contax G itincreased to 12 mm. In all ZM series lenses,the shortest back focal length is 15 mm. Forthis reason, the distortion is also slightly

greater, but still almost indiscernible. Onemight say that a few Distagon geneshave been incorporated in todays Biogonlenses. Ultimately, this slightly blurs thedistinction between the two types. Theeven shorter focal lengths of the ZM series

are thus called Distagon, butnonetheless there are enormousdifferences between a Distagon for theSLR camera and one for a rangefindercamera. This is because the 35 mm SLRrequires a back focal length of at least 38to 40 mm to move the mirror. With amoderate wide-angle lens (35 mm forsmall image, 24 mm for APS), the backfocal length is thus about the same as thefocal length and clearly requires a designof the Distagon type.

Optical construction of the Biogon T* 2,8/21ZM; compared to the original Biogon designs, ithas a back focal length increased to 15 mm forTTL exposure metering.

Biogon T* 2,8/28 ZM; the simpler it is to meetthe back focal length requirement, the greaterthe similarity of the design to the classicBiogon.


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Wide-angle lenses and digitalsensors

Even if the camera has no mirror or otherobstacles in the image space, the designof a wide-angle lens can have greatimportance, particularly when the camerahas a digital sensor which it nearly alwaysdoes today. This is attributable to a propertyof lenses that can be recognized from theexterior appearance of the lens without anyknowledge of its internal design:

Entrancepupils of the Biogon T* 2,8/21 ZM andDistagon T* 2,8/21 ZE. The virtual images of theaperture seen from the front appear the samesize to us, because the focal length and f-stopare the same. The f-stop is the ratio of the focallength to the entrance pupil diameter.

Exit pupil of the Biogon T* 2,8/21 ZM andDistagon T* 2,8/21 ZE. The virtual images of theaperture seen from behindare of various sizes.Since the f-stop is also the ratio of the exit pupildiameter to its distance from the image plane,this figure shows that the exit pupil of the

Distagon is farther away.

Incidentally, the entrance pupil is theprojection center of the lens for centralperspective imaging. For panoramaphotographs, one must swivel around theentrance pupil if the position of

foreground details with respect to thebackground is to be the same in adjacentpictures. Thus this point can be seenrather simply. By the way, in some lensesit is either in or even behind the image

plane, but not in those discussed in thisarticle.

The position of the pupils relative to theprincipal planes from which the focallength is to be measured can also beidentified by their size ratio:

With symmetric lenses, the entrance andexit pupils are the same size; this is thecase for the old Biogon lenses as well asthe Planar types for the rangefindercamera. The Biogon types slightly

modified for TTL metering display slightasymmetry of the pupil ratio (for example,entrance pupil to exit pupil = 7.7 / 10.3 mmfor the Biogon 2.8/21 ZM, 9.9 / 10.9 mmfor the Biogon 2.8/28 ZM). This is also thecase for Planar lenses for the SLRcamera, which also tend slightly towardDistagon characteristics, because therefractive powers in the front part of theGaussian type lens are somewhat smallerto achieve a sufficiently large back focallength.

If the entrance pupil is significantly smallerthan the exit pupil, then you have aDistagon-type lens. (For example,entrance pupil to exit pupil = 7.5 / 22.6 mmfor the Distagon T* 2,8/21, 17.6 / 35 for theDistagon T* 2/35.) For the telelenses witha shortened back focal length, such as aSonnar, it is exactly the reverse.

The exit pupil is the area from which allrays of light headed for an image pointappear to come. If it is far removed from

the image, then rays toward the edge orcorner of the image have a lower angle ofinclination with respect to the image plane.Lenses in which this angle is made assmall as possible are referred to astelecentric, because the exit pupil isvery far removed from the image.

However, telecentric lenses require verylarge bayonet diameters, so themechanical dimensions of the camera setlimits.


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It is also not at all the case that all rays oflight strike the image plane perpendicularlyin telecentric lenses. In all lenses, theaperture angle of the ray cone depends onlyon the f-stop and is identical at the sameaperture regardless of where the exit pupil

lies. With telecentric lenses, the angleschange less in the image field only.

But in any case, symmetrical wide-anglelenses are exactly the opposite oftelecentric ones, because their exit pupil isclose to the image. That has three importantconsequences:

1)The greater beam tilt at the edge causes agreater natural fall-off of light as per thecos

4 law in which the change in distance

between the pupil and image from themiddle to the edge and the photometriceffect of the oblique projection is expressed.Usually these lenses only have a littleartificial vignetting from the edges of themount, and the uniformity of the brightnessdistribution in the image changes little withchanges of the f-stop.The situation is different for Distagon types;in that case the artificial vignetting isdominating at full aperture, and as itdisappears when stopping down, the imagebrightness becomes much more uniform.

When stopped down, the Distagon hasbrighter corners.

2)Digital sensors do not respond very well tovery oblique incident rays of light. At thevery least, they become more inefficient orrequire compensatory measures such as asuitable shift of the light-gatheringmicrolenses relative to the pixel grid. Thatwas not necessary with film, as it wasessentially independent of direction.

3)Lenses with a very large beam tilt react in amuch more sensitive manner to a change ofrefractive index in the image space causedby filter plates in front of the sensor (suchas low pass and IR-blocking filters). If thefilter plate is not considered in the design ofthe lens, the edge definition will suffer. Theeffect of the additional path through theglass grows exponentially with the beaminclination. A Distagon which neverachieves more than 20

beam tilt in the corner of the image reactsmore tolerantly than a symmetrical wide-angle lens, which might reach a 45 tilt.This is why filters in digital Leicas are verythin to remain compatible with olderoptics.


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MTF curves of a Biogon T* 2,8/21 ZM, shownin the APS-C format ideal quality anduniformity up to the corners. But unfortunatelythese curves apply only to the thin Leica filters,and not for all cameras to which this lens canbe attached.

If the filter is significantly thicker, thecontrast transfer for the image edgebecomes worse for tangential structures.In the graph of the curves, this looks likethe old retrofocus lenses but is caused byastigmatism rather than lateral chromaticaberration. The focus is shifted to greaterdistances for tangential structures by theadditional path through the glass. If thebest edge definition is to be achieved, thenall that can be done is to stop downfurther.


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MTF curves of the same lens as above, butwith a thicker filter in front of the digital sensor.


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The two types of wide-angle lensesdiscussed in this article thus each have veryspecific advantages and disadvantages:

Advantages of nearly symmetrical wide-angle lenses:

Small size and low weight

Very good, uniform definition despitemoderately high effort required

Usually excellent freedom from ghostimages

Disadvantages of nearly symmetrical wide-angle lenses:

Cannot be used with every camera

Require specially matched digitalsensors

More sensitive to the change of opticalparameters in the image space

Greater natural fall-off of brightnesstoward the edge of the image

Size comparison of nearly symmetrical andretrofocus wide-angle lenses with the same focallength and maximum aperture.

Advantages of asymmetric wide-anglelenses:

Usable for all cameras in principle

Favorable characteristics for digitalsensors

Very uniform image field illumination atmedium apertures

High maximum apertures possible

A legend among camera objectivesThe importance of the beam inclinationangle described above is the reason why acomeback of some great legendaryobjectives is hardly imaginable. TheHologonfrom 1966was an extreme wide-

angle lens with a 110 diagonal fieldangle, which was popular for its highdefinition up to the corners of the imageand its complete absence of distortion.Thus it's no surprise that we are askedtime and again when it will bereintroduced. Unfortunately, we mustdisappoint its fans, because a beaminclination of about 55 in the corner of theimage is not compatible with digitalsensors, at least not today.The name of the lens is derived in partfrom the Greek word holos, meaning

everything or complete. It was builtfrom just three elements, two highlycurved, very thick negative meniscuslenses on the outside and a positive lensin the middle. One might describe it as aninverse triplet.However, the simple appearance of itsdesign does not mean that it was easy tomake. The precision requirements for theshape of the lenses and their centering areextremely high. Because of the difficultiesof production, the Hologon 16 mm for theContax G, which came later, had five

lenses, a technical trick to simplifymanufacturing, with the cementedelements made of the same types ofglass.

Optical design of the Hologon 8/15 mm for the

35 mm format. Its back focal length was only4.5 mm.


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CarlZeissAG

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meraLensDivision

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Some members of the family of wide-angle lenses:

1. Distagon T* 2,8/15 ZM for 35mm rangefinder camera

2. Distagon 3,5/15 for CONTAX 35mm-SLR

3. Distagon 2,8/25 for Contarex 35mm-SLR

4. Distagon 5,6/60 for Hasselblad 1000 F 2 x 2

5. Distagon 4/50 for Hasselblad 500 C 2 x 2

6. F-Distagon 3,5/30 Fisheye-lens for Hasselblad V-System

7. Distagon 4/40 IF for Hasselblad V-System 2 x 2

8. Distagon 4/40 for Hasselblad 500 C 2 x 2

9. F-Distagon 3,5/24 Fisheye with circular image for Hasselblad

10. Distagon 2,8/21 for CONTAX 35mm-SLR

11. Distagon T* 2,8/21 ZE for Canon EF-mount

12. Distagon T* 1,4/35 ZF.2 for Nikon F-mount

13. PC-Distagon 2,8/35 Shift-lens, automatic diaphragm (CONTAX)

14. PC-Distagon 4/18 Shift-lens for 35mm motion picture camera

15. Hologon 8/16 for CONTAX-G electronic rangefinder camera

16. Biogon 4,5/21 for Contarex 35mm-SLR

17. Biogon 2,8/21 for CONTAX-G electronic rangefinder camera

18. Biogon T* 2,8/21 ZM for 35mm rangefinder camera

19. Biogon 4,5/38 on Hasselblad Superwide 2 x 2

20. Biogon 4,5/38 in NASA-version for space photography

21. Biogon 2,8/38 Prototype of 38mm Biogon with higher speed

22. S-Biogon 5,6/40 for close distance copy applications

23. Biogon 4,5/76 9-lens version for 114x114 mm aerial photo

24. Hologon 8/110 for large format 13x18 cm

25. Distagon 12/T1.3 for 35mm motion picture camera, PL-mount

26. Distagon 8/T1.3 for 16mm motion picture camera, PL-mount27. Distagon 2/10 for 35mm motion picture camera, PL-mount

28. Distagon 2.8/8R for 35mm motion picture camera, 130 field

29. Distagon 1.7/3.9 for 2/3 3-chip camera

30. Distagon 1.5/70 for 2/3 3-chip camera (not a wide-angle!)

31. P-Distagon 3,5/75 Projection lens for 2 x 2

En CLB41 Nasse LensNames Distagon

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