And please donīt tell me "to buy the asph one"; you know I really like this lens the only thing that disturbes me is itīs closest focus capability of 1 meter.Can you figure out of a single reasonable reason?

-- roberto watson (al1231234@hotmail.com), June 14, 2001

Answers

When a lens focus close, its abberation correction will change, therefore lens manufacuturers limit the close focus distance of their lens, beyound which, the abberation would be out of their specification.

You can add extension ring to focus closer, but you will see the edge sharpness are not good.

-- martin tai (martin.tai@capcanada.com), June 14, 2001.

All the early M lenses focused to 1 metre. It was not until the introduction of the 35/2 (and the 21/4) in 1958 that the first lenses that focused to .7 metre appeared. The 35/1.4 was introduced in 1961 and focused to 1 metre throughout its production run that ended in 1995. The M3 version, with the eyes to correct the field of view, focused down to .65 metre. The reasons are probably as suggested above though why the M3 version would be designed to focus closer is a mystery to me. As all the lenses that had "eyes" added to adjust the field of view for the M3 focused closer than their M2/4 counterparts, perhaps it was a mechanical/optical quirk of the conversion?

Cheers,

-- John Collier (jbcollier@powersurfr.com), June 14, 2001.

Yes I know about the DR! But it did not focus closer without a little help.

Cheers,

-- John Collier (jbcollier@powersurfr.com), June 14, 2001.

Well as far as I know the 35/1.4 preasph is the same design as the 35/2 preasph, but with an extra f/stop that produces all the softness and flare that we know, a price to pay for an extra f/stop, and the 35/1.4 preasph is a previous design to the 35/2 preasph,and before from the first 35/2 of the begining of 50īs, Iīll try to make some test to see if abberrations grow at closer distances than 1 mt. I have my doubts since other summiluxes and summicrons like those for the M3 do focus closer.

-- r watson (al1231234@hotmail.com), June 14, 2001.

Let me tell you the reason why Iīm so upset about this limited focus.

yesterday I went to a photographers meeting here in my hometown, (all profesional photographers with big nikons and 20-500 zooms and things like that), we suposed to talk about abberrations on lenses, but end up talking about the equipment we had at hand at the moment, a nikon 90s with a 24-120 zoom, some other olympus with a small zoom, a minolta, and all focused closer than my M4P and itīs 35/1.4,

That insignificant small and wire camera, that only focuses to one meter, well of course I know what I have, a leica was there a camera that hardly any one knew, and I hate to presume on my leicas, but felt stupid holding a $1600 camera that canīt focus closer than 1 meter, yes I know it was a silly thing.

-- r watson (al1231234@hotmail.com), June 14, 2001.

Well if you were getting together to talk about abberations, you picked the right lens to bring. Wide open that 35/1.4 has them all. There really is no plane of sharpness wide open just areas of reduced fuzziness! For its day, it was an excellent lens up to f/2 with an emergency reserve of f/1.4.

Cheers,

-- John Collier (jbcollier@powersurfr.com), June 14, 2001.

The sensitivity of abberation correction to distance is different from lens to lens; some lens form are more sensitive to change in dinstance than others. The fact that normal lens does have problem at close distance can be illustrated by the need for macro lens. When a standard lens focus close, the spherical abberation and astigmatism become undercorrected. Standard lens prevent this deterioration of performace by limiting the close range to certain limit (0.65m or 1 m, depending on lens type), while macro lens uses floating element to compensate for close focus effect.

-- martin tai (martin.tai@capcanada.com), June 14, 2001.

Roberto, to which of the apparently several versions of the 35mm f/2 is the f/1.4 equivalent in optical design? Early, middle. or late?

I've only used my 35 Lux wide open in situations where its softness would not be a problem: shots of my girlfriend across a table from me, and for recording paintings--mostly impressionist--in museums. In the former case, once or twice I have been up against the limit of its close focus capabilities--when we're seated at a small table. In both cases, critical sharpness is not needed. Stopped down, and used for landscapes, I've been pleased with its color, but haven't put it to the test for critical sharpness. That's what my Summicron is for. But I think the Lux actually has one less element than my 8- element Summicron, which might explain its nice color saturation. It never occurred to me until reading these posts that it might be the equal of my 35 Summicron. I'll have to check that out.

-- Bob Fleischman (RFXMAIL@prodigy.net), June 14, 2001.

The fourth version pre-asph 35/2 (1979 - 1997) is the one with a similar design to the 35/1.4.

Cheers,

-- John Collier (jbcollier@powersurfr.com), June 15, 2001.

Roberto, set your 35/1.4 at f2, and look into the front of the lens, the outer area covered by the diaphram, is equal to the uncovered area. This outer ring is the extra area gained by f1.4 over f2, it gives it one stop more speed; however, it is also the reason why that lens was made not to focus closer than 1m. Because light rays going through that area (when lens is wide open at f1.4 ) is bent more than rays through other area of the lens; more bent means more abberation, in particular spherical abberation and stimigmatism. Particular those rays coming from left or right edges of field of view passing through the edge of wide open f1.4 lens are bent most; the closer the object, the greater the bent angle and harder to correct the abberations. So it is necessary to limit the closest focus distance to preserve the edge sharpness at wide open

Rays passing the edges of 35/2 lens do not bent as much, therefore 35/f2 lens can be allowed to focus closer,

-- martin tai (martin.tai@capcanada.com), June 15, 2001.

Why would anyone want to use a wide angle lens for close-ups, anyhow?

-- Bill Mitchell (bmitch@home.com), June 15, 2001.

Granted the 35 isn't the ideal close-up lens for either an RF or an SLR. But if you're doing a one body, one lens scenario there are some limits and it's a point worth thinking about. I use both SLRs and RFs, and the 35 on an SLR generally will go down to .3 meters; the best any RF I have will do is about .8.

-- Joe Brugger (jbrugger@pcez.com), June 15, 2001.

Bob as John wrote it is the foufth version of the 35 summicron that has a similar layout design as tha 35/1.4, I wander how good is the performace of a 35/1.4 designed for the M3, the one that focuses to 65 cm.; about the close focusing range usage in a wide angle is for me very important, specialy in wider lenses, not so much for portraits but for very first planes some times

-- r watson (al1231234@HOTMAIL.COM), June 15, 2001.

In rare occasion, if closer focus is necessary, there is always the possibility of adding a close lens (pro lens in front. A close up lens of about 200 cm focal length may pull the close focus distance to around 65cm It is not as easy to use close up attachment for rangefinder, as is the case for SLR, but it can be done.

-- martin tai (martin.tai@capcanada.com), June 16, 2001.

Thanks to your answers to all of you; Martinīs solution realy amazed me. Well I have a summaron for my M3 that goes to 65cm, but I usualy go out with one camera and one lens, and I like the 1.4 posibility of the īlux, the plasticity of the īcron, and among other things the 65cm of the summaron; donīt tell me that I need a īlux asph 1.4; because I already belive I do; next time I go to usa Iīll take all the stuff that I donīt use and get a nice asph īlux, if i go to jail, i just hope they got computers there.

-- r watson (al1231234@hotmail.com), June 16, 2001.

Roberto, I get the idea of close up lens from my Zeiss Ikon Contaflex super B camera, it has a fix 50mmf/2.8 Tessar lens; it comes with a set of four Zeiss Ikon coated Proxar lenses: 20cm,30cm,50cm and 100 cm To use, these lenses without focusing, set the Contaflex Tessar lens to infinity, then using 20cm, the camera can close focus to 20cm, using 30 cm, the camaera can close focus to 30cm, etc.

Applying the same concept to Leica 35/1.4, if you use a 50cm close up lens, focus the Summilux to infinity, measure exactly 50cm from the front of the "Proxar"(Zeiss's name for close up lens).

You need stop down a bit to get sharp picture.

Yes, Leica has close up attachments for their R lenses, called ELPRO.

The ELPRO thread may fit the 35/1.4. But I use primarily my Macro-Elmarit 60/2.8 and my Minox cameras for close up (close focus to 20cm),so I don't know the thread detail of ELPRO lens.

I even use the Zeiss 20cm Proxar on my Minox camera, to bring the close focus distance down to 10 cm !

-- martin tai (martin.tai@capcanada.com), June 17, 2001.

The difference of using ELPRO or Proxar type close up lens on SLR vs rangefinder is that with SLR, no measurement is necessary, all one have to do is to look through the SLR viewfinder.

Also with SLR, the focus is continuous, and the lens don't necessarily focused at infinity.

With rangefinder, the viewfinder and rangefinder is not functional with elpro, the easiest way is to set the lens at infinity, and set set the focus distance equals to the ELPRO focal length.

The reason of "focuse at infinity" works with Elpro on M camera is because, when an object is placed at a the focal point of ELPRO, the light out from ELPRO is parallel, as if at infinity; then the Summilux when focus at infinity focuse the object exactly on the film plane.

-- martin tai (martin.tai@capcanada.com), June 17, 2001.

Ernst Leitz used to make close focusing devices for LTM and M;

• BEEOOY front attachment lens #2,#3 for use with LTM Elmar 50/3.5
• BOOWU copy stand with four adjustable extension legs for Elmar 50/f3.5 to make 1.4,1:6 and 1:9 close up copy
• BOOWU-M copy stand for 50mm M lens

-- martin tai (martin.tai@capcanada.com), June 17, 2001.

Just to clarify a point, normal lenses are generally symmetrical or close to it and usually Double Gauss designs. They do quite well in macro and infinity situations without the need for floating elements. Very few macro lenses have floating elements. Standard lenses that are symmetrical do not have problems with spherical aberration in close focus situations for the most part. This is the reason most copier lenses are symmetrical. It is the asymmetrical designs that need the floating elemnets the most.

-- Steve Rasmussen (srasmuss@flash.net), June 19, 2001.

Steve,

actually VERY few stand lens are symmetrical design.

Summilux, Summicron, Zeiss Planar are double Gauss, but unsymmetrical.

Symmetrical design is limited to slow speed lens, as there are only half the number of parameter available as unsymmetrical design. Therefore, AFAIK, no fast lens are symmetrical.

-- martin tai (martin.tai@capcanada.com), June 19, 2001.

Symmetrical lenses have very small aperture, for example Goerz Dagor f6.8, Goerz red dot Artar f9, f11. Goerz Dagor f4.5

The reason copy lens must use symmetrical design because symmetrical design automatically elimiated any distortion (barrel, distortion ), but it cannot be made into faster lens, because of spherical abberation at larger aperture.

-- martin tai (martin.tai@capcanada.com), June 19, 2001.

Leitz does like symmetrical design. Elmar, Hektor, Summar, Sumarit, Thumbar, Xenon, Summitar, Summaron, Summilux, Summicron, none are symmetrical. Summarex appears to be near symmetric.

Carl Zeiss have a number of symmetrical lens. The original Paul Ruldoph 1896 Planar f4.5 was symmetrical, so was Zeiss Dogmar (originally a Goerz design, merged with Zeiss Ikon in 1926); the most outstanding Carl Zeiss symmetric lens is Hologon 15mm/f8 super wide lens for Contax camera (recemtly recomputed for G1/G2

-- martin tai (martin.tai@capcanada.com), June 19, 2001.

I meant Leitz does not like symmetric design.

-- martin tai (martin.tai@capcanada.com), June 19, 2001.

wow this is getting very interesting. Thankīs Steve, thankīs Martin. I feel Iīm a frustrated mathematic; love all that has to do with lens design; would you recomend some good literature to keep me up.

-- r watson (al1231234@hotmail.com), June 19, 2001.

so 35/2.8 summaron is not symetrical? neather latest 50 summicron? I would bet they were?; why if they look symetrical in thier lens drowing design?; I mean same glass on one side of the diafragm and the other; I must be missing something.

-- r watson (al1231234@hotmail.com), June 19, 2001.

Symmetrical double gauss lens: Goerz Geotar, Plaubel Precostigmat Rodenstock Ronar, Scheider Isconar, Wollensak Rapter, Zeiss Topogon.

Unsymmetric double gauss: Kodak Ektar, Rodenstock Heligon, Schneider Xenogon, Wray copy lens, Zeiss Biotar, Planar, Leitz Summar,Summitar, Summicron 1953, 1968, Noctilux; Leitz Summilux 35mm (Mandler 1960) is a double gauss with an insertion of a thin meniscus lens.

-- martin tai (martin.tai@capcanada.com), June 19, 2001.

Roberto, a truely symmetrical lens no only has identical looking glasses, the surface curvatures, glass thicnkess, airspace curvature thickness and glass characteristics must be identical.

-- martin tai (martin.tai@capcanada.com), June 19, 2001.

I see Martin, have you read an article in the net on lens manufacture by Heinz Richter (Manufacture & preformace of photographic lenses), it is some of the most interesting; wish I could find something on the same level about lens design.

-- r watson (al1231234@hotmail.com), June 19, 2001.

this is it >http://www.f32.com/articles/article.asp?artlD=102<

-- r watson (al1231234@hotmail.com), June 19, 2001.

Roberto, imo, one of the best lens design book is

Warren J. Smith: "Modern Lens Design, A Resource Manual". McGraw Hill.

-- martin tai (martin.tai@capcanada.com), June 19, 2001.

Apparently, Martin, to classify a lens as symmetrical, we have to be a stickler for detail. Everything Perfectly symmetrical. Is there any room for "basically Symmetrical" or "Pseudosymmetrical" or "quasi- symmetrical." After Roberto's question about the 35mm f/2.8 Summaron, I looked it up in Morgan & Morgan. It's got 3 elements on each side of the diaphragm. the front and rear groups are both single elements. the groups closest to the diaphragm are both cemented doublets. each doublet has a concave surface facing each other across the diaphragm, and a convex surface facing the next element. If you looked fast, you'd think it was symmetrical. A close look reveals slight differences in the shapes of corresponding elements. So, it's not, strictly speaking, symmetrical, I guess. But it's a lot closer to it than an Elmar, for instance.

I think we need a term for almost-but-not-quite symmetrical lenses. Pseudo-symmetrical? Quasi-symmetrical? But what I like best is to borrow an idea from psychology, when someone is close to a certain diagnosis, but not quite the same. If we used the same kind of word manipulation, we could say the Summaron is "symmetroform" or "Symmetromimetic."

-- Bob Fleischman (RFXMAIL@prodigy.net), June 19, 2001.

Or, "symmetrotype"

-- Bob Fleischman (RFXMAIL@prodigy.net), June 19, 2001.

Bob, semi-symmetrical sounds good as well. The cross section you described sounds like a Double Gauss type. What I said in my post above was "symmetrical or close to it". Yes, very few normal lenses are exactly symmetrical and the same goes for macro lenses. Designers have found that they can take advantage of the virtues of symmetry without having to make the lens exactly symmetrical. Symmetrical lenses automatically correct lateral color, coma and distortion and to some degree curvature of field. But, it was found that some designs did not correct these aberrations out to an acceptable degree. The symmetrical Biogon was one. It had trouble with field curvature and so it was made slightly asymmetrical/unsymmetrical. Recent Plasmats and Double Gausses also benefited from the slight modification from symmetry as well. My five elment macro lens(not Leitz but for MF) is a Dynar design(semi-symmetrical) that is optimized for spherical correction at close focus. If it had a floating element, it would be for infinity correction.

-- Steve Rasmussen (srasmuss@flash.net), June 19, 2001.

Bob, AFAIK, in technical books on lens design, there are only symmetric or unsymmetric. Because lens design is high precision stuff, in a symmetric design the front group and the rear group can be interchanged, otherwise it is not.

Unsymmetrical "double Gauss" has already the connotation that the lens is modified from a symmetrical double gauss type.

-- martin tai (martin.tai@capcanada.com), June 20, 2001.

One draw back of symmetrical design: it does not correct field curature, on the contrary, it doubles what ever the curvature of one half.

-- martin tai (martin.tai@capcanada.com), June 20, 2001.

There is a misunderstanding, symmetrical design referes to two groups of identical lens group place on EACH side of the stop. The number of element and group thus must be plural, there cannot be any five element three group "symmetrical" design. There can be 6 element 4 group, eight element 2 group etc.

Voigtlander Dynar is a five element three group lens, modified from voigtlander Heliar. The Heliar and Dynar, look "symmetrical" only without the stop, but that is a no no. Heliar/Dynar is completely unsymmetrical. The placement of stop is three element 2 groups on one side, two element one group one the other side of stop

-- martin tai (martin.tai@capcanada.com), June 20, 2001.

Martin, FYI, there are many symmetrical lenses that are anastigmatic(corrected for astigmatism and have a flat field).

-- Steve Rasmussen (srasmuss@flash.net), June 21, 2001.

Steve, symmetry has nothing do do with correction of field curvature; the correction must be done by one half.

Petval sum is additivie, if the PZVL of one part os A, a symmetrical lens's PZVL = 2A, PERIOD.

If A =0, 2A =0 as simple as that.

-- martin tai (martin.tai@capcanada.com), June 21, 2001.

One often used method for the reduction or elimination of Petzval field curvature is by a combination of high refractive index glass (crown glass )positive element with lower reflective glass (flint glass ) negative element.

For example if a positive lens with power p1 and refractive index n1 combines with a lens with smaller negative power p2 and lower refractive index n2; ( n1 >n2, |p1|> |p2|

If p2/n2 = - p1/n1

or p2 = - p1* n2/n1 then Petzval sum = p1/n1 + p2/n2 =0, and field curvature is zero. But since the combined power p is

p= |p1|-|p2| still a positlve number, the result is a compound lens with positive power but no field curvature.

Of course, in actual lens design, the situation is much more complex, due the the consideration of other abberation, total elemination of field curvature may make other abberation harder to reduce; often resulting in compromise, with small amount of residue field curvature

Symmetry has nothing to do with correction of field curvature, on the contrary, asymmetry is needed.

An Ernst Leitz Summilux 35/1.4 has a field curvature of about 930 mm

-- martin tai (martin.tai@capcanada.com), June 21, 2001.

martin, think of me as a three years old kid; what does "fiel curvature of 930mm" means?

-- r watson (al1231234@hotmail.com), June 21, 2001.

Roberto, Summilux 35/1.4 lens field curvature is like part of a sphere with a radius of about 930 mm

-- martin tai (martin.tai@capcanada.com), June 21, 2001.

Martin, after reading what you've said, I agree that symmetry and field flatness are not related. I guess what misled me was the fact that I never see field flateners on symmetrical and unsymmetrical anastigmats. I was thinking their flatness was due to symmetry or near symmetry. Kingslake also says what you say. Is it safe to say that the curvature of field for symmetrical and unsymmetrical Double Gauss or Plasmats needs less work to correct than say a telephoto? Is this why field flateners are used on most telephotos and not on the others mentioned? When the Petzval sum comes out to zero, the field is flat but does it also bring the sagital and tangential surfaces together?

-- Steve Rasmussen (srasmuss@flash.net), June 21, 2001.

Steve, unlike standard lens, telephoto lens has different field curvature problem, its Petzval curvature tends to strongly backward curved, this makes more difficult to correct, hence field flattener may be added.

When Petzval sum is amde to zero, the field curvature of the tangental focus becomes flat (or nearly ); however stigmatism is a different abberation, it has to be corrected too, otherwise, there will be sagittal locus will not be coincide with the tangential focal surface. And and correcting the stigmatism, particular the higher order ones, may need to compromise field curvature with stimagtism. The common solution is to make the tangential focus surface curved inward, the sagital one curved outwards, so that the composite focus surface is in between, slightly curved inwards. The solution which makes a real flat composite turned out to be not the best solution in terms of image sharpness. Lens design is always a compromise, get some, give away some.

-- martin tai (martin.tai@capcanada.com), June 22, 2001.

A lot to learn from you fellows;

Martin I think I understand whatīs curvature of field; what I donīt is itīs radius of 930mm; do you mean 930mm from the plane of focus?, so from 930mm and further it decreases?; and so thatīs the reason why itīs focus limit is to 1mt?

-- r watson (al1231234@hotmail.com), June 22, 2001.

roberto, there are curvature and curvature, some curve more, some less. Soppose you cut a piece approxiately 24x36mm from a basket ball, that piece has less curvature than a piece cut out from ping pong ball; because ping pong ball has smaller diameter.

A curvature of radius 930mm means that the field curvature of the said lens, is just like a cut out (24x36mm) piece from a ball of diameter 2 x 930mm.

Miniumum focus distance is a different matter; as discussed before, only marco lens has widest focusing range, standard, or semi wideangle lens no.

-- martin tai (martin.tai@capcanada.com), June 23, 2001.

you just opended my mind, now I see it clearly; but I have more questions Martin; curvature of field; does it change with diferent f/stops?, or it is just masked by deep of field?; it is diferent from diferent focusing distances? or what happen at infinity and 1 mt focusing setting?; and martin let me thank you for your very kind explanations.sincerely roberto watson

-- r watson (al1231234@hotmail.com), June 23, 2001.

Roberto, field curvature is independent of fstop and focus distance. Even with front element focusing lens (such as some Tessar lens), the field curvature remains the same when the lens is focused at different distances, and the internal airspace changed.

Small aperture has greater depth of field, therefore, yes, the field curvature is masked.

-- martin tai (martin.tai@capcanada.com), June 23, 2001.

dear martin; I have read and test the flat field of the 35/1.4 non asph, in itīs two largest apertures (1.4 and 2), I understand it is part of itīs design, then it begins to have curvature of field from 2.8 and it is masked at about 4.5 or so; what am I missing here?, is this info rigth?, this flat field wide open is just part of itīs design?, does it happen to all kind of lenses?

The more I know the more questions I have, thankīs indeed martin

-- r watson (al1231234@hotmail.com), June 23, 2001.

Martin, I notice that most telephotos use a negative element or negative achromat as a field flattener. This indicates a forward curving field that has been corrected to be flat in these designs. A positive element as a flattener would indicate a backward curving field that was corrected. The Petzval Orthoskop was the only exception that I know of where it had a backward curving field in a telephoto. There are telescope designs that have a backward curving field as well. So Martin, when are you going to start a Photographic Optics site here on LUSENET? Steve --Forum Administrator--LUSENET's Pentax 6x7 SLR forum

-- Steve Rasmussen (srasmuss@flash.net), June 23, 2001.

Steve , "I notice that most telephotos use a negative element or negative achromat as a field flatte".

Are your sure about that ? AFAIK, it is not the case. A basic telephoto lens consists of a positive front group and negative rear group; the existence of negative element at the rear not necessarily indicated that it has a field flattner. It is a part of the lens.

Fleid flattner is not used in ordinary photographic lenses, it is not posssble with focal plane shutter. A a genuine field flattner touches the film surface, it plays the duo functions of flattening the field and physically keeps the film surface flat-- ie field curvature flattener and film surface flattenr.

Field flatter is used in astrophotography and aerophotography, not in most telephoto lens.

The most famous use of field flattener is the COMPLAN lens desgined by ex-Leitz designer Arthur Seibert for Minox II camera, the Minox camera has a shutter in front of the lens, he was possible to add a field flattener, which literally touchs the film. But he abandoned the field flattner as it scratches the film. The COMPLAN lens on susequent models of Minox camera has a curved field, and the camera film plane is curved to fit the field curvature.

Leica M and R has focal plane shutter, R has a mirror, there is no way to use "field flattener".

Lens design is a complex matter, it is risky to derived own conclusion based on personal observation.

As for discussion forum, I don't think it is a good idea, it is a strictly professional business, just as heart surgery, better leave it to professionals.

-- martin tai (martin.tai@capcanada.com), June 24, 2001.

roberto, I don't have the 35mm/1.4, so I cannot answer your question.

I looked at the ray tracing abberation plots of two Summilux 35mm/1.4 designed by Walter Mandler, these two lenses do exhibit field curvature. I don't think they exhibit flat field at wide open.

-- martin tai (martin.tai@capcanada.com), June 24, 2001.

One reason I like to use Minox camera is its very close focusing distance of 8" (20 cm) in a 4 oz camera; a SLR with a macro weights more than 2 pounds.

A pair of Buchere Spoon

-- martin tai (martin.tai@capcanada.com), June 24, 2001.

I have a Macro-Elmarit 60mm/f2.8. I use it more than my Summicro 50/2 because the macro lens has broad focusing range.

It must be very difficult to make macro lens high speed, most macro lens by Leica, Nikon, Canon are f2.8 max.

For high speed and wide angle lens, it must be very difficult.

How nice it would be if there is a 35mm/f2 macro-summicron !

-- martin tai (martin.tai@capcanada.com), June 24, 2001.

Martin, is it true that the current Minox cameras have a curved film "plane"?

-- Bill Mitchell (bmitch@home.com), June 24, 2001.

Martin, there was a telephoto lens used on a Kodak Disc camera that had a field flattener in which it did not touch the film. This was described by Kingslake. I guess this was an exception to the rule.

Thanks for all the optics info.

-- Steve Rasmussen (srasmuss@flash.net), June 24, 2001.

Bill, the curved film plane COMPLAN lens ended in the middle of older Minox C, some Minox C model has curved film plane, some C has flat film plane lens MINOX. The Minox lens was recomputed with newer glasses to get flat film plane. Current run titanium finished TLX, chrome finished CLX all has 4 element 3 group Tessar type 15mm/f3.5 flat field MINOX lens.

I tested the curved film plane COMPLAN vs flat field MINOX lens. The COMPLAN lens is indeed slightly sharper than the newer MINOX lens. However, TLX/CLX is much more expensive than older models with COMPLAN lens, even though the later is slightly sharper.

-- martin tai (martin.tai@capcanada.com), June 24, 2001.

Martin, You mentioned that field curvature is significant with the 35mm f/1.4 pre-ASPH. In using this lens over the past year or so for close-range wide-open shots, I am becoming convinced that what many of you have said about this lens being soft at full aperture is quite true. I've been using it wide-open for shots of paintings in art museums. The results have been gerally soft, although with the softness built into many impressionist paintings, it's often hard to tell how soft the lens is. Portraits from 3 feet, very carefully focused on the eyes at done at very high shutter speeds, are flatteringly soft, but soft nonetheless. I am wondering to what extent field curvature explains the problem, especially with the canvases; and to what extent the lens is just plain soft. I think I'll dedicate part of a roll to exploring this, and if the results confirm what I know so far, I believe this lens is going on consignment. (Then I can grap that 35mm Cron ASPH sitting on a local shelf.)

-- Bob Fleischman (RFXMAIL@prodigy.net), June 24, 2001.

Bob, all fast lens are soft at wide open, the best resolution for f1.4 lens is about f4 to f5.6. The asph improves the edge performance, however I think the its best performance is still stop down to f4.

For testing lens sharpness at wide open, I find that so times it may need to bracket distance to isolate any problem due to rangefinder out of alignment.

IMO, softness is a useful mean for artistic expression.:)

-- martin tai (martin.tai@capcanada.com), June 25, 2001.

Popular Photography published test results on M6 and Summilux 35,50,75 in August 1994, "We tested the legendary M6"

On the Summilux 35: "center sharpness well above average at center at all apertures, sharpness in corners, average f1.4 and 2, above average 4 to 8, well above average at f11 and f16.Optimum performance from f5.6 to f11. Very slight barrel distortion "

From pop SQF chart, the Summilux 35/1.4 delivers 2 grade A+ 20x24" prints, at f5.6 and f8, and 3 A grade 20x24" for a total of five grade A+/A 20x24" from f4 to f16, and outstanding lens.

The 50mm Summilux got one A+ and four A at 20x24" enlargement. The 35mm/1.4 is slightly sharper then the 50mm/1.4

Summilux 35 0.4 barrel, Summilux 50 0.9 barrel. The 35mm/1.4 also outperforms the 50/1.4 in lower distortion.

Summilux 35 can deliver A+/A grade 5x7" at all apertures. A+/A grade 8x10" from F2.8 to f11. A+ grade 11x14 from f4 to f16

PoP also provided film plane curvature tangential and sagittal plots for these three lenses.

-- martin tai (martin.tai@capcanada.com), June 30, 2001.

Martin, thanks for going to all that trouble. Those are impressive figures for the 35 Lux.

Regards,

-- Bob Fleischman (RFXMAIL@prodigy.net), July 01, 2001.

The problem with Popular Photography's SQF chart method is that there is no clear indication of lens performance of edge vs center, and the amount of distortion.

After Mason Resnick, (moderator of several B&W Photo forums in Lusenet ) took over the job of managing editor of POP, the SQF method was abandoned in favour of the traditional line per mm chart for center and edge used by old Modern Photography lpmm chart method, which IMO, is the best format for lens test data as compared with the presentation format of other photo magazines, including Pop's own SQF

-- martin tai (martin.tai@capcanada.com), July 08, 2001.