Biogon, planar, technical names or marketing?

[elmer3.5]

Hi, i´ve been around for a while and i can see there are different desing for lenses and each one has a name, but what i cannot tell is the reason for each name.

The biogon 35/2 is larger than the summicron 35/2.
Is this so, because the design itself means biogon to be larger or it´s because costs issues or pure marketing.
I remember both zm and contax G 28mm f2.8 biogons to be so different (beside the mount issue) in term of optic elements.

I read once the planar 50 zm has a short transition from focus area to ofa, and the site (i can´t recall where) told it was an advantage of the planar design.

Besides focal length, does lens design means longer or shorter transition through focus to out of focus areas?

Hope you can help me out with this one!

Bye and thanks in advance!

 

[Roger Hicks]

Both Biogon and Planar are designs, though there are variations in detail with speed and focal length: you might call them 'underlying' designs, or 'groups of designs'.

Some lenses have however been mislabelled for marketing reasons. The current 85/4 Tele Tessar, for example, is neither tele nor Tessar.

Try to get hold of Arthur Cox's book on photographic optics, or Sidney Ray's.

'Transition to out of focus' doesn't really mean all that much. Like Geoffrey Crawley's definition of bokeh -- 'good bokeh (preservation of subject shape in out of focus planes)' -- it's as much subjective as scientific.

Cheers,

R.

 

[Pico]

Roger has given a good answer.

I still wonder a bit about the origin of the name Biogon. It strikes me as a mix of ancient Greek (bio 'life') and (gon 'angle'), inferring a lens that encompasses what the eye can.

 

[tlitody]

The design names are not 100% truly scientific. The designer of a new type of design can call it what they want. And there is some crossover between lens designs. It's all very complex.

There is a useful freebie piece of lens software at the Linos site called Pre-Designer which gives several lens design types which you don't see on lens names.
Is an Angulon the same type of design as a Biogon? I don't know but I suspect so.

 

[Roger Hicks]

Is an Angulon the same type of design as a Biogon? I don't know but I suspect so.

I'm pretty sure that the answer is no. As far as I recall, an Angulon is completely symmetrical, and Biogons are quite a long way from symmetrical: I think they're triplet derivatives. But as you say, designs converge, and some Biogon sections look quite like some Super Angulon sections.

Cheers,

R.

 

[tlitody]

I don't think any lens is completely symmetrical or it would focus to the same distance as the subject. But I know little of lens design. I did read up on gaussian optics some years ago and found the maths so complex it took me an age to even begin to understand it. But I'm no mathematician and have forgotten most of it now.

 

[Roger Hicks]

I don't think any lens is completely symmetrical or it would focus to the same distance as the subject. But I know little of lens design. I did read up on gaussian optics some years ago and found the maths so complex it took me an age to even begin to understand it. But I'm no mathematician and have forgotten most of it now.

No. Many lenses are completely symmetrical, in order to cancel out aberrations: consider a Rapid Rectilinear. Focus is how far you hold it from the film/sensor. At the focal legth, it's at infinity. Wind it out, and it focuses closer.

Cheers,

R.

 

[tlitody]

No. Many lenses are completely symmetrical, in order to cancel out aberrations: consider a Rapid Rectilinear. Focus is how far you hold it from the film/sensor. At the focal legth, it's at infinity. Wind it out, and it focuses closer.

Cheers,

R.

Take a 150mm symmar lens. Focus at infinity. Focal distance will be 150mm. So on the principal that symmetrical is "cancelling out" then it will not only cancel out abberations but also the refraction caused by the front elements and therefore focus at infinity and not 150mm if it was truly symmetrical. Symmetrical designs are not truly symmetrical. I think we may have to agree to disagree on this one.

 

[Roger Hicks]

Take a 150mm symmar lens. Focus at infinity. Focal distance will be 150mm. So on the principal that symmetrical is "cancelling out" then it will not only cancel out abberations but also the refraction caused by the front elements and therefore focus at infinity and not 150mm if it was truly symmetrical. Symmetrical designs are not truly symmetrical. I think we may have to agree to disagree on this one.

No. Really. There's no need to 'agree to disagree'. Read any book on optics, such as Cox or Ray. Cox, 15th ed. 1974, p. 234, 'What was used extensively during the last century was a lens consisting of two identical doublets with a stop between them . . .' and on page 240, 'The great virtue of the symmetrical lens construction is the almost automatic correction for coma, distortion and lateral chromatic aberration. One set of glasses really constitutes a lens with a stop behind it, and the other set constitutes a lens with a stop in front of it.'

Yes, there are tiny departures from symmetry for lenses used for normal photography (a perfectly symmetrical lens is by its nature optimized for 1:1 reproduction) 'But the lack of balancing, which is now introduced, is not responsible for more than a small amount of any of these [coma, distortion and lateral chromatic aberration] appearing in the lens. What coma, disortion and lateral colour are introduced, by the change from copying to normal conditions, can be removed by making slight changes to the curves of one set of glasses, while retaining the other set unchanged'. (page 242)

In other words, departures from symmetry are absolutely nothing to do with the lens not focusing at its nominal focal length, but are for the better correction of aberrations at infinity. A perfectly symmetrical lens certainly doesn't 'cancel out the refraction'. The only way you could do that is with gross asymmetry, via one positive lens (fatter in the middle) and one negative (thinner in the middle).

Alternatively, perform a simple experiment. Take two identical magnifying glasses. Hold one between your eye and the subject. Put the second one in front of (or behind) the first. Hold them at varying distances apart. Does the magnifying effect disappear? No. This is a completely symmetrical lens, and the refraction will NEVER cancel out.

Cheers,

R.

 

[ferider]

90% of lens names today are used for marketing reasons only. A ZM Biogon today is not the original Biogon, by no stretch. A ZM Planar is a planar-based design much like a 50 Summicron. And the 85mm ZM Sonnar is actually a double Gauss design. Etc.

 

[Roger Hicks]

90% of lens names today are used for marketing reasons only. A ZM Biogon today is not the original Biogon, by no stretch. A ZM Planar is a planar-based design much like a 50 Summicron. And the 85mm ZM Sonnar is actually a double Gauss design. Etc.

The figure of 90% is probably too high, and the idea that there is an 'original Biogon' ignores the fact that all lens designs evolve. The earliest Tessars are f/6.3. Does this mean that later, faster Tessars are no longer Tessars? And an original pre-war 35/2.8 Biogon (6-glass, 4-group triplet derivative) is quite a lot different from an original 1950 21mm to 75mm Biogon (8-glass, 5-group).

Cheers,

R.

 

[ferider]

All lenses are derived from a basic single element design 🙂

I was trying to answer the OPs question.


My point is, the names mean very little nowadays, if not nothing, for the user.

During its evolution, the Planar, for instance, has evolved into a myriad of lenses of very different characteristics. Take the Canon 50/1.2 LTM with little center resolution and high corner softness, vs. a modern Summicron or ZM Planar with outstanding performance and smooth rendition across the field. All derived from the same basic design, and hugely different for the user. For the Biogons, a Jupiter-12 will perform very differently from the ZM 35/2. In use, I can find no difference between the Elmarit-M 90/2.8 (modified Tessar) and M-Hexanon 90/2.8 (modified Ernostar).

Etc.

Today, lens names are just that.

Roland.

 

[trisberg]

Roger has given a good answer.

I still wonder a bit about the origin of the name Biogon. It strikes me as a mix of ancient Greek (bio 'life') and (gon 'angle'), inferring a lens that encompasses what the eye can.

That's pretty much it - at least according to the Zeiss web site http://www.zeiss.com/c12567a8003b58b9/Contents-Frame/dff2c1c5fb1a1b3ec12570fa005fed69. It gives some background on the brand names they use.

-Thomas

 

[elmer3.5]

Thanks!

Thanks!

Hi, thanks to all of you, great answers!

Nice explanations about zeiss lenses, sonnar: sonne, sun! Like summilux! very fast lenses! Also few glass-to-air surfaces!

On zeiss site they refer to planar as flat design among other qualities. Very helpful.
When i see the front part of the zm biogons i remember fisheye lenses, but i think it´s because correction and resolution matters more than lens design based on name.
Anyway i think contax g 28 biogon is much like a planar type!😀

Thought maybe biogon would mean something more technical like planar.

Bye and thanks again!