Zoom...today vs yesterday

[Nodda Duma]

CAD has been used since the 1950s for lens design, a fact well known in my professional community. However, the use of such was paid for (heavily) by the hour, and it wasn’t until the late 1970s and the advent of microcomputers and adaptation of optical design software to them that computer optimization, design, and analysis really began to cause a significant transition to a new generation of designs.

And as AgX mentions, new computer-designed optical glass types as well as computer-aided manufacturing in the 1980s also made a huge difference. Things just got better and more consistent.

 

[whojammyflip]

There is a difference between computers being used, and intelligent algorithm implementation yielding increases in lens performance. From comparison of the various series 1 Vivitar lenses, the performance of the later lenses is *slightly* better, but its a close run thing. I think the age gap between these lenses is something like 5 years, with the Vivitar 28-90 appearing around 1982/1983. From my measurements, which may be flawed, the Vivitar 28-90's performance is *slightly* better than the Kino Vivitar 35-85...when stopped down. This doesnt mean that the Kino made lens is junk! Wide open, the difference is more stark. I have a little Pentax M 28 3.5, which is particularly good relative to other lenses when wide open. Take a look at the MTF curves plotting contrast from the centre of the frame to the edge of the APS-C sensor of a K7. I have plotted the 20/40/80 lpmm curves, as the 10lpmm curve doesnt really show much as its jammed up near 100%.

Obviously, these MTF curves dont look as good as the published curves for something like a Zeiss Distagon 28 2.8. I need to get a Zeiss lens on a Leitax mount and put it through the same testing procedure, in order to be able to make a fair comparison. I guess Zeiss would logically have produced the most flattering results possible, as its marketing material.


Wide open shots, f2.8-f3.5

Vivitar Series 1 28-90mm, 28mm, at f2.8

Vivitar Series 1 35-85mm, 35mm, at f2.8

Pentax M 28mm 3.5, at f3.5

Optimal apertures, f8-f11

Vivitar Series 1 28-90mm, 28mm, at f8

Vivitar Series 1 35-85mm, 35mm, at f8

Pentax M 28mm 3.5, at f11

 

[Diapositivo]

Glass aspheric elements are not as expensive as you think with modern production techniques (molded glass, deterministic polishing, MRF). I think you’ll find that most aspheric elements in modern optics actually *are* glass....once you get above the disposable camera level of quality.

It’s not the 1990s anymore.

Btw the optics in the most prevalent consumer cameras — smart phone cameras — consist of molded aspheric glass elements. Equivalent plastic elements would be too large.

You must be right. I did not follow industry progress after the 90's. I remember the great progress due to plastic lenses. The progress was due to lenses being "printable" rather than having to work them in an aspheric shape.

From what I get, the same molding technique can now be applied to "true glass" lenses.

In any case, those lenses can now be produced at much lower cost, which represents a great progress in cost, performance (and maybe weight, maybe not. That depends on the effect of the aspherical elements on the optical scheme).

I think zoom lenses exhibited great progress in the last decades in any case. The progress appears clear to me in terms of zoom ratio, weight, cost. Fixed-focal lenses improved "less" because they are less complex and there were, 30 years ago, fixed-focal lenses with wonderful optical qualities.

 

[locutus]

Leitz Wetzlar (Leica) received its Zuse Z5 computer in 1953.

http://www.horst-zuse.homepage.t-online.de/z5.html

An Incredibly primitive machine, but a fully programmable computer none the less.

 

[ph]

Leica & optics expert Erwin Puts does believe that zooms can be made to compete with fixed focal lengths and cites some examples,

As to computer use "designed by computer" is about as informative as "hand made". Programming for finding optimum solutions is of course better than just doing ray-tracing. Apparently Zeiss owned and used a SUSE computer in the mid 1950es. If so, hourly charges would not have held them back from continuous use. Still,, there is quite a distance between using the computations and to actually make and mount the elements.

p.

 

[Nodda Duma]

Leica & optics expert Erwin Puts does believe that zooms can be made to compete with fixed focal lengths and cites some examples,

As to computer use "designed by computer" is about as informative as "hand made". Programming for finding optimum solutions is of course better than just doing ray-tracing. Apparently Zeiss owned and used a SUSE computer in the mid 1950es. If so, hourly charges would not have held them back from continuous use. Still,, there is quite a distance between using the computations and to actually make and mount the elements.

p.

Yep. The bridge is called experience.

Historically, a good lens designer was good at simplifying ray tracing to derive aberration values, and knew how to tweak a design to correct what the ray tracing told him. Pre-1980s, the computer was used to speed up this process...which was about all they could do, and the optimization was primitive.

As computers became more powerful, so did the optimization, as well as the capability to perform tolerancing, ghost and stray light analysis, and non-traditional optical layouts. This drove a change in how lens design is practiced, and the emphasis today is placed on setting up an initial condition (selecting the proper baseline design form) to meet the design requirements. Additionally, millions of rays today can be traced every second...as opposed to dozens or thousands of rays a minute in the days of mainframe computing. The designer now need not be “distracted” by the need to simplify ray tracing for speed. This has led to greater flexibility in design, and a much deeper understanding of how perturbations impact the optics and imager as a system. It has also led to a much deeper understanding of how fabrication and assembly tolerances affect the range of performance that a production run will experience (i.e. the potential for “lemons” or “golden units”). More importantly, tolerancing can be optimized for more consistent performance.

This is why, even though computers were used pre-1980, the *real* computer revolution occurred after that timeframe, when computing power really opened up the full potential of optical designers to flex their mental muscle.



Experienced designers call experience “design best practices” and put it in documents and power points so that unexperienced lens designers don’t stubbornly dismiss advice provided by those of us who have been designing and producing optics for decades. Younger folks tend to pay more attention to a document or power point than the suggestions of acetone-tinged cranky old optics SOB’s.

As you can guess, people with no in-depth knowledge of a subject often ignore the advice of experienced folks...being as they are in the “I don’t know what I don’t know” stage of learning.

 

[AgX]

Leitz Wetzlar (Leica) received its Zuse Z5 computer in 1953.

http://www.horst-zuse.homepage.t-online.de/z5.html

An Incredibly primitive machine, but a fully programmable computer none the less.

And already substituted in 1958.

 

[AgX]

In this context seemingly fits my question, why a Canon 100-200mm 5.6 made it all the years from the FL- over the FD- to the New-FD-mount?

Any ideas?

 

[Nodda Duma]

Any ideas?

Nothing magical, if it propagated forward, then it means it has always been a solid design that was probably tweaked over time and improved with improved tolerancing, coatings, and glass / lens polishing manufacturing capability....I’m sure there were tweaks to radii, thickness to tighten up the performance in parallel with those improvements.

 

[whojammyflip]

As you can guess, people with no in-depth knowledge of a subject often ignore the advice of experienced folks...being as they are in the “I don’t know what I don’t know” stage of learning.

This sounds similar to the Dunning Kruger effect.

 

[Diapositivo]

Nothing magical, if it propagated forward, then it means it has always been a solid design that was probably tweaked over time and improved with improved tolerancing, coatings, and glass / lens polishing manufacturing capability....I’m sure there were tweaks to radii, thickness to tighten up the performance in parallel with those improvements.

My second ever lens, and first ever zoom, was the Minolta Rokkor MD 100-200 f/5,6, which is, I think, the "same" optical scheme of the Canon 100-200.
Sharp it is sharp, great contrast, low flare problems. I think this is due to the small number of lenses/groups.
It is affected by great distortion, low luminosity (but it's a constant aperture, at least), and an evidently "tragic" size when it is extended.
But love is love, and I love it.

http://forum.mflenses.com/testing-minolta-md-zoom-rokkor-100-200mm-5-6-t76172.html

I think now it would be unthinkable to put such a hugely long lens on the market.

 

[AgX]

Nothing magical, if it propagated forward, then it means it has always been a solid design that was probably tweaked over time and improved with improved tolerancing, coatings, and glass / lens polishing manufacturing capability....I’m sure there were tweaks to radii, thickness to tighten up the performance in parallel with those improvements.

As far as I know the optical design of that 5.6 lens was not changed over all those years.

My idea was, why marketing or using a 100-200mm F5.6 lens when the same manufacturer not only offered at F4.0 a 80-200mm but also a 70-210mm lens?
Using a 5.6 lens with a screen with split-image finder is no joy.

 

[Nodda Duma]

As far as I know the optical design of that 5.6 lens was not changed over all those years.

I agree. I didn’t imply it had been changed. The tweaks I mentioned would not be considered a change. But I sincerely doubt the design went all these years without review and respecification to track advances in manufacturing to get better quality control. Again, no change to the design, but tightening up of tolerances/tweaking of radii to better match evolving glass types (there was a reformulation of all glass two-three decades ago to remove lead) to get better/more consistent quality out of the production line.