Bad copy of a lens?

I returned to photography as a serious hobby around 1996 and, of course,
started using the Internet as a resource. To make a long story short, I
keep reading about good and bad copies of lenses. I also note that some
qualified users have posted information on their websites including pictures
and carefully(?) controlled test shots that support the conjecture that
there are good and bad copies of lenses.

My background is engineering technology, manufacturing, and ISO 9000 and I
cannot wrap my head around the wide range of variations that are being
reported. I respect the credentials behind many of the sources reporting,
and so am left in a quandary. Add to this mess the combination of lenses
with various camera bodies, and it gets even worse.

Any ideas out there? Thanks in advance.

"Charles Schuler" wrote in message
...
I returned to photography as a serious hobby around 1996 and, of course,
started using the Internet as a resource. To make a long story short, I
keep reading about good and bad copies of lenses. I also note that some
qualified users have posted information on their websites including
pictures
and carefully(?) controlled test shots that support the conjecture that
there are good and bad copies of lenses.

A "copy" generally refers to a unit that copies someone else's design, but
usually with poorer materials and construction techniques... "cheap
knockoff" is the more colloquial term.

My background is engineering technology, manufacturing, and ISO 9000 and I
cannot wrap my head around the wide range of variations that are being
reported. I respect the credentials behind many of the sources reporting,
and so am left in a quandary. Add to this mess the combination of lenses
with various camera bodies, and it gets even worse.

It's not hard to understand variations in quality in lenses. Take a good
lens, build a copy off the same blueprints, but use substandard glass or
even plastic for the elements, work to slightly wider tolerances, use flimsy
metals or plastics instead of stronger, more durable metals... you can see
all the places quality can start to go downhill. Impure or misaligned lens
elements may distort the light; loose-fitting moving components in zoom and
focus mechanisms can also bring distortion, or may tend to shift or wobble
with even the slightest movement.

Any ideas out there? Thanks in advance.

Ideas on what?

Here's a tried and true rule of thumb: you get what you pay for. Looking at
two lenses that look and spec identically, the more expensive one will nine
times out of ten give you better results.

"Charles Schuler" wrote in message
...
I returned to photography as a serious hobby around 1996 and, of course,
started using the Internet as a resource. To make a long story short, I
keep reading about good and bad copies of lenses. I also note that some
qualified users have posted information on their websites including
pictures
and carefully(?) controlled test shots that support the conjecture that
there are good and bad copies of lenses.

A "copy" generally refers to a unit that copies someone else's design, but
usually with poorer materials and construction techniques... "cheap
knockoff" is the more colloquial term.

My background is engineering technology, manufacturing, and ISO 9000 and I
cannot wrap my head around the wide range of variations that are being
reported. I respect the credentials behind many of the sources reporting,
and so am left in a quandary. Add to this mess the combination of lenses
with various camera bodies, and it gets even worse.

It's not hard to understand variations in quality in lenses. Take a good
lens, build a copy off the same blueprints, but use substandard glass or
even plastic for the elements, work to slightly wider tolerances, use flimsy
metals or plastics instead of stronger, more durable metals... you can see
all the places quality can start to go downhill. Impure or misaligned lens
elements may distort the light; loose-fitting moving components in zoom and
focus mechanisms can also bring distortion, or may tend to shift or wobble
with even the slightest movement.

Any ideas out there? Thanks in advance.

Ideas on what?

Here's a tried and true rule of thumb: you get what you pay for. Looking at
two lenses that look and spec identically, the more expensive one will nine
times out of ten give you better results.

A "copy" generally refers to a unit that copies someone else's design, but
usually with poorer materials and construction techniques... "cheap
knockoff" is the more colloquial term.

I did not explain it very well, so it seems. In this case (my post), "copy"
means one sample of a production run.

A "copy" generally refers to a unit that copies someone else's design, but
usually with poorer materials and construction techniques... "cheap
knockoff" is the more colloquial term.

I did not explain it very well, so it seems. In this case (my post), "copy"
means one sample of a production run.

"Charles Schuler" wrote in message
...
I returned to photography as a serious hobby around 1996 and, of course,
started using the Internet as a resource. To make a long story short, I
keep reading about good and bad copies of lenses. I also note that some
qualified users have posted information on their websites including
pictures
and carefully(?) controlled test shots that support the conjecture that
there are good and bad copies of lenses.
Yes, there are variations in the quality of lenses. Some people do indeed
make better lenses than others, and some have tighter tolerances than
others. Nearly all of the really bad ones have gone out of business.

As for one manufacturer copying the design of another, that is rare because
most of the designs are patented. Anybody can make a Tessar lens because
the patents ran out years ago.
Jim

"Charles Schuler" wrote in message
...
I returned to photography as a serious hobby around 1996 and, of course,
started using the Internet as a resource. To make a long story short, I
keep reading about good and bad copies of lenses. I also note that some
qualified users have posted information on their websites including
pictures
and carefully(?) controlled test shots that support the conjecture that
there are good and bad copies of lenses.
Yes, there are variations in the quality of lenses. Some people do indeed
make better lenses than others, and some have tighter tolerances than
others. Nearly all of the really bad ones have gone out of business.

As for one manufacturer copying the design of another, that is rare because
most of the designs are patented. Anybody can make a Tessar lens because
the patents ran out years ago.
Jim

Charles Schuler wrote:
I returned to photography as a serious hobby around 1996 and, of
course, started using the Internet as a resource. To make a long
story short, I keep reading about good and bad copies of lenses. I
also note that some qualified users have posted information on their
websites including pictures and carefully(?) controlled test shots
that support the conjecture that there are good and bad copies of
lenses.

My background is engineering technology, manufacturing, and ISO 9000
and I cannot wrap my head around the wide range of variations that
are being reported. I respect the credentials behind many of the
sources reporting, and so am left in a quandary. Add to this mess
the combination of lenses with various camera bodies, and it gets
even worse.

Any ideas out there? Thanks in advance.

I am not sure of how much of a difference you are reading about between
copies (samples) of a specific lens. There are differences, always have
been always will. I think you will generally find a wider range of
differences with cheaper lenses, More expensive lenses tend to be built to
tighter standards. In a given case, a cheap lens may give outstanding
optical results, while the next one is poor. In both cases the mechanical
parts are almost certainly at best fair in a cheap lens.

It reminds me of an inspection I made while working for the government
at a soup factory. They had an area where rejected soup was sold. I assumed
it was cans with less meat than their quality standards would allow. I was
close. They also rejected it when there was too much meat. Why?, I asked.
Well it seems if someone gets one can with too much meat, they expect the
same from all the cans, so they make sure every can has the same amount.

I never saw that in the lesser brands. They seemed to be happy as long
as each can had the minimum amount.



--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

Charles Schuler wrote:
I returned to photography as a serious hobby around 1996 and, of
course, started using the Internet as a resource. To make a long
story short, I keep reading about good and bad copies of lenses. I
also note that some qualified users have posted information on their
websites including pictures and carefully(?) controlled test shots
that support the conjecture that there are good and bad copies of
lenses.

My background is engineering technology, manufacturing, and ISO 9000
and I cannot wrap my head around the wide range of variations that
are being reported. I respect the credentials behind many of the
sources reporting, and so am left in a quandary. Add to this mess
the combination of lenses with various camera bodies, and it gets
even worse.

Any ideas out there? Thanks in advance.

I am not sure of how much of a difference you are reading about between
copies (samples) of a specific lens. There are differences, always have
been always will. I think you will generally find a wider range of
differences with cheaper lenses, More expensive lenses tend to be built to
tighter standards. In a given case, a cheap lens may give outstanding
optical results, while the next one is poor. In both cases the mechanical
parts are almost certainly at best fair in a cheap lens.

It reminds me of an inspection I made while working for the government
at a soup factory. They had an area where rejected soup was sold. I assumed
it was cans with less meat than their quality standards would allow. I was
close. They also rejected it when there was too much meat. Why?, I asked.
Well it seems if someone gets one can with too much meat, they expect the
same from all the cans, so they make sure every can has the same amount.

I never saw that in the lesser brands. They seemed to be happy as long
as each can had the minimum amount.



--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

"Charles Schuler" writes:

My background is engineering technology, manufacturing, and ISO 9000 and I
cannot wrap my head around the wide range of variations that are being
reported. I respect the credentials behind many of the sources reporting,
and so am left in a quandary. Add to this mess the combination of lenses
with various camera bodies, and it gets even worse.

Lens design is a balancing act. Take any one single element out of a
lens and test it, and you'll find that its performance is awful - bad
chromatic and spherical aberration. The simple achromat uses two types
of glass with two different dispersion values to create a positive and
negative lens pair with the property that:

- The unwanted colour dispersion of the positive lens is mostly
cancelled by the opposite dispersion of the negative lens, giving
exactly the same image for two wavelengths of light, and much less
variation in image size and focus with change in wavelength than a
simple lens

- At the same time, the overall light-bending power of the positive and
negative lenses do *not* cancel, leaving a overall positive or negative
lens that can do useful work

- In the case of a cemented achromat, the rear radius of the front
element has to match the front radius of the rear element.

That's with just two elements. Modern lenses use 6 or 8 or more
elements, and the design process is a matter of varying curvature and
thickness and spacing of elements (and sometimes even adding an aspheric
surface or two) to get simultaneous correction for multiple aberrations.

But it all depends on "subtraction", where nearly equal but opposite
errors combine to almost cancel. Sometimes very tiny errors in lens
element spacing or alignment can effectively destroy the designed
cancellation, and the lens performs badly.

If all lenses of a particular design perform badly, it's a bad design.
If some perform well and some poorly, it's either a design that
requires unachievably tight manufacturing tolerances (not good), or a
good design manufactured inconsistently.

Dave