Re: How a [Canon] lens is made:

In article <45F4BB10.3030704@xxxxxxxxx>, "Roger N. Clark (change
username to rnclark)" <username@xxxxxxxxx> writes
Prometheus wrote:
In article <1173569901.818983.279830@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
RichA <rander3127@xxxxxxxxx> writes

On Mar 9, 12:50 am, Slack <dont_even_th...@xxxxxxx> wrote:

I'm sure many of you already know the manufacturing process, but for the
rest of us:

http://www.canon.com/camera-museum/tech/l_plant/index2.html
-- Slack

Fascinating video!
Have you watched the video?

Thank you.
I doubt that you have watched it.

A fast, and oddly enough, economical way to make lenses.

Pardon! It's anything but.

Actually, Rich is correct.

Pressing,
slumping, etc, are not as good as grinding lens from a blank that has
been cast and ground,
Obviously you did not watch the video. The pressing and annealing is
used to produce a 'blank' of approximately the correct shape so as to
reduce the time required to grind and polish it to shape.

Again, Rich is correct. The annealing step is necessary to
mitigate the stresses created in the molding step.
The larger the lens the more difficult this is.

I fully understand the necessity of the annealing process, but did you
watch the whole video?

First Part
Material Processing Process
1 Material blending
2 Pre-fusing
3 Fusing / Cooling
4 Quality inspection
5 Press / forming
6 Annealing
Second Part
Lens Machining Process
1 Rough grinding *
2 Fine grinding *
3 Polishing
4 Inspection
5 Alignment
6 Coating
Third Part
Lens Assembly Process
1 Assembly 1, Front Unit
2 Assembly 2, Back Unit
3 Comprehensive Inspection, Completion

* What do you thing is the purpose of these steps if the lens is pressed
to its final shape?

but camera lenses are not asked to achieve
extreme resolution (until they come out with 5x - 10x tele-extenders,
Who uses a "tele-extender"? They are toys for use on toy cameras.

Well, most pro wildlife photographers use telextenders, as do most
advanced amateurs wildlife photographers.
For example, check how many of these images used a TC:
http://www.clarkvision.com/galleries/gallery.africa

I was thinking nomenclature:
Tele-converter goes on the rear of a lens
Tele-extender goes on the front.
The former are not known for highest performance.

that is) so any inhomogeneity caused by pressing won't be noticed.
How many times, they do not press the final lens.

But the pressing step does create problems internal to the glass
blank, which annealing tries to mitigate,

I fully understand the necessity of the annealing process, but did you
watch the whole video?

Pressing is the only economical way to quickly achieve a aspheric
surface and if Canon's 500mm f4 used a ground from scratch aspherical
element, the cost of the lens would be at least $16,000.
Wrong, wrong, and wrong! Also stupid.

No, again he is right in that it would be more expensive.

Obviously you did not watch the video. The pressing and annealing is
used to produce a 'blank' of approximately the correct shape so as to
reduce the time required to grind and polish it to shape.

Perhaps it was my fault, I should not have assumed that you would
consider that "reducing the time required to grind" would also reduce
the cost.

Do you have actual experience grinding optical glass optical surfaces?

None.

I do.

Accepted.

I have also had personal tours of lens manufacturing
plants to learn about the processes to understand
manufacturing of optics for scientific satellite.

If pressing, annealing, and polishing are all that is required why do
Canon introduce two stages of grinding between annealing and polishing?

But then you have a reputation for not letting the truth divert you.

Rich has a reputation for making outrageous and off-the-wall
statements.

This is true.

But sometimes he is absolutely correct, yet
because of his reputation, he is dismissed and attacked
regardless of whether or not what he says is true.

On the balance of probability this also can be true.

If you and others would take Rich's posts as a challenge
to see when he is right, everyone might learn something,
including both you and Rich. ;-)

Oh, I d-o take Rich as a challenge.

--
Ian G8ILZ
There are always two people in every picture: the photographer and the viewer.
~Ansel Adams
.

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