Schneider APO Artar

In article ,
(Hemi4268) wrote:

Since f-stop controls the amount of depth of focus

Depth of focus or depth of field?

--
To reply no_ HPMarketing Corp.

"Hemi4268" wrote in message
...
How about lateral color, which is a difference in image
size with color of light.

Yes this would be true and a true APO would correct for
this regardless of
f-stop. It makes for easy overlap of seperation
negatives. I am not sure
though that the APO correction would hold for much more
the the design 1:1
scale that this lens is designed for.

Larry
The lateral color correction stays pretty good but also
depends on the lens design. Lateral color is automatically
corrected in a symmetrical lens, but like coma and
geometrical distortion, the cancellation is complete only
when the entire system is symmetrical, that is at equal
image and object distances, but generally stays good at
infinity. Not all Apo Artars are symmetrical. Most of the
Red-Dot series were sold with some element spacing ajustment
to optimise them for middle distances. The adjustment
depended on the focal length and whether the lens was sold
in a shutter or a barrel. Long barrel mounted lenses, which
were used mostly for photomechanical use, were still
symmetrical but shorter focal lengths in shutters were
adjusted for magnification of up to about 1:10, which is
effectively infinity.
Kodak Commercial Ektar lenses are Tessar types,
definitely NOT symmetrical but are corrected for lateral
color. Kodak claimed that the color correction was good
enough to allow their use in making color separation plates.
Kodak also claims the corrections are good over a distance
from ingfinity to around 5 times the lens focal length.
I am sure you are aware that few of the lenses now being
sold with "Apo" attached to their names are actually
apochromatic. Apochromatic correction is defined as bringing
three colors to a common focus and correcting for spherical
aberration at two colors. Most of the "apo" lenses on the
market currently are actually acromats (corrected for two
colors for focus and one color for spherical) but having
little deviation in color correction. The apending of apo to
these lenses is really misleading. It turns out that
somewhere in the German DIN standards is one written so
sloppily that it allows for lens manufacturers to use this
appelation and get away with it. The Apochromatic Artar is
an actual apochromat, corrected for focus at three colors
and being corrected for lateral color through symmetry or
semi-symmetry.


--
---
Richard Knoppow
Los Angeles, CA, USA

"Hemi4268" wrote in message
...
How about lateral color, which is a difference in image
size with color of light.

Yes this would be true and a true APO would correct for
this regardless of
f-stop. It makes for easy overlap of seperation
negatives. I am not sure
though that the APO correction would hold for much more
the the design 1:1
scale that this lens is designed for.

Larry
The lateral color correction stays pretty good but also
depends on the lens design. Lateral color is automatically
corrected in a symmetrical lens, but like coma and
geometrical distortion, the cancellation is complete only
when the entire system is symmetrical, that is at equal
image and object distances, but generally stays good at
infinity. Not all Apo Artars are symmetrical. Most of the
Red-Dot series were sold with some element spacing ajustment
to optimise them for middle distances. The adjustment
depended on the focal length and whether the lens was sold
in a shutter or a barrel. Long barrel mounted lenses, which
were used mostly for photomechanical use, were still
symmetrical but shorter focal lengths in shutters were
adjusted for magnification of up to about 1:10, which is
effectively infinity.
Kodak Commercial Ektar lenses are Tessar types,
definitely NOT symmetrical but are corrected for lateral
color. Kodak claimed that the color correction was good
enough to allow their use in making color separation plates.
Kodak also claims the corrections are good over a distance
from ingfinity to around 5 times the lens focal length.
I am sure you are aware that few of the lenses now being
sold with "Apo" attached to their names are actually
apochromatic. Apochromatic correction is defined as bringing
three colors to a common focus and correcting for spherical
aberration at two colors. Most of the "apo" lenses on the
market currently are actually acromats (corrected for two
colors for focus and one color for spherical) but having
little deviation in color correction. The apending of apo to
these lenses is really misleading. It turns out that
somewhere in the German DIN standards is one written so
sloppily that it allows for lens manufacturers to use this
appelation and get away with it. The Apochromatic Artar is
an actual apochromat, corrected for focus at three colors
and being corrected for lateral color through symmetry or
semi-symmetry.


--
---
Richard Knoppow
Los Angeles, CA, USA

"Bob Salomon" wrote in message
...
In article ,
(Hemi4268) wrote:

Since f-stop controls the amount of depth of focus

Depth of focus or depth of field?

--
To reply no_ HPMarketing Corp.

Well, these are really the same thing. Depth of field is
the depth in the object space, depth of focus is the depth
in the image space. The way Larry used the term it is
correct, he is talking abuot the image space.
Since longitudinal chromatic aberration is a measure of
the variation in focus with wavelength a reduction of the
effect of defocusing by stopping down would tend to
alleviate the fringing produced by chromatic although that
is not the same as correcting it. Stopping down changes the
rate at which the size of the blur spot changes with change
in focus. The smaller the stop, that is, the smaller the
hole in the iris, the narrower the angle of the fan of light
rays from lens to film and, hense, the smaller the blur spot
will be for a given amount of defocusing.
Since chromatic correction also affects spherical
correction, and since spherical is proportional to the stop
size, stopping down will also tend to reduce the effect of
spherochromatism.
Lateral color is a measure of the size of the image at
different wavelengths. It is possible (and actually pretty
common) to have a lens which is correced for focus at
different colors but where the iamges vary in size despite
being in common focus. This is sometimes called chromatic
variation of magnification. Symmetry will correct this but
it can be corrected in asymmetrical lenses by very careful
design. stopping down has no effect whatever on lateral
color.

--
---
Richard Knoppow
Los Angeles, CA, USA

"Bob Salomon" wrote in message
...
In article ,
(Hemi4268) wrote:

Since f-stop controls the amount of depth of focus

Depth of focus or depth of field?

--
To reply no_ HPMarketing Corp.

Well, these are really the same thing. Depth of field is
the depth in the object space, depth of focus is the depth
in the image space. The way Larry used the term it is
correct, he is talking abuot the image space.
Since longitudinal chromatic aberration is a measure of
the variation in focus with wavelength a reduction of the
effect of defocusing by stopping down would tend to
alleviate the fringing produced by chromatic although that
is not the same as correcting it. Stopping down changes the
rate at which the size of the blur spot changes with change
in focus. The smaller the stop, that is, the smaller the
hole in the iris, the narrower the angle of the fan of light
rays from lens to film and, hense, the smaller the blur spot
will be for a given amount of defocusing.
Since chromatic correction also affects spherical
correction, and since spherical is proportional to the stop
size, stopping down will also tend to reduce the effect of
spherochromatism.
Lateral color is a measure of the size of the image at
different wavelengths. It is possible (and actually pretty
common) to have a lens which is correced for focus at
different colors but where the iamges vary in size despite
being in common focus. This is sometimes called chromatic
variation of magnification. Symmetry will correct this but
it can be corrected in asymmetrical lenses by very careful
design. stopping down has no effect whatever on lateral
color.

--
---
Richard Knoppow
Los Angeles, CA, USA

Depth of focus or depth of field?


DEPTH OF FOCUS!!!

Hemi4268 wrote:

As far as telescopes, we all know that mirror telescopes by design have no
color errors "what-so-ever" and are APO by defult. That is why we see very
little glass lens telescopes except ones sold by K-mart for $99.

Apo or not Apo isn't the real question when deciding between a mirror
or a lens telescope. The real problem is making large lenses to _real_
tight tolerances...

The largest refractors commonly used (for an amateur) are 6" diameter,
the cost rising exponentially with diameter. A mirror telescope
with 8" is a beginners tool, costing about 20% of the cost for a 6"
refractor.

Martin

Hemi4268 wrote:

As far as telescopes, we all know that mirror telescopes by design have no
color errors "what-so-ever" and are APO by defult. That is why we see very
little glass lens telescopes except ones sold by K-mart for $99.

Apo or not Apo isn't the real question when deciding between a mirror
or a lens telescope. The real problem is making large lenses to _real_
tight tolerances...

The largest refractors commonly used (for an amateur) are 6" diameter,
the cost rising exponentially with diameter. A mirror telescope
with 8" is a beginners tool, costing about 20% of the cost for a 6"
refractor.

Martin

On 23 Sep 2004 06:38:15 -0700, (brian) wrote:

True
apochromatic correction is a big deal in the realm of refracting
telescope objectives, where f/9 is considered *fast*.

Then my old 6" f/8 must be a real mover or a good spotting
scope ;))


Regards,

John S. Douglas, Photographer - http://www.puresilver.org
Please remove the "_" when replying via email

On 23 Sep 2004 06:38:15 -0700, (brian) wrote:

True
apochromatic correction is a big deal in the realm of refracting
telescope objectives, where f/9 is considered *fast*.

Then my old 6" f/8 must be a real mover or a good spotting
scope ;))


Regards,

John S. Douglas, Photographer - http://www.puresilver.org
Please remove the "_" when replying via email