Some basic questions about process lenses vs. "regular" lenses

(Thor Lancelot Simon) wrote in message ...
In article ,
Dan Fromm wrote:

I appreciate that many Apo Artars and Apo Ronars, both dialyte types,
come to market and that some of my lenses are less common. Still and
all, it isn't safe to generalize about the category quite as broadly
as you did.

Nonetheless, the generalization that _does_ seem safe, to me at least
and I suspect to many others, is that for a lens of the same focal
length, a modern fast Plasmat is about as _large_ a lens as you're
going to get -- leaving older, lower-aperture lenses, especially f/9
or f/11 process lenses of any design, much smaller and lighter.

Earlier in this thread we had a comment about the size and weight of
a 1000mm Artar. This left me scratching my head wondering if the
person who wrote that had ever seen a 1000mm or even a 600mm "taking"
lens, whether a modern Plasmat or even an older Tessar type; either
is _much_, _much_ larger and heavier than a 1m Artar is.

Yes and of course, at least most of the time. I've seen considerable
variation in weights of Apo Ronars of the same focal length. My
600/9, for example, weighs nearly 8 pounds. A monster, and much
heavier, for example, that the comparable Apo Nikkor.

Cheers,

Dan

(Thor Lancelot Simon) wrote in message ...
In article ,
Dan Fromm wrote:

I appreciate that many Apo Artars and Apo Ronars, both dialyte types,
come to market and that some of my lenses are less common. Still and
all, it isn't safe to generalize about the category quite as broadly
as you did.

Nonetheless, the generalization that _does_ seem safe, to me at least
and I suspect to many others, is that for a lens of the same focal
length, a modern fast Plasmat is about as _large_ a lens as you're
going to get -- leaving older, lower-aperture lenses, especially f/9
or f/11 process lenses of any design, much smaller and lighter.

Earlier in this thread we had a comment about the size and weight of
a 1000mm Artar. This left me scratching my head wondering if the
person who wrote that had ever seen a 1000mm or even a 600mm "taking"
lens, whether a modern Plasmat or even an older Tessar type; either
is _much_, _much_ larger and heavier than a 1m Artar is.

Yes and of course, at least most of the time. I've seen considerable
variation in weights of Apo Ronars of the same focal length. My
600/9, for example, weighs nearly 8 pounds. A monster, and much
heavier, for example, that the comparable Apo Nikkor.

Cheers,

Dan

Marco Milazzo wrote in message . ..
I've never really understood the following -- maybe someone can
enlighten me:

1. What's the difference between "flat field" and curved field?" I
know that enlarger lenses and process lenses have "flat fields" -- but
what exactly does this mean? Is the subject-field flat -- or the
"image-field?" What's a non-flat field?

2. If process lenses are used for general photography (landscapes,
portraits, etc.), what is compromised or lost? If the answer is
"nothing," then why don't we all use process lenses for everything?

3. Reproduction ratios (may not be the corret term). Some lenses are
alleged to be "optimized" (whatever that means) for 1-to-1
reproduction. I assume that means that a 1-inch subect is rendered
as a 1-inch image on the film. Is that correct? What is the optimal
ratio for general photography lenses.

Thanks for any help.

Marco


Its important to understand what a process lens is. These lenses
were originally intended for copying flat material, either line or
continuous tone, onto a flat negative which was then used for making a
printing plate. The requirements were than the image of a flat object
also be flat, so it would be in focus everyewhere, the the lens not
introduce geometrial distortion, and that it be well corrected for
aberrations so that the image was sharp.
Nearly all lenses are designed to produce a flat field, however,
the requirements for a process lens are somewhat more stringent than
those for a general purpose lens. Lenses do not naturally produce a
flat field. Its well known that the distance a lens is for sharp focus
varies with the distance of the object. When we image a flat object
the edges are more distant than the center from the lens. A simple
lens will image the center at a further distance from the lens than
the edges so that the center of the image field curves toward the back
of the camera. In order to correct this a more complex lens must be
made. In actual lenses the curvature of field may be corrected by the
balance of powers of the elements and by their spacing.
Copy lenses and enlarging lenses also have stringent requirements
for flatness of field.
Occasionally lenses are designed for curved fields for special
purposes but general photographic lenses are all approximately flat
field.
Any lens with fixed position elements can be corrected for all
aberrations at only one object distance. The amount the aberrations
beging to increase at other distances depends on the type of lens.
This design choice is sometimes called optimization although there are
other meanings for that word in lens design. Camera lenses for general
photography are optimized for infinity. For mostr lenses this results
in good corrections down to about 5 to 10 focal lengths, perpaps
somewhat closer when the lens is stopped down. Since copy and process
lenses are generally used to make same size copies, or nearly so, they
are optimized for equal image and object distance, which is also the
condition for same size copying. For enlarging the lens is optimized
for the object distance which corresponds to the magnification the
lens is intended to be used at. This can vary from perhaps 1:5 for
large format lenses to about 1:10 for 35mm lenses and even more for
lenses used for making photomurals.
Often the aberrations from using a lens far from its optimized
object distance can be reduced by stopping down, but, in the case of
the lens for photomurals for instance, one does not want to stop down
too much.
Many process lenses work fine for general photography. There are
two general types of process lenses found now: one is the older type,
generally intended for making half-tone plates. These are very slow
and usually fairly simple lenses with rather narrow coverage. The
Goerz/Schneider Apochromatic Artar is an example. The other type of
process lens is a more complex lens made to cover a much wider angle
than the older type. These are intended for making large photo-off-set
plates. They are larger and heavier than the older type and may not
perform as well when used at infinity focus.
The Artar and similar are four-element, air-spaced lenses of a type
known generally as a Dialyte. These have the useful property that the
corrections are very stable with distance so they are quite
satisfactory at infinity focus although generally optimized for 1:1.
The slight amount of coma introduced at infinity can be corrected by
stopping down. At the stops normally used for photoraphy the
aberration is gone. Typical process lenses of this type vary from f/9
to about f/16 depending on the focal length, the longer the lens, the
slower it is made. Coverage is usually given as around 45 to 48
degrees at infinity focus but generally they will cover a diagonal
equal to the focal length. Not all process lenses are this well
behaved but for the most part they are quite useful for general
photography where the slow speed and relatively narrow coverage are
acceptable. Even the so called wide-angle process lenses have narrower
coverage than their general photography counterparts. The limitation
of coverage is done to improve corrections.
The Dialyte type lenses are relatively small and light compared to
general purpose lenses fo the same focal length but the wide angle
types are about the same. They are ususally of the "Plasmat" type, a
six element lens, and are often as fast as standard lenses although
most are slower.
The main advantage process lenses have now is that a great many of
these excellent lenses are available used at very cheap prices because
the old method of making half-tone plates has been almost entirely
replaced by electronic means.


Richard Knoppow
Los Angeles, CA, USA

Marco Milazzo wrote in message . ..
I've never really understood the following -- maybe someone can
enlighten me:

1. What's the difference between "flat field" and curved field?" I
know that enlarger lenses and process lenses have "flat fields" -- but
what exactly does this mean? Is the subject-field flat -- or the
"image-field?" What's a non-flat field?

2. If process lenses are used for general photography (landscapes,
portraits, etc.), what is compromised or lost? If the answer is
"nothing," then why don't we all use process lenses for everything?

3. Reproduction ratios (may not be the corret term). Some lenses are
alleged to be "optimized" (whatever that means) for 1-to-1
reproduction. I assume that means that a 1-inch subect is rendered
as a 1-inch image on the film. Is that correct? What is the optimal
ratio for general photography lenses.

Thanks for any help.

Marco


Its important to understand what a process lens is. These lenses
were originally intended for copying flat material, either line or
continuous tone, onto a flat negative which was then used for making a
printing plate. The requirements were than the image of a flat object
also be flat, so it would be in focus everyewhere, the the lens not
introduce geometrial distortion, and that it be well corrected for
aberrations so that the image was sharp.
Nearly all lenses are designed to produce a flat field, however,
the requirements for a process lens are somewhat more stringent than
those for a general purpose lens. Lenses do not naturally produce a
flat field. Its well known that the distance a lens is for sharp focus
varies with the distance of the object. When we image a flat object
the edges are more distant than the center from the lens. A simple
lens will image the center at a further distance from the lens than
the edges so that the center of the image field curves toward the back
of the camera. In order to correct this a more complex lens must be
made. In actual lenses the curvature of field may be corrected by the
balance of powers of the elements and by their spacing.
Copy lenses and enlarging lenses also have stringent requirements
for flatness of field.
Occasionally lenses are designed for curved fields for special
purposes but general photographic lenses are all approximately flat
field.
Any lens with fixed position elements can be corrected for all
aberrations at only one object distance. The amount the aberrations
beging to increase at other distances depends on the type of lens.
This design choice is sometimes called optimization although there are
other meanings for that word in lens design. Camera lenses for general
photography are optimized for infinity. For mostr lenses this results
in good corrections down to about 5 to 10 focal lengths, perpaps
somewhat closer when the lens is stopped down. Since copy and process
lenses are generally used to make same size copies, or nearly so, they
are optimized for equal image and object distance, which is also the
condition for same size copying. For enlarging the lens is optimized
for the object distance which corresponds to the magnification the
lens is intended to be used at. This can vary from perhaps 1:5 for
large format lenses to about 1:10 for 35mm lenses and even more for
lenses used for making photomurals.
Often the aberrations from using a lens far from its optimized
object distance can be reduced by stopping down, but, in the case of
the lens for photomurals for instance, one does not want to stop down
too much.
Many process lenses work fine for general photography. There are
two general types of process lenses found now: one is the older type,
generally intended for making half-tone plates. These are very slow
and usually fairly simple lenses with rather narrow coverage. The
Goerz/Schneider Apochromatic Artar is an example. The other type of
process lens is a more complex lens made to cover a much wider angle
than the older type. These are intended for making large photo-off-set
plates. They are larger and heavier than the older type and may not
perform as well when used at infinity focus.
The Artar and similar are four-element, air-spaced lenses of a type
known generally as a Dialyte. These have the useful property that the
corrections are very stable with distance so they are quite
satisfactory at infinity focus although generally optimized for 1:1.
The slight amount of coma introduced at infinity can be corrected by
stopping down. At the stops normally used for photoraphy the
aberration is gone. Typical process lenses of this type vary from f/9
to about f/16 depending on the focal length, the longer the lens, the
slower it is made. Coverage is usually given as around 45 to 48
degrees at infinity focus but generally they will cover a diagonal
equal to the focal length. Not all process lenses are this well
behaved but for the most part they are quite useful for general
photography where the slow speed and relatively narrow coverage are
acceptable. Even the so called wide-angle process lenses have narrower
coverage than their general photography counterparts. The limitation
of coverage is done to improve corrections.
The Dialyte type lenses are relatively small and light compared to
general purpose lenses fo the same focal length but the wide angle
types are about the same. They are ususally of the "Plasmat" type, a
six element lens, and are often as fast as standard lenses although
most are slower.
The main advantage process lenses have now is that a great many of
these excellent lenses are available used at very cheap prices because
the old method of making half-tone plates has been almost entirely
replaced by electronic means.


Richard Knoppow
Los Angeles, CA, USA

Kirk Fry writes:

Also the only reason process lenses are cheap right now is that every
graphics arts house and newspaper has dumped their copy cameras for
digital processes.

Do I understand correctly that a "process lens" is a lens used in a
camera originally intended to record graphic images on paper or other
media onto film? The kind that printers or prepress places used to have
to prepare plate films from line art or photos?

If so, what's so special about these lenses? Do they have some sort of
special characteristics that ordinary photo lenses don't?

Does anyone still use these cameras?

--
Transpose hotmail and mxsmanic in my e-mail address to reach me directly.

Kirk Fry writes:

Also the only reason process lenses are cheap right now is that every
graphics arts house and newspaper has dumped their copy cameras for
digital processes.

Do I understand correctly that a "process lens" is a lens used in a
camera originally intended to record graphic images on paper or other
media onto film? The kind that printers or prepress places used to have
to prepare plate films from line art or photos?

If so, what's so special about these lenses? Do they have some sort of
special characteristics that ordinary photo lenses don't?

Does anyone still use these cameras?

--
Transpose hotmail and mxsmanic in my e-mail address to reach me directly.

Mxsmanic wrote:

Do I understand correctly that a "process lens" is a lens used in a
camera originally intended to record graphic images on paper or other
media onto film? The kind that printers or prepress places used to have
to prepare plate films from line art or photos?

Yes.

If so, what's so special about these lenses? Do they have some sort of
special characteristics that ordinary photo lenses don't?

They are apochromatic, so that the red, green, and blue light all focus at
the same plane and have the same size images.

Does anyone still use these cameras?

Probably, but less than when everyone used crossline half-tone screens.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 11:35:00 up 30 days, 14:30, 6 users, load average: 4.04, 4.12, 4.09

Mxsmanic wrote:

Do I understand correctly that a "process lens" is a lens used in a
camera originally intended to record graphic images on paper or other
media onto film? The kind that printers or prepress places used to have
to prepare plate films from line art or photos?

Yes.

If so, what's so special about these lenses? Do they have some sort of
special characteristics that ordinary photo lenses don't?

They are apochromatic, so that the red, green, and blue light all focus at
the same plane and have the same size images.

Does anyone still use these cameras?

Probably, but less than when everyone used crossline half-tone screens.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 11:35:00 up 30 days, 14:30, 6 users, load average: 4.04, 4.12, 4.09

Mxsmanic wrote:

Do I understand correctly that a "process lens" is a lens used in a
camera originally intended to record graphic images on paper or other
media onto film? The kind that printers or prepress places used to have
to prepare plate films from line art or photos?

Yes.

If so, what's so special about these lenses? Do they have some sort of
special characteristics that ordinary photo lenses don't?

They are apochromatic, so that the red, green, and blue light all focus at
the same plane and have the same size images.

Does anyone still use these cameras?

Probably, but less than when everyone used crossline half-tone screens.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 11:35:00 up 30 days, 14:30, 6 users, load average: 4.04, 4.12, 4.09

Jean-David Beyer wrote in message ...

They are apochromatic, so that the red, green, and blue light all focus at
the same plane and have the same size images.


I doubt that many process lenses are apochromatic. In fact, I suspect
that none of them are. My 240mm "Apo" Ronar, although a fine lens, is
certainly *not* apochromatic in any way, but rather is an ordinary
achromat with two color crossings. Note that lateral chromatic
aberration is automatically corrected for any symmetrical lens used at
1:1, and this has nothing to do with whether the lens is apochromatic
or not.

Brian
www.caldwellphotographic.com