Some basic questions about process lenses vs. "regular" lenses
Marco Milazzo
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
Shelley
discusses most of these questions in some detail. See
http://wisner.com/myth.htm.
"Marco Milazzo" <hgar...@elp.rr.com> wrote in message
news:diknp09n2bg2qk3fa...@4ax.com...
brian
> Ron Wisner wrote an article entitled "The Myth of the Flat Field Lens" that
> discusses most of these questions in some detail. See
> http://wisner.com/myth.htm.
>
Ron Wisner is way out of his league when discussing technical details
about lens design, and as a result there are some glaring errors in
this article. Nevertheless, he is correct that virtually all
photographic lenses are flat field lenses.
Kirk Fry
huge and heavy (G clarons are an exception) and 2)Don't come and don't
fit in regular shutters and if they do they are either huge old
shutters and or large copal 3 shutters and the lenses have to be
machined to fit which then makes them very expensive. A minor
problem is that they really weren't designed to work at infinity, but
at f22 most of them are very sharp anyway. The real killer is the
HUGE and HEAVY part. Also most of these lenses are true APO lenses,
but only in the design range, not at infinity (not a big deal).
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. These originally very expensive lenses became a
drug on the market on ebay.
Remember the HUGE and HEAVY part, they make great paper weights... A
terrific conversation piece. That 1000mm Goerz Red Dot ARTAR woud be
able to hold down a whole pile of paper in a hurricane.
brian...@aol.com (brian) wrote in message news:<3c459ba.04111...@posting.google.com>...
Thor Lancelot Simon
Kirk Fry <kir...@msn.com> wrote:
>There are two main problems with process lenses: 1) they are usually
>huge and heavy (G clarons are an exception) and 2)Don't come and don't
You're kidding, right?
Because of their simple designs and small maximum apertures, most
process lenses are significantly smaller than most modern large format
taking lenses. A 19" Artar is significantly smaller than a 480mm
"general-purpose" plasmat; and, as another point of comparison, I have
used, over the years, as my standard 8x10 lens, a 14" Caltar (Commercial
Ektar copy), a 305mm Computar -- which is a plasmat process lens -- and
a 360mm Symmar-MC (which is almost exactly the same size as today's Apo
Symmar and Apo Rodagon).
Of all those lenses, the Comptar was by far the smallest, lightest, and
fit in the smallest shutter. In fact, of the lenses I own that cover
8x10, only the 180mm Protar V is smaller -- and *that* is an f/18 lens
in a Supermatic.
--
Thor Lancelot Simon t...@rek.tjls.com
But as he knew no bad language, he had called him all the names of common
objects that he could think of, and had screamed: "You lamp! You towel! You
plate!" and so on. --Sigmund Freud
Jean-David Beyer
> There are two main problems with process lenses: 1) they are usually
> huge and heavy (G clarons are an exception)
Why would that be? They are usually 4 element four group symmetrical (or
very nearly) air spaced lenses with maximum aperture f/9. I would expect
them to be smaller and lighter than a normal Plasmat f/5.6 of the same
focal length.
--
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Dan Fromm
> Kirk Fry wrote (in part):
> > There are two main problems with process lenses: 1) they are usually
> > huge and heavy (G clarons are an exception)
>
> Why would that be? They are usually 4 element four group symmetrical (or
> very nearly) air spaced lenses with maximum aperture f/9. I would expect
> them to be smaller and lighter than a normal Plasmat f/5.6 of the same
> focal length.
You're kidding, at least about lens design, aren't you?
I just took inventory of the process lenses I own.
6/2 double anastigmat: 240/9 G-Claron. Don't thump me about this
lens, that's what Schneider says it is and a count of reflections
agrees. Current G-Clarons are 6/4 Plasmats but older ones are Dagor
clones.
Tessar: 6"/9 Cooke Copying lens, tiny; 10.16"/9 Taylor Hobson Copying
lens, very small; 30 cm/9 Cooke Apotal, big enough to see.
Dialyte: 14"/10 Wray Apo-Process Lustrar Ser. II, large; 600/9 Apo
Ronar, huge, weighs about 8 pounds.
Four element double Gauss: 260/10 Process Nikkor, enormous.
Sort of Heliar (5/3, anyway): 180/10 and 360/10 Boyer Apo Saphirs,
both small.
More complex: 210/9 Konica Hexanon GRII, this lens is not a 6/4
Plasmat.
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.
Cheers,
Dan
Thor Lancelot Simon
Dan Fromm <daniel...@att.com> 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.
Kirk Fry
I agree it is not good to over generalize and I may have done that,
BUT I will stand on the generally huge part (obviously there are
exceptions as were pointed out). Let's start with one of the most
commonly availble process lens out there, a 19in Goerz red dot APO
Artar, a super duper optical performer. Almost always found in barrel
(the in shutter ones were special and cost real money). The one I have
weighs a bunch, not because of the glass but because it is mounted in
a heavy brass barrel (Goerz didn't discover aluminum until way late
just before they went bye bye). Then if you want it in a shutter you
have pay $300 or $400 for a #3 copal shutter and get it mounted for
another $400 (yes there is the Packard solution, another light weight,
small affair, or there is the lens cap trick). So what is the
compitition: A 450 M Nikkor in Compal #3, a bit smaller and lighter or
a Fujinon C450 f12 I think in Copol #1, way lighter. So what about
the 300 mm focal length. A 305 Apo Nikkor f9 copy lens is almost
always for sale on E bay. Again very samll glass and huge heavy mount
of brass. Again, very expensive to get mounted in a shutter. The
compition; a 300mm M Nikkor in Copal #1 or Fujinon makes a C lens that
is really small, also in 300mm focal length.
So, do you every wonder why these originally very expesive lenses that
are excellent optical preformers sell for pennies on the dollar on
ebay? Let me stand on my original hypothesis, Huge and Heavy and not
in Shutter.
The ones in shutter and which are not huge and heavy are not cheap.
Ya tend to get what you pay for. Have you noticed what 300mm
G-Clarons (plasmats by the way) sell for? Why is that?
And now let me close with the 300mm MC-Schneider f5.6 plasmat I own.
This one makes a 305mmm f9 Nikkor copy lens look like a midget. They
sell for pennies on the dollar compared to new prices, usually about
2X over what their copal 3 shutter is worth. Why do you suppose that
is? Anyone with any sense using 4X5 bought a 300mm M Nikkor and how
many folks are using 8X10 in the Studio any more? The huge and heavy
part killed that lens too.
In lenses, light weight and fast is good (along with a bunch of other
stuff), process lenses never had to be carried anywhere so the light
weight part was never even considered in the design.
Kirk
daniel...@att.com (Dan Fromm) wrote in message news:<d32d23bf.04112...@posting.google.com>...
Dan Fromm
> In article <d32d23bf.04112...@posting.google.com>,
> Dan Fromm <daniel...@att.com> 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
Richard Knoppow
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
dick...@ix.netcom.com
Mxsmanic
> 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.
Jean-David Beyer
> 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.
--
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brian
> 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.