Enlarger lens options.

"Nicholas O. Lindan" wrote in message
m...

The law of diminishing returns. When something is close to
perfection the cost of even a miniscule gain becomes
astronomical.

Sometimes astronauts become miniscule. It evens out.

spend the
savings on something worthwhile that will make a noticeable
and unequivocal improvement: a trip to someplace photogenic,
a workshop, a really good timer ...

I got a good timer but I'm not having a good time.

Richard Knoppow wrote:
A high power grain focuser will often show up
differences in lenses that are much harder to see in a print
but may also introduce its own problems, for instance, some
grain focusers are not very well achromitized and will show
color fringes due to its own optics which are not present in
the image from the enlarging lens.

I made a comparison between some better enlarging lenses for 24x36mm
(Apo-Rodagon 2.8/50, Componon-S 2.8/50, Focotar 4.5/50, Focotar 2.8/40
and Rodagon 4/60) and compared them at about 8x enlargement (20x30cm
paper size). Each was perfectly adjusted using a Peak #1, a glass carrier
and all enlarger planes were adjusted parallel using a laser tool. All
lenses were closed 2 stops from wide open.

The result: The only one you could distinguish from the others was the old
Focotar 4.5/50. It had a little curvature of field visible at the extreme
edges. That's all... no visible difference for the other lenses.

You can see the differences between the lenses with the Peak #1. The curvature
of field is readily visible for the two Focotars. The two Rodagon
and the Componon-S were much better and nearly identical. The Apo-Rodagon was
a little better wide open than the others, but all 2.8 lenses were unuseable
with this opening (for my view of quality...). Stopped down, all
were excellent.

Martin

"Martin J" wrote in message
...
Richard Knoppow wrote:
A high power grain focuser will often show up
differences in lenses that are much harder to see in a
print
but may also introduce its own problems, for instance,
some
grain focusers are not very well achromitized and will
show
color fringes due to its own optics which are not present
in
the image from the enlarging lens.

I made a comparison between some better enlarging lenses
for 24x36mm
(Apo-Rodagon 2.8/50, Componon-S 2.8/50, Focotar 4.5/50,
Focotar 2.8/40
and Rodagon 4/60) and compared them at about 8x
enlargement (20x30cm
paper size). Each was perfectly adjusted using a Peak #1,
a glass carrier
and all enlarger planes were adjusted parallel using a
laser tool. All
lenses were closed 2 stops from wide open.

The result: The only one you could distinguish from the
others was the old
Focotar 4.5/50. It had a little curvature of field visible
at the extreme
edges. That's all... no visible difference for the other
lenses.

You can see the differences between the lenses with the
Peak #1. The curvature
of field is readily visible for the two Focotars. The two
Rodagon
and the Componon-S were much better and nearly identical.
The Apo-Rodagon was
a little better wide open than the others, but all 2.8
lenses were unuseable
with this opening (for my view of quality...). Stopped
down, all
were excellent.

Martin

That's quite interesting. I suspect the Rodagon and
Componon designs are quite similar although I don't have the
actual prescriptions. Since its likely all the relatively
modern lenses were designed with the aid of computers I
suspect the performance should be much alike. I think the
Focotar is an older design. One of the characteristics of
the generic Plasmat type, which is what the Rodagon and
Componon are, is that they can be unusually well corrected
for astigmatism. Forgoing an explanation of what exactly
that is (different in a camera lens than in opthalmic
lenses) it leads to being able to get a very flat field.
While both manufacturers claim superiority I suspect its
pretty much a draw. Some think the Rodagon is mechanically
superior to the Componon. Do your lenses have metal or
plastic iris blades?


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

Richard Knoppow wrote:

That's quite interesting. I suspect the Rodagon and Componon designs are
quite similar although I don't have the actual prescriptions. Since its
likely all the relatively modern lenses were designed with the aid of
computers I suspect the performance should be much alike. I think the
Focotar is an older design. One of the characteristics of the generic
Plasmat type, which is what the Rodagon and Componon are, is that they
can be unusually well corrected for astigmatism. Forgoing an explanation
of what exactly that is (different in a camera lens than in opthalmic
lenses) it leads to being able to get a very flat field. While both
manufacturers claim superiority I suspect its pretty much a draw. Some
think the Rodagon is mechanically superior to the Componon. Do your
lenses have metal or plastic iris blades?

When I first got into 4x5" work, in the mid 1970s, I got a Schneider
Componon-S f/5.6 to f/45 180mm enlarging lens, # 11 973 xxx. It works fine.
Its diaphragm has lots of blades (about 19 of them), enough to make the
aperture look round, and they appear to be metal. At least 10 years later, I
got a Componon-S f/5.6 to f/45 150mm lens, # 14 588 yyy. It has only 5
blades, so the aperture looks approximately like a pentagon (except the
edges are not quite straght. I cannot tell if they are metal or plastic; the
180 blades are shinier than the 150 and darker, reminding me of blackened
brass (but I do not know what they are for sure), and the 150 blades are
duller, but slightly lighter in color and rougher, reminding me of anodized
aluminum (but I very much doubt they would actually be aluminum). Perhaps
that is what plastic blades look like.

For normal photograph use, is there any benefit to having a round aperture?
I know in half-tone work with a sealed half-tone screen, there is a benefit
to having a square aperture, but round holes work OK -- you just get a
little bit of a different transfer function from the original to the half-tone.

Unless you use the lens in the hot sun or something, there might even be a
slight benefit to having plastic iris blades: less likely to rust or corrode.

--
.~. Jean-David Beyer Registered Linux User 85642.
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"Jean-David Beyer" wrote in message
news:rbfVj.1212$OT1.79@trnddc03...
Richard Knoppow wrote:

That's quite interesting. I suspect the Rodagon and Componon designs are
quite similar although I don't have the actual prescriptions. Since its
likely all the relatively modern lenses were designed with the aid of
computers I suspect the performance should be much alike. I think the
Focotar is an older design. One of the characteristics of the generic
Plasmat type, which is what the Rodagon and Componon are, is that they
can be unusually well corrected for astigmatism. Forgoing an explanation
of what exactly that is (different in a camera lens than in opthalmic
lenses) it leads to being able to get a very flat field. While both
manufacturers claim superiority I suspect its pretty much a draw. Some
think the Rodagon is mechanically superior to the Componon. Do your
lenses have metal or plastic iris blades?

When I first got into 4x5" work, in the mid 1970s, I got a Schneider
Componon-S f/5.6 to f/45 180mm enlarging lens, # 11 973 xxx. It works
fine.
Its diaphragm has lots of blades (about 19 of them), enough to make the
aperture look round, and they appear to be metal. At least 10 years later,
I
got a Componon-S f/5.6 to f/45 150mm lens, # 14 588 yyy. It has only 5
blades, so the aperture looks approximately like a pentagon (except the
edges are not quite straght. I cannot tell if they are metal or plastic;
the
180 blades are shinier than the 150 and darker, reminding me of blackened
brass (but I do not know what they are for sure), and the 150 blades are
duller, but slightly lighter in color and rougher, reminding me of
anodized
aluminum (but I very much doubt they would actually be aluminum). Perhaps
that is what plastic blades look like.

For normal photograph use, is there any benefit to having a round
aperture?
I know in half-tone work with a sealed half-tone screen, there is a
benefit
to having a square aperture, but round holes work OK -- you just get a
little bit of a different transfer function from the original to the
half-tone.

Unless you use the lens in the hot sun or something, there might even be a
slight benefit to having plastic iris blades: less likely to rust or
corrode.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 06:35:01 up 2 days, 23:07, 3 users, load average: 4.19, 4.16, 4.08

"Jean-David Beyer" wrote in message
news:rbfVj.1212$OT1.79@trnddc03...
Richard Knoppow wrote:

That's quite interesting. I suspect the Rodagon and
Componon designs are
quite similar although I don't have the actual
prescriptions. Since its
likely all the relatively modern lenses were designed
with the aid of
computers I suspect the performance should be much alike.
I think the
Focotar is an older design. One of the characteristics of
the generic
Plasmat type, which is what the Rodagon and Componon are,
is that they
can be unusually well corrected for astigmatism. Forgoing
an explanation
of what exactly that is (different in a camera lens than
in opthalmic
lenses) it leads to being able to get a very flat field.
While both
manufacturers claim superiority I suspect its pretty much
a draw. Some
think the Rodagon is mechanically superior to the
Componon. Do your
lenses have metal or plastic iris blades?

When I first got into 4x5" work, in the mid 1970s, I got a
Schneider
Componon-S f/5.6 to f/45 180mm enlarging lens, # 11 973
xxx. It works fine.
Its diaphragm has lots of blades (about 19 of them),
enough to make the
aperture look round, and they appear to be metal. At least
10 years later, I
got a Componon-S f/5.6 to f/45 150mm lens, # 14 588 yyy.
It has only 5
blades, so the aperture looks approximately like a
pentagon (except the
edges are not quite straght. I cannot tell if they are
metal or plastic; the
180 blades are shinier than the 150 and darker, reminding
me of blackened
brass (but I do not know what they are for sure), and the
150 blades are
duller, but slightly lighter in color and rougher,
reminding me of anodized
aluminum (but I very much doubt they would actually be
aluminum). Perhaps
that is what plastic blades look like.

For normal photograph use, is there any benefit to having
a round aperture?
I know in half-tone work with a sealed half-tone screen,
there is a benefit
to having a square aperture, but round holes work OK --
you just get a
little bit of a different transfer function from the
original to the half-tone.

Unless you use the lens in the hot sun or something, there
might even be a
slight benefit to having plastic iris blades: less likely
to rust or corrode.

--
.~. Jean-David Beyer Registered Linux User
85642.
/V\ PGP-Key: 9A2FC99A Registered Machine
241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 06:35:01 up 2 days, 23:07, 3 users, load average:
4.19, 4.16, 4.08

It appears that the shape of the iris affects out of
focus areas of the image. This is perhaps part of the effect
called bokeh by the Japanese. In any case bright points
which are not sharply focused are rendered in the shape of
the iris. This may not be as noticable for enlarging where a
flat surface is imaged onto another flat surface.
In making half-tone plates the iris is imaged by the
half tone screen as an array of spots or dots. By using a
square aperture the intestices of the dots are at the
corners so the variation is smoother. For color work each of
the images is photographed using an iris with a
lozenge-shaped aperture at a different angle. I can't
remember now if this is to prevent moir but I think it is.
In any case there is an optimum set of angles for the
apertures. These apertures are usually in the form of
Waterhouse stops and is the reason process lenses usually
have a slot in the side. My barrel mounted Apo-Artars have
the slot but the shutter mounted one does not. The barrel
mounted Artars also have 20 blade irises and a very nearly
perfectly round hole.


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

Richard Knoppow wrote:

It appears that the shape of the iris affects out of focus areas of the
image. This is perhaps part of the effect called bokeh by the Japanese.
In any case bright points which are not sharply focused are rendered in
the shape of the iris. This may not be as noticable for enlarging where a
flat surface is imaged onto another flat surface.

In making half-tone plates the iris is imaged by the half tone screen as
an array of spots or dots. By using a square aperture the intestices of
the dots are at the corners so the variation is smoother.

Right, although I find that a round hole is not too bad. But I do halftone
starting with a continuous tone negative (a positive print or other positive
flat art is usually used) and make the half-tone on OrthoLith. These dots
have soft edges (undesirable) so I contact print them onto another piece of
OrthoLith to get a suitable half-tone negative.

For color work each of the images is photographed using an iris with a
lozenge-shaped aperture at a different angle.

That might be so, but I never heard that.

I can't remember now if this is to prevent moir[e] but I think it is.

When my great grandfather (F. E. Ives) devised the process, he angled the
half-tone screen to prevent moire, but AFAIK did not use lozenge shaped
diaphragms.

In any case there is an optimum set of angles for the apertures.

This is true for the angles of the half-tone screens as well.

In fact an amusing thing happened to F.E.Ives. When he first made color
half-tones, he naturally angled the screens between the different colors. He
did not bother to patent that because it was obvious. Years later someone
else patented the idea of angling the screens and sued Ives. Ives had to go
to court at considerable expense to prove that the patent was invalid both
because it was obvious (kiss of death for patents) and because of over a
decade of prior use.

These apertures are usually in the form of Waterhouse stops and is the
reason process lenses usually have a slot in the side.

In any case a slot is needed to set the aperture (square or not) to the
correct angle. This is all about sealed glass half-tone screens, not the
plastic contact screens more recently used. Of course, with a round
aperture, none of this makes any difference.

My barrel mounted Apo-Artars have the slot but the shutter mounted one
does not. The barrel mounted Artars also have 20 blade irises and a very
nearly perfectly round hole.

The 150 mm Componon-S 5-blade iris does not make a geometric pentagon. What
would be straight edges are actually semi-circular convex to the edge of the
lens. I.e., at the "corners" of the iris the diameter is larger than in the
middle of what would be a straight line. In other words, the corners are
farther from the center than would be expected if a true pentagon were used.
This clearly because the iris blades are made that way. It would be
perfectly easy to make them straight if Schneider had wanted to. I assume
this was done for optical reasons and not to make the mechanics cheaper.


--
.~. Jean-David Beyer Registered Linux User 85642.
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"Jean-David Beyer" wrote in message
news:uujVj.930$%X1.495@trnddc08...
Richard Knoppow wrote:

It appears that the shape of the iris affects out of
focus areas of the
image. This is perhaps part of the effect called bokeh by
the Japanese.
In any case bright points which are not sharply focused
are rendered in
the shape of the iris. This may not be as noticable for
enlarging where a
flat surface is imaged onto another flat surface.

In making half-tone plates the iris is imaged by the half
tone screen as
an array of spots or dots. By using a square aperture the
intestices of
the dots are at the corners so the variation is smoother.

Right, although I find that a round hole is not too bad.
But I do halftone
starting with a continuous tone negative (a positive print
or other positive
flat art is usually used) and make the half-tone on
OrthoLith. These dots
have soft edges (undesirable) so I contact print them onto
another piece of
OrthoLith to get a suitable half-tone negative.

For color work each of the images is photographed using
an iris with a
lozenge-shaped aperture at a different angle.

That might be so, but I never heard that.

I can't remember now if this is to prevent moir[e] but I
think it is.

When my great grandfather (F. E. Ives) devised the
process, he angled the
half-tone screen to prevent moire, but AFAIK did not use
lozenge shaped
diaphragms.

In any case there is an optimum set of angles for the
apertures.

This is true for the angles of the half-tone screens as
well.

In fact an amusing thing happened to F.E.Ives. When he
first made color
half-tones, he naturally angled the screens between the
different colors. He
did not bother to patent that because it was obvious.
Years later someone
else patented the idea of angling the screens and sued
Ives. Ives had to go
to court at considerable expense to prove that the patent
was invalid both
because it was obvious (kiss of death for patents) and
because of over a
decade of prior use.

These apertures are usually in the form of Waterhouse
stops and is the
reason process lenses usually have a slot in the side.

In any case a slot is needed to set the aperture (square
or not) to the
correct angle. This is all about sealed glass half-tone
screens, not the
plastic contact screens more recently used. Of course,
with a round
aperture, none of this makes any difference.

My barrel mounted Apo-Artars have the slot but the
shutter mounted one
does not. The barrel mounted Artars also have 20 blade
irises and a very
nearly perfectly round hole.

The 150 mm Componon-S 5-blade iris does not make a
geometric pentagon. What
would be straight edges are actually semi-circular convex
to the edge of the
lens. I.e., at the "corners" of the iris the diameter is
larger than in the
middle of what would be a straight line. In other words,
the corners are
farther from the center than would be expected if a true
pentagon were used.
This clearly because the iris blades are made that way. It
would be
perfectly easy to make them straight if Schneider had
wanted to. I assume
this was done for optical reasons and not to make the
mechanics cheaper.


--
.~. Jean-David Beyer Registered Linux User
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4.16, 4.13, 4.08

I think you may be right that its the screens which are
made at an angle rather than the aperture, its been too long
since I learned about this stuff and the books are not
handy.
Soft dot edges have always been a problem. Monckhoven's
intensifier was intended to remedy this. It has the peculiar
property of being both an intensifier and reducer because
the cyanide will dissolve the low density silver before the
intensifier works so the net result is to increase the
contrast of the edges of the dots.


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

Richard Knoppow wrote:

I think you may be right that its the screens which are made at an angle
rather than the aperture, its been too long since I learned about this
stuff and the books are not handy.

Soft dot edges have always been a problem. Monckhoven's intensifier was
intended to remedy this. It has the peculiar property of being both an
intensifier and reducer because the cyanide will dissolve the low density
silver before the intensifier works so the net result is to increase the
contrast of the edges of the dots.

I know F.E.Ives used special treatment of the negatives, and careful control
of their condition for best results. They did not have litho film in those
days. They do now (for a while more, at least), so I make contact prints of
the soft-dot stuff onto another piece of litho film and that makes
hard-dots. Exposure is tricky at first, because if you change the exposure,
you change the diameter of the dots. I make some 50% dots (my densitometer
will measure % dot area) and make the contact prints 50% also -- or pretty
close anyway.

--
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On 5/10/2008 8:02 AM Richard Knoppow spake thus:

In making half-tone plates the iris is imaged by the
half tone screen as an array of spots or dots. By using a
square aperture the intestices of the dots are at the
corners so the variation is smoother. For color work each of
the images is photographed using an iris with a
lozenge-shaped aperture at a different angle. I can't
remember now if this is to prevent moir but I think it is.

Yes, the screens are angled to prevent moiré.

By the way, the standard screen angles for 4-color (CMYK) printing a

K (black): 45°
M (magenta): 75°
Y (yellow): 90°
C (cyan): 105°

So far as I know, these have been in use as long as 4-color halftone
printing has been around.


--
The best argument against democracy is a five-minute
conversation with the average voter.

- Attributed to Winston Churchill