Enlarger lens options.

Re: Enlarger lens options.

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
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Re: Enlarger lens options.


"Jean-David Beyer" <jeandavid8@verizon,net > 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

Re: Enlarger lens options.


"Jean-David Beyer" <jeandavid8@verizon,net > 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
dickburk@ix,net com,com

Re: Enlarger lens options.

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.
/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http :// counter.li.org
^^-^^ 11:35:01 up 3 days, 4:07, 3 users, load average: 4.16, 4.13, 4.08

Re: Enlarger lens options.


"Jean-David Beyer" <jeandavid8@verizon,net > 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
> 85642.
> /V\ PGP-Key: 9A2FC99A Registered Machine
> 241939.
> /( )\ Shrewsbury, New Jersey http :// counter.li.org
> ^^-^^ 11:35:01 up 3 days, 4:07, 3 users, load average:
> 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
dickburk@ix,net com,com

Re: Enlarger lens options.

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.

--
.~. Jean-David Beyer Registered Linux User 85642.
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^^-^^ 18:40:01 up 4 days, 11:12, 4 users, load average: 4.31, 4.37, 4.31

Re: Enlarger lens options.

"Jean-David Beyer" <jeandavid8@verizon,net > wrote

> I make some 50% dots (my densitometer will measure % dot area)
> and make the contact prints 50% ...

Brings back memories ... My firm designed a graphic arts exposure
integrator that had exposure adjustment in % dot gain (along with
stops, OD (for step-wedge test results), and straight %). Then
we designed nuVac for stochastic screening and the hell with
dot-gain. All about 20 years ago ... the dénouement of analog
pre-press.

--
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation: F-Stop Timers, Enlarging Meters
http :// www .darkroomautomation,com /index2.htm
n o lindan at ix dot netcom dot com

Re: Enlarger lens options.

Nicholas O. Lindan wrote:
> "Jean-David Beyer" <jeandavid8@verizon,net > wrote
>
>> I make some 50% dots (my densitometer will measure % dot area)
>> and make the contact prints 50% ...
>
> Brings back memories ... My firm designed a graphic arts exposure
> integrator that had exposure adjustment in % dot gain (along with
> stops, OD (for step-wedge test results), and straight %). Then
> we designed nuVac for stochastic screening and the hell with
> dot-gain. All about 20 years ago ... the dénouement of analog
> pre-press.
>
I just use a Macbeth densitometer TD-901 that has a %dot scale.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http :// counter.li.org
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Re: Enlarger lens options.

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 are:

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

Screen angles

On 5/11/2008 5:09 PM David Nebenzahl spake thus:

> By the way, the standard screen angles for 4-color (CMYK) printing are:
>
> K (black): 45°
> M (magenta): 75°
> Y (yellow): 90°
> C (cyan): 105°

Interesting explanation of screen angles can be found at
http :// www .dtp-aus,com /hlftone.htm (scroll down to "Screen(#) Ruling
and Angles").

Interestingly, it's not just a matter of reducing moiré effects; the
screen angles are selected to create "rose" patterns which, apparently,
are the least bad alternative (there will always be some kind of pattern
generated by multiple halftone screens, and this is thought to be the
most pleasing one).


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

- Attributed to Winston Churchill