Square pinhole

"Lobster" <lobster685 RemoveThis @hotmail.com> wrote in message
news:_C9Sd.445517$Xk.169873@pd7tw3no...
 > Just curious... what would be the effect of a square pinhole (or a
 > pinhole the same aspect ratio as the film format). Would vignetting still
 > be radial? Would overall sharpness be less? Would overall sharpness be
 > less/more/same than an equivalent circular pinhole of the rectangular
 > diagonal? Could one get a zoneplate made from concentric rectangles to do
 > anything useful?
 > Any idea what the effects might be anyone.

A square aperture/pinhole averages out the small differences to make a
circular image.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

I'm just guessing here but I suspect you would get worse resolution with
a square hole and that vignetting would still occur since it partially
depends on the distance rays have to travel within the camera. The
center rays would still travel less distance and so the center would
still be brighter.

As far as the zone plate, again I think you would lose resolution.
IIRC, the zone plate depends on a geometric progression related to
integer multiples of the radii of concentric circles in order to cancel
interfering amplitudes (via the black rings) and multiply others (via
the clear rings) in order to get the effect. Since a pinhole is really
a zone plate with the number of circles reduced to one, I suspect the
use of a rectangular hole would reduce the resolution or definition that
a circular hole or ring provides. Plus, it would be much more difficult
to manufacture a small rectangular hole, at least by hand.

Joe



Lobster wrote:
 > Just curious... what would be the effect of a square pinhole (or a pinhole
 > the same aspect ratio as the film format). Would vignetting still be radial?
 > Would overall sharpness be less? Would overall sharpness be less/more/same
 > than an equivalent circular pinhole of the rectangular diagonal? Could one
 > get a zoneplate made from concentric rectangles to do anything useful?
 > Any idea what the effects might be anyone.
 >
 > JH
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

Lobster wrote:
 > Just curious... what would be the effect of a square pinhole (or a
pinhole
 > the same aspect ratio as the film format). Would vignetting still be
radial?
 > Would overall sharpness be less? Would overall sharpness be
less/more/same
 > than an equivalent circular pinhole of the rectangular diagonal?
Could one
 > get a zoneplate made from concentric rectangles to do anything
useful?
 > Any idea what the effects might be anyone.
 >
 > JH


The shape will make little difference to the image although it will
affect the shape of out of focus highlights. Actually square stops have
been used in the past. One of the simplest variable diaphragms is made
by sliding two wedges against each other. This forms a square of
varying size. This sort of stop was used in some very old cameras.
There is some theoretical difference in the effects of diffraction
but in practice they are not significant in normal photography.
In another reply to this is mentioned the special stops used in
making cross-screen half tone negatives. This is the method used for
years for printing photographs by letterpress. The stop of the lens is
actually imaged on the film by the cross hatch of the cross screen,
which is located near the film. It acts like a multiplicity of pin-hole
lenses. It was discovered that shapes other than round were superior
for this purpose. Most process lenses have a slot for inserting special
stops. However this effect does not apply to normal photography.

Richard Knoppow
Los Angeles, CA, USA
dickburk DeleteThis @ix.netcom.com<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

Richard Knoppow wrote:
 > Lobster wrote:
 >
  >>Just curious... what would be the effect of a square pinhole (or a
 >
 > pinhole
 >
  >>the same aspect ratio as the film format). Would vignetting still be
 >
 > radial?
 >
  >>Would overall sharpness be less? Would overall sharpness be
 >
 > less/more/same
 >
  >>than an equivalent circular pinhole of the rectangular diagonal?
 >
 > Could one
 >
  >>get a zoneplate made from concentric rectangles to do anything
 >
 > useful?
 >
  >>Any idea what the effects might be anyone.
  >>
  >>JH
 >
 >
 >
 > The shape will make little difference to the image although it will
 > affect the shape of out of focus highlights. Actually square stops have
 > been used in the past. One of the simplest variable diaphragms is made
 > by sliding two wedges against each other. This forms a square of
 > varying size. This sort of stop was used in some very old cameras.
 > There is some theoretical difference in the effects of diffraction
 > but in practice they are not significant in normal photography.
 > In another reply to this is mentioned the special stops used in
 > making cross-screen half tone negatives. This is the method used for
 > years for printing photographs by letterpress. The stop of the lens is
 > actually imaged on the film by the cross hatch of the cross screen,
 > which is located near the film. It acts like a multiplicity of pin-hole
 > lenses. It was discovered that shapes other than round were superior
 > for this purpose. Most process lenses have a slot for inserting special
 > stops. However this effect does not apply to normal photography.
 >

To amplify on what Richard has said, in the case of crossline screens for
half-tone, the square (or nearly square) holes in the diaphragm of the
copy cameralens were there to improve the characteristic curve of the
process. The halftone screen (the array of pinholes) which was almost
always composed of square holes; first, because it is much easier to make
them that way on a ruling engine, and also because, except for screwball
artistic effects, it just works better that way.

The reason for using non round (usually square or nearly so) apertures in
the copy camera lens is to affect the shape of the transfer function of
the optical system. This is analagous to changing the characteristic curve
of the film when doing "normal" photography. A square aperture is nearly
ideal. Making a slight change from square helps eliminate an abrubt shift
in the mid tones it is said. Since my lens has a 20 (or maybe 19) piece
diaphragm assembly, it is almost exactly round, and I have never had any
trouble with it.

--
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/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey <a style='text-decoration: underline;' href="http://counter.li.org" target="_blank">http://counter.li.org</a>
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 >> Stay informed about: Square pinhole 

On 2/21/2005 8:37 AM Jean-David Beyer spake thus:

 > Richard Knoppow wrote:
  >
  >> The shape will make little difference to the image although it will
  >> affect the shape of out of focus highlights. Actually square stops have
  >> been used in the past. One of the simplest variable diaphragms is made
  >> by sliding two wedges against each other. This forms a square of
  >> varying size. This sort of stop was used in some very old cameras.
 >
 > To amplify on what Richard has said, in the case of crossline screens for
 > half-tone, the square (or nearly square) holes in the diaphragm of the
 > copy cameralens were there to improve the characteristic curve of the
 > process. The halftone screen (the array of pinholes) which was almost
 > always composed of square holes; first, because it is much easier to make
 > them that way on a ruling engine, and also because, except for screwball
 > artistic effects, it just works better that way.
 >
 > The reason for using non round (usually square or nearly so) apertures in
 > the copy camera lens is to affect the shape of the transfer function of
 > the optical system. This is analagous to changing the characteristic curve
 > of the film when doing "normal" photography. A square aperture is nearly
 > ideal. Making a slight change from square helps eliminate an abrubt shift
 > in the mid tones it is said. Since my lens has a 20 (or maybe 19) piece
 > diaphragm assembly, it is almost exactly round, and I have never had any
 > trouble with it.

Just a little tangent to this discussion: even today, with digital imaging
methods, the "dots" used in printing halftone screens are not necessarily round.

The RIP I had in my shop (which wasn't particularly up-to-date, the software
being ca. 1998 or so) gave me the choice of many shapes: round, "Euclidean"
(basically elliptical), plus square and some bizarre "specialty" shapes for
special effects (like lines!). There is indeed a dramatic difference between,
say, round and Euclidean dots in smooth gradients; round dots will often show
a marked break at the 50% transition point which the elliptical dots do not.
(This is because at some point around 50% the dots start to touch each other
which increases the ink density on the printed sheet.) Plus there are more
subtle differences in tonality between the two dot shapes. Plus, all of the
above are affected by further variables downstream, such as the amount of dot
gain of the printing press (basically, how much larger dots are on the paper
than on the printing plate).

And of course this doesn't even cover the latest development in halftone
process printing, which is the so-called "stochastic" dot. These aren't even
really dots at all, but instead are more-or-less random patterns generated by
the RIP. These dots can be much smaller than conventional halftone dots
(typically 200-line screen equivalent and above), and if properly printed can
really give the impression* of a continuous-tone image. No problems with moire
caused by overlapping screens as with conventional grid-pattern screens.
Pretty amazing stuff. (This process goes by the trade name of "Staccato" among
others.)

* pun intended


--
Today's bullshit job description:

• Collaborate to produce operational procedures for the systems management
of the production Information Technology infrastructure.

- from an actual job listing on Craigslist (http://www.craigslist.org)<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

"Richard Knoppow" <dickburk DeleteThis @ix.netcom.com> wrote

 > square stops have been used in the past. One of the simplest
 > variable diaphragms is made by sliding two wedges against each other.

Still used today in about every P&S made. Also used in Polaroids.

There are all sorts of variations, one being a tadpole shape sliding
over a hole -- this gives a somewhat linear stops-to-distance
relationship.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
To reply, remove spaces: n o lindan at ix . netcom . com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

"Richard Knoppow" <dickburk.DeleteThis@ix.netcom.com> wrote in message
news:1108985232.562617.268720@f14g2000cwb.googlegroups.com...
 >
 > Lobster wrote:
  >> Just curious... what would be the effect of a square pinhole (or a
 > pinhole
  >> the same aspect ratio as the film format). Would vignetting still be
 > radial?
  >> Would overall sharpness be less? Would overall sharpness be
 > less/more/same
  >> than an equivalent circular pinhole of the rectangular diagonal?
 > Could one
  >> get a zoneplate made from concentric rectangles to do anything
 > useful?
  >> Any idea what the effects might be anyone.
  >>
  >> JH
 >
 >
 > The shape will make little difference to the image although it will
 > affect the shape of out of focus highlights. Actually square stops have
 > been used in the past. One of the simplest variable diaphragms is made
 > by sliding two wedges against each other. This forms a square of
 > varying size. This sort of stop was used in some very old cameras.
 > There is some theoretical difference in the effects of diffraction
 > but in practice they are not significant in normal photography.
 > In another reply to this is mentioned the special stops used in
 > making cross-screen half tone negatives. This is the method used for
 > years for printing photographs by letterpress. The stop of the lens is
 > actually imaged on the film by the cross hatch of the cross screen,
 > which is located near the film. It acts like a multiplicity of pin-hole
 > lenses. It was discovered that shapes other than round were superior
 > for this purpose. Most process lenses have a slot for inserting special
 > stops. However this effect does not apply to normal photography.
 >
 > Richard Knoppow
 > Los Angeles, CA, USA
 > dickburk.DeleteThis@ix.netcom.com
 >

I think I was tending to some ludicrous degree of misconception and
personally speculating that vignetting was a product of the image being some
sort of meta-image of the pinhole iteself, whereas I now see that it must be
due to light intensity varying at the film plane as function of distance to
the aperture.

Half way through building a 50mm 4x5 pinhole camera designed to work with a
grafmatic hence the interest. Thanks for all the informative answers.
JH<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

"Lobster" <lobster685 DeleteThis @hotmail.com> wrote in message
news:mJrSd.458929$6l.390229@pd7tw2no...

 > I think I was tending to some ludicrous degree of misconception and
 > personally speculating that vignetting was a product of the image being
 > some sort of meta-image of the pinhole iteself, whereas I now see that it
 > must be due to light intensity varying at the film plane as function of
 > distance to the aperture.
 >
 > Half way through building a 50mm 4x5 pinhole camera designed to work with
 > a grafmatic hence the interest. Thanks for all the informative answers.

Curiosity is a good thing! Have you checked into The Pinhole Journal? It's
got about everything about pinholes ever considered. I kid you not: from
oatmeal boxes, to pinholes at both ends of a box, even the 'mouth camera'
(and in one rare issue, The Asshole Camera (picture it)).

But seriously, check them out. I have something like 30 issues in the
library. Very informative, quite serious stuff.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

"Lobster" <lobster685 RemoveThis @hotmail.com> wrote in message
news:_C9Sd.445517$Xk.169873@pd7tw3no...
 > Just curious...

 > Could one
 > get a zoneplate made from concentric rectangles to do anything useful?
 > Any idea what the effects might be anyone.

Opposite to pinholes Zone plates do "focus" light by diffracting it (glass
lenses do it by refracting it), something else, the distance from infinity
to the edge of ring "n" and then to the center of the film plane should be
exactly 1/2 wavelength longer than the same distance for ring "n+1",
concentric circles (or zones) based on the square root of the ring number
(SQRT(n)) nicely comply with the requirement and the effect is that all of
their diffractions add up to increase the signal at the film plane. If you
change from circles to squares, the only point diffracting light having the
full additive effect would be the points of the squares tangent to the
imaginary concentric circle they are replacing. Having said that, a lot of
the light circular zone plates let thru is un-diffracted, the same can be
said for a "square-zoneplate", the difference is that virtually non of the
light diffracted by a square zone plate interfere constructively. The
effect, I think, would be a less "sharp" image with a smaller signal/noise
ratio, the later being what gives the characteristic effect of zone plate
images or pinhole sieve images, for that matter.

If you want to read couple of small articles on zoneplates and pinhole
sieves:
<a style='text-decoration: underline;' href="http://members.rogers.com/penate/zoneplate.html" target="_blank">http://members.rogers.com/penate/zoneplate.html</a>
<a style='text-decoration: underline;' href="http://members.rogers.com/penate/sieve/photonsieve.html" target="_blank">http://members.rogers.com/penate/sieve/photonsieve.html</a>

Guillermo<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

"Richard Knoppow" <dickburk.DeleteThis@ix.netcom.com> wrote in message
news:1108985232.562617.268720@f14g2000cwb.googlegroups.com...
 >
 > Lobster wrote:
  >> Just curious... what would be the effect of a square
  >> pinhole (or a
 > pinhole
  >> the same aspect ratio as the film format). Would
  >> vignetting still be
 > radial?
  >> Would overall sharpness be less? Would overall sharpness
  >> be
 > less/more/same
  >> than an equivalent circular pinhole of the rectangular
  >> diagonal?
 > Could one
  >> get a zoneplate made from concentric rectangles to do
  >> anything
 > useful?
  >> Any idea what the effects might be anyone.
  >>
  >> JH
 >
 >
 > The shape will make little difference to the image
 > although it will
 > affect the shape of out of focus highlights. Actually
 > square stops have
 > been used in the past. One of the simplest variable
 > diaphragms is made
 > by sliding two wedges against each other. This forms a
 > square of
 > varying size. This sort of stop was used in some very old
 > cameras.
 > There is some theoretical difference in the effects of
 > diffraction
 > but in practice they are not significant in normal
 > photography.
 > In another reply to this is mentioned the special
 > stops used in
 > making cross-screen half tone negatives. This is the
 > method used for
 > years for printing photographs by letterpress. The stop of
 > the lens is
 > actually imaged on the film by the cross hatch of the
 > cross screen,
 > which is located near the film. It acts like a
 > multiplicity of pin-hole
 > lenses. It was discovered that shapes other than round
 > were superior
 > for this purpose. Most process lenses have a slot for
 > inserting special
 > stops. However this effect does not apply to normal
 > photography.
 >
 > Richard Knoppow
 > Los Angeles, CA, USA
 > dickburk.DeleteThis@ix.netcom.com
 >
I realized after posting this that the question was about
pin holes, not lens stops. However, my answer is still
applicable. In fact the shape of the pinhole probably does
affect the diffusion pattern somewhat. If one looks on books
on optics one will find descriptions of the effect of
diffusion from round holes, slits, arrays of slits, and, in
some books other shapes.
The shape of the image of an object will still be the
shape of the object but the surrounding diffuse field will
change shape.


--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk.DeleteThis@ix.netcom.com<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

"Lobster" <lobster685.TakeThisOut@hotmail.com> wrote in message
news:mJrSd.458929$6l.390229@pd7tw2no...
 >
 > "Richard Knoppow" <dickburk.TakeThisOut@ix.netcom.com> wrote in
 > message
 > news:1108985232.562617.268720@f14g2000cwb.googlegroups.com...
  >>
  >> Lobster wrote:
   >>> Just curious... what would be the effect of a square
   >>> pinhole (or a
  >> pinhole
   >>> the same aspect ratio as the film format). Would
   >>> vignetting still be
  >> radial?
   >>> Would overall sharpness be less? Would overall sharpness
   >>> be
  >> less/more/same
   >>> than an equivalent circular pinhole of the rectangular
   >>> diagonal?
  >> Could one
   >>> get a zoneplate made from concentric rectangles to do
   >>> anything
  >> useful?
   >>> Any idea what the effects might be anyone.
   >>>
   >>> JH
  >>
  >>
  >> The shape will make little difference to the image
  >> although it will
  >> affect the shape of out of focus highlights. Actually
  >> square stops have
  >> been used in the past. One of the simplest variable
  >> diaphragms is made
  >> by sliding two wedges against each other. This forms a
  >> square of
  >> varying size. This sort of stop was used in some very old
  >> cameras.
  >> There is some theoretical difference in the effects of
  >> diffraction
  >> but in practice they are not significant in normal
  >> photography.
  >> In another reply to this is mentioned the special
  >> stops used in
  >> making cross-screen half tone negatives. This is the
  >> method used for
  >> years for printing photographs by letterpress. The stop
  >> of the lens is
  >> actually imaged on the film by the cross hatch of the
  >> cross screen,
  >> which is located near the film. It acts like a
  >> multiplicity of pin-hole
  >> lenses. It was discovered that shapes other than round
  >> were superior
  >> for this purpose. Most process lenses have a slot for
  >> inserting special
  >> stops. However this effect does not apply to normal
  >> photography.
  >>
  >> Richard Knoppow
  >> Los Angeles, CA, USA
  >> dickburk.TakeThisOut@ix.netcom.com
  >>
 >
 > I think I was tending to some ludicrous degree of
 > misconception and personally speculating that vignetting
 > was a product of the image being some sort of meta-image
 > of the pinhole iteself, whereas I now see that it must be
 > due to light intensity varying at the film plane as
 > function of distance to the aperture.
 >
 > Half way through building a 50mm 4x5 pinhole camera
 > designed to work with a grafmatic hence the interest.
 > Thanks for all the informative answers.
 > JH
 >
In halftone work with a cross-screen the image of the
diaphram of the lens is imaged on the film. It is an unsharp
image and the degree of unsharpness is important because it
is what changes the size of the dots with brightness. The
square holes in the cross screen act as an array of pinhole
lenses to image the diaphragm of the lens. Sometimes a
square stop is used in the lens for monochrome work because
it results in dots which are more square shaped, which is
desirable. For color work the stops are eliptical and are at
three different angles for the three colors.
The distance of the cross screen from the film and the
distance of the lens from the screen (and of course film)
are critical to getting good results.
The cross screen method was in use for very many years
but began to be replaced by "screened" film around the early
1940's. The original method was capable of exceptionally
fine quality provided it was carried out by extremely good
technicians, but it was also very critical of the skill of
the operator, so, for routine work the self screening film
won out.
Self screening films were used for the bulk of half-tone
work until all photographic methods were supplanted by
electronic methods a few years ago.
BTW, Jean-David Beyer is related to the inventor of the
cross screen and the method of making photogrpahic plates
for use in letter press printing.


--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk.TakeThisOut@ix.netcom.com<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

"jjs" <john@xstafford.net> wrote in message
news:111kjh94916oe20@news.supernews.com...
 > "Lobster" <lobster685.TakeThisOut@hotmail.com> wrote in message
 > news:mJrSd.458929$6l.390229@pd7tw2no...
 >
  >> I think I was tending to some ludicrous degree of misconception and
  >> personally speculating that vignetting was a product of the image being
  >> some sort of meta-image of the pinhole iteself, whereas I now see that it
  >> must be due to light intensity varying at the film plane as function of
  >> distance to the aperture.
  >>
  >> Half way through building a 50mm 4x5 pinhole camera designed to work with
  >> a grafmatic hence the interest. Thanks for all the informative answers.
 >
 > Curiosity is a good thing! Have you checked into The Pinhole Journal? It's
 > got about everything about pinholes ever considered. I kid you not: from
 > oatmeal boxes, to pinholes at both ends of a box, even the 'mouth camera'
 > (and in one rare issue, The Asshole Camera (picture it)).
 >
 > But seriously, check them out. I have something like 30 issues in the
 > library. Very informative, quite serious stuff.
 >

No never run into a copy of this, but I see Pinhole Resource publish it.
I'll check out a copy sometime. I'm afraid I can't face picturing the
asshole camera... I mean the mouth camera sounds tricky enough, with all
that f512 lip puckering; the thought of ragged sprocket holes is making my
eyes water.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole 

"Richard Knoppow" <dickburk.RemoveThis@ix.netcom.com> wrote

 > The cross screen method was in use for very many years
 > but began to be replaced by "screened" film around the early
 > 1940's.

The 'screened film' (now just called a 'screen') was made by
making a continuous tone shadow-image of the ruled
cross-screen. The screen then has 'grey dots' that merge
into one another.

In (not-so) modern lithography the negative is contact
printed with the screen on to lith film. The density of
the negative combines with the gradated dots on the screen
to produce black dots whose size is proportional to the
negative density.

Film lithography has the advantage of having more resolution
than the dot-density would have you believe. The shape of
the dots is not round, but follows the details in the original
continuous tone negative.

Lithographic image setting by computer requires a _true_ resolution
of 2000 DPI in the imagesetter to give the same result as a
100 DPI screen.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
To reply, remove spaces: n o lindan at ix . netcom . com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Square pinhole