Diffraction and F64
Kerry Thalmann
Richard Knoppow wrote:
>
> vilnt...@aol.com (VILNTFLUID) wrote:
>
> >It has confused me that Adams and some of his friends were enthusiastic about
> > stopping down to F64 for maximum sharpness and DOF.
> >Aren't most lenses diffraction limited at apertures this small?
> >Perhaps I did not understand correctly what the F64 group was advocating.
> >Keith
> The Group f/64 was formed by Weston, Adams, and others in protest
> of the kind of hazy, soft-focus style then prevalent in pictorial
> photography. The name of the group was not literally indicative of
> their technique.
> It is sometimes necessary to use very small stops with LF cameras
> but it is to be avoided when some other way i.e. using swings and
> tilts will accomplish the purpose.
Hi Keith and Richard,
Also, keep in mind the lenses and formats these folks were using.
Shooting 8x10, and larger, and with some of the older lenses, f64 may
have, in some instances, yielded the best combination of overall
sharpness and depth of field. Even with modern lenses, many 8x10
shooters regularly use f45, and f64 is not unheard of. Personally, with
4x5, I try to shoot at f22 most of the time, and rarely stray beyond one
stop in either direction. Still, there are occasionally special
situations that require me to stop down further than f32 (or open up
wider than f16). The important thing is to know the effects of those
choices, and use them only when beneficial.
Kerry
VILNTFLUID
Richard Knoppow
vilnt...@aol.com (VILNTFLUID) wrote:
The Group f/64 was formed by Weston, Adams, and others in protest
of the kind of hazy, soft-focus style then prevalent in pictorial
photography. The name of the group was not literally indicative of
their technique.
It is sometimes necessary to use very small stops with LF cameras
but it is to be avoided when some other way i.e. using swings and
tilts will accomplish the purpose.
---
Richard Knoppow
Los Angeles, Ca.
dick...@ix.netcom.com
Dell Elzey
Kerry Thalmann <K.Tha...@worldnet.att.net> wrote:
>Also, keep in mind the lenses and formats these folks were using.
>Shooting 8x10, and larger, and with some of the older lenses, f64 may
>have, in some instances, yielded the best combination of overall
>sharpness and depth of field. Even with modern lenses, many 8x10
>shooters regularly use f45, and f64 is not unheard of. Personally, with
>4x5, I try to shoot at f22 most of the time, and rarely stray beyond one
>stop in either direction. Still, there are occasionally special
>situations that require me to stop down further than f32 (or open up
>wider than f16). The important thing is to know the effects of those
>choices, and use them only when beneficial.
>Kerry
Hi Kerry,
Dang, I shoot more at f64 with 4x5 view than any other f stop.
Guess my work ain't as sharp as it should be...
Dell Elzey
Large Format black and white Photography
http://www.geocities.com/SoHo/Lofts/9083/
Roger Cole
On Wed, 19 Nov 1997 23:44:06 -0800, Kerry Thalmann <K.Tha...@worldnet.att.net>
wrote:
>Hi Keith and Richard,
>
>Also, keep in mind the lenses and formats these folks were using.
>Shooting 8x10, and larger, and with some of the older lenses, f64 may
>have, in some instances, yielded the best combination of overall
>sharpness and depth of field. Even with modern lenses, many 8x10
>shooters regularly use f45, and f64 is not unheard of. Personally, with
>4x5, I try to shoot at f22 most of the time, and rarely stray beyond one
>stop in either direction. Still, there are occasionally special
>situations that require me to stop down further than f32 (or open up
>wider than f16). The important thing is to know the effects of those
>choices, and use them only when beneficial.
>
>Kerry
Very true. Also keep in mind that their 8x10 negatives were often contact
printed, or enlarged a comparatively small amount, and you can tolerate a lot
more unsharpness in the negative when contact printing, or enlarging 2x, than
when enlarging a 35mm frame by a factor of 8x to 16x. In an 8x10 contact print,
I don't think you'd ever see any degradation of sharpness from using f/64. As
others said, it was an aesthetic statement, not a technical one.
Roger Cole
Steve Kaiser
Kerry Thalmann <K.Tha...@worldnet.att.net> wrote:
>Richard Knoppow wrote:
>>
>> vilnt...@aol.com (VILNTFLUID) wrote:
>>
>> >It has confused me that Adams and some of his friends were enthusiastic about
>> > stopping down to F64 for maximum sharpness and DOF.
<snip>
Hey All...
I too was interested in the Group f64...I was reading through the
Ansel Adams "The Camera" last night and came across an image which is
captioned "This represents an image typical of the Group f64 period
(1932)..." and yet the image was only exposed at f32.
I think Richard hit it right on...
>> The Group f/64 was formed by Weston, Adams, and others in protest
>> of the kind of hazy, soft-focus style then prevalent in pictorial
>> photography. The name of the group was not literally indicative of
>> their technique.
Steve Kaiser
Toronto, Canada
NOSPAM*ska...@globalserve.net
Michael A. Smith/Paula Chamlee
Keith & Richard & Kerry & Roger wrote
>>
>> vilnt...@aol.com (VILNTFLUID) wrote:
>>
>> >It has confused me that Adams and some of his friends were enthusiastic about stopping down to F64 for maximum sharpness and DOF.
Perhaps I did not understand correctly what the F64 group was
advocating.
>> >Keith
>> The Group f/64 was formed by Weston, Adams, and others in protest of the kind of hazy, soft-focus style then prevalent in pictorial photography. The name of the group was not literally indicative of their technique.
It is sometimes necessary to use very small stops with LF cameras
but it is to be avoided when some other way i.e. using swings and
tilts will accomplish the purpose.
>
>Hi Keith and Richard,
>
>Also, keep in mind the lenses and formats these folks were using.
>Shooting 8x10, and larger, and with some of the older lenses, f64 may
>have, in some instances, yielded the best combination of overall
>sharpness and depth of field. Even with modern lenses, many 8x10
>shooters regularly use f45, and f64 is not unheard of. Personally, with 4x5, I try to shoot at f22 most of the time, and rarely stray beyond one stop in either direction. Still, there are occasionally special situations that require me to stop down further than f32 (or open up wider than f16). The important thing is to know the effects of those choices, and use them only when beneficial.
Kerry
Very true. Also keep in mind that their 8x10 negatives were often
contact printed, or enlarged a comparatively small amount, and you can
tolerate a lot more unsharpness in the negative when contact printing,
or enlarging 2x, than when enlarging a 35mm frame by a factor of 8x to
16x. In an 8x10 contact print, I don't think you'd ever see any
degradation of sharpness from using f/64. As others said, it was an
aesthetic statement, not a technical one.
Roger Cole
Hi allã
Paula and I usually photograph at f64, and we often use f90 or a
smaller aperture if we have it, and we have no degradation of
sharpness. Of course, we only make contact prints and that is one
explanation, but there is anotherãone that everyone has overlooked.
Diffraction is a function of the absolute size of the diameter of the
opening of the diaphragmãit is not a function of the f-stop used. On a
normal 12" lens (for an 8x10), at f64 the diameter of the opening is
larger than it is with a 50mm lens on a 35mm camera set at f16. And
with our long lensesã19", 24", 30", at f64 the opening is
hugeãcertainly far too great to have any diffraction effect
whatsoever. I suspect that with those who do notice a fall-off in
sharpness at the smaller f-stops that they are using wide angle lenses
on a 4x5. With those short lenses, yes, I can see that diffraction
might be a problem at the smaller stops.
Theoretically, any lens is sharpest at two-three stops from wide open
(for reasons most of you already know), and this can readily be seen
with any enlarging lensãbut those lenses are all of short focal length
and the diffraction would readily show up there.
Confusion also arises, I think, because most people originally started
photographing with a 35mm camera, and from that experience, conceive
of f64 as an impossibly small opening. They also assume that f64 will
give far greater depth of field, but of course depth of field, too, is
a function of the absolute size of the opening, not the fstopãwhich is
why, with our long lenses we need to use such relatively small
openings. And even then, with a 30" or 35" lens, without using camera
movements, f90 does not give as much depth of field as does f16 on a
50mm lens on a 35mm camera.
Michael A. Smith
Karl Juul
Michael A. Smith/Paula Chamlee wrote in message <3474DC...@epix.net>...
>Paula and I usually photograph at f64, and we often use f90 or a
>smaller aperture if we have it, and we have no degradation of
>sharpness. Of course, we only make contact prints and that is one
>explanation, but there is anotherãone that everyone has overlooked.
>Diffraction is a function of the absolute size of the diameter of the
>opening of the diaphragmãit is not a function of the f-stop used. On a
>normal 12" lens (for an 8x10), at f64 the diameter of the opening is
>larger than it is with a 50mm lens on a 35mm camera set at f16. And
>with our long lensesã19", 24", 30", at f64 the opening is
>hugeãcertainly far too great to have any diffraction effect
>whatsoever. I suspect that with those who do notice a fall-off in
>sharpness at the smaller f-stops that they are using wide angle lenses
>on a 4x5. With those short lenses, yes, I can see that diffraction
>might be a problem at the smaller stops.
This contrary to technical descriptions I have read regarding diffraction.
I was under the impression that diffraction varies directly with
_effective_ f-stop which is the marked f-stop plus any increase for bellows
extension for focus closer than infinity...
-Karl.
Timo_R...@online.tietokone.fi
vilnt...@aol.com,Usenet5 writes:
>It has confused me that Adams and some of his friends were enthusiastic
>about
> stopping down to F64 for maximum sharpness and DOF.
>Aren't most lenses diffraction limited at apertures this small?
>Perhaps I did not understand correctly what the F64 group was advocating.
>Keith
Keith,
As I remember it right, one of Adams' friends - Edward Weston - used at
least one soft focus lens with his 8x10 camera but later decided to strive
for more sharpness by stopping down beyond the optical "limitations" of the
SF lens.
So, I believe the F64 group simply wanted to make it known that they had
evolved from the soft focus era of their contemporaries.
"Sharper and sharper I stopped down my lens..." (Edward Weston, Daybooks)
-Timo-
Willem-Jan Markerink
In article <3474e...@news.wizvax.net>,
It does make sense to me to use fysical size of aperture....look at it as
circumference of the opening divided by surface of the opening.
The circumference is an indicator of the absolute amount of diffraction,
the surface of the opening dictates how important it is....
With an increase in diameter, circumference grows linear, surface with
power 2, as in [2 x Pi x R] vs [Pi ^ 2]....so fysical large apertures have
an advantage.
Further note that diffraction is also linear with wavelength....at 800nm
(infrared) it is twice as worse as with 400nm (blue).
--
Bye,
Willem-Jan Markerink
The desire to understand
is sometimes far less intelligent than
the inability to understand
<w.j.ma...@a1.nl>
[note: 'a-one' & 'en-el'!]
Joseph O'Neil
Karl Juul wrote:
> Michael A. Smith/Paula Chamlee wrote in message <3474DC...@epix.net>...
> >Diffraction is a function of the absolute size of the diameter of the
> >opening of the diaphragmãit is not a function of the f-stop used. On a
> >normal 12" lens (for an 8x10), at f64 the diameter of the opening is
> >larger than it is with a 50mm lens on a 35mm camera set at f16. And
> >with our long lensesã19", 24", 30", at f64 the opening is
> >hugeãcertainly far too great to have any diffraction effect
> >whatsoever. This contrary to technical descriptions I have read regarding
> diffraction.
-snip-
> I was under the impression that diffraction varies directly with
> _effective_ f-stop which is the marked f-stop plus any increase for bellows
> extension for focus closer than infinity...
> -Karl.
Hi Karl;
I suspect both of you are correct. This may soudn confusing,
but let me give
you an an example from a differnt form of photograph - astro-photography.
One of the biggest problems in explaining astro-photography to newcommers is
the
F-ratio VS effective true diameter of the lens (or mirror) used. It works like
this:
Stars in the sky are point images. No matter how much magnification you
place
upon them, you will only have points of light. Therefore, what you need the
most
to record them is the largest diameter lens or mirror possible to collect the
largest
amount of light. F-ratio is totaly irrellevant to stars only. However...
Other objects, such as planets, nebula, galaxies are "extened" objects,
they can be magnified, and one's ability to record them on film is directly
related to the F ratio of the lens used.
Problems arrise when you try and find the "perfect balance" between a large
enough diameter lens to record both stars and extended objects (since the
objects in question are very dim, and you still need a lot of light to record
them too.)
and the correct f-ratio and magnification to not only record the extended
object,
but also not fog up your exposure form background skyglow. Trying to find
this
correct mix is something you quickly learn there is no perfect answer for.
So, in a long winded way, what I am trying to say is your statement is
essentially
correct, but physical size of the lens involved also has direct effect in any
equation
involving optics & light. I have a good friend who is an optician that builds
telescopes
for a living, and he explained it to me in a very eleoquent manner before, but
my
explaination to you is very simple here - sorta like trying to repeat Enstien's
reasoning
behind "E-Mc2" - you pick up bits and pices, but a lot still flies over your
head.
In the end, a couple of people have told me in reguards to
astro-photography, that the
whole field of expertise is sometimes more "black art" than it is sceince, no
matter
how many computers, formulas, tech sheets, etc, that you have, and that
sometimes you
just have to learn from expereince and go with your gut feeling about a
situation. I
do not see why the same thing cannot be said about LF photography.
take care
joe
http://www.multiboard.com/~joneil
Richard M. Koolish
"Michael A. Smith/Paula Chamlee" <smit...@epix.net> writes:
>Diffraction is a function of the absolute size of the diameter of the
>opening of the diaphragm, it is not a function of the f-stop used. On a
>normal 12" lens (for an 8x10), at f64 the diameter of the opening is
>larger than it is with a 50mm lens on a 35mm camera set at f16. And
>with our long lenses, 19", 24", 30", at f64 the opening is
>huge, certainly far too great to have any diffraction effect
>whatsoever. I suspect that with those who do notice a fall-off in
>sharpness at the smaller f-stops that they are using wide angle lenses
>on a 4x5. With those short lenses, yes, I can see that diffraction
>might be a problem at the smaller stops.
This is somewhat wrong. The angular size of the diffraction disk is a
function of aperture diameter. The linear size of the diffraction disk at
the film plane depends only on f-stop. For example, any f/11 system
produces the same size diffraction disk, regardless of lens diameter and
focal length.
The diameter of the Airy disk is: 2.44 * wavelength * f-number. For a
wavelength of 550 nm (yellow-green), an f/11 system produces a diffraction
disk of .0148 mm diameter . An f/64 system would produce a diffraction
disk of .086 mm diameter, about 6 times bigger.
>Theoretically, any lens is sharpest at two-three stops from wide open
>(for reasons most of you already know), and this can readily be seen
>with any enlarging lens, but those lenses are all of short focal length
>and the diffraction would readily show up there.
I think this is a rule of thumb rather than a theory. You want to stop
down the lens to the point where the lens abberations don't dominate
the image degradation as compared to diffraction.
K-...@msn.com
In article <19971120043...@ladder02.news.aol.com>,
vilnt...@aol.com (VILNTFLUID) wrote:
>
> It has confused me that Adams and some of his friends were enthusiastic about
> stopping down to F64 for maximum sharpness and DOF.
> Aren't most lenses diffraction limited at apertures this small?
> Perhaps I did not understand correctly what the F64 group was advocating.
> Keith
Hi Keith, F64 was a name only and not indicative that all photos were
taken at F64. Why this myth has persisted I don't know. As to where
diffraction may take place, well it can happen at 1 stop closed down to
the tiniest f stop. Is it noticeable ? Not till the smaller stops USUALLY
! As to using tiny stops I have one question, WHY??? Larger
apertures=slower shutter speeds=more likelyhood that the wind etc will
blur the image. Are you using a 20 x loupe to examine the prints. I hope
you are going to view the prints at a decent distance. 8 X 10 at arms
lenth maybe ? Think about how others view our prints. They dont have the
appreciation of our technique and skill in the darkroom. They dont care
if you took the photo with that f 6.8 APO Egocentar. And I have found
out through a few shows where my prints are shown they dont care. If
they like a print there is an emotional connection and they buy. I like
going to shows and not tell anyone that I,m there and just listen. THAT
TELLS YOU MORE THAN ANYTHING!! I have not used those tiny stops for
years. I do use swings and tilts. and that helps DOF greatly. Please
folks, Make prints not lore. Ken Hough K-...@MSN.COM
-------------------==== Posted via Deja News ====-----------------------
http://www.dejanews.com/ Search, Read, Post to Usenet
mc...@serv.net
maximum sharpness is usually obtained around 1-2 stops down from max
aperature
Andrei Calciu
it all depends on the design of the lens. i have tested planar and
xenotar lenses (i know they are mostly for medium format, but that is
what i tested) and found that the planar was sharpest at f/16 while the
xenotar was at its best at f/22.
any statements that generalize "best apperture", "maximum sharpness"
will be right about some lens designs and wrong about other lens
designs.
has anybody done any substantive testing with some of the more popular
lenses around: angulons, xenars, ektars nikkors, grandagons, etc?
andre
Benson
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It's true, Group f/64 was in name only. The intent of this group of west coast
photographers were "Straight Photography" No soft focus, No impressionistic
interpretation of the subject matter. The original members of Group f/64 were:
Ansel Adams, Edward Weston, Imogen Cunningham, John Paul Edwards, Sonia
Noskowiak, Willard Van Dyke, Henry F. Smith. Van Dyke suggested the name, "f/64"
This name was chosen to reflect the idea that f64 would deliver high resolution
and great depth of field when using a view camera. Ansel Adams felt that
membership should be limited to "those workers who are striving to define
photography as an art form by simple and direct presentation through purely
photographic methods." In November 15,1932. group f/64 sponsored a exhibit with
works from; Alma Lavenson, Consuelo Kanaga, Preston Holder, Brett Weston at the
M.H. De Young Memorial Museum in San Francisco. The art world of Pictoralism
after the exhibit was quite shaken. William Mortensen a leading spokesman of
pictorialist wrote with anger in "Camera Craft" over the vision of group f/64.
This battle with Van Dyke and Adams lasted for a year and a half in Camera Craft.
Later in 1933 Ansel Adams opened a gallery on Geary Blvd. in San Francisco to
show the vision of Group f/64. Van Dyke continued to show similar works at his
Brockhurst gallery in Oakland, CA, 683- Brockhurst St. The Group f/64 disbanded
in 1935. The world of photography was never the same after Group f/64. This group
of individuals had a major influence on the world of photography and art.
The Resolution of a lens depends on many factors. If we were not interested in
gathering a large amount of light on the film plane, a pin hole camera would work
fine. But this would make exposures very long and the film under extremely low
light conditions might not even record the image. Film has a minimum light
threshold. so we need a lens to collect enough light to allow reasonable exposure
times. Using a lens also allows us to change the angle of view and perspective of
a image. But all this comes with a price, lenses have aberrations and other
faults limited by the laws of physics and the creativity of the lens designer to
work with these limits. Diffraction is one of them. I here is a link;
Photographic Resolution regarding this fact. It is oriented towards 35 mm, But I
think it's a pretty good explanation of photographic resolution . On a view
camera I never stop down past f45, the resolution is too low. Resolution on film
is only one of many factors that determines how well a lens performs. In my
images I try to limit the enlargement factor to 5x. This allows a on film
resolution of aprox; 50Lpm. and a print resolution of aprox; 10Lpm. The human
eye can resolve aprox. 8-10Lpm under good conditions. I feel these are realistic
limits for modern film/lens/enlargement systems. Trying to get more on sheet film
is not easy under real world conditions. I have a specification sheet for a areo
recon. lens, 75 mm f4.5 Biogon. This lens covers a 5"x5" sheet of film, using
ultra fine grain, thin emulsion areo recon film the resolution is aprox; 170Lpm
at f4.5 across the entire 5"x5" image. But the lens itself will produce close to
400Lpm at f4.5 it is a example of what happens when film and lens are combined
together as a system. This is a extreme case but under the condition they are
working with, this is what can be done. The best images do not always have the
greatest resolution, It's the content that really counts.
VILNTFLUID wrote:
> It has confused me that Adams and some of his friends were enthusiastic about
> stopping down to F64 for maximum sharpness and DOF.
> Aren't most lenses diffraction limited at apertures this small?
> Perhaps I did not understand correctly what the F64 group was advocating.
> Keith
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<HTML>
It's true, Group f/64 was in name only. The intent of this group of west
coast photographers were "Straight Photography" No soft focus, No impressionistic
interpretation of the subject matter. The original members of Group f/64
were: Ansel Adams, Edward Weston, Imogen Cunningham, John Paul Edwards,
Sonia Noskowiak, Willard Van Dyke, Henry F. Smith. Van Dyke suggested the
name, "f/64" This name was chosen to reflect the idea that f64 would deliver
high resolution and great depth of field when using a view camera. Ansel
Adams felt that membership should be limited to "those workers who are
striving to define photography as an art form by simple and direct presentation
through purely photographic methods." In November 15,1932. group f/64 sponsored
a exhibit with works from; Alma Lavenson, Consuelo Kanaga, Preston Holder,
Brett Weston at the M.H. De Young Memorial Museum in San Francisco. The
art world of Pictoralism after the exhibit was quite shaken. William Mortensen
a leading spokesman of pictorialist wrote with anger in "Camera Craft"
over the vision of group f/64. This battle with Van Dyke and Adams lasted
for a year and a half in Camera Craft. Later in 1933 Ansel Adams opened
a gallery on Geary Blvd. in San Francisco to show the vision of Group f/64.
Van Dyke continued to show similar works at his Brockhurst gallery in Oakland,
CA, 683- Brockhurst St. The Group f/64 disbanded in 1935. The world of
photography was never the same after Group f/64. This group of individuals
had a major influence on the world of photography and art.
<BR>The Resolution of a lens depends on many factors. If we were not interested
in gathering a large amount of light on the film plane, a pin hole camera
would work fine. But this would make exposures very long and the film under
extremely low light conditions might not even record the image. Film has
a minimum light threshold. so we need a lens to collect enough light to
allow reasonable exposure times. Using a lens also allows us to change
the angle of view and perspective of a image. But all this comes with a
price, lenses have aberrations and other faults limited by the laws of
physics and the creativity of the lens designer to work with these limits.
Diffraction is one of them. I here is a link; <A HREF="http://members.aol.com/daveswager/resolut.htm">Photographic
Resolution</A> regarding this fact. It is oriented towards 35 mm,
But I think it's a pretty good explanation of photographic resolution .
On a view camera I never stop down past f45, the resolution is too low.
Resolution on film is only one of many factors that determines how well
a lens performs. In my images I try to limit the enlargement factor to
5x. This allows a on film resolution of aprox; 50Lpm. and a print resolution
of aprox; 10Lpm. The human eye can resolve aprox. 8-10Lpm under good
conditions. I feel these are realistic limits for modern film/lens/enlargement
systems. Trying to get more on sheet film is not easy under real world
conditions. I have a specification sheet for a areo recon. lens, 75 mm
f4.5 Biogon. This lens covers a 5"x5" sheet of film, using ultra fine grain,
thin emulsion areo recon film the resolution is aprox; 170Lpm at f4.5 across
the entire 5"x5" image. But the lens itself will produce close to 400Lpm
at f4.5 it is a example of what happens when film and lens are combined
together as a system. This is a extreme case but under the condition they
are working with, this is what can be done. The best images do not always
have the greatest resolution, It's the content that really counts.
<BR>VILNTFLUID wrote:
<BLOCKQUOTE TYPE=CITE>It has confused me that Adams and some of his friends
were enthusiastic about
<BR> stopping down to F64 for maximum sharpness and DOF.
<BR>Aren't most lenses diffraction limited at apertures this small?
<BR>Perhaps I did not understand correctly what the F64 group was advocating.
<BR>Keith</BLOCKQUOTE>
</HTML>
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Kerry Thalmann
Benson wrote:
(excellent history of Group f64 snipped to save bandwidth)
> On a view camera I never stop down past f45,
> the resolution is too low. Resolution on film is only one of many
> factors that determines how well a lens performs. In my images I try
> to limit the enlargement factor to 5x. This allows a on film
> resolution of aprox; 50Lpm. and a print resolution of aprox; 10Lpm.
> The human eye can resolve aprox. 8-10Lpm under good conditions. I feel
> these are realistic limits for modern film/lens/enlargement systems.
Hi Benson,
A very informative posting. Thank you, I enjoyed it.
I think the above passge may be the source of some minor disagreement in
this thread. Some have stated that they often work at f64 and beyond
and get very acceptable sharpness, while others have said they never go
beyond f32 or f45 due to the effects of diffraction. I think the big
difference is that while we are all large format shooters, some of us
shoot 4x5 and enlarge and others shoot 11x14 (or larger - one of the
previous posters in this thread shoots with an 18x22) and contact print.
So, your 5x enlargement limit may not be applicable to those who contact
print from ULF negatives. In their case, on film resolution would only
have to be (using your numbers) 8 - 10 lpm. Also, since they are using
very long focal length lenses, they must often stop way down to get
acceptable depth of field.
Perhaps to reduce this confusion, we should all state what format we are
referring to when recommending the smallest aperture we use and still
achieve acceptable sharpness. As I stated previously, I try to stay
within plus or minus one stop of f22 when working in 4x5 (with
occasional exceptions in either direction as the situation warrants).
Based on my experience, that seems to yield the optimum combination of
overall sharpness and depth of field. Now that I am dabbling in 11x14
and will be contact printing, I'm sure f64 will be used regularly and
f90 will not be unusual.
Kerry
Gary Hunt
Kerry Thalmann wrote:
> Perhaps to reduce this confusion, we should all state what format we are
> referring to when recommending the smallest aperture we use and still
> achieve acceptable sharpness. As I stated previously, I try to stay
> within plus or minus one stop of f22 when working in 4x5 (with
> occasional exceptions in either direction as the situation warrants).
> Based on my experience, that seems to yield the optimum combination of
> overall sharpness and depth of field. Now that I am dabbling in 11x14
> and will be contact printing, I'm sure f64 will be used regularly and
> f90 will not be unusual.
Excellent point. Hopefully someone can correct this if not true,
but I believe diffraction effects are rather strongly related
to the actual physical size of the lens opening. Obviously for
the longer focal length lenses one would use on very large
formats, f/64 is a larger physical opening that it would be
on a shorter lens. This is in addition to the reduced magnification
typically used on the larger formats as well.
Michael Gudzinowicz
More or less... The size of the opening determines the _angular_
diffraction/resolution limit, which is often used in astronomy and physics.
To determine the linear size of the diffraction pattern/resolution limit
expressed as lpmm, the distance from the lens to film plane is required as
well. Therefore the linear size of the pattern/resolution limit is related
to the f-number.
Although f/22 will usually give optimal center to edge sharpness for flat
subjects, depth of field is limited in most circumstances. If movements
can't solve a problem, I use a programmed pocket calculator to optimize
sharpness for both a near point and far point. The program uses the print
magnification, focal length and near an far distances to calculate the
distance to focus upon, the f# which places the limits of dof at the near
and far points, the f# which provides optimum sharpness at those points by
trading off dof vs. diffraction, and calculates the maximum print
magnification for the situation.
For example, for a 4X print with a 150 lens, and near/far distances of 15
and 45 feet: Focus at 22.5'; f/26.8 places limits at 15' & 45'; f/49.5
gives optimal sharpness at 15' & 45', with limits at 11.6' and 296.5'.
Daniel
On Sun, 23 Nov 1997 mc...@serv.net wrote:
> maximum sharpness is usually obtained around 1-2 stops down from max
> aperature
On some old lenses, the advantages of stopping down are relatively greater
than on some newer lenses. If the lens is not inherently brilliant, it is
worth avoiding as much as possible of the edges of the lens by stopping
down, and sometimes best resolution is found at minimum aperture.
Diffraction here is a minor force compared to the quality of the part of
the lens in use.
Some more recent lenses may be inherently sharper, allowing the effect of
diffraction to be more apparent at very small appertures. i.e. the lens is
so sharp that we notice the diffraction more, even thought the amount of
diffraction is the same. We notice it more because the lens is sharp
enough to reveal it!
I think if the lens was PERFECT, resolution (but not depth of field!)
would be at the maximum with MAXIMUM aperture, and since the only thing
limiting resolution would be diffraction. And this gets unavoidably worse
at smaller aperture.
I don't have the book with me in this city, but in part of Ansel Adam's
correspondence with Edward Weston, Weston has had a lens adapted to stop
down way beyond f/64, and isn't getting as good resolution as he would
like. Adams recommends a newer lens stopped down less (I think!)
Daniel Barker,
Biocomputing Research Unit,
Institute of Cell and Molecular Biology,
Swann Building,
King's Buildings,
Mayfield Road,
Edinburgh
EH9 3JR
UK
Bill Harris
Kerry Thalmann <K.Tha...@worldnet.att.net> writes (in part):
>I think the above passge may be the source of some minor disagreement in
>this thread. Some have stated that they often work at f64 and beyond
>and get very acceptable sharpness, while others have said they never go
>beyond f32 or f45 due to the effects of diffraction. I think the big
>difference is that while we are all large format shooters...
>...
>Perhaps to reduce this confusion, we should all state what format we are
>referring to when recommending the smallest aperture we use and still
>achieve acceptable sharpness.
It does depend on the format used and what the expectations of the
printed image are. With small format, I rarely go below f/16.
With 4x5 I find that f/22 +/-1 gives the best results. However, if
the image needs extreme DOF, I'll use f/45-f/64; OTOH, if selective
focus is needed, I'll stop down only 1-2 stops. I've not done my own
critical testing, but if straying from the "optimum" aperture gives
less resolution, this is one of the compromises that one deals with in
obtaining an image.
But then, I am not the sort who walks up to a 16x20 print and examines
it with a 4x loupe-- if the print looks sharp at a "normal" viewing
distance, then it is acceptably sharp.
Bill Harris
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Ben Weiner
>Karl Juul wrote:
> Michael A. Smith/Paula Chamlee wrote in message <3474DC...@epix.net>...
> >Diffraction is a function of the absolute size of the diameter of the
> >opening of the diaphragmãit is not a function of the f-stop used. On a
> >normal 12" lens (for an 8x10), at f64 the diameter of the opening is
> >larger than it is with a 50mm lens on a 35mm camera set at f16. And
> >with our long lensesã19", 24", 30", at f64 the opening is
> >hugeãcertainly far too great to have any diffraction effect
> >whatsoever. This contrary to technical descriptions I have read regarding
> diffraction.
> I was under the impression that diffraction varies directly with
> _effective_ f-stop which is the marked f-stop plus any increase for bellows
> extension for focus closer than infinity...
> -Karl.
The *angular* size of the diffraction spot is a function of
the physical diameter of the aperture opening:
(1) angular size in radians = wavelength of light / aperture diameter.
However the *linear* size of the diffraction spot, such as
the circle of confusion on the film due to diffraction, is
a function of the f-number:
(2) c-o-c diameter = wavelength of light * f-number.
This is because longer focal length lenses have a smaller
angle of view, i.e. they magnify more. f/64 on a 400mm lens
causes a diffraction angle which is half as large as from
f/64 on a 200mm lens. However, the 400mm lens magnifies
the angle twice as much, so the size of the circle of confusion
on the film is the same.
For lenses in general:
image size on film = angular size in radians * focal length
and of course f-number = focal length / aperture diameter.
A little multiplication and division shows that eqs. (1) and (2)
are equivalent. However, the circle-of-confusion size is
more likely to be of interest to a photographer, so eq (2)
is more useful. Thus saying that the effects of diffraction depend
on f-stop (and the tolerable circle-of-confusion!) is the more
useful definition.
You can get away with smaller stops on a large format camera
compared to smaller format because you are not magnifying
as much to make the print, and therefore can tolerate a
larger circle of confusion.
Don Norris
I have found that in 35mm, my Leitz lenses are sharpest between f2.8 and
f5.6, the Nikkors between f5.6 and f11, in 4X5 my older (only) lenses are
sharpest in the f16 to f32 range, and that in 8x10 (contacts only) I choose
the f stop for DOF and lighting conditions, and don't worry about the
sharpness.
--
post reply to group,or remove ??? from address.
Bill Harris <NOSPAM....@mindspring.com> wrote in article
<65d1hk$g...@camel21.mindspring.com>...
Jess4203
We all seem to have no compunction about sharing our opinions on this issue
without benefit of actual knowledge. Mine is limited, but I seem to remember
that the resolution is limited by 1600/f-stop. This would mean that at f32 the
resolution on the film was limited to about 50 lpm. On a 16x20 print from 4x5
film, this leaves 12.5 lpm, about the recommended limit, if I remember right.
I think it;'s 12 lpm at a normal viewing distance. Viewing distance changes
with the size of the print. There my actual knowledge ends. Most of my photo
books are packed away, but some of you should be able to find a mention of the
computation of viewing distance. HTH.
Richard Knoppow
jess...@aol.com (Jess4203) wrote:
This isn't quite as simple as it seems on the surface. The
resolution of the eye for green light is somewhere around 5 to 7
line/mm at 10 inches. Actually, its stated as an angular limit but
the above will do. Lens resolution is diffraction limited in a way
that varies with the angle of the light going through the lens, its
wavelength and whether the lines are radial or tangential. resolution
is usually calculated for some wavelength in the green, near the
center of the band of colors of interest in photography. The
resolution for white light is less than for monochromatic light
because of the smearing out of the lines.
An indication of the way the limit varies with angle and direction
fo the lines is the folowing. The diffraction is calculated for
589.3mu
F/8, at center, 174 l/mm; at 20deg, 145 l/mm tangential, 163 l/mm
radial. At f/64 the values are: 0deg, 22 l/mm, 18 l/mm, 20 l/mm
If we extend the half angle to 30deg, which is a little more than
the diagonal for a "normal" lens the resolution becomes 14 l/mm
Tangential and 19 l/mm radial. Again, the actual white light
resolution will be less than this. Obviously, the resolution at f/64
is adequate for contact printing but will become noticeably blurry
when large magnifications are used. For an 8x10 made from a 35mm
negative the resolution would be around 2.5 l/mm at the center, well
under the eye's resolution, a contact print from an 8x10 neg would
look just fine. That's why lenses for 35mm cameras seldom stop down
farther than f/16 or f/22.
Cheryl Claxton
po...@mindspring.com (Dell Elzey) wrote:
>Kerry Thalmann <K.Tha...@worldnet.att.net> wrote:
>>Also, keep in mind the lenses and formats these folks were using.
>>Shooting 8x10, and larger, and with some of the older lenses, f64 may
>>have, in some instances, yielded the best combination of overall
>>sharpness and depth of field. Even with modern lenses, many 8x10
>>shooters regularly use f45, and f64 is not unheard of. Personally, with
>>4x5, I try to shoot at f22 most of the time, and rarely stray beyond one
>>stop in either direction. Still, there are occasionally special
>>situations that require me to stop down further than f32 (or open up
>>wider than f16). The important thing is to know the effects of those
>>choices, and use them only when beneficial.
>>Kerry
>Hi Kerry,
>Dang, I shoot more at f64 with 4x5 view than any other f stop.
>Guess my work ain't as sharp as it should be...
>Dell Elzey
>Large Format black and white Photography
>http://www.geocities.com/SoHo/Lofts/9083/
It looks pretty damn sharp to me.
Kerry Thalmann
Cheryl Claxton wrote:
> >Hi Kerry,
> >Dang, I shoot more at f64 with 4x5 view than any other f stop.
> >Guess my work ain't as sharp as it should be...
>
> >Dell Elzey
> >Large Format black and white Photography
> >http://www.geocities.com/SoHo/Lofts/9083/
>
> It looks pretty damn sharp to me.
Hi Cheryl (and Dell),
I have visited Dell's web site and think he has some terrific images.
HOWEVER, I don't think low resolution jpeg images posted on a web site
are sufficient to judge critical sharpness. His images may very well be
extremely sharp, but the proof is in the final print (at the desired
size and normal viewing distance), not in a 72 dpi compressed online
image.
I'm not knocking Dell's images here, quite the contrary, they're very
nice (his whole web site presentation is very clean and attractive).
It's just a fact of the current state of our online world, that the
images need to be kept small enough to load quickly and that puts an
upper limit on the quality it is possible to realistically obtain for
online images. I am struggling with this myself as I am preparing my
own web site that I hope to have up and running soon. I can do high
quality scans at 1000 dpi from a 4x5 transparency. Problem is that
creates a 60MB file. Most people won't wait around for a 60K file to
load, let alone 60MB. So, I have to keep them small enough that people
will actually see them, and the quality suffers in the process.
Kerry