rec.photo.digital
http://groups.google.com/group/rec.photo.digital?hl=en
rec.photo.digital@googlegroups.com
Today's topics:
* Telephoto Picture & Technical Analysis - 13 messages, 7 authors
http://groups.google.com/group/rec.photo.digital/t/9003759f40db60ae?hl=en
* photo organising SW - 5 messages, 3 authors
http://groups.google.com/group/rec.photo.digital/t/bef72d4e7bd83942?hl=en
* Photographic rights - 3 messages, 3 authors
http://groups.google.com/group/rec.photo.digital/t/95ce520de64e5844?hl=en
* Scenic areas in England - 4 messages, 3 authors
http://groups.google.com/group/rec.photo.digital/t/1076be556766c491?hl=en
* Eyes Resolution & Monitor Pixel Size - 1 messages, 1 author
http://groups.google.com/group/rec.photo.digital/t/09dbe56e6b23a7d9?hl=en
==============================================================================
TOPIC: Telephoto Picture & Technical Analysis
http://groups.google.com/group/rec.photo.digital/t/9003759f40db60ae?hl=en
==============================================================================
== 1 of 13 ==
Date: Tues, May 5 2009 11:56 pm
From: Hughes
On May 6, 2:27 pm, Tomtom <tom...@spamcan.org> wrote:
> >Here may be a reasonable rule of thumb for
> >sampling to be used in terrestrial photography:
>
> >http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
>
> >In their diffraction java calculator, there is a
> >statement "Set Circle of Confusion = Twice Pixel Size".
> >I think here's how they derived at it (although I
> >maybe wrong). For example, my monitor has a
> >pixel pitch of 0.264mm.
>
> >When I view it at a distance of of 800mm (0.8 mtr).
> >The 0.264mm pixel subtends at an angle of
>
> >theta = 2 arctan (0.5 (0.264)/800) * 206265
> > = 68.07 arcsec
>
> >Now our eyes have a resolution of = 60 arcsecond.
> >This is for very bright object. We can assume
> >it's 120 arcsec at worse (at monitor viewing).
>
> >Then theta of pixels 68.07 x 2 = 136 arcsec. I
> >guess this is how they derived at
> >"Set Circle of Confusion = Twice Pixel Size"
>
> >Now what he is saying is that the airy disc
> >in linear size must not be larger than the circle
> >of confusion or twice the pixel size for it to be
> >"Diffraction limited". If the pixel of the digicam
> >is 7.5 micron. Twice (Circle of Confusion) is
> >14.8 micron. With a F/10 system with airy
> >disc of 13.42 micron, it is inside the Circle of
> >Confusion of 14.8 micron. So it is optimum.
> >Hence for monitor viewing, Canon 300D with
> >6 MP is sufficient, although to avoid Artifact
> >like aliasing, smaller pixels can be used.
> >This means even if 15 MP is used, it may
> >not be "Diffraction limited" when you zoom
> >it 100% because the eyes can detect the
> >diffraction (his term meaning airy disc is
> >overlapping hence image more blur than
> >usual). But if you resize it to 6 MP (from
> >15 MP), the artifacts would be gone and
> >it would be "Diffraction limited" again (note
> >Diffraction limited is his term or used in
> >photography to denote pixel to airy disc size).
> >Now the question is. If 6 MP is optimum for
> >monitor viewing to avoid diffraction for
> >an f/10 system (as shown in the calculations
> >above). What must be the higher MP that
> >can be used so that that artifacts like aliasing,
> >fringing, moire patterns can't be seen? Is 6.7
> >micron 8 MP sufficient, or 5.7 10 MP
> >pixels?? Hope someone can help in the
> >analysis. Master first this website for photography
> >perspective of it all:
>
> >http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
>
> >H
>
> That whole site is not to be taken seriously. The owner(s)/author(s) don't
> even realize that airy-disk size is directly dependent on physical aperture
> size. They ignorantly assume it's just related to f-ratio, in complete and
> total error.
Airy disc angular size is dependent on aperture but
airy disc linear size is dependent on focal ratio. This
is the famous postulates of imaging.
>They're not too bright. Neither are those that refer to them
> as any kind of reputable information or they would have educated all of
> them on their glaring displays of ignorance years ago. Though, it is fun to
> watch who is stupid enough to refer others to that site for "accurate"
> information. :-)- Hide quoted text -
>
> - Show quoted text -
I'm trying to analysis the mindset of terrestrial
photography folks. In the web site. I think he
made the same mistake as I did thinking that
the airy disc is the smallest resolvable size
when the resolving power is even smaller
than the airy disc. This is why you set your ccd
pixel 1/2 the size of the resolving power and
not the airy disc.
Another, they follow mostly the rule of thumb that
higher focal ratio (like f/22) automatically assumes
smaller aperture, so they say f/22 has bad
diffraction. But then, isn't that in astrophotograpy,
one uses barlows to increase the focal length.
When this occurs using constant aperture
size, you can indeed resolve more. So f/22
is not necessarily bad for deep sky where
photonic exposure can be made longer.
Another thing which bugs me a lot. When
diffraction is bigger than a pixel, the images seen
thru monitor is supposed to be bad. But the
consequence of reducing the airy disc size is to
reduce the focal length by a focal reducer and
this can make the focal ratio smaller and hence
the airy disc smaller, but the image scale would
be 1/2 smaller as well. If airy disc must be matched
to pixel size for ultimate sharpness. Then I think
we must just resize the monitor megapixels to
make it smaller and hence the airy disc becoming
one pixel again. But then comparing to images
taken with bigger CCD sensels (or pixels) with
a one to one pixel to airy disc correspondent, I
wonder if this would be sharper than images taken
with smaller pixels (hence airy disc making up
many pixels) and then image downsized to
make one pixel correspond to one airy disc.
But then, even if one sensel (pixel) corresponds to
one airy disc, the pixel color still has to get the
information from the scene or interpolate the colors,
so you still get blurring even at one pixel per airy disc.
But I wonder if it would be much sharper than
many pixels composing one airy disc (which we
may not need because the information contents
inside 5 pixels in airy disc would be so blurred
in the first place).
Comments, clarifications welcomed.
Hughes
== 2 of 13 ==
Date: Wed, May 6 2009 12:44 am
From: Tomtom
On Tue, 5 May 2009 23:56:04 -0700 (PDT), Hughes <eugenhughes@gmail.com>
wrote:
>Airy disc angular size is dependent on aperture but
>airy disc linear size is dependent on focal ratio. This
>is the famous postulates of imaging.
Not true.
Which has a smaller airy-disk diameter (linear size) at the image plane? A
16-inch f/4.5 reflector or a 6-inch f/4.5 reflector?
This is precisely why you can use much higher magnification on larger
primary mirrors. If the optics are all ground to diffraction-limited
precision (1/4th-1/8th wavelength or better) the larger primaries create
much smaller airy-disks to resolve finer detail. Buying a larger diameter
telescope is not all about light-grasp, it's often more about resolving
finer detail--resolving tight globular star clusters to the core, as
opposed to just viewing a nondescript large blob of light. The reason that
the 16" diameter telescope is so popular with hobbyists and pros alike is
that it butts right up against the best, but rare, seeing conditions when
there is low atmospheric turbulence. After 16-inches of aperture size you
probably won't often resolve finer details (smaller airy-disks) except in
the thinner atmosphere at higher altitudes. Larger (fixed, not adaptive
optics) telescopes won't give you much more resolution, just more
light-grasp after that. It's not uncommon to use a 800-1000x magnification
on a 16" diameter diffraction-limited primary. Rule of thumb for
magnification on diffraction-limited optics is 50 to 60 X inches of
aperture, or 2 to 2.5 X mm of aperture. The larger the primary-lens
aperture size the smaller the resolvable details due to smaller airy-disks
at the imaging plane. An f-ratio explanation is a layman's way of trying to
comprehend this, yet be in total error.
This is why I laugh so hard when DSLR owners think they own
diffraction-limited optics yet they get less resolution at wider apertures,
when in fact they should be getting even better resolution. If their images
soften at wider apertures it only means they invested in and overpaid for
really crappy glass that's nowhere near being polished to
diffraction-limited precision. The world is full of easily deceived and
self-deceived fools. They keep claiming that they get what they pay for.
All that they really paid for is a hearty laugh from me.
== 3 of 13 ==
Date: Wed, May 6 2009 2:18 am
From: "David J Taylor"
Tomtom wrote:
> On Tue, 5 May 2009 17:33:33 -0700 (PDT), Hughes
[]
>> http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
>>
>> H
>
> That whole site is not to be taken seriously. The owner(s)/author(s)
> don't even realize that airy-disk size is directly dependent on
> physical aperture size. They ignorantly assume it's just related to
> f-ratio, in complete and total error. They're not too bright. Neither
> are those that refer to them as any kind of reputable information or
> they would have educated all of them on their glaring displays of
> ignorance years ago. Though, it is fun to watch who is stupid enough
> to refer others to that site for "accurate" information. :-)
See:
http://en.wikipedia.org/wiki/Airy_disk
for why f/number matters when you look at the problem in sensor-space,
rather than in object-space.
[cross-posting removed]
== 4 of 13 ==
Date: Wed, May 6 2009 2:46 am
From: Tomtom
On Wed, 06 May 2009 09:18:54 GMT, "David J Taylor"
<david-taylor@blueyonder.not-this-part.nor-this.co.uk.invalid> wrote:
>Tomtom wrote:
>> On Tue, 5 May 2009 17:33:33 -0700 (PDT), Hughes
>[]
>>> http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
>>>
>>> H
>>
>> That whole site is not to be taken seriously. The owner(s)/author(s)
>> don't even realize that airy-disk size is directly dependent on
>> physical aperture size. They ignorantly assume it's just related to
>> f-ratio, in complete and total error. They're not too bright. Neither
>> are those that refer to them as any kind of reputable information or
>> they would have educated all of them on their glaring displays of
>> ignorance years ago. Though, it is fun to watch who is stupid enough
>> to refer others to that site for "accurate" information. :-)
>
>See:
> http://en.wikipedia.org/wiki/Airy_disk
>
>for why f/number matters when you look at the problem in sensor-space,
>rather than in object-space.
>
>[cross-posting restored]
I know all about that wiki page. I helped author some of it. It doesn't
refute what I stated. You shouldn't take tiny bits of info out of context
in the hopes that it will support your misinformation and ignorance. Since
the OP is trying to find the optimum photo-sensor size to image the
airy-disk of a given optical system, "sensor space" is a full variable and
cannot be considered, therefore f-ratio is inconsequential. You might as
well spend your time always multiplying everything by zero if that's your
reasoning.
== 5 of 13 ==
Date: Wed, May 6 2009 3:13 am
From: "David J Taylor"
Tomtom wrote:
> On Wed, 06 May 2009 09:18:54 GMT, "David J Taylor"
> <david-taylor@blueyonder.not-this-part.nor-this.co.uk.invalid> wrote:
>
>> Tomtom wrote:
>>> On Tue, 5 May 2009 17:33:33 -0700 (PDT), Hughes
>> []
>>>> http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
>>>>
>>>> H
>>>
>>> That whole site is not to be taken seriously. The owner(s)/author(s)
>>> don't even realize that airy-disk size is directly dependent on
>>> physical aperture size. They ignorantly assume it's just related to
>>> f-ratio, in complete and total error. They're not too bright.
>>> Neither are those that refer to them as any kind of reputable
>>> information or they would have educated all of them on their
>>> glaring displays of ignorance years ago. Though, it is fun to watch
>>> who is stupid enough to refer others to that site for "accurate"
>>> information. :-)
>>
>> See:
>> http://en.wikipedia.org/wiki/Airy_disk
>>
>> for why f/number matters when you look at the problem in
>> sensor-space, rather than in object-space.
>>
>> [cross-posting restored]
>
> I know all about that wiki page. I helped author some of it. It
> doesn't refute what I stated. You shouldn't take tiny bits of info
> out of context in the hopes that it will support your misinformation
> and ignorance. Since the OP is trying to find the optimum
> photo-sensor size to image the airy-disk of a given optical system,
> "sensor space" is a full variable and cannot be considered, therefore
> f-ratio is inconsequential. You might as well spend your time always
> multiplying everything by zero if that's your reasoning.
The Wiki page shows that the resolution, in linear measure in
sensor-space, depends on the f/number, and this is borne out in practice,
so your comments about the Cambridge in Colour site are somewhat
misleading.
David
== 6 of 13 ==
Date: Wed, May 6 2009 3:13 am
From: Hughes
On May 6, 3:44 pm, Tomtom <tom...@spamcan.org> wrote:
> On Tue, 5 May 2009 23:56:04 -0700 (PDT), Hughes <eugenhug...@gmail.com>
> wrote:
>
> >Airy disc angular size is dependent on aperture but
> >airy disc linear size is dependent on focal ratio. This
> >is the famous postulates of imaging.
>
> Not true.
>
> Which has a smaller airy-disk diameter (linear size) at the image plane? A
> 16-inch f/4.5 reflector or a 6-inch f/4.5 reflector?
They are same size. Here are the calculations and proof.
Airy Disc_linear size_mm = 2.44 x wavelength x f/D
= 2.44 x 0.00055 x 4.5
= 6.039 micron
Both 16-inch f/4.5 reflector and 6-inch f/4.5 reflector
have similar 6.039 micron airy disc in *linear size*.
What differs is their angular size. The 16" subtends
0.006039 / 1800 * 206265 = 0.692 arcsecond while the 6" subtends
0.006039 / 675 * 206265 = 1.84 arcsecond
in the sky.
What this means is that the same linear size of 6.039
micron airy disc in both subtends different angles in
the sky. In the case of the 16" reflector, the airy disc
is representative of 0.692 arcsecond in the sky while
the airy disc in the 6" is representative of 1.84 arcsecond
in the sky hence the 16" has greater resolving power.
Gets?
Don't worry, it took me a year to understand this :)
It's an important fact that is missed & confused by many
amateur astronomers and photographers including
the author of the web site. You can only understood
it perfectly if you fully understand how image
formation works in a telescopes especially alpha, beta
angle subtended in each side of the objective lens.
Hughes
>
> This is precisely why you can use much higher magnification on larger
> primary mirrors. If the optics are all ground to diffraction-limited
> precision (1/4th-1/8th wavelength or better) the larger primaries create
> much smaller airy-disks to resolve finer detail. Buying a larger diameter
> telescope is not all about light-grasp, it's often more about resolving
> finer detail--resolving tight globular star clusters to the core, as
> opposed to just viewing a nondescript large blob of light. The reason that
> the 16" diameter telescope is so popular with hobbyists and pros alike is
> that it butts right up against the best, but rare, seeing conditions when
> there is low atmospheric turbulence. After 16-inches of aperture size you
> probably won't often resolve finer details (smaller airy-disks) except in
> the thinner atmosphere at higher altitudes. Larger (fixed, not adaptive
> optics) telescopes won't give you much more resolution, just more
> light-grasp after that. It's not uncommon to use a 800-1000x magnification
> on a 16" diameter diffraction-limited primary. Rule of thumb for
> magnification on diffraction-limited optics is 50 to 60 X inches of
> aperture, or 2 to 2.5 X mm of aperture. The larger the primary-lens
> aperture size the smaller the resolvable details due to smaller airy-disks
> at the imaging plane. An f-ratio explanation is a layman's way of trying to
> comprehend this, yet be in total error.
>
> This is why I laugh so hard when DSLR owners think they own
> diffraction-limited optics yet they get less resolution at wider apertures,
> when in fact they should be getting even better resolution. If their images
> soften at wider apertures it only means they invested in and overpaid for
> really crappy glass that's nowhere near being polished to
> diffraction-limited precision. The world is full of easily deceived and
> self-deceived fools. They keep claiming that they get what they pay for.
> All that they really paid for is a hearty laugh from me.
== 7 of 13 ==
Date: Wed, May 6 2009 3:19 am
From: Chris Malcolm
In rec.photo.digital Chris L Peterson <clp@alumni.caltech.edu> wrote:
> On 5 May 2009 15:18:45 GMT, Chris Malcolm <cam@holyrood.ed.ac.uk> wrote:
>>Although strictly speaking the f number is just a ratio of focal
>>length to aperture, in camera lenses it has come to be used as a guide
>>to setting exposure.
> Yes, that's what I meant by needing to be careful with using focal ratio
> in conventional photography.
>>Since my Sony 500mm f8 catadioptric lens produces the same autoexposed
>>shutter speeds on the same subject matter as my other ordinary
>>refractor lenses, that seems to be what they have done in specifying
>>that lens as an f8 and arranging for it to report itself to the
>>camera's electronics as an f8 lens.
> That's really ugly if they did that.
I agree. But they're selling lenses to photographers who talk about
the "sunny 16" rule in similar defiance of strict technical accuracy
:-)
> Basically, it's the same as putting
> a filter on your lens and arguing that it now has a different focal
> ratio because the exposure time needs to be adjusted. And it breaks all
> your depth-of-field calculations. T-stops were created to give an
> equivalent to f-stops, but calibrated for light transmission. Although
> you don't usually see these used in ordinary camera lenses, it's the
> obvious choice for specifying transmission in a lens with a large
> obstruction.
I agree. I guess it's possible that Sony really regard the f8 of that
lens as a simple popular expression of the lens T-stop.
> Are you sure the Sony lens focal ratio isn't simply determined by an
> internal aperture stop? Many camera lenses don't utilize the full
> apparent aperture.
I'll need to think of an experiment to discover that. It won't fall
easily out of simple exposure reading since the camera provides those
only to 1/3 stop accuracy.
>>Of course not all catadioptric lens makers may have adjusted the
>>specified f number of their lenses in that way.
> Good for them!
Most cat lenses are manual and don't report aperture to the camera, so
the specification is only a paper specification for the benefit of
people. But the Sony is an AF and autoexposure lens which reports
aperture to the camera's computer. It's possible the camera's computer
software has made the simplifying assumption that aperture is a
measurement of lens light gathering power and therefore requires the
fudge of adjusting the aperture for that. It would be a bit odd if the
camera reported the lens as f8 and the technical spec said it was f7
or whatever.
Does Nikon's cat lens report aperture to the camera? If it does, it
would be interesting to check out the lens spec and see how they've
dealt with this issue.
--
Chris Malcolm
== 8 of 13 ==
Date: Wed, May 6 2009 3:25 am
From: Chris Malcolm
In rec.photo.digital Doug McDonald <mcdonald@nospamscs.uiuc.edu> wrote:
> When analyzing the performance of systems with central
> obstructions, for reasonable size obstructions (i.e. effective obstruction sixe
> less than half effective outside diameter) there is
> a simple rule of thumb:
> The effect of diffraction on image quality is proportional to
> the difference between the effective outside diameter and effective
> obstruction size.
So if the obstruction gets bigger the diffraction effect gets smaller?
That doesn't sound right. Do you mean inversely proportional?
--
Chris Malcolm
== 9 of 13 ==
Date: Wed, May 6 2009 3:40 am
From: Chris Malcolm
In rec.photo.digital Tomtom <tomtom@spamcan.org> wrote:
> Rule of thumb for
> magnification on diffraction-limited optics is 50 to 60 X inches of
> aperture, or 2 to 2.5 X mm of aperture. The larger the primary-lens
> aperture size the smaller the resolvable details due to smaller airy-disks
> at the imaging plane. An f-ratio explanation is a layman's way of trying to
> comprehend this, yet be in total error.
> This is why I laugh so hard when DSLR owners think they own
> diffraction-limited optics yet they get less resolution at wider apertures,
> when in fact they should be getting even better resolution.
But that may not be what they mean. If you have a lens and camera
which gets (say) sharper up to f8 and then gets fuzzier at smaller
apertures, is it not correct to say that at smaller apertures than f8
diffraction is limiting the resolution?
Of course it may be true that a better lens would start showing
diffraction limited resolution at a wider aperture, but the claim
isn't being made that this is a lens made to diffraction limited
quality, the claim is simply that for this less than optimal lens
and camera diffraction starts reducing resolution at f8.
--
Chris Malcolm
== 10 of 13 ==
Date: Wed, May 6 2009 4:18 am
From: Helpful person
On May 6, 2:27 am, Tomtom <tom...@spamcan.org> wrote:
>
> That whole site is not to be taken seriously. The owner(s)/author(s) don't
> even realize that airy-disk size is directly dependent on physical aperture
> size. They ignorantly assume it's just related to f-ratio, in complete and
> total error. They're not too bright. Neither are those that refer to them
> as any kind of reputable information or they would have educated all of
> them on their glaring displays of ignorance years ago. Though, it is fun to
> watch who is stupid enough to refer others to that site for "accurate"
> information. :-)
>
Before definitively stating "facts" in such a rude and ignorant
manner please make sure that what you say is correct. Please do not
disseminate false or misleading information.
The physical size of the airy disk is independent of the physical
aperture size. It is a function of F/#, wavelength and the refractive
index at the image (to a first order).
== 11 of 13 ==
Date: Wed, May 6 2009 4:31 am
From: Bob Larter
Hughes wrote:
> On May 6, 7:13 am, Doug McDonald <mcdon...@NoSpAmscs.uiuc.edu> wrote:
>> When analyzing the performance of systems with central
>> obstructions, for reasonable size obstructions (i.e. effective obstruction sixe
>> less than half effective outside diameter) there is
>> a simple rule of thumb:
>>
>> The effect of diffraction on image quality is proportional to
>> the difference between the effective outside diameter and effective
>> obstruction size.
>>
>> More technically, the MTF in the important low to mid frequency range
>> depends on that quantity.
>>
>> This says nothing about plain old aberrations nor flare, which
>> are always huge problems with reflective camera lenses.
>>
>> Doug MCDonald
>
> This may be important when imaging low contrast
> planetary details, but may not be in terrestrial photography.
> I'm reading the following site:
Trust me, it's even more important for regular photography! ;^)
--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
== 12 of 13 ==
Date: Wed, May 6 2009 4:37 am
From: Martin Brown <|||newspam|||@nezumi.demon.co.uk>
Chris Malcolm wrote:
> In rec.photo.digital Doug McDonald <mcdonald@nospamscs.uiuc.edu> wrote:
>
>> When analyzing the performance of systems with central
>> obstructions, for reasonable size obstructions (i.e. effective obstruction sixe
>> less than half effective outside diameter) there is
>> a simple rule of thumb:
>
>> The effect of diffraction on image quality is proportional to
>> the difference between the effective outside diameter and effective
>> obstruction size.
>
> So if the obstruction gets bigger the diffraction effect gets smaller?
> That doesn't sound right. Do you mean inversely proportional?
No. He means what he said, but it is a funny way of expressing it. And I
have never found that particular rule of thumb expecially helpful.
Essentially the effect of the central obstruction diameter d or lens
diameter D is to block all light that would have gone through that
central part of the aperture. The total damage is proportional to the
area obscured but the shape is determined by the diameter d.
This curtails the lens sensitivity to low frequency components in the
image, but for higher spatial frequencies that result from correlations
over length scales beyond D+d/2 the central obstruction makes no
difference.
In practice this means that the resolving power for point sources is
slightly improved by a central obstruction but at the cost of putting
more power into the surrounding diffraction rings.
A reasonable simulation page is online at:
http://www.damianpeach.com/simulation.htm
Regards,
Martin Brown
== 13 of 13 ==
Date: Wed, May 6 2009 4:38 am
From: Bob Larter
Tomtom wrote:
[...]
>> [cross-posting restored]
Fuck off, troll.
--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
==============================================================================
TOPIC: photo organising SW
http://groups.google.com/group/rec.photo.digital/t/bef72d4e7bd83942?hl=en
==============================================================================
== 1 of 5 ==
Date: Wed, May 6 2009 12:09 am
From: Chris H
In message <gtq5o4$5i4$1@reader1.panix.com>, Jeremiah DeWitt Weiner
<jdw@panix.com> writes
>G Paleologopoulos <gpaleo@ath.forthnet.gr> wrote:
>> Why every week to DVD-R and not at any time to external HardDisk??
>> Terra byte drives are quite cheap now.
>
> A hard drive attached to your system is not a backup. It's online
>local storage.
As is a DVD until, like the HD, you remove it.
> The two are not the same thing. IMO, an ideal backup
>system should be
>
>A) read-only (so a mistake, malware, or hardware error can't delete or
>corrupt it)
>B) physically distant (so fire, flood, etc. won't take it out at the
>same time as your main copy)
>C) immediately available
>D) incrementally expandable
>E) long-lived
>F) cheap
>
> Some of these conditions are somewhat mutually incompatible, but
>that's the problem with ideals. Again IMO, external media satisfy
>conditions A, B, and D. A hard drive attached to your system satisfies
>C; if you only attach it to your system when you're actually backing up
>or restoring, it satisfies A only as long as it doesn't satisfy C. I
>don't trust just about anything to satisfy E, unfortunately...
A hard drive satisfies
C,d,e,f
It also satisfies B in that you can remove it to another location when
ever you like just as easily as a DVD.
So the only thing a hard drive does not meet is A BUT you can set files
and directories to read only which is a partial A
--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
== 2 of 5 ==
Date: Wed, May 6 2009 12:31 am
From: nospam
In article <XhCT+hAdeTAKFASS@phaedsys.demon.co.uk>, Chris H
<chris@phaedsys.org> wrote:
> >A) read-only (so a mistake, malware, or hardware error can't delete or
> >corrupt it)
> So the only thing a hard drive does not meet is A BUT you can set files
> and directories to read only which is a partial A
or get a read-only firewire or usb bridge. or if the backup is done to
a disk image file, that can be locked while the drive itself is not.
== 3 of 5 ==
Date: Wed, May 6 2009 2:24 am
From: Chris H
In message <060520090031522733%nospam@nospam.invalid>, nospam
<nospam@nospam.invalid> writes
>In article <XhCT+hAdeTAKFASS@phaedsys.demon.co.uk>, Chris H
><chris@phaedsys.org> wrote:
>
>> >A) read-only (so a mistake, malware, or hardware error can't delete or
>> >corrupt it)
>> So the only thing a hard drive does not meet is A BUT you can set files
>> and directories to read only which is a partial A
>
>or get a read-only firewire or usb bridge. or if the backup is done to
>a disk image file, that can be locked while the drive itself is not.
SO a hard drive meets all the criteria and in a better way than DVD's
and in fact the prepares of DVD's has also a fatal flaw in his argument.
I started with IDE hard drives and then moved on to Ultra IDE and now
SetialATA... also moving from the 2GB limit to (no idea now but it is
over a couple of terabytes) all seamlessly.
However how did the "dvd" proponent move from floppies to CD to DVD and
how will he move to blue ray when DVD become obsolete?
--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
== 4 of 5 ==
Date: Wed, May 6 2009 5:00 am
From: Bob Larter
whisky-dave wrote:
> "Bob Larter" <bobbylarter@gmail.com> wrote in message
> news:49fc32f0$1@dnews.tpgi.com.au...
>> G Paleologopoulos wrote:
>>> "Bob Larter" <bobbylarter@gmail.com> wrote
>>> news:49fad0f0$1@dnews.tpgi.com.au...
>>>> .................................................
>>>> Ditto. I create \photography\year-month-day\shoot\ & throw all my photos
>>>> in there. Every week or so, I burn them to DVD-R. It's probably not the
>>>> best backup scheme on earth, but it's worked okay for me so far.
>>>> .................................................
>>> Why every week to DVD-R and not at any time to external HardDisk??
>> Hard disks die of old age. Hopefully, DVD-Rs don't.
>>
>
> They do, and can deterate quicker than HDs, although that does depend on
> how you handle them.
Everything depends on how you handle it! ;^)
> I've heard DVDs are typically 20 years, but it does depend on storage.
I keep mine locked up in a black box with desiccant gel.
> The coating on them is similar to film in that it's an organic gelatine that
> can get mould
> growing on it.
Yes, I've seen that with some of my cheap & nasty CDRs. Very ugly.
Hopefully, keeping mine away from moisture will improve their life. Last
night, I pulled out a 3 year old DVD-R to get a really nice photo of a
deceased relative, & the disk read without any problems. Time will tell
me whether it's going to be a problem with older disks.
> Hard drives should be accessed (started up) about every 6 months as the
> motors
> can stick due to oil solidifying.
The industry term is 'stiction'. It's not due to oil solidifying,
though, it's when the heads stick to the platters, usually due to
moisture (ie; humidity) ingress. Firing up a cold drive under those
circumstances will result in the heads being ripped clean off the arm.
This will, obviously, render your data useless.
> One person advised changing the
> orientation of an
> unused HD every 6 months in order to avoid the possibility of the Earths
> magnetic field
> affecting the data.
That's complete bullshit. The coercivity of the platters is *way* higher
than can be affected by the earths magnetic field. You could stick a big
magnet on the case, & it wouldn't harm the data in the slightest.
What will *help* preserve your data is spinning up the drive every now
& then. Drives that are in use 24x7 don't suffer from stiction, although
old drives sometimes do when they're power-cycled for the first time in
years. That's why it's a bad idea to power-cycle servers that have been
running for years. If you have to do it, you back up the data first, in
case the drive doesn't come back up with the system.
> The above I heard on a popcast about such things, although obviously soem
> have other
> opinions.
Trust me, as someone who earns a living worrying about these sorts of
things, I can tell you that it's an old wives tale. ;^)
>>> Terra byte drives are quite cheap now.
>> Not cheap enough to replace a hundred DVD-Rs. ;^)
>
> There's not really much difference price wise once you factor in sleeves or
> some sort of
> storage for DVDs.
> 1 DVD disc ~4.5Gb
> 1TB ~ 222 DVDs
Well, I'm up to about 150 DVD-Rs, so far. And I've seen more hard disks
fail than DVD-Rs.
> I tend to use a HD, but use DVDs as well if something is extra important.
Good. Between the two media, hopefully at least one will survive.
> I must consider some sort of on-line storage too at some point.
Buy a NAS box & run automated backups to that & DVD-R, if you really
want to be sure.
--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
== 5 of 5 ==
Date: Wed, May 6 2009 5:03 am
From: Bob Larter
Chris H wrote:
> In message <gtpjsg$sdq$1@qmul>, whisky-dave <whisky-
> dave@final.front.ear> writes
>> "Bob Larter" <bobbylarter@gmail.com> wrote in message
>> news:49fc32f0$1@dnews.tpgi.com.au...
>>> G Paleologopoulos wrote:
>>>> "Bob Larter" <bobbylarter@gmail.com> wrote
>>>> news:49fad0f0$1@dnews.tpgi.com.au...
>>>>> .................................................
>>>>> Ditto. I create \photography\year-month-day\shoot\ & throw all my photos
>>>>> in there. Every week or so, I burn them to DVD-R. It's probably not the
>>>>> best backup scheme on earth, but it's worked okay for me so far.
>>>>> .................................................
>>>> Why every week to DVD-R and not at any time to external HardDisk??
>>> Hard disks die of old age. Hopefully, DVD-Rs don't.
>>>
>> They do, and can deterate quicker than HDs, although that does depend on
>> how you handle them.
>> I've heard DVDs are typically 20 years, but it does depend on storage.
>
> I have none of the HD's I had when I started but most of the data. It
> is usually VERY easy and quite quick to copy data from one HD to
> another. So I do.
>
> Every few years (about 5) when I upgrade the hard disks/pc's etc the
> data gets moved. So it stays fresh. It generally costs a lot less
> than lots of floppies, tapes CD's. DVD's Blue Ray etc
Yeah, every time I upgrade, I dump the old data onto the new drive. So
far, I haven't lost any data since 1998, when the old drive had
developed read errors, which I didn't discover until I'd handed back the
machine (laptop) to my previous employer. That kind of sucked, but I was
too busy to worry about it at the time.
--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
==============================================================================
TOPIC: Photographic rights
http://groups.google.com/group/rec.photo.digital/t/95ce520de64e5844?hl=en
==============================================================================
== 1 of 3 ==
Date: Wed, May 6 2009 12:59 am
From: Ofnuts
Peabody wrote:
> Could someone recommend an online explanation of how copyrights work
> in photography? I thought I understood, but have concluded I don't.
>
> Well, here's an example. The photographer takes a picture of a
> friend as the model, and "gives" the picture to the friend as a
> birthday present, including delivering the negative along with the
> prints. But there's no documentation transferring anything. Does
> posession of the negative mean anything? I think it probably
> doesn't. Wouldn't the photographer need to sign something
> transferring his copyright to the model?
>
> Anyway, I was hoping there was a long, detailed explanation of who
> has what rights, and how they need to be transferred.
>
Whatever the law is, by giving the negative the photographer has made it
extremely difficult for him to prove that he has taken the picture,
unless he has kept negatives of shots from the same shooting session, or
an expert is ready to compare scratches on the negative with those of
other negatives taken with the photographer's camera body.
--
Bertrand
== 2 of 3 ==
Date: Wed, May 6 2009 3:36 am
From: "MC"
"Ofnuts" <o.f.n.u.t.s@la.poste.net> wrote in message
news:4a01435d$0$14538$426a74cc@news.free.fr...
> Peabody wrote:
>> Could someone recommend an online explanation of how copyrights work in
>> photography? I thought I understood, but have concluded I don't.
>>
>> Well, here's an example. The photographer takes a picture of a friend as
>> the model, and "gives" the picture to the friend as a birthday present,
>> including delivering the negative along with the prints. But there's no
>> documentation transferring anything. Does posession of the negative mean
>> anything? I think it probably doesn't. Wouldn't the photographer need
>> to sign something transferring his copyright to the model?
>>
>> Anyway, I was hoping there was a long, detailed explanation of who has
>> what rights, and how they need to be transferred.
>>
>
> Whatever the law is, by giving the negative the photographer has made it
> extremely difficult for him to prove that he has taken the picture, unless
> he has kept negatives of shots from the same shooting session, or an
> expert is ready to compare scratches on the negative with those of other
> negatives taken with the photographer's camera body.
>
Negatives can be copied.
MC
== 3 of 3 ==
Date: Wed, May 6 2009 4:26 am
From: "whisky-dave"
"Ofnuts" <o.f.n.u.t.s@la.poste.net> wrote in message
news:4a01435d$0$14538$426a74cc@news.free.fr...
> Whatever the law is, by giving the negative
Exactly what century or planet are you living on, what's a 'Negative' ;-)
I thumbed through an old photography book which was printed on some sort of
substance made from dried leaves. It seemed to suggest that this negative
was produced
by exposing it to light and after development you could enlarge this image.
I used a really strong magnifier and I couldn't see any image on my SD card
;-)
But more seriously I've heard that facebook want to own any image you
upload,
although I didn't; take much notice as it's not the sort of place I'd put
images that
might be worth anything financially speaking.
==============================================================================
TOPIC: Scenic areas in England
http://groups.google.com/group/rec.photo.digital/t/1076be556766c491?hl=en
==============================================================================
== 1 of 4 ==
Date: Wed, May 6 2009 3:33 am
From: barnaby@barnabypage.com
On May 4, 12:12 pm, Shawn Hirn <s...@comcast.net> wrote:
> Hi everyone;
>
> I will be visiting England on a very brief stay. I will have two days in
> London, two days in Norwich, and two days in Liverpool early next month.
> I am an avid amateur photographer. I am wondering if anyone on this
> newsgroup can suggest areas of those three cities where I can go to
> shoot some interesting photographs, but that are not like the ones
> everyone else who visits those areas is likely to shoot. For example, is
> there any tall buildings where I can get access to the roof legally
> where I can shoot some interesting photos, or some unique parks, etc.?
> Note that I will be relying 100% on public transportation.
I'm not sure what the highest point open to the public is in Norwich
but you can get pretty good views from around the castle. I don't know
offhand if you can go on the roof, which probably is the highest point
in the city. There are also very good streetscape/roofscape views over
the market place - try the bike racks next to St. Peter Mancroft or
maybe the steps of City Hall as a vantage point.
Check out Heigham Park and the wilder Mousehold Heath.
The University of East Anglia, as someone else has mentioned, has an
eclectic array of interesting buildings from the 60s onwards. You can
roam the campus freely.
If you're into interiors, you must visit the Edwardian Norwich Union
building on Surrey Street with its "marble hall", one of the best-kept
secrets of Norwich. They welcome visitors and I imagine photography is
okay if you ask.
For industrial dereliction mixed with medieval remnants, wander along
King Street away from the city centre. The river in the other
direction (the other side of Prince of Wales Road) is also photogenic
in a much prettier way.
You won't really need much in the way of public transport in Norwich -
the centre is entirely walkable. The university is a bit of a trek out
but there's a regular bus service.
== 2 of 4 ==
Date: Wed, May 6 2009 3:43 am
From: Chris Malcolm
In rec.photo.digital John McWilliams <jpmcw@comcast.net> wrote:
> Chris H wrote:
>> In message <o1c0059k4js2a9fii7e5bs6a3gag4u82ge@4ax.com>, Grimly
>> Curmudgeon <grimly4REMOVE@REMOVEgmail.com> writes
>>> We were somewhere around Barstow, on the edge of the desert, when the
>>> drugs began to take hold. I remember "boris spider"
>>> <boris1066@gmail.com> saying something like:
>>>
>>>> Access to many other tall vantage points in Central London has been ended
>>>> for reasons of "security".
>>>
>>> Indeed. When I was a lad I was up the Post Office Tower, but it was shut
>>> to the public just a few years later because of the fucking IRA.
>>> What a waste.
>>
>> You mean there was terrorism before 9/11/2001?
>>
>> I will not say If I have been up the PO Tower as it would date me
>> somewhat :-)
>>
>> There is a lot of paranoia about terrorism. Most of it unfounded.
> I am curious as to what might constitute founded paranoia! Can you give
> an example or two?
Martin Luther King thinking assassins were plotting to kill him.
--
Chris Malcolm
== 3 of 4 ==
Date: Wed, May 6 2009 4:45 am
From: "Mike"
On Mon, 04 May 2009 07:12:46 -0400, Shawn Hirn <srhi@comcast.net>
wrote:
> I am wondering if anyone on this
>newsgroup can suggest areas of those three cities where I can go to
>shoot some interesting photographs,
try some of the street markets, Borough is the trendy one. The balcony
of Tate Modern is a good viewpoint, the London Eye isn't as its all
glazed in.
--
Mike
== 4 of 4 ==
Date: Wed, May 6 2009 4:49 am
From: "Mike"
On Tue, 5 May 2009 13:38:51 +0100, Chris H <chris@phaedsys.org> wrote:
>>Indeed. When I was a lad I was up the Post Office Tower, but it was shut
>>to the public just a few years later because of the fucking IRA.
>>What a waste.
>
>You mean there was terrorism before 9/11/2001?
yes, on 11/9/2001 and many dates before that outside of US, much of
the London attacks being funded by Americans via NORAID. AS London
bombs have tended to be set off by individuals carrying them in, its
not so surprising some places like major communications centres have
security issues.
--
Mike
==============================================================================
TOPIC: Eyes Resolution & Monitor Pixel Size
http://groups.google.com/group/rec.photo.digital/t/09dbe56e6b23a7d9?hl=en
==============================================================================
== 1 of 1 ==
Date: Wed, May 6 2009 4:08 am
From: "whisky-dave"
"Hughes" <eugenhughes@gmail.com> wrote in message
news:dfd8101a-99ea-49ec-ae93-4e2577301019@x31g2000prc.googlegroups.com...
> Hi,
>
> I wonder if this is just a coincidence or design.
>
> Human eyes have a average resolution of 60 arcseconds for brightly
> illuminated target.
>
> My monitor has a pixel pitch of 0.264mm.
Not all monitors are the same.
> When I view it at a distance of of 800mm (0.8 mtr).
I view mine at about 500mm
The 0.264mm pixel
> subtends at an angle of
> theta = 2 arctan (0.5 (0.264)/800) * 206265
> = 68.07 arcsec
>
> The angle of the pixel subtended at a viewing
> distance of 0.8 mtrs is 68 arcseconds close to
> human eyes resolution of 60 arcseconds. Is this
> just a coincidence or did they make the pixel
> size of the monitor to match the resolution
> specification of human eyes by design?
If you take your 800mm that's 31.49 inches.
That's about 10 times pi . but so what.
What makes you think 800mm has any meaning.
If such a meaning was meant surely they'd set distance of 1 metre
a true SI unit.
Playing with numbers can prove anything, i.e Captain Kirk caused 911
Well the numbers in 1701 add up to 9 the first and last are 1s 911
The word Enterprise has 9 letters, and there's 11 in captain Kirk . 911
Coincidence well some don't think so, but they are, or should be
in specially padded homes and kept away from sharp objects ;-)
==============================================================================
You received this message because you are subscribed to the Google Groups "rec.photo.digital"
group.
To post to this group, visit http://groups.google.com/group/rec.photo.digital?hl=en
To unsubscribe from this group, send email to rec.photo.digital+unsubscribe@googlegroups.com
To change the way you get mail from this group, visit:
http://groups.google.com/group/rec.photo.digital/subscribe?hl=en
To report abuse, send email explaining the problem to abuse@googlegroups.com
==============================================================================
Google Groups: http://groups.google.com/?hl=en
0 comments:
Post a Comment