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Technology to stop a digital camera from taking a picture

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Anonymous
September 22, 2005 4:49:54 AM

Archived from groups: rec.photo.digital (More info?)

Hi all,

I have put up an article on www.dimagemaker.com about some early
research work being done to block digital cameras of taking a picture
of something or someone that is to be protected.

Food for thought.

Cheers,

Wayne

Wayne J. Cosshall
Publisher, The Digital ImageMaker, www.dimagemaker.com
Assistant Director, International Digital Art Award
Freelance writer and educator in graphic design, photography, digital
technology
Personal art site www.artinyourface.com
wayne@dimagemaker.com
Anonymous
September 22, 2005 10:09:19 AM

Archived from groups: rec.photo.digital (More info?)

Wear theodolight jewelry ? Might work if flash is used.
Gene










wayne wrote:

> Hi all,
>
> I have put up an article on www.dimagemaker.com about some early
> research work being done to block digital cameras of taking a picture
> of something or someone that is to be protected.
>
> Food for thought.
>
> Cheers,
>
> Wayne
>
> Wayne J. Cosshall
> Publisher, The Digital ImageMaker, www.dimagemaker.com
> Assistant Director, International Digital Art Award
> Freelance writer and educator in graphic design, photography, digital
> technology
> Personal art site www.artinyourface.com
> wayne@dimagemaker.com
Anonymous
September 22, 2005 3:27:01 PM

Archived from groups: rec.photo.digital (More info?)

In article <1127375394.899694.189610@g49g2000cwa.googlegroups.com>,
wayne <wayne@dimagemaker.com> wrote:
>Hi all,
>
>I have put up an article on www.dimagemaker.com about some early
>research work being done to block digital cameras of taking a picture
>of something or someone that is to be protected.
>
>Food for thought.

Quick, someone invent film!
Related resources
Anonymous
September 22, 2005 6:24:48 PM

Archived from groups: rec.photo.digital (More info?)

wayne <wayne@dimagemaker.com> spewed:
> Hi all,
>
> I have put up an article on www.dimagemaker.com about some early
> research work being done to block digital cameras of taking a
> picture of something or someone that is to be protected.

A direct link would be appreciated. Attempting to navigate that site hurts
my weary eyes... blue, green, red, yellow, black, blinky ads...

*squint*

--
Visit My Site: http://www.rubbertoe.com
Anonymous
September 22, 2005 8:34:39 PM

Archived from groups: rec.photo.digital (More info?)

In article <Q8zYe.15877$ib1.6514@tornado.ohiordc.rr.com>,
"Robert J Batina" <rbatina@columbus.rr.com> wrote:

> wayne <wayne@dimagemaker.com> spewed:
> > Hi all,
> >
> > I have put up an article on www.dimagemaker.com about some early
> > research work being done to block digital cameras of taking a
> > picture of something or someone that is to be protected.
>
> A direct link would be appreciated. Attempting to navigate that site hurts
> my weary eyes... blue, green, red, yellow, black, blinky ads...

True, but the link took all of 2 seconds to find. Even so, it seems to
me, this idea is easily subverted simply by putting the camera into
manual mode and the correct use of shutter and aperture settings.
September 22, 2005 11:45:22 PM

Archived from groups: rec.photo.digital (More info?)

Wayne

For someone with such artistic talent (www.artinyourface.com), your website
is terrible!


"wayne" <wayne@dimagemaker.com> wrote in message
news:1127375394.899694.189610@g49g2000cwa.googlegroups.com...
> Hi all,
>
> I have put up an article on www.dimagemaker.com about some early
> research work being done to block digital cameras of taking a picture
> of something or someone that is to be protected.
>
> Food for thought.
>
> Cheers,
>
> Wayne
>
> Wayne J. Cosshall
> Publisher, The Digital ImageMaker, www.dimagemaker.com
> Assistant Director, International Digital Art Award
> Freelance writer and educator in graphic design, photography, digital
> technology
> Personal art site www.artinyourface.com
> wayne@dimagemaker.com
>
Anonymous
September 23, 2005 3:15:56 AM

Archived from groups: rec.photo.digital (More info?)

"wayne" <wayne@dimagemaker.com> writes:


> I have put up an article on www.dimagemaker.com about some early
> research work being done to block digital cameras of taking a picture
> of something or someone that is to be protected.
>
> Food for thought.

Indeed. I'm hoping it's technically unfeasible; that seems fairly
likely. Otherwise we need to resort to making it illegal, much as I
dislike the invocation of state power.
--
David Dyer-Bennet, <mailto:D d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
Pics: <http://dd-b.lighthunters.net/&gt; <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
Dragaera/Steven Brust: <http://dragaera.info/&gt;
Anonymous
September 23, 2005 6:53:56 AM

Archived from groups: rec.photo.digital (More info?)

Robert and Tom,
The site was put up 3 months ago. I've been concentrating on content
but a redesign is in the works.

Cheers,

Wayne

Wayne J. Cosshall
Publisher, The Digital ImageMaker, www.dimagemaker.com
Assistant Director, International Digital Art Award
Freelance writer and educator in graphic design, photography, digital
technology
Personal art site www.artinyourface.com
wayne@dimagemaker.com
Anonymous
September 23, 2005 8:08:40 AM

Archived from groups: rec.photo.digital (More info?)

Actually I am not sure. Yes, going manual could help with the current
system but I can conceive of ways to overload the actual CCD. The long
telephoto or zoom lens also may not be an answer.

I learnt a long time ago that when it comes to engineering, if someone
says it can't be done, they are usually wrong. The right question is
whether it can be done in a cost effective (whatever that means) and
readily deployable manner that can cope with real world variance. The
reality is that after posting the article I sat down and worked out a
number of other possible approaches that could readily be used to
shutdown a digital camera by attacking the electronics. Not hard if you
don't mind the risk of frying the odd camera or two.

Cheers,

Wayne

Wayne J. Cosshall
Publisher, The Digital ImageMaker, www.dimagemaker.com
Assistant Director, International Digital Art Award
Freelance writer and educator in graphic design, photography, digital
technology
Personal art site www.artinyourface.com
wayne@dimagemaker.com
September 23, 2005 8:20:17 AM

Archived from groups: rec.photo.digital (More info?)

On 22 Sep 2005 00:49:54 -0700, "wayne" <wayne@dimagemaker.com> wrote:

>Hi all,
>
>I have put up an article on www.dimagemaker.com about some early
>research work being done to block digital cameras of taking a picture
>of something or someone that is to be protected.
>
>Food for thought.
>
>Cheers,
>
>Wayne
>
>Wayne J. Cosshall
>Publisher, The Digital ImageMaker, www.dimagemaker.com
>Assistant Director, International Digital Art Award
>Freelance writer and educator in graphic design, photography, digital
>technology
>Personal art site www.artinyourface.com
>wayne@dimagemaker.com


Wouldn't something like this be effective?

http://www.glock.com/g17.htm
Anonymous
September 23, 2005 8:20:18 AM

Archived from groups: rec.photo.digital (More info?)

Charles wrote:
> On 22 Sep 2005 00:49:54 -0700, "wayne" <wayne@dimagemaker.com> wrote:
>
>> Hi all,
>>
>> I have put up an article on www.dimagemaker.com about some early
>> research work being done to block digital cameras of taking a picture
>> of something or someone that is to be protected.
>>
>> Food for thought.
>>
>> Cheers,
>>
>> Wayne
>>
>> Wayne J. Cosshall
>> Publisher, The Digital ImageMaker, www.dimagemaker.com
>> Assistant Director, International Digital Art Award
>> Freelance writer and educator in graphic design, photography, digital
>> technology
>> Personal art site www.artinyourface.com
>> wayne@dimagemaker.com
>
>
> Wouldn't something like this be effective?
>
> http://www.glock.com/g17.htm

Yes, but that means all cameras suddenly become downgraded to "single use"
units...
:) 
Anonymous
September 23, 2005 10:31:54 AM

Archived from groups: rec.photo.digital (More info?)

In article <87wtl85shv.fsf@gw.dd-b.net>,
David Dyer-Bennet <dd-b@dd-b.net> wrote:

> "wayne" <wayne@dimagemaker.com> writes:
>
>
> > I have put up an article on www.dimagemaker.com about some early
> > research work being done to block digital cameras of taking a picture
> > of something or someone that is to be protected.
> >
> > Food for thought.
>
> Indeed. I'm hoping it's technically unfeasible; that seems fairly
> likely. Otherwise we need to resort to making it illegal, much as I
> dislike the invocation of state power.

Geez! What're you people doing, taking stupid pills?

Here's a tip: Its not feasible and even if it is, its easily
side-stepped simply by placing a camera into manual mode or using a
powerful telephoto or zoom lens.
Anonymous
September 23, 2005 2:06:34 PM

Archived from groups: rec.photo.digital (More info?)

wayne wrote:

> Actually I am not sure.

Physical reality doesn't care whether or not you are "sure".

> Yes, going manual could help with the current
> system but I can conceive of ways to overload the actual CCD. The long
> telephoto or zoom lens also may not be an answer.

The inverse-square-law will have a word with you.

> I learnt a long time ago that when it comes to engineering, if someone
> says it can't be done, they are usually wrong.

They were wrong because their statements were not backed up by
empirical evidence/theory. Are yours?

> The right question is
> whether it can be done in a cost effective (whatever that means) and
> readily deployable manner that can cope with real world variance.

And the answer is, right now, "almost certainly not".

> The
> reality is that after posting the article I sat down and worked out a
> number of other possible approaches that could readily be used to
> shutdown a digital camera by attacking the electronics. Not hard if you
> don't mind the risk of frying the odd camera or two.

The fact of the matter is that the counter-measures are trivial and
inexpensive, while the other end of the problem is difficult and likely
to be very expensive (both in terms of cost and power requirements).
You tell us: who is going to lay out alot of money for a system that
can be easily defeated? (Excepting the USG who is still doling out
billions on 'star wars' ineffectiveness). Who would even bother trying
to build as much without a _solid_ theory, and corresponding analysis?

Personally, it would be alot cheaper, and vastly more effective, to
just wand people with NLJD's (see http://en.wikipedia.org/wiki/TSCM) at
the door and kick in the teeth of anyone who trips them. But hey,
knock yourself out if you want...
Anonymous
September 23, 2005 3:17:04 PM

Archived from groups: rec.photo.digital (More info?)

Shawn Hirn wrote:
> In article <87wtl85shv.fsf@gw.dd-b.net>,
> David Dyer-Bennet <dd-b@dd-b.net> wrote:
>
>
>>"wayne" <wayne@dimagemaker.com> writes:
>>
>>
>>
>>>I have put up an article on www.dimagemaker.com about some early
>>>research work being done to block digital cameras of taking a picture
>>>of something or someone that is to be protected.
>>>
>>>Food for thought.
>>
>>Indeed. I'm hoping it's technically unfeasible; that seems fairly
>>likely. Otherwise we need to resort to making it illegal, much as I
>>dislike the invocation of state power.
>
>
> Geez! What're you people doing, taking stupid pills?
>
> Here's a tip: Its not feasible and even if it is, its easily
> side-stepped simply by placing a camera into manual mode or using a
> powerful telephoto or zoom lens.

I think the only way this would work is for a mandate for all digital
cameras to have a special radio or IR sensor built in, and for protected
targets to have the appropriate signal to disable cameras aimed at it.
Obviously that would (a) raise free speech issues, and (b) create a
cottage industry of technologies to circumvent it.
Anonymous
September 23, 2005 8:28:54 PM

Archived from groups: rec.photo.digital (More info?)

"wayne" <wayne@dimagemaker.com> writes:
>Actually I am not sure. Yes, going manual could help with the current
>system but I can conceive of ways to overload the actual CCD. The long
>telephoto or zoom lens also may not be an answer.

No, it's a turkey. As the article itself points out, it won't work with
cameras where the CCD is covered before exposure. That means all DSLRs,
and that's what professional paparazzi are going to be using. But there
are P&S cameras that will close their mechanical shutter simply by
turning off the LCD display and using the optical viewfinder instead.

In addition, it seems like the system is going to be triggered by
retroreflective safety strips or paint used in some clothing, since they
will return a stronger reflection than the camera. I have one Tshirt
that does this, my backpack has a strip of it, and some jackets and even
shoes use these reflectors.

In addition, human and animal eyes act as retroreflectors. If the
system isn't sensitive to them, it's also not going to detect some of
the small P&S cameras that have smaller apertures and reflect even less
light back than a human eye.

So any such system is going to have lots of false alarms, triggering
the "light projector" to "blast" the nearby spectators needlessly. I
predict the system would be so annoying that it would quickly get
turned off.

>The
>reality is that after posting the article I sat down and worked out a
>number of other possible approaches that could readily be used to
>shutdown a digital camera by attacking the electronics. Not hard if you
>don't mind the risk of frying the odd camera or two.

If it can affect a digital camera at a distance, it can also affect or
damage cellphones, PDAs, computers, hearing aids etc. Depending on
strength, it might affect pacemakers. You're suggesting this could be
set up in a public place and left to fire automatically whenever it
detects a camera?

Dave
Anonymous
September 23, 2005 8:32:50 PM

Archived from groups: rec.photo.digital (More info?)

yoda2k@verizon.net writes:

>2> Blanket the area with something that virtually all cameras can
>"see/record" by "humans can't. UV & Near IR comes to mind & powerful
>enough laser(s) fired into a high speed rotating mirror might blanket
>an area with enough energy to impend/impair a quality digital image
>from being recorded, especially @ night.

A digital camera's spectral response is easily restricted to visible
light with the appropriate filter. Casual photographers won't have one,
but professional paparazzi will once they encounter this system.

Dave
Anonymous
September 23, 2005 9:32:05 PM

Archived from groups: rec.photo.digital (More info?)

Shawn Hirn <srhi@comcast.net> writes:

> In article <87wtl85shv.fsf@gw.dd-b.net>,
> David Dyer-Bennet <dd-b@dd-b.net> wrote:
>
> > "wayne" <wayne@dimagemaker.com> writes:
> >
> >
> > > I have put up an article on www.dimagemaker.com about some early
> > > research work being done to block digital cameras of taking a picture
> > > of something or someone that is to be protected.
> > >
> > > Food for thought.
> >
> > Indeed. I'm hoping it's technically unfeasible; that seems fairly
> > likely. Otherwise we need to resort to making it illegal, much as I
> > dislike the invocation of state power.
>
> Geez! What're you people doing, taking stupid pills?

Why pick on me? I *said* I thought it was "fairly likely" that it was
"technically unfeasible".
--
David Dyer-Bennet, <mailto:D d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
Pics: <http://dd-b.lighthunters.net/&gt; <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
Dragaera/Steven Brust: <http://dragaera.info/&gt;
Anonymous
September 24, 2005 4:20:50 AM

Archived from groups: rec.photo.digital (More info?)

in genera, if you can lock it, you can unlock it.
There is no such a thing as unbreakable lock or code.
Someone will find a way around it.
to stop cameras from firing, they would have to be fitted with some
sort or receiver. Currently, none has it.
mirrors, lasers etc - can do much harm, there is always a pola filter,
there are skilled retouchers to correct an image.
but you can increase a distance or put extra few feet of a fence.
May help, may not.
Anonymous
September 24, 2005 4:34:37 AM

Archived from groups: rec.photo.digital (More info?)

just finished the article.
Locks are to keep HONEST people away.
such stupid idea, sorry for harsh word.
it is not going to work, I can already use something to beat it. But I
will not tell you, not to make your life easier.

If you want to keep something away from prying eyes, do just that.
Hide it. If it is on a public display, you will not be able to control
it.
A knowledgeable person will find a counter-method. Quicker than you
think.
Show me one piece of software that would not be cracked by youngster
cracker?
All the schemes from microsoft, adobe, symantec,autodesk.....

Some museums, (Vienna)use difficult illumination and ban you from
taking photographs. Yet I managed to do, what I wanted, without a
flash (with digital camera).
Anonymous
September 24, 2005 4:57:54 AM

Archived from groups: rec.photo.digital (More info?)

Dave,

I can certainly think of places where a government would be willing to
do that. Can't you or am I just more cynical about governments?

Cheers,

Wayne

Wayne J. Cosshall
Publisher, The Digital ImageMaker, www.dimagemaker.com
Assistant Director, International Digital Art Award
Freelance writer and educator in graphic design, photography, digital
technology
Personal art site www.artinyourface.com
wayne@dimagemaker.com
Anonymous
September 24, 2005 6:03:24 AM

Archived from groups: rec.photo.digital (More info?)

Why the aggression in your replies?

Inverse square law does not apply to this. If you are close enough that
the inverse square law has not dimmed the light reflected by the
subject so much that you can't get a pic then it will also not have
dimmed any countermeasure.

Actually to my comment about engineering I was referring to your reply.
You seem very definite, so to mirror your statement, can you back your
statements up? Since your inverse square reference shows a lack of
understanding, I suspect the issue my be with your reasoning.

No, I agree, probably not possible right now. But that can change real
fast.

As to who would use, I actually never thought it would appeal to many
beyond government.

Cheers,

Wayne
Wayne J. Cosshall
Publisher, The Digital ImageMaker, www.dimagemaker.com
Assistant Director, International Digital Art Award
Freelance writer and educator in graphic design, photography, digital
technology
Personal art site www.artinyourface.com
wayne@dimagemaker.com
Anonymous
September 24, 2005 10:31:13 AM

Archived from groups: rec.photo.digital (More info?)

On 22 Sep 2005 00:49:54 -0700
"wayne" <wayne@dimagemaker.com> wrote:

> Hi all,
>
> I have put up an article on www.dimagemaker.com about some early
> research work being done to block digital cameras of taking a picture
> of something or someone that is to be protected.
>
> Food for thought.

The technology already exits: mass media and cops with guns.

Jeff
Anonymous
September 24, 2005 10:22:17 PM

Archived from groups: rec.photo.digital (More info?)

"wayne" <wayne@dimagemaker.com> writes:

>I can certainly think of places where a government would be willing to
>do that. Can't you or am I just more cynical about governments?

I can think of areas where governments would like to know about *all* of
the electronics you are carrying, and whether it can transmit or record
audio or video. It seems to me that the best way to protect such areas
is to search people entering them, not to use devices that
indiscriminately disrupt most electronic devices.

But this particular gadget was proposed as a way of protecting people
who don't want to be photographed in public. For that purpose, I think
both it and your inventions are not practical.

Dave
Anonymous
September 24, 2005 10:27:03 PM

Archived from groups: rec.photo.digital (More info?)

"wayne" <wayne@dimagemaker.com> writes:
>Inverse square law does not apply to this. If you are close enough that
>the inverse square law has not dimmed the light reflected by the
>subject so much that you can't get a pic then it will also not have
>dimmed any countermeasure.

Sure it applies. The detection system is vulnerable to the inverse
square law - the amount of light returned by the camera to the
detection system is reduced to 1/4 if you double the distance to the
camera. So the system won't work beyond some particular range for a
given camera.

If you're using a point&shoot camera, this may place you beyond flash
range (inverse square again) but shooting by ambient light is still
possible. And if you're professional paparazzi, you'll just bring a
larger flash and/or increase ISO so you can shoot from further away.

Dave
September 24, 2005 10:27:04 PM

Archived from groups: rec.photo.digital (More info?)

Dave Martindale wrote:
> "wayne" <wayne@dimagemaker.com> writes:
>
>>Inverse square law does not apply to this. If you are close enough that
>>the inverse square law has not dimmed the light reflected by the
>>subject so much that you can't get a pic then it will also not have
>>dimmed any countermeasure.
>
>
> Sure it applies. The detection system is vulnerable to the inverse
> square law - the amount of light returned by the camera to the
> detection system is reduced to 1/4 if you double the distance to the
> camera. So the system won't work beyond some particular range for a
> given camera.
>
> If you're using a point&shoot camera, this may place you beyond flash
> range (inverse square again) but shooting by ambient light is still
> possible. And if you're professional paparazzi, you'll just bring a
> larger flash and/or increase ISO so you can shoot from further away.
>
> Dave


....or a telescope if my subject is on a different mountain.


--
jer
email reply - I am not a 'ten'
Anonymous
September 26, 2005 3:30:42 AM

Archived from groups: rec.photo.digital (More info?)

Shawn Hirn <srhi@comcast.net> writes:

> In article <Q8zYe.15877$ib1.6514@tornado.ohiordc.rr.com>,
> "Robert J Batina" <rbatina@columbus.rr.com> wrote:
>
> > wayne <wayne@dimagemaker.com> spewed:
> > > Hi all,
> > >
> > > I have put up an article on www.dimagemaker.com about some early
> > > research work being done to block digital cameras of taking a
> > > picture of something or someone that is to be protected.
> >
> > A direct link would be appreciated. Attempting to navigate that site hurts
> > my weary eyes... blue, green, red, yellow, black, blinky ads...
>
> True, but the link took all of 2 seconds to find. Even so, it seems to
> me, this idea is easily subverted simply by putting the camera into
> manual mode and the correct use of shutter and aperture settings.

No, if I remember the article, it used infrared to measure the reflection from
the coating of the lens, and then turn on a strong light to overexpose anybody
taking a picture. Obviously there the solution is to get cheap uncoated lenses
:-) Or possibily a new lens coating that doesn't reflect the light bakc.

--
Michael Meissner
email: mrmnews@the-meissners.org
http://www.the-meissners.org
Anonymous
September 26, 2005 5:51:13 AM

Archived from groups: rec.photo.digital (More info?)

Dave,

Sorry, but you don't seem to get what I mean. Yes, the inverse square
law applies, of course. But it applies to everything. So if you are
going to get enough light to make an exposure, then the countermeasure
can also put out enough light to upset the exposure system. The area
most vulnerable is the IR detection system, but I think the real issue
is actually the field of view issue with longer lenses. And of course
if you are using an SLR then the issue goes away except for a very
small time window when the mirror pops up and the shutter opens.

Also, if I remember my optics correctly, the inverse square law applies
to point sources. For area light sources, ie light reflecting off of
real objects the relationship is a bit different. I've never noticed a
2 stop extra exposure if I halved the distance to a real subject.

Cheers,

Wayne

Wayne J. Cosshall
Publisher, The Digital ImageMaker, www.dimagemaker.com
Assistant Director, International Digital Art Award
Freelance writer and educator in graphic design, photography, digital
technology
Personal art site www.artinyourface.com
wayne@dimagemaker.com

Dave Martindale wrote:
> "wayne" <wayne@dimagemaker.com> writes:
> >Inverse square law does not apply to this. If you are close enough that
> >the inverse square law has not dimmed the light reflected by the
> >subject so much that you can't get a pic then it will also not have
> >dimmed any countermeasure.
>
> Sure it applies. The detection system is vulnerable to the inverse
> square law - the amount of light returned by the camera to the
> detection system is reduced to 1/4 if you double the distance to the
> camera. So the system won't work beyond some particular range for a
> given camera.
>
> If you're using a point&shoot camera, this may place you beyond flash
> range (inverse square again) but shooting by ambient light is still
> possible. And if you're professional paparazzi, you'll just bring a
> larger flash and/or increase ISO so you can shoot from further away.
>
> Dave
Anonymous
September 26, 2005 11:15:26 AM

Archived from groups: rec.photo.digital (More info?)

Michael Meissner <mrmnews@the-meissners.org> writes:

>No, if I remember the article, it used infrared to measure the reflection from
>the coating of the lens, and then turn on a strong light to overexpose anybody
>taking a picture. Obviously there the solution is to get cheap uncoated lenses
>:-) Or possibily a new lens coating that doesn't reflect the light bakc.

I don't think it has anything to do with lens coating; it depends on the
camera behaving like a retroreflector, like the eyes of people or
animals. If the shutter is open, and the aperture is reasonably wide,
and the lens is focused at about the distance of the IR source, then the
lens collects a fair bit of IR and focuses it on the film or CCD. Some
of that light is scattered back towards the lens, which then collimates
it back into a parallel beam and sends it back towards the source.

This is called autocollimation, and it's a method used to determine
whether a camera/lens pair is focusing properly at infinity. It's also
how glass-beaded retroreflective road signs work.

Adding an IR-absorbing filter would prevent this from working, since no
IR would be returned. An IR-reflecting filter (hot mirror) would work
just as well too, since the reflection wouldn't go back towards the IR
source. But just keeping the shutter closed until exposure time is just
as good.

Dave
Anonymous
September 26, 2005 8:07:41 PM

Archived from groups: rec.photo.digital (More info?)

"wayne" <wayne@dimagemaker.com> writes:

>Sorry, but you don't seem to get what I mean. Yes, the inverse square
>law applies, of course. But it applies to everything. So if you are
>going to get enough light to make an exposure, then the countermeasure
>can also put out enough light to upset the exposure system.

Sure, but that's not what *I* meant, nor the person you were originally
replying too. The inverse square law matters in determining whether the
IR detection system can detect the camera. If the system cannot detect
the camera, it does not trigger, and the photograph is taken without
interference. It simply doesn't matter whether the countermeasure
system *could have* put out enough light if it had triggered, since it
did not.

>Also, if I remember my optics correctly, the inverse square law applies
>to point sources. For area light sources, ie light reflecting off of
>real objects the relationship is a bit different. I've never noticed a
>2 stop extra exposure if I halved the distance to a real subject.

It certainly does apply to light from the subject, but it doesn't change
the exposure. If you halve the distance to a real subject, the lens
does capture 4 times as much light from each point on that subject. But
the image also occupies 4 times as much area on the image plane, so the
intensity per unit area remains the same, and that's what determines the
exposure you need.

Dave
!