Gareth Taylor
Member
Yes, but this case is "ONL" (outside normal limits).
Refer to my later post:
http://forums.dpreview.com/ ... ... read.asp?forum=1024&message=4864467
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Is the human eye capable of seing infrared?
- Thread starter Daniella68313
- Start date
Refer to my later post:
http://forums.dpreview.com/ ... ... read.asp?forum=1024&message=4864467
Gareth Taylor
Member
Petteri Sulonen
Forum Pro
Correct, of course. Thanks for setting me straight.
Petteri
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kenw
Veteran Member
Sigh,
OK, once again that is a linear graph. The ratio of sensitivity of the human eye from threshold of detection of the dark adapted eye to the threshold of damage is 1:100,000,000,000,000. That's 1E14. You need to look at a log graph of spectral sensitivity if you want to examine the extemes of detection or sensitivty. Check out:
http://www.intl-light.com/handbook/ch02.html
And look at figure 2.3 near the bottom of the page. Notice that as the curves push into the near IR they are exponentially declining. This curve shows a sensitivity of 2E-5 at a wavelength of 770nm. The curve keeps going all the way out to 1000nm, not shown on this graph, still droping exponentially. A similar extension on the UV side goes to 300nm. Now, of course on a linear graph 2E-5 is going to look a lot like zero. But it isn't, your eye is sensitive out here and past it, but in any "normal" viewing setting light in the "visible" spectrum will totally swamp out your response in this region (we are, after all talking about a factor of 1,000,000 or more). Any sort of black body emitter (sun, light bulb, hot metal) will always trigger your red response before the near IR. Any sort of normal filter will not adequately filter out the visible spectrum enough to reveal the near IR. The filter just isn't sharp enough. To use a poor analogy, it is like trying to listen to someone whispering 100 ft away at a rock concert. You can hear a person whisper at 100 ft, just not with all that other noise around.
Now, if I use an interference filter, or a monochromatic light source (laser) or near monochromatic source (LED) I can in fact produce a lot of light in the near IR to produce a response in the human eye without emitting any light in the visible spectrum to mask it. The lens will still focus images at these wavelengths. This is not an easy thing to do. We are talking about making up for a factor of a close to a million at 800nm compared to our response at green. You need have a dark adapted eye (total darkness for at least 15 minutes) in a truely dark room and really bright near IR sources.
The linear CIE curves you see are practical for 99.999999% of all viewing situations, no one walks around with sharp near IR filters by day or near IR lasers in darkened rooms. But to say there is no response past 750nm is patently false. There is exceptionally poor response, which in contrived situations can be measured and used.
As far as crapola goes, I guess my experience is that there are two kinds of doctors on the web, those who know what they are talking about and those that use the letters "Dr", "MD", or "PhD" somewhere in their handle. Hope I didn't step on any toes
.
On an unrelated note:
For those of you actually interested in what super narrow band filters can reveal in the visible spectrum (not near IR) check out:
That's the sun, filtered at the H-alpha line with a plane from LAX in the way. Sad to say, I didn't take the photo, the filter costs about $20,000 and is too expensive for my blood. Definately pulling a whisper from the rock concert...
---------------------------
Ken W
Sony DSC-S85
& lots of 35mm and 4x5 in the closet
OK, once again that is a linear graph. The ratio of sensitivity of the human eye from threshold of detection of the dark adapted eye to the threshold of damage is 1:100,000,000,000,000. That's 1E14. You need to look at a log graph of spectral sensitivity if you want to examine the extemes of detection or sensitivty. Check out:
http://www.intl-light.com/handbook/ch02.html
And look at figure 2.3 near the bottom of the page. Notice that as the curves push into the near IR they are exponentially declining. This curve shows a sensitivity of 2E-5 at a wavelength of 770nm. The curve keeps going all the way out to 1000nm, not shown on this graph, still droping exponentially. A similar extension on the UV side goes to 300nm. Now, of course on a linear graph 2E-5 is going to look a lot like zero. But it isn't, your eye is sensitive out here and past it, but in any "normal" viewing setting light in the "visible" spectrum will totally swamp out your response in this region (we are, after all talking about a factor of 1,000,000 or more). Any sort of black body emitter (sun, light bulb, hot metal) will always trigger your red response before the near IR. Any sort of normal filter will not adequately filter out the visible spectrum enough to reveal the near IR. The filter just isn't sharp enough. To use a poor analogy, it is like trying to listen to someone whispering 100 ft away at a rock concert. You can hear a person whisper at 100 ft, just not with all that other noise around.
Now, if I use an interference filter, or a monochromatic light source (laser) or near monochromatic source (LED) I can in fact produce a lot of light in the near IR to produce a response in the human eye without emitting any light in the visible spectrum to mask it. The lens will still focus images at these wavelengths. This is not an easy thing to do. We are talking about making up for a factor of a close to a million at 800nm compared to our response at green. You need have a dark adapted eye (total darkness for at least 15 minutes) in a truely dark room and really bright near IR sources.
The linear CIE curves you see are practical for 99.999999% of all viewing situations, no one walks around with sharp near IR filters by day or near IR lasers in darkened rooms. But to say there is no response past 750nm is patently false. There is exceptionally poor response, which in contrived situations can be measured and used.
As far as crapola goes, I guess my experience is that there are two kinds of doctors on the web, those who know what they are talking about and those that use the letters "Dr", "MD", or "PhD" somewhere in their handle. Hope I didn't step on any toes
.On an unrelated note:
For those of you actually interested in what super narrow band filters can reveal in the visible spectrum (not near IR) check out:
That's the sun, filtered at the H-alpha line with a plane from LAX in the way. Sad to say, I didn't take the photo, the filter costs about $20,000 and is too expensive for my blood. Definately pulling a whisper from the rock concert...
--
---------------------------
Ken W
Sony DSC-S85
& lots of 35mm and 4x5 in the closet
Dr. Don Sandell
Senior Member
I stand by my previous post.
Parker North
Forum Enthusiast
I will stand behind you, the two of us. How it goin bro'.
How it goin bro'.keith caldwell
Leading Member
I'm not actually saying that Daniella can see IR - in fact I think that she has already acknowledged that this is unlikely but she has contributed some very interesting information for anyone wanting to take IR photos.I don't think an eye doctor will be able to tell me those
things...this is probably something out of this world for them
In any case, I am not ready to pay a 40$ consultation just to have
an opinion on this..yike.
I am very interested in the contributiond from Dr Don. It is not sufficient to quote from any medical textbook. Most are out of date by the time they are published - that is if they were ever in date to begin with. Most textbooks endlessly repeat received 'wisdom' copied from other books.I've lost my geography book which claims that the earth is flat but I did see it in print so it must be true!
It should be remembered that seeing is not just a physical process - rod & cones - light of a particuar wavelength etc but is also a brain mediated psychlogical interpretation. We do not have miniature film projectors at the back of our heads whcih turn nerve impulses from the retina into images.Various cells resond to staight lines ,curves, light & dark, wavelength etc and the end result is what we think is an accurate representation of the world. The truth is that we don't reaaly know what the material world 'looks' like but it is fortunate that we usually have enough information to avoid walking under buses.
Pity poor flatworms who 'see' their environments in terms of hydrogen ion concentrations and who use this insight to avoid hostile extremes of acid which coud upset their digestions. This would only be of use to us in MacDonalds!
--
keith c
Daniella68313
Forum Pro
thanks for the link and technical stuff. That is a really cool photo!
anyone with a R72 filter can try it and see what I see. The trick is to cut off any ambiant light as much as possible and wait long enough for the eye to adapt to darkness.
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com
c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya R72.
anyone with a R72 filter can try it and see what I see. The trick is to cut off any ambiant light as much as possible and wait long enough for the eye to adapt to darkness.
--OK, once again that is a linear graph. The ratio of sensitivity
of the human eye from threshold of detection of the dark adapted
eye to the threshold of damage is 1:100,000,000,000,000. That's
1E14. You need to look at a log graph of spectral sensitivity if
you want to examine the extemes of detection or sensitivty. Check
out:
http://www.intl-light.com/handbook/ch02.html
And look at figure 2.3 near the bottom of the page. Notice that as
the curves push into the near IR they are exponentially declining.
This curve shows a sensitivity of 2E-5 at a wavelength of 770nm.
The curve keeps going all the way out to 1000nm, not shown on this
graph, still droping exponentially. A similar extension on the UV
side goes to 300nm. Now, of course on a linear graph 2E-5 is
going to look a lot like zero. But it isn't, your eye is
sensitive out here and past it, but in any "normal" viewing setting
light in the "visible" spectrum will totally swamp out your
response in this region (we are, after all talking about a factor
of 1,000,000 or more). Any sort of black body emitter (sun, light
bulb, hot metal) will always trigger your red response before the
near IR. Any sort of normal filter will not adequately filter out
the visible spectrum enough to reveal the near IR. The filter just
isn't sharp enough. To use a poor analogy, it is like trying to
listen to someone whispering 100 ft away at a rock concert. You
can hear a person whisper at 100 ft, just not with all that other
noise around.
Now, if I use an interference filter, or a monochromatic light
source (laser) or near monochromatic source (LED) I can in fact
produce a lot of light in the near IR to produce a response in the
human eye without emitting any light in the visible spectrum to
mask it. The lens will still focus images at these wavelengths.
This is not an easy thing to do. We are talking about making up
for a factor of a close to a million at 800nm compared to our
response at green. You need have a dark adapted eye (total
darkness for at least 15 minutes) in a truely dark room and really
bright near IR sources.
The linear CIE curves you see are practical for 99.999999% of all
viewing situations, no one walks around with sharp near IR filters
by day or near IR lasers in darkened rooms. But to say there is
no response past 750nm is patently false. There is exceptionally
poor response, which in contrived situations can be measured and
used.
As far as crapola goes, I guess my experience is that there are two
kinds of doctors on the web, those who know what they are talking
about and those that use the letters "Dr", "MD", or "PhD" somewhere
in their handle. Hope I didn't step on any toes
On an unrelated note:
For those of you actually interested in what super narrow band
filters can reveal in the visible spectrum (not near IR) check out:
That's the sun, filtered at the H-alpha line with a plane from LAX
in the way. Sad to say, I didn't take the photo, the filter costs
about $20,000 and is too expensive for my blood. Definately
pulling a whisper from the rock concert...
--
---------------------------
Ken W
Sony DSC-S85
& lots of 35mm and 4x5 in the closet
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com
c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya R72.
Daniella68313
Forum Pro
wow, I would not like to have that vision...
It would probably help if a qualified person would try the filter and see for themselves what happen. It's hard to describe.
Some one suggest that the same effect can be seen through a deep red filter, not only an IR filter, so I will go to the local photo store today and try it (I am curious)
--
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com
c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya R72.
Parker North
Forum Enthusiast
Same here.
astrnmrtom
Member
Daniella:
First, a correction about my explanation of the IR filter. I mentioned the filter should have a bell shapped transmission curve, and this isn't always true. IR filters can be considered cut-off filters and as such have a transmission curve that for all practical purposes is 1/2 of the bell shaped curve.
Ok, that said.
When we talk about visible light and IR light we are talking about areas of a constantly changing spectrum. When we try to decide if you are seeing IR light it is a matter of how one defines IR light as well as visible light.
Without putting specific names to it, lets just say your eye's ability to see tapers off at the red and violets ends of the spectrum, where exactly, is different for each person. The IR filter you are using transmits light that tapers off as one heads "up" spectrum from the IR toward red. If your eye's curve of visibility overlaps where the filters transmission curve still transmists light, you see an image. This as I said, is deep in the "red" or "slightly" in the IR depending on how one defines this portion of the spectrum. The reason you can't see the remote LED is it's transmission is "deeper" into the infra-red or longer wavelengths where your eye's curve is zero.
PHEW!
I have a couple red filters and took them out today to have an answer to your question.
The one filter is a #25 red which is a "medium" red of about 15% transmission. The other is a dark red hydrogen-alpha filter used for B&W photography. I bet it transmits less than 10% but I'm not sure.
The medium red filter darkened follage when I looked through it. The dark red h-alpha filter darkened most follage, but new growth, light green folage appeared lighter. I also noticed light green moss in my lawn seemed brighter in both filters - YIKES do I have THAT much moss in my lawn!!!???. I suspect this is because the filters darkened the surrounding grass making the moss stand out.
My guess is, follage doesn't reflect red light too well until one gets to fairly long wavelengths approaching the IR. It makes sense, if follage reflected red light it wouldn't appear so green! DUH!! But it also makes sense that plants would like to reflect IR. It may help protect the plant from overheating as it bakes away in the midday sun.
Anyway.... looks like you stirred up quite a hornet's nest with this question. Haven't had a chance to check all responses as my dial-up connection makes wading through looooong posting very slow going. Good thread though.
Its fun seeing the world in a different "light".
Tom
Daniella wrote:
SNIP> > > >
First, a correction about my explanation of the IR filter. I mentioned the filter should have a bell shapped transmission curve, and this isn't always true. IR filters can be considered cut-off filters and as such have a transmission curve that for all practical purposes is 1/2 of the bell shaped curve.
Ok, that said.
When we talk about visible light and IR light we are talking about areas of a constantly changing spectrum. When we try to decide if you are seeing IR light it is a matter of how one defines IR light as well as visible light.
Without putting specific names to it, lets just say your eye's ability to see tapers off at the red and violets ends of the spectrum, where exactly, is different for each person. The IR filter you are using transmits light that tapers off as one heads "up" spectrum from the IR toward red. If your eye's curve of visibility overlaps where the filters transmission curve still transmists light, you see an image. This as I said, is deep in the "red" or "slightly" in the IR depending on how one defines this portion of the spectrum. The reason you can't see the remote LED is it's transmission is "deeper" into the infra-red or longer wavelengths where your eye's curve is zero.
PHEW!
I have a couple red filters and took them out today to have an answer to your question.
The one filter is a #25 red which is a "medium" red of about 15% transmission. The other is a dark red hydrogen-alpha filter used for B&W photography. I bet it transmits less than 10% but I'm not sure.
The medium red filter darkened follage when I looked through it. The dark red h-alpha filter darkened most follage, but new growth, light green folage appeared lighter. I also noticed light green moss in my lawn seemed brighter in both filters - YIKES do I have THAT much moss in my lawn!!!???. I suspect this is because the filters darkened the surrounding grass making the moss stand out.
My guess is, follage doesn't reflect red light too well until one gets to fairly long wavelengths approaching the IR. It makes sense, if follage reflected red light it wouldn't appear so green! DUH!! But it also makes sense that plants would like to reflect IR. It may help protect the plant from overheating as it bakes away in the midday sun.
Anyway.... looks like you stirred up quite a hornet's nest with this question. Haven't had a chance to check all responses as my dial-up connection makes wading through looooong posting very slow going. Good thread though.
Its fun seeing the world in a different "light".
Tom
Daniella wrote:
SNIP> > > >
astrnmrtom
Member
Daniella:
Its all about contrast. The "brighter" follage appears brighter because it is reflecting light deep into the red that your eye can still see and the filter can transmit. Other objects, not reflecting as much light of this wavelength appear darker. This is probably where the reflection curve of the follage starts to rise again. The vision curve of your eye, overlaping the transmission curve of the filter, overlapping the reflection curve of some of the follage, makes it look brighter. This may only be 1% or 2% brighter but because the rest of the view is so dark it looks bright.
GACK!!! Did I even make sense on that one!!!????
Must be past my bedtime!
Tom Blah blah blah...
Its all about contrast. The "brighter" follage appears brighter because it is reflecting light deep into the red that your eye can still see and the filter can transmit. Other objects, not reflecting as much light of this wavelength appear darker. This is probably where the reflection curve of the follage starts to rise again. The vision curve of your eye, overlaping the transmission curve of the filter, overlapping the reflection curve of some of the follage, makes it look brighter. This may only be 1% or 2% brighter but because the rest of the view is so dark it looks bright.
GACK!!! Did I even make sense on that one!!!????
Must be past my bedtime!
Tom Blah blah blah...
Gareth Taylor
Member
Finally someone who knows what they're talking about!
OK, once again that is a linear graph. The ratio of sensitivity
of the human eye from threshold of detection of the dark adapted
eye to the threshold of damage is 1:100,000,000,000,000. That's
1E14. You need to look at a log graph of spectral sensitivity if
you want to examine the extemes of detection or sensitivty. Check
out:
http://www.intl-light.com/handbook/ch02.html
And look at figure 2.3 near the bottom of the page. Notice that as
the curves push into the near IR they are exponentially declining.
This curve shows a sensitivity of 2E-5 at a wavelength of 770nm.
The curve keeps going all the way out to 1000nm, not shown on this
graph, still droping exponentially. A similar extension on the UV
side goes to 300nm. Now, of course on a linear graph 2E-5 is
going to look a lot like zero. But it isn't, your eye is
sensitive out here and past it, but in any "normal" viewing setting
light in the "visible" spectrum will totally swamp out your
response in this region (we are, after all talking about a factor
of 1,000,000 or more). Any sort of black body emitter (sun, light
bulb, hot metal) will always trigger your red response before the
near IR. Any sort of normal filter will not adequately filter out
the visible spectrum enough to reveal the near IR. The filter just
isn't sharp enough. To use a poor analogy, it is like trying to
listen to someone whispering 100 ft away at a rock concert. You
can hear a person whisper at 100 ft, just not with all that other
noise around.
Now, if I use an interference filter, or a monochromatic light
source (laser) or near monochromatic source (LED) I can in fact
produce a lot of light in the near IR to produce a response in the
human eye without emitting any light in the visible spectrum to
mask it. The lens will still focus images at these wavelengths.
This is not an easy thing to do. We are talking about making up
for a factor of a close to a million at 800nm compared to our
response at green. You need have a dark adapted eye (total
darkness for at least 15 minutes) in a truely dark room and really
bright near IR sources.
The linear CIE curves you see are practical for 99.999999% of all
viewing situations, no one walks around with sharp near IR filters
by day or near IR lasers in darkened rooms. But to say there is
no response past 750nm is patently false. There is exceptionally
poor response, which in contrived situations can be measured and
used.
As far as crapola goes, I guess my experience is that there are two
kinds of doctors on the web, those who know what they are talking
about and those that use the letters "Dr", "MD", or "PhD" somewhere
in their handle. Hope I didn't step on any toes
On an unrelated note:
For those of you actually interested in what super narrow band
filters can reveal in the visible spectrum (not near IR) check out:
That's the sun, filtered at the H-alpha line with a plane from LAX
in the way. Sad to say, I didn't take the photo, the filter costs
about $20,000 and is too expensive for my blood. Definately
pulling a whisper from the rock concert...
--
---------------------------
Ken W
Sony DSC-S85
& lots of 35mm and 4x5 in the closet
Daniella68313
Forum Pro
So probably what I see is the very near infrared then.
It is interesting to hear that you see vegetation differently with both filters. It's also funny to note that people doing film IR are often using a red filter with it. Not infrared but just red.
--
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com
c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya R72.
Daniella68313
Forum Pro
Thanks for doing the tests with the red filters.
and for the explanation as well, very interesting.
and for the explanation as well, very interesting.
Parker North
Forum Enthusiast
Thought you might like to see it, saw it wile I was visiting elsewhere.
http://forums.dpreview.com/forums/read.asp?forum=1009&message=4872462
Not for quality, just to show you.
http://forums.dpreview.com/forums/read.asp?forum=1009&message=4872462
Not for quality, just to show you.
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