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Infrared photography



 
 
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  #21  
Old September 26th 08, 03:45 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
DaveC
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Posts: 15
Default Infrared photography

http://farm4.static.flickr.com/3085/...e6058929_o.jpg

CS,
Thanks for your reply.

I'm unclear whether you hacked your camera. Did you remove the IR filter from
the image sensor? Or did you just add IR filters to your lens?

Thanks,
--
DaveC

This is an invalid return address
Please reply in the news group

  #22  
Old September 26th 08, 03:51 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
Dave Platt
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Posts: 53
Default Infrared photography

In article .net,
DaveC wrote:

Seems straightforward (notice the absence of the term "simple").

Can you give a URL for such a piece?

The proper thickness of the replacement glass should be...? Should it be the
same thickness as the filter removed from the imager?


Edmund Optics (the "pro" side of Edmund Scientific) was a recommended
source for this sort of optical glass, in one article I read on a P&S
IR conversion. http://www.edmundoptics.com/

Yes, you want a piece that is as thick as the "hot mirror" filter that
you are removing from the camera's existing optical path.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
  #23  
Old September 26th 08, 05:20 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
James Silverton
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Posts: 155
Default Infrared photography

"Dave Platt" wrote in message

In article .net,
DaveC wrote:

Seems straightforward (notice the absence of the term "simple").

Can you give a URL for such a piece?

The proper thickness of the replacement glass should be...? Should
it be the same thickness as the filter removed from the imager?


Edmund Optics (the "pro" side of Edmund Scientific) was a recommended
source for this sort of optical glass, in one article I read on a P&S
IR conversion. http://www.edmundoptics.com/

Yes, you want a piece that is as thick as the "hot mirror" filter that
you are removing from the camera's existing optical path.


I haven't got the nerve (or ability, probably) to perform surgery on a
camera but how expensive a camera do you need for IR photography? I have
been impressed by the artistic quality of many IR photographs but not
their sharpness and those were taken with conventional film cameras.


--
James Silverton
Potomac, Maryland

  #24  
Old September 26th 08, 06:37 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
Dave Platt
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Posts: 53
Default Infrared photography

In article ,
James Silverton not.jim.silverton.at.verizon.not wrote:

I haven't got the nerve (or ability, probably) to perform surgery on a
camera but how expensive a camera do you need for IR photography? I have
been impressed by the artistic quality of many IR photographs but not
their sharpness and those were taken with conventional film cameras.


I've successfully taken some interesting-looking IR photos using
inexpensive Nikon Coolpix cameras - specifically, the Coolpix 800 and
Coolpix 950. These use a 2.1-megapixel sensor (made by Sony I believe)
which has a less-than-efficient hot mirror... enough near-IR comes
through to allow IR photos to be taken in daylight with an exposure in
the 1/8- second range, as long as an IR-pass/visible-light-blocking
filter is added to the lens. I bought these cameras last year via
eBay auctions... around $25 for an 800 and around $45 for a 950, if I
recall properly.

I homebrewed a simple IR-pass filter as a "proof of concept", before
buying a good one. The simplest approach is to use several layers of
exposed photographic film. Another approach is to go to a plastic
store, and buy a scrap piece of black acrylic plastic sheet... this
stuff is made with a dye that passes a reasonable amount of IR. In
either case, the plastic or exposed photographic film can be mounted
to the front of a piece of opaque plastic tubing, which can then be
slid over the front of the camera lens assembly.

Better quality can be achieved with a purpose-made IR filter... the
Hoya RM-72 is the usual suspect. These filters pass more IR than the
simple homebrew type, I think.

Removing the hot filter from a camera of this sort, and replacing it
with clear glass would greatly increase the IR sensitivity and allow
for much shorter exposures (you'd still need an RM-72 or similar).
Removing the hot filter, and replacing it with a piece of IR-pass
filter glass would convert the camera to a high-sensitivity IR-only
camera... which is what several commercial camera shops can do for
you, for a significant fee.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
  #25  
Old September 26th 08, 07:01 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
Whiskers
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Posts: 188
Default Infrared photography

On 2008-09-26, James Silverton wrote:

[...]

I haven't got the nerve (or ability, probably) to perform surgery on a
camera but how expensive a camera do you need for IR photography? I have
been impressed by the artistic quality of many IR photographs but not
their sharpness and those were taken with conventional film cameras.


IR rays come to a focus further from the lens than visible rays do, so
after visually focusing you need to adjust the distance setting on the
lens to compensate for the difference [1]. But if your IR-passing filter
isn't restricted to a narrow waveband, there will still be some IR rays
with much longer wavelength than others getting through to the
film/sensor and they won't all be focused at a single point. Normal
camera lenses are designed to overcome this 'chromatic aberration' for
visible wavelengths, but they don't do it for UV or IR. So IR pictures
are seldom as sharp as those the same equipment can make using only
visible light. Using a small aperture can help a little - at the cost
of a longer exposure, of course.

[1] Some lenses have an IR focus index as well as the visible-light one;
after focusing visually, move the focusing ring so that the distance next
to the usual focus index is next to the IR one instead. If there isn't an
IR index, use the 'closer' depth of field indicator for f/5.6. Of course
with an auto-focus-only or fixed-focus compact camera, you're stuck with
what the camera does, which will be 'wrong' - but the large 'depth of
field' that goes with a tiny sensor might offset the problem somewhat.

--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~
  #26  
Old September 26th 08, 07:02 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
carlislestamford
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Posts: 8
Default Infrared photography

On Fri, 26 Sep 2008 07:45:14 -0700, DaveC wrote:


I'm unclear whether you hacked your camera. Did you remove the IR filter from
the image sensor? Or did you just add IR filters to your lens?


No need to remove any internal filter or hack these cameras. Just screw-on
standard IR filters to the front of the lens to cut out any visible light. They
come with a built-in infrared photography mode in them. Along with the usual use
for a digital camera, these were designed with their "Night Shot" mode. When you
turn the switch to that mode the camera flips its internal IR filter out of the
way, the one that everyone else has to hack out of their camera and end-up
destroying it for normal photography. The camera then readjusts the focusing
distance to account for IR wavelengths only and turns on some high-power IR LEDs
in front to illuminate subjects in the dark. You can then see, photograph, and
video-record in the total dark with it. I recall during a night-hike one time
that my headlamp batteries went out so I used my Sony camera like a night-vision
scope to find my way down a precarious outcrop of rock. Looking through the
camera's viewfinder for my next safe perch to land on.

These are also the only cameras that can quickly auto-focus in complete dark.
Along with their "Night-Shot" mode they also have what is called their "Night
Framing" mode. It uses the IR mode with its IR LED floods for you to focus and
frame a shot in the total dark, undetected, but then fires the flash for
properly exposed full-color images.

I also obtained two inexpensive (~ $30-$40 USD) high-power IR floods that Sony
sells for their "Night Shot" capable digicams and videocams. Model # HVL-IRM.
They attach to the hot-shoe but also come with an extender plate so you may
attach it to the tripod socket and have it alongside of instead of on top of the
camera, or use it to stack/gang more than one. They use the same Li-Ion battery
as used in the camera or you can use 2 AAs with them, a switch on the IR flood
to select which power source you want. A full charge, when using either battery
source, seems to last forever. They also have a continuous adjustment dial for
how much IR light level you want. I use those two floods (along with the
camera's built-in IR LEDs) to photograph and take videos of nocturnal wildlife
from as far away as 60 ft. in the total dark. The animals see and hear nothing
while being recorded but you can see your subject clearly in the viewfinder by
the IR light alone. It's the only way to photograph and take video of nocturnal
wildlife without your presence changing their natural behavior. If you put the
ISO mode to Auto then when in "Night Shot" mode the camera will crank up the
gain to ISO3200 when needed. It is grainy but perfectly acceptable for an IR
night photo. It looks like using high ISO film. Images at ISO3200 also clean up
very nice with good noise-removal software. Since it will be a B&W image when
done any color noise is averaged out. You can of course still use all the
manually set low ISOs too for noise-free IR images at night. You would use
ISO100 or 200 for daytime IR photography.

One interesting aspect of IR photography that I didn't know. I was photographing
some vast forest fires in the Rocky Mountains. The haze from the smoke for
hundreds of miles was making seeing the tops of any distant mountains impossible
during the many weeks that we were camping/hiking/kayaking in the area. Putting
on that filter-stack on my Sony camera, clicking the camera into "Night Shot"
mode in the daytime, I could then look through the camera's viewfinder to see
all the invisible distant mountain-tops and glaciers right through all that
dense haze. Appearing just as crisp and clear as if there were no fires. It was
pretty neat to be able to see what nobody else could see at the time. It
afforded some unique images that nobody else could get. Photos of the forest
fires right along with the usual majestic mountain scenery and glaciers.
Everyone else was just getting shots of fires, dense smoke, and nearby hazy
hills that could have taken place nearly anywhere on the planet. My photos
clearly showed where these fires were. They also look all the more artistic and
interesting with the mountain peaks towering over their immense fires below.

While hunting on the net just now for something, I notice that this year's Sony
Cybershot DSC-H50 also has "Night Shot" mode in it, for about $350.

Clipped from that page online:

Sony Cyber-shot DSC-H50 Digital Camera (Black)
9.1 Megapixel
15x Optical Zoom
3.0" Tilt-up LCD Display
Super SteadyShot Image Stabilization
Face Detection with Smile Shutter
High Sensitivity (ISO 3200)
NightShot Infrared System
HDTV Compatibility

  #27  
Old September 26th 08, 07:43 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
nospam
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Posts: 21,134
Default Infrared photography

In article ,
Whiskers wrote:

[1] Some lenses have an IR focus index as well as the visible-light one;
after focusing visually, move the focusing ring so that the distance next
to the usual focus index is next to the IR one instead. If there isn't an
IR index, use the 'closer' depth of field indicator for f/5.6. Of course
with an auto-focus-only or fixed-focus compact camera, you're stuck with
what the camera does, which will be 'wrong' - but the large 'depth of
field' that goes with a tiny sensor might offset the problem somewhat.


it depends on the camera. a compact digicam which focuses off the
sensor itself won't be 'wrong' if there's a bandpass filter in the
optical path.
  #28  
Old September 26th 08, 08:36 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
Whiskers
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Posts: 188
Default Infrared photography

On 2008-09-26, nospam wrote:
In article ,
Whiskers wrote:

[1] Some lenses have an IR focus index as well as the visible-light one;
after focusing visually, move the focusing ring so that the distance next
to the usual focus index is next to the IR one instead. If there isn't an
IR index, use the 'closer' depth of field indicator for f/5.6. Of course
with an auto-focus-only or fixed-focus compact camera, you're stuck with
what the camera does, which will be 'wrong' - but the large 'depth of
field' that goes with a tiny sensor might offset the problem somewhat.


it depends on the camera. a compact digicam which focuses off the
sensor itself won't be 'wrong' if there's a bandpass filter in the
optical path.


Well, I can imagine an auto-focus system based on signals from the image
sensor itself getting focus 'right' for IR if that's all the sensor is
getting. Do many, or any, compacts use that approach to auto-focus? (My
Samsung Digimax V700 appears to use a near-IR 'electronic rangefinder'
external to the image optics). Is
http://electronics.howstuffworks.com/autofocus.htm no longer accurate?

--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~
  #29  
Old September 26th 08, 10:37 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
nospam
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Posts: 21,134
Default Infrared photography

In article ,
Whiskers wrote:

Well, I can imagine an auto-focus system based on signals from the image
sensor itself getting focus 'right' for IR if that's all the sensor is
getting. Do many, or any, compacts use that approach to auto-focus? (My
Samsung Digimax V700 appears to use a near-IR 'electronic rangefinder'
external to the image optics). Is
http://electronics.howstuffworks.com/autofocus.htm no longer accurate?


it doesn't appear that it ever was particularly accurate. it describes
passive versus active, but only mentions contrast detection for passive
and cites an slr as an example. unfortunately, slr cameras use phase
detection autofocus, not contrast detection. since an slr has a
separate optical path for autofocus (via a semi-silvered mirror), there
may be a focus error with infrared.

as for the digimax, i don't have that camera but from a brief look at
dpreview, it looks like it uses contrast detection off the sensor, just
as other compact digicams do, not a separate rangefinder.

here's a more detailed article:
http://en.wikipedia.org/wiki/Autofocus
  #30  
Old September 26th 08, 11:40 PM posted to rec.photo.digital,rec.photo.digital.point+shoot
Whiskers
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Posts: 188
Default Infrared photography

On 2008-09-26, nospam wrote:
In article ,
Whiskers wrote:

Well, I can imagine an auto-focus system based on signals from the image
sensor itself getting focus 'right' for IR if that's all the sensor is
getting. Do many, or any, compacts use that approach to auto-focus? (My
Samsung Digimax V700 appears to use a near-IR 'electronic rangefinder'
external to the image optics). Is
http://electronics.howstuffworks.com/autofocus.htm no longer accurate?


it doesn't appear that it ever was particularly accurate. it describes
passive versus active, but only mentions contrast detection for passive
and cites an slr as an example. unfortunately, slr cameras use phase
detection autofocus, not contrast detection. since an slr has a
separate optical path for autofocus (via a semi-silvered mirror), there
may be a focus error with infrared.


I'm a mechanical type - I understand how a traditional manual-focus SLR
works, and I prefer to use a manual range-finder camera because not only
do I understand how that works, but also I can actually see it working (my
eyesight doesn't go well with SLR viewfinders). I use a point-n-shoot
autofocus digicam, but I don't like not being able to focus quickly and
accurately for myself, as I can with my beloved (but bulky) range-finder
cameras.

as for the digimax, i don't have that camera but from a brief look at
dpreview, it looks like it uses contrast detection off the sensor, just
as other compact digicams do, not a separate rangefinder.


It isn't clear from the user manual; the specification only says 'through
the lens autofocus' but there is also an 'autofocus lamp' on the camera
body. Perhaps that is only there to ensure sufficient illumination for
the TTL 'contrast detection' system to work?

here's a more detailed article:
http://en.wikipedia.org/wiki/Autofocus


That certainly reads better than the 'howstuffworks' article.

--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~
 




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