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#21
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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
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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
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"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
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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
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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
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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
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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
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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
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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
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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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