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In article <(E-Mail Removed) .net>,
DaveC <(E-Mail Removed)> wrote:

> I want to photograph and video in infrared mode.
>
> I understand that some point-and-shoot cameras provide this style of
> photography/videography. Alternately, some people have "hacked" a camera by
> removing the IR filter from in front of the imaging element. There are
> instructions on-line to DIY this, or to send in your P&S to have it done.
>
> Basically, the IR filter is removed and replaced with another (not a
> procedure for the faint at heart). The replacement filter is $$$.

yea, and the price has dramatically increased in the past year or so.

> My question is this: is this replacement filter that passes rather than
> blocks IR available as a gelatin or other commonly available filter that I
> can source elsewhere other than from these camera-mod services?

sure. generally it's 2mm thick optical glass that's typically a 2" or
3" square piece and you'll need to cut it to fit the camera.

> Or can I just strip off the existing filter and not replace it with anything?
> I'm looking for quantitative data (the existence of IR) not qualitative data
> (a pretty picture). What function does the replacement filter provide (other
> than passing IR data)?

you can, but the focusing might be adversely affected.

> To clarify, I want to "see" IR images real-time in the viewfinder, not
> post-process the image data to reveal the IR.

that's exactly what you'll get.

In article <(E-Mail Removed) .net>,
DaveC <(E-Mail Removed)> wrote:

> > sure. generally it's 2mm thick optical glass that's typically a 2" or
> > 3" square piece and you'll need to cut it to fit the camera.
>
> Seems straightforward (notice the absence of the term "simple").

if you know how to cut glass it should be fairly easy. however, opening
up the camera to replace the filter is usually not easy at all.

> Can you give a URL for such a piece?

here's a few:
<http://www.alpineastro.com/filters/filters.htm>
<http://www.controloptics.com/product_colorglassfilters.htm>
<http://www.edmundoptics.com/onlineca...cfm?productID=
1918>

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

it should. if it's not that close, you might lose either infinity
focus or close-up focus, but stopping down should compensate for that.
depending on the camera, the autofocus might need adjusting.

the other problem is the only way to know how thick a filter to get is
open up the camera and measure it. it varies depending on the camera,
and sometimes it varies with the *same* camera, depending on the
revision. i've also heard of using microscope slides to match the
thickness.

"Dave Platt" <(E-Mail Removed)> wrote in message
news:dg9vq5-(E-Mail Removed)
> In article <(E-Mail Removed) .net>,
> DaveC <(E-Mail Removed)> 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

On 2008-09-26, James Silverton <(E-Mail Removed)> 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
-- ~~~~~~~~~~

In article <(E-Mail Removed)>,
Whiskers <(E-Mail Removed)> 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.

On 2008-09-26, nospam <(E-Mail Removed)> wrote:
> In article <(E-Mail Removed)>,
> Whiskers <(E-Mail Removed)> 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
-- ~~~~~~~~~~

In article <(E-Mail Removed)>,
Whiskers <(E-Mail Removed)> 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>

On 2008-09-26, nospam <(E-Mail Removed)> wrote:
> In article <(E-Mail Removed)>,
> Whiskers <(E-Mail Removed)> 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
-- ~~~~~~~~~~

In article <(E-Mail Removed)>,
Whiskers <(E-Mail Removed)> wrote:

> It isn't clear from the user manual; the specification only says 'through
> the lens autofocus'

that's the key. it's off the sensor, not something separate.

> 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?

yep.