Atelier Bonryu(E)

infrared photography

 
 

Laboratory: Infrared Photography

Taking Infrared Photographs

2-4 Full Spectrum Camera

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Wavelength of Light and Sensitivity of Sensor: As described previously the sensor of a digital camera can perceive the infrared and the ultraviolet lights whose wavelengths are outside the range of the visible lights.  Therefore, a photograph of an object looks different from what we see directly by our naked eyes if the sensor of the digital camera records the incident lights of these wavelength.  To avoid this phenomenon an infrared cut filter is placed in front of the sensor so that it records an image produced only by visible lights.  As this filter does not block the infrared light completely, we can take an infrared photograph by blocking a visible light and using the scant infrared light passing through the infrared cut filter of the non-converted camera, which was the scenario we took an infrared photograph by using an non-converted digital camera.  Unfortunately, long exposure time is necessary for this method because the intensity of the infrared light coming at the sensor through the infrared cut filter is very weak.  The necessary multiplication factor of the exposure time over the visible light photography  is from several hundred times to several ten thousand times as described previously. 


To overcome this difficulty there are two methods.  One is to replace the infrared cut filter by an infrared-transparent and visible-cut filter.  And the other method is to replace the infrared cut filter by a clear and colorless glass filter, and put an infrared-transparent and visible-cut filter in front of a taking lens.  In the latter case the converted camera is called a full spectrum camera, because the camera can take a photographic image of the full spectral light which the sensor can perceive.  The range of the wavelength is from the near ultraviolet to the short wavelength part of the near infrared lights.  This corresponds to the wavelength range from ~300 nm to ~1000 nm,  which is far larger than the wavelength range of the visible light, i.e., from ~400 nm to ~700 nm.

Full Spectrum Camera and Dedicated Infrared Camera: There are good and bad points in both the above methods to convert a camera to infrared-sensitive one.  The good point of a full spectrum camera is, at all events, that an external filter put in front of a taking lens can is changed freely  and one can take a photograph for a various wavelength range.  Though a converted camera dedicated for infrared lights can be used only for infrared photography, the full spectrum camera can be used for taking photographs from ultraviolet to infrared lights.  On the other hand, an advantage of a camera dedicated for the infrared photography  is easiness of operation in comparison to a full spectrum camera.  One of problems of the full spectrum SLR camera is that a photogenic object cannot be seen through an optical finder when an external visible-cut filter is put in front of the taking lens.  In the case of an infrared-dedicated camera we are not suffered from such a problem because an external visible-cut filter is not necessary, and we can decide a picture composition viewing the object through the optical finder.  However, recently many SLR cameras are equipped with live-view finders which display the images by the light passing through the taking lenses and the image sensor, which solves the above problem.  Moreover, there is no such problem when we use a single lens mirrorless camera which becomes widespread recently.

Conversion of Camera: It is not necessarily very difficult to convert a camera to a full spectrum or an infrared-dedicated one by replacing an IR cut filter by a clear colorless glass filter or a visible cut IR transparent filter.  There are some web sites where conversion process is described, and in books on Digital Infrared Photography  such as “Digital Infrared Pro Secrets” by D.D. Bush it is also described.  But this conversion should be carried out with the greatest possible care because a sensor is the heart of a camera and such a conversion will repudiate warranty for the camera.  Therefore, it may be a good choice to ask a camera conversion company to convert a camera.  Examples of such companies are LDP, Life PixelSpencer’s Camera & Photo, and Kolari vision, which are often mentioned in books or web sites on Digital Infrared Photography.  To these companies I ordered the conversion of a camera (Lumix DMC-TZ30) or purchased converted full-spectrum cameras (Olympus E-620, OM-D E-M5), which work now satisfactorily as full-spectrum cameras.

Full Spectrum Olympus E-620 : As Olympus E-620 is equipped with a live-view finder an image of a photogenic object can be seen on a LCD monitor even when a visible-cut IR transparent filter is put in front of a taking lens.  AF can be operated for the image on the LCD monitor (imager AF).  In the user’s manual it is described that the imager AF is usable only for a limited number of compatible ZUIKO lenses.  I am using regularly ZUIKO DIGITAL 18-180 mm F3.5-6.3 zoom lens but this lens is not in the list of the imager AF-compatible lenses.  However, the imager AF can be operated during the enlarged display operation mode.  Therefore, it is not practically inconvenient to take an IR photograph by using the above zoom lens with E-620 fs.  Though it is a full spectrum camera an image on the LCD display becomes rather dark when an external visible cut IR transparent filter is used.  Therefore, in such a situation it is necessary to brighten the monitor by making the live view boost on.  Moreover, it should be remarked that the appropriate light exposure can not determined automatically for an IR photograph.  Generally, measured light exposure is lower than actual one when the visible cut IR transparent filter is used.  Therefore, an overexposed photograph is taken when the measured value of exposure is adopted.  According to may experience exposure compensation of -1 ~ -4 EV is necessary.  Please visit Gallery to see photographs taken by using E-620 fs.

Filters: For the infrared photography I use the infrared filter IR76 mainly and, sometimes, the sharp cut filters, SC70 and SC66.  These sharp cut filters were used at one time for the infrared photography by an analogue camera. As an external filter I use the same visible cut IR transparent filter used for the infrared photography by the non-converted camera.


By the way, if we take a photograph by the full spectrum camera without an external filter,  we obtain a full-spectrum image of an object similar to a photographic image taken by a conventional non-converted camera but it seems rather out of ordinary because coloring is considerably different due to existence of the infrared light.  Therefore, if we would like to take an ordinary photograph by the visible light it is necessary to put a visible transparent IR-UV cut filter before the taking lens.  Several filters for such a purpose are now obtainable (Marumi ir-uv cut filter, B&W 486 uv-ir cut filter, Maxmax X-NiteCC1, CC2, etc).  These are interference filters made of multiple interference layers and steep transmission edges.  Graphs of transmission vs. wavelength are published on internet except for the Marumi filter.  Though I have not measured the performance quantitatively, the filters of Marumi and B&W have given almost the same results qualitatively.

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Full Spectrum Olympus OM-D E-M5: The second camera I converted is Olympus OM-D E-M5.  As this camera is a single lens mirrorless camera and it is equipped with an EVF (electronic view finder) an infrared image of an object can be seen through the finder even when a visible cut filter is set in front of the taking lens.  Because the live view screen of the E-620 may not be considered important when designing this camera, the live view screen becomes heated within a short time and, moreover, it is difficult to see in a sunny place.  However, in the case of E-M5, there is no such difficulty and it can be very easy to take an infrared photograph as taking a visible light photograph.

Full Spectrum Panasonic Lumix DMC-TZ-30:  DMC-TZ-30 is a point-and shoot camera and there is not a screw for mounting a filter.  Therefore a step-up ring was glued to the lens-barrel to fix an infrared filter in front of the lens (Fig.2-8).  This camera can be used for the infrared photography very satisfactorily.  In order to avoid that an asymmetric torque damages the lens barrel when it is withdrawn several circular cushions are glued to the back of the step-up ring (Fig.2-9).

Fig.2-8 The IR converted DMC-TZ-30 camera with a screw mount made of a step-up ring

Fig.2-9 The IR converted DMC-TZ-30 camera with a screw mount made of a step-up ring

On the back surface of the step-up ring small cushions are glued.