Saturday, August 25, 2007

Modify the Sony 717 for IR -- Reassembly

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Pin and cog wheel. Pin P and cog wheel T in the part of the hot mirror chamber that is still connected to the main lens assembly. P and T move the hot mirror stage (the 'click' you hear when Nightshot mode is enabled or disabled). Study this very well, because the camera will only function if you assemble the stage with the correct positions of the cog wheel and hot mirror stage. If the position is wrong, you cannot close the hot mirror chamber, or you will lock the stage in the wrong position (making it impossible to move the hot mirror, which again makes it impossible for the camera to focus).

Reassembly. Now reassemble the camera in reverse order. Check the inside of the hot mirror chamber for any dust etc. before it is closed. If you have problems closing the chamber, the inside mechanism is probably in the wrong position. When mounting the CCD sensor PCB, make sure that you put the flex cable IN the connector and not BELOW the connector (between the connector and the PCB). This is not easy to see, you can lock the brown clamp even when the cable is inserted in the wrong place. If you make a mistake the CCD image sensor will not work (camera powers up with black LCD/viewfinder) and the sensor may possibly be damaged permanently. Check connector with inserted flex cable very carefully before you continue!

Modification complete! Insert the battery, power up the camera and check if everything (including hot mirror movement in Nightshot mode and focusing) is working normally. The DSC-F717 is now fully infrared-enabled and you can use all program modes for infrared photography. Instead of Nightshot's 1/60 sec. or longer exposure, you can now use any shutter speed for infrared photography. Even with the strongest infrared filters you can take pictures handheld, no tripod needed! Most camera functions will work as before the modification, including exposure and autofocus.

Using filters: Mount the filter of your choice on the lens to select the desired wavelength band. For normal photography with visible light (400-700 nm) use no filter at all or an external hot mirror filter. Standard white balance settings like sunny, cloudy etc. will be off unless you use an external hot mirror, but most of the time setting a custom white balance will solve this. For infrared (700-1100 nm) use an infrared pass filter like the Hoya or B+W filters. Theoretically you can take UV pictures as well, but filters that pass just UV light (below 400 nm) are expensive, and the 7x7 zoom is not the best choice for UV photography. Make sure you use a lens hood for infrared, because the camera will be more sensitive to internal reflections, hot spot etc. caused by infrared light. Use the highest JPEG quality (or TIFF if you can stand the write times); this will help when postprocessing. Because of diffraction effects, it is best to use apertures between f/2.0 and f/4.0. With smaller apertures, resolution will suffer. With infrared this is more of a problem than with visible light because of the longer wavelength.

IR Filter choice: If you are new to IR photography I recommend using the Hoya R72 or similar filter; it is high quality, relatively cheap and will work with almost every digital camera for IR photography. For pseudo-color IR photography with the (modified) 7x7, use a filter that transmits both infrared and some visible light, like Hoya R72, B+W 092, Wratten 89B. I recommend setting a custom white balance with the IR filter installed. If you don't do this there will be a strong color cast that can give problems with processing. You can also experiment with filters like 025 red, 099 infracolor, 403 dual band filter etc. However, with these special filters the 7x7 cannot provide a neutral in-camera whitebalance, making postprocessing difficult. Pseudo-color IR with the 7x7 is not easy because there is often very little color present to work with; check my pbase website for some examples. Filter Info

For black-and-white IR photography I prefer the stronger filters like B+W 093 and Hoya RM90 as they usually give a stronger IR effect and often more 'punch'. Of course one can also use an R72 filter and choose at a later time if B/W postprocessing is desired. I also tested some cheap infrared filters that are sold on Ebay. They work, but I found the results disappointing compared to similar Hoya filters. The cheaper filters transmit less light (1-3 stops difference) and the contrast is often lower, requiring more postprocessing. Your mileage may vary though ... other people seem to be happy with these filters.

External hot mirror: Because the internal hot mirror was removed, color accuracy and sharpness can suffer when working in visible light because of infrared contamination. This will show as a orange/brown coloration of green foliage and grass, a shift of the blue sky color to cyan and reddish/brown coloration on certain black metal parts or fine fabrics. This problem cannot be completely solved by adjusting the white balance. In my experience, an external hot mirror is only necessary for optimal color in bright sunlight (in summertime) or with other strong IR source (check my pbase site for more details). Hot Mirror Details

Using converters: With a standard 7x7 in Nightshot mode, using converters is not an option. With the modified 7x7 converters can be used, but attention is needed for best results. If you are using an infrared filter it will increase the distance between converter and lens, causing loss of corner sharpness and sometimes vignetting. Stopping down will sometimes cure the corner problems, but using small apertures is generally not recommended. Instead of the usual glass IR filters I now often use polyester IR filters, cut to size, for better corner performance (especially at wide apertures). When using optical converters corner resolution may also suffer because they are not well corrected for the longer IR wavelengths, causing the light to 'smear' in the corners of the image. High quality wide converters like Olympus WCON-07 and Raynox DCR-7900pro (effective focal length 27-30 mm) work very well; picture quality in infrared is much better than with the wideangle zoom setting of the Sony DSC-H9 that I tested earlier this year. Make sure that you don't stop down too much, just 1-2 stops down from full aperture usually gives the best results. Converters like Raynox DCR5000 (effective 19 mm equivalent!!) give a huge field of view (dynamic perspective), but corner sharpness is low even when stopped down; for some subjects the soft corners will be a problem.

My experience with tele converters in infrared is less favourable; even the high quality converters like Olympus TCON-17 give a big drop in resolution outside the center of the image. The major cause of this is probably chromatic abberation in the Sony Zeiss lens at tele settings, as the same problem appears at the tele end of the zoom (without any converter added). Still the modification helps, because you are now able to take IR pictures handheld in tele position, instead of the former situation where getting a blurred image due to camera shake was unavoidable.

My Final thoughts: why choose the DSC-F7x7 for infrared, and not a more recent digicam? The 7x7 has a relatively large imaging sensor, high quality f/2.0 Zeiss lens, and plenty of user control, while being relatively easy to use. For infrared, a big image sensor and bright lens help to keep noise levels down (without using aggressive noise reduction like in most recent digicams). Many 7x7 owners now probably have a DSLR too, which makes it even more attractive to dedicate the 7x7 for IR photography (and besides, it can still take normal pictures if necessary!). You may get better IR picture quality with an IR-converted DSLR, but the 7x7 is a flexible tool and is much easier to use compared to an IR-DSLR with its framing/focusing/exposure issues.

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