Archived posting to the Leica Users Group, 2006/12/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Lucien.....I read through the entire Kodak datasheet on the sensor..... It is very interesting ( for those of us that like these things). Warning to others..... Tech Talk going on here......Use Delete key as required dependent on your personal constitution.......WARNING>>>> Very nerdy, tech talk going on here...... The section you quoted is the description of how the light gets put into electrical signals for the camera. It refers to the over-charged functions. What happens when too much light hits the sensor and it overloads.... ( and gets dumped into an overload area on chip to be dumped later). The black bias offset is done using pixels outside the image area. There is an area in there that is covered by the blue mask. Could be used for IR correction SW. ( nice touch Kodak!) Nice graph of spectral response of the bare chip with standard cover glass installed ..... Leica is a special case, so this chart is not the one for the M8..... But there is another graph of quantum efficiency with increasing oblique angle of light that is just plain fascinating.... at 33 degrees from perpendicular, the QE drops to 50% of perpendicular. As this is a known effect, a calibration can be done to null out the effect, if you know what lens has what is the amount of the oblique rays. Thus a reason for the lens coding, if Leica uses this functionality. Lest I drive some poor digital guy nuts, I will not comment on the number of defect location that are acceptable on the chip....... I further chased the application information of this chip. There is an evaluation board, but the tech info for the board is not on line. So I went to a similar sensor, the KAF-31600. While not the same sensor as Leica, the in-application use of the two parts should be the same... so here goes.... Now for those that wish to not read tech talk.... go away... push delete.....do not read......if you do read, do not make a fuss just because it is tech talk.... The app board shows the integration of the device with a Altera PLD logic device to program and code the sensor so you can get something into and out of it. In real applications, it is most likely that the logic device would be supplemented by a uP, but maybe not. You might need both the logic device and the uP to make a real M8 In any event, the app board shows timing, signals, and to some degree, how the system actually operates. Mind you, I am reading the Kodak info, I am not reading a Leica tech write up on the M8... The Altera device may be in circuit programmable. ( Altera have both "field" programmable and non-changeable coded devices.). In addition, some of the filed programmable parts are not really field programmable but programmable in the factory. This may be the device that needs to be updated by Leica for the Germany recall for various striping issues..... I am not going to get into the 1's and 0's of the application. ( It would bore even me...) But I am going to call out some signals and their purpose.... First the Integration clock. A 1ms ( precision) pulse that is used to set internal timing in the sensor, and " May also be used to control precise integration times for the image sensor." The timing of the integration of the light into a electronic signal is controlled by this. This is part of the shutter speed timing circuitry. After the integration time is complete, the frame is transferred to the outputs. ( the image is actually recorded during the integration time ALL ELEMENTS AT ONE TIME.) This is important because it really tells us that the entire sensor array is collecting photons at the same time... so a slit shutter can NOT work with this sensor. Further, there is an auxiliary chip that sets timing for the CCD ( KSC-1000). The datasheet is a bit older, but assuming it is still correct, it gives more information on the operation of the Integration function... " INTG_STRT Setup Register Electronic shuttering is used with the Kodak family of interline sensors. The figure below illustrates the electronic shutter timing with respect to the image sensor horizontal and vertical clocks. " It gets MUCH more nerdy after this.... so enough already..... Since, according to drPreview, the "shutter" in the M8 seems alike to the shutter in the R8 ( R9 ?), then I can makes some comment on the M8 shutter .... If the shutter on the R8 is fully open at one time up to 1/250 of a second, and then goes to a slit shutter for high speeds; and if the shutter in the M8 is the same or basically similar, then the maximum mechanical shutter speed available in the M8 is the same, 1/250. This is true because the M8 must have the entire sensor active at one time to get an image. A slit shutter will not work. Further, there is no higher speed on the mechanical shutter on the M8 than the 1/250 of a second, or what I call a fully open shutter. Talking flash, there still is no reason for limiting the flash to a shutter speed 1/250 that is obvious at this point. Second the Flush commands..... This is a set of commands to flush the entire sensor array from residual charge. Basically a no light - black bias point. This precedes the actual integration timing, and sets up the sensor for image collection. OK, I could go further, but I think tech time talk is over. Ted is probably drinking his Single malt and finished the bottle after all this stuff. But I have proven to myself, using the available technical information published by Kodak, that the M8 is a fully electronic gated sensor/shutter. That the mechanical shutter is used for some purposes, but it has nothing to do with the operation of image capture. It is a baffle. I am still open to correction and further information may require that statement by me. But at this point, it is pretty clear to me that the image capture in the M8 is totally digital. That the shutter has no purpose in image capture, and therefore I call it a baffle. What does all of this mean? That your M8 should never have to go to the shop for a shutter CLA to make your camera capture images. Not much more. But I did have a really good time reading timing charts and understanding how the sensor works..... What's a few hours of quiet reading worth? Priceless? Frank Filippone red735i@earthlink.net INTG_STRT Setup Register Electronic shuttering is used with the Kodak family of interline sensors. The figure below illustrates the electronic shutter timing with respect to the image sensor horizontal and vertical clocks. Tel, the electronic shutter setup time, is the time from the end of the horizontal clocks to the start of the electronic shutter pulse. Ts is the electronic shutter pulse width. Tsd, the electronic shutter hold time, is the time from the trailing edge of the electronic shutter pulse to the start of the vertical clocking interval. Note that the line time on which the integrate start pulse is generated is extended by the setup time, shutter pulse width and hold time. Tvccd and Thd are the standard vertical clock pulse width and delay time from the completion of the vertical clock sequence to the start of horizontal clocking. These times are defined in the Line Tables.