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Old May 1, 2005, 1:27 AM   #1
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I've had my *ist DS for about two weeks and have been extremly happy with the camera. I however have found one very interesting issue.

When taking long exposures, over 15 seconds in JPEG Best mode, my card reader on my pc won't read the files, SANDISK 1 GB card. I can still hook the camera up via USB and get the data. Can anyone else see if this occurs with their cameras? I'm trying to find out if this is a problem with the camera or firmware in general, or just a problem with mine.
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Old May 1, 2005, 5:21 AM   #2
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When an image is saved it's irrelevant how long the exposure was; the charge on the CCD i.e. RAW data is, converted & saved into JPEG.

You say that the files can be transferred to the PC vis the USB camera interface; presumably, you can then read OK in a graphics package.

Try using a different card reader or SD card.
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Old May 1, 2005, 6:41 AM   #3
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The only problem i have is for some reason the length of the xposure is about how long it takes to write to the sd card. Like if i have for 3s, it takes about 3s to write it, if i take it for 20s it takes aboutg 20s to write. Any reason?
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Old May 1, 2005, 4:53 PM   #4
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Most modern Digital Cameras invoke a dark frame subtraction noise reduction system for longer exposures to map out hot pixels (pixels that are reading at a value that is too high). Unfortunately, hot pixels are a problem for Digital Cameras, with more pixels impactedas exposure lengths increase.

This type of system makes note of the exposure length when youtake a photo. Then,it takes adark frame photo (shutter closed) for the same amount of time.

It then locates any hot pixels in the dark frame exposure (since hot pixels are common with longer exposures) and maps them out in the actual exposure by interpolating values from adjacent pixels to replace them. It knows where hot pixels are likely to be in the actual exposure, since it can more easily locate them in the dark frame exposure.

Since the tw0 exposures are for identical lengths of time, taken at the same time, with the camera at the same temperature, thechances of any hot pixels being in the same pixel locations is very good. That's how this kind of system can be effective (to a point). But, the longer the exposure, the more likely it will miss some hot pixels (pixels that are hot in the actual exposure, but not in the dark frame exposure, and vice-versa).

Not long ago, cameras didn't have this type of system. So, for longer exposures, you'd need to take your own dark frame (with the lens cap on), and use software to compare and map out the offending pixels.

In any event, that's what you are seeing when you see it take just as long to complete processing an image, as it does to take one. It's not the write times, it's the taking of a dark frame exposure and processing your actual exposure to replace hot pixels found. With noise reduction enabled, if you take a 20 second exposure, it's going to take a second 20 second dark frame exposure with the shutter closed (for finding the locations of hot pixels).

As for the Original Posters problem (files unreadable), I'd suspect corrupted media. For example, if you interrupted a write in progress, it may corrupt the image in a way that some devices have problems reading it. I'd suggest formatting the card with the camera before using it again to see if that fixes the problem.


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Old May 1, 2005, 7:47 PM   #5
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JimC wrote:
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Most modern Digital Cameras invoke a dark frame subtraction blah-blah-blah....
Thanks for info, Jim. I never know it before
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Old May 2, 2005, 1:45 AM   #6
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I have duplicated the experiment with my 128mb Lexar card. Same results. The write is not being interrupted, and the issue is repeatable after multiple formatts. When taking normal time range exposures, less than a second, I have no problems. On the longer exposures I can read the data using the USB cable to the camera. I don't doubt that there may be a problem with my camera, the reader, or my drivers. It was for this reason that I asked if someone else could try and duplicate the issue with their system.

I was previously state thanks for the lesson on how the camera processes data on long exposures; I'm an electrical engineer in my day job, and I find this kind of information great.


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Old May 2, 2005, 2:53 AM   #7
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mgarula wrote:
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I have duplicated the experiment with my 128mb Lexar card......
You mean that you can not read data at all? I.e. you got I/O error? Or you can transfer data to PC, but can not open pix to see it? Actually both sounds very strange indeed considering that you can transfer data from camera via USB cable. Going to check mine today
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Old May 2, 2005, 3:34 AM   #8
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I get an I/O error. The PC responds that the card is not formatted. I'm wondering is after a minute of CCD activity, 30 secs for exposure, 30 secs for Hot Pixel Correction, if the NiMh batteries are writing at a lower voltage. If they are writing 1's at only slighly over VOH, and a similar system would be the 0's may not be discharged to below VOL. If the data is read in the camera using a differential circuit aprouch the data may still be intack when read from the PC, but the data coupling to the PChostis degraded,
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Old May 2, 2005, 4:32 AM   #9
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mgarula wrote:
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...the NiMh batteries are writing at a lower voltage...
You can easy check this in two ways. You can use AC adapter or if you have not got one you can use fresh CR-V3. Will try to check mine anyway.
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Old May 2, 2005, 7:19 AM   #10
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Well, I checked around some of the other forums (performing searches for posts mentioning long exposure), and I have not come up with anyone experiencing this problem (even where camera owners are using even longer exposureswith Bulb).

Are you using known good high capacity NiMH Batteries?

I have seensimilar problems in the past with some media types, in some cameras due to compability problems with media.

But, since you've tried more than one memory card, I'd be inclined to suspect you've got a defective camera if the batteries are good (perhaps something in the voltage regulation circuitry, since your voltage theory seems to make sense).

If a different set of batteries doesn't solve it, I'd be inclined to return it for repair.

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