Strange continuous drive issue with DCS 760

Discuss older Nikon-based Kodak digital SLRs, including DCS 100, DCS 200, NC2000, DCS 400/600/700-series, etc. Ask questions, post general comments, anecdotes, reviews and user tips.
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Anssi Krooks
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Strange continuous drive issue with DCS 760

Post by Anssi Krooks » Thu Nov 10, 2005 6:49 pm

http://turbaani.1g.fi/kuvat/Junat/04101 ... 2.jpg/full

This is quite typical result when shooting with continuous drive with my 760. The first picture is perfect, but the rest look more or less like this. Same thing happens also in S-drive when taking picture right after another. Everything else works perfectly with newest firmware, so I suspect that this is a card issue (I'm using standard Sandisk 1 GB cf with pcmcia-adapter), but has enyone else experienced similar problems? To me this is not so important, because I don't use continuous drive. Howerer this is quite annoying when it happens.

Stan Disbrow
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Location: Raleigh, NC USA

Post by Stan Disbrow » Thu Nov 10, 2005 9:52 pm

Hi,

Looks more like an issue with the CCD analog-to-digital readout section, or the buffer memory than the CF memory card.

The camera does not take the data off the CCD and put it straight out to the PCMCIA card slot, but sticks it into another type of memory within the camera first.

The buffer memory is dual-ported, which is a fancy term to mean that it can be read from one end while it's being written to at the other. If it gets 'out of whack' when opetating in dual-port mode, which is has to to store shot #2 while writing shot #1 to the CF card, then I can see where it'd screw up the data like that.

It could also be a clock timing issue with regards to the bucket-brigade of data out of the rows of the CCD itself. The energy from the light to electrical conversion is stored in capacitors, which are like little buckets, at each pixel site. When the chip is read, the electrical charge is moved from one cap to the next until it reaches the end of the line, where the charge is converted into a digital value by the A/D converter, which is then sent to the buffer memory.

If the timing get off with respect to the bucket brigade, you can offset the A/D reading such that early pixels have no value, and are black, while pixels at the end get lost. that'd account for your offset in the data in the sample image, but there's something odd about it.

The Kodak CCDs read 'full frame' which means that they take all the data off one end of the chip (as opposed to off opposite sides of the chip in even/odd rows in the case of interleaved chips). If there's a timing issue with the data clock, I'd expect to see the same cut off of data in the entire image, as in a black line down the entire side, not stepped like you have it. I'd also expect it to happen on all shots as well, not just ones taken quickly after another.

The entire first shot has to be read out thru the A/D converters and the chip completely cleared before the next shot can be made. The only place I see where a fault is likely occuring is in the buffer memory.

If you think it's the CF card, then there's an easy test you can try: Just change to a couple other cards of different sizes and speeds and see if the problem occurs on all of them or not. If it happens all the time, with multiple cards, then I'm pretty sure that you have an issue within your buffer memory inside the body......

Now, if the camera has a problem, I'd say it's time to go on eBay and get another one. They're selling so cheaply these days that it's far less costly to biy a replacement than to send the thing off for repair....

Stan
Amateur Photographer
Professional Electronics Development Engineer

Anssi Krooks
Posts: 54
Joined: Wed Aug 24, 2005 2:45 pm
Location: Espoo, Finland
Contact:

Post by Anssi Krooks » Fri Nov 11, 2005 7:27 am

Hi,

Thanks for your reply. After reading it, I'm also convinced, that this is a camera issue, but I'll test another cf later. I discovered this iproblem a year ago when I first time played with continuous drive (1,5 fps KATHUNKATHUNKKATHUNKKATHUNK ;)), after that I have made 20 000 actuations (62 000 altogether) without a fail, so I just hope that this problem doesn't get worse. These Kodaks are risk investments for "real" use: IIRC, I heard that replaicing shutter here in Finland costs 999€ (about the same in $). ;) Maybe it's time to retire 760 and go for D200.

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