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  1. #221
    Rudeofus's Avatar
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    Murray, while it is nice to read a voltage which is easily convertible into a temperature, one would still have to use this temperature information to somehow manually correct the pH measurement. The advantage of the thermistors seems to be that pH meters can use these directly to temperature compensate their pH readings. Kirk's post indicates that his method creates a temperature probe working just like this at a fraction of the cost of the original part.
    Trying to be the best of whatever I am, even if what I am is no good.

  2. #222

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    Yes, that's exactly right.

    The LM35 is a nice device, but you want to integrate the temp probe straight into the pH meter and a simple thermistor can do that.

    For future reference, check into one-wire sensors like the ones from Maxim:
    http://www.maximintegrated.com/products/1-wire/
    They have a one-wire temp sensor that sends digital data on the same wire that supplies it power. Hook a small computer to it like an Arduino, and you can make a data logging temp sensor. Also - companies like Maxim will send samples of these just for asking!

    Also, I just got a computer that's the size of a pack of cigarettes called a Raspberry Pi - cost like $50. It runs on USB power, has a 800 MHz CPU, and uses a SD card for memory. Not sure what I'll use it for, but it runs Linux and is pretty cool on the gadget scale!
    Last edited by Kirk Keyes; 09-18-2012 at 12:58 AM. Click to view previous post history.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  3. #223

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    Does PE or anyone else have an idea of how long a latent image lasts in hot weather? We just had a record-breaking heat-wave for a couple of days, and below are graphs of test-strips developed (1) just after exposure and just after the XTOL was mixed, and (2) 19 days later. The house has no air-conditioning, so the temperature has been 25-30 most of the time, getting a little above 30 during the heat-wave.

    Click image for larger version. 

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    Does that graph look like a latent image that has deteriorated? Notice that the toe has dropped a little. I'm wondering if the latent image has faded, or if the XTOL has weakened. The XTOL was from a completely filled unopened bottle, and my own developers are also delivering lower than expected density, so I'm suspecting the film, but wanted confirmation of this based on the graphs.

    Mark Overton

  4. #224
    Rudeofus's Avatar
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    Mark, take a look at this thread ....
    Trying to be the best of whatever I am, even if what I am is no good.

  5. #225
    Photo Engineer's Avatar
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    Mark;

    Film was not designed (for the most part) to be exposed and processed. The assumption is that there will be a reasonable lag between exposure and development. This lag is on the order of a minute or so, not seconds. On the other end, the LIK is supposed to be stable for up to a year or so, and I have verified this myself. Hot weather does make it worse.

    Stephen's data in the reference from Rudi shows pretty much what I have seen, only his effect is more pronounced at longer times (days). Of course I refer to Kodak film, and we always over designed Kodak film to exceed ANSI standards. I did not see a reference to the type of film used in the referenced test, but you will find that id varies quite a bit from product to product.

    That said, I suspect it is LKI due to a short time in the first test and a long time in the second. You might try exposing and then waiting about 2 hours and then processing. Something like that. Or, you could make up a batch of test strips at the same time, keep them for 1 day, and then freeze all but one. Use that one as the base and then take one from the freezer and use it as your reference when you need one. Make sure you protect all film from moisture, freezer burn, and also make sure you thaw it properly before use.

    PE

  6. #226

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    @Rudeofus:
    Wow! Thanks for the pointer to that great thread. I had no idea that the latent image decayed rapidly in the first minutes and hours after exposure.

    From now on, I'll certainly wait hours, if not 1-2 days, before developing the first frame. In my graphs, the first strip was developed 30-60 minutes after exposure, which was too soon. And I've been creating developers all this time that have been pushing a mildly decayed image up to that level, and actually got good results.

    Quote Originally Posted by Photo Engineer View Post
    Mark; Film was not designed (for the most part) to be exposed and processed. The assumption is that there will be a reasonable lag between exposure and development. This lag is on the order of a minute or so, not seconds. On the other end, the LIK is supposed to be stable for up to a year or so, and I have verified this myself. Hot weather does make it worse.
    Stephen's data in the reference from Rudi shows pretty much what I have seen, only his effect is more pronounced at longer times (days). Of course I refer to Kodak film, and we always over designed Kodak film to exceed ANSI standards. I did not see a reference to the type of film used in the referenced test, but you will find that id varies quite a bit from product to product.
    Do you mind if I quote you out of context as saying, "Film was not designed to be exposed and processed."? That'll make people ask, "Then what is film designed for?"

    Quote Originally Posted by Photo Engineer View Post
    That said, I suspect it is LKI due to a short time in the first test and a long time in the second. You might try exposing and then waiting about 2 hours and then processing. Something like that. Or, you could make up a batch of test strips at the same time, keep them for 1 day, and then freeze all but one. Use that one as the base and then take one from the freezer and use it as your reference when you need one. Make sure you protect all film from moisture, freezer burn, and also make sure you thaw it properly before use. PE
    I've been reluctant to refrigerate or freeze exposed film for fear of forming condensation. Do you think the 35mm cartridge could be refrigerated if I first drove some inert gas into the can to drive down the humidity? BTW, I pull each frame out of the 35mm cartridge as needed, counting 8 sprocket-holes so the cut will be on a frame-boundary. A 36-shot roll can last a while this way, so refrigeration is tempting. OTOH, I could pre-cut the frames as you describe above, but I'd need a light-free container of some kind, and condensation would still be a worry.

    Thanks for these responses. They are obviously helpful.

    Mark Overton

  7. #227

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    I have a number of plastic film cans that I purchased a few years ago. I have never had any problem with condensation with film stored in them either refrigerating them or even freezing them. If refrigerated I allow 2 hours for film in them to come up to room tenperature or overnight if they are frozen.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  8. #228
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    Mark;

    Pack each exposed strip in a separate plastic package, then pack all of the strip/bag combinations in one big bag and then freeze. Thus you only have to remove one to thaw. This should work. And, I agree with Jerry. There should be no problem.

    PE

  9. #229

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    Jerry and Ron,

    I shot a new roll last night, and it's in a metal can to age a little.
    Assuming I have 38 black plastic/metal film cans (from Fuji etc.), and if I can figure out how to reliably measure and cut the frames in the dark, I'll cut 'em up and freeze them.
    Thanks for the idea.

    BTW, do you know if the latent image can decay rapidly at some point in time? My images were consistent until the two-day heat-wave, and then they nose-dived. It's as if some threshold was crossed causing rapid decay.

    Mark

  10. #230
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    Mark;

    Kodak uses frozen strips sent to customers as reference control strips. A frozen image has virtually no LIK at all.

    PE



 

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