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  1. #11

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    I have an Escali Liberta that I bought cheap on eBay. It's got a capacity of 100g, a precision of 0.05g, and the accuracy seems OK (at least, it consistently gives me the same reading when I weigh the same object). It comes with a 50g calibration weight. I fully expect it'll die sooner than would a more expensive model. If I were doing it again, I'd probably go one of two routes:

    • Buy two cheap scales: One with 0.01g precision and (probably) 50g or less capacity and a second with 1g or coarser precision and a capacity of over 100g.
    • Buy a more expensive scale with 0.01g precision and 100g or greater capacity.


    In cheap scales, as precision improves (that is, goes to smaller numbers), the capacity goes down, and vice-versa. The problem is that when mixing photochemistry, you sometimes need to measure large quantities of stuff (say, sodium thiosulfate for a fixer), but you don't generally need great precision when making such measurements; and other times you need to measure small quantities (say, small fractions of a gram of phenidone for some developers) with high precision. Thus, a single cheap scale won't do a good job unless you split up the big stuff into multiple batches, create percentage solutions of the small stuff, or both. The Escali scale I bought is something of a compromise, with its peculiar 0.05g precision and 100g capacity, but I think two scales or a single more expensive and capable scale would do better.

  2. #12
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    I bought an Ohaus on eBay. Looked great in the picture. Description was 'excellent'. It's basically a $30 paper weight. Needs service. The service will come close to what a new scale would cost. Avoid the temptation of buying a used mechanical scale on eBay. I believe that that is a hit or miss proposition, and the money is better spent on a new scale from a reputable dealer.
    YMMV
    Neal

  3. #13
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    Weighing precision in photography is rarely needed. And most of the scales floating around are "consumer" scales with enough accuracy - pick up a test weight (200g) does not need to be certified.

    I sell scales for a living - all of them would be overkill for photography. An old mechanical would also be fine. Understand that a "good" load cell is at least $70 - that is the heart of the scale. Then put a cabinet around it and electronics to do the conversion and then the math ... a decent industrial commercial scale is at least $750. The costly items are a good 24bit a/d chip and the buffering and protection around it. A good power supply - any fluctuation in voltage will reduce accuracy. And don't forget good software, which includes Finite Infinate Response filtering - and linearization - none of these come on the calculator chip used in the cheap scales I see floating around. So know you know more than you ever needed to know about scales - and it doesn't really matter.

    The scale I use retails for $800, it is a 500g scale at .01g displayed resolution with a million internal counts of resolution and an on board database for recipes. Very cool. I can weigh my phenidone for small batches. There is better yet .. a lab balance - we have a pill counter at 310g with .001g resolution and a database. It uses forced restoration technology to do the weighment. At $3100, way overkill - We sold 6,000 last year.
    My photos are always without all that distracting color ...

  4. #14
    Ole
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    Quote Originally Posted by fhovie View Post
    I sell scales for a living - all of them would be overkill for photography. An old mechanical would also be fine.
    I believe that what you're trying to say here is that we don't need precision as much as repeatability. And that even in that we have a pretty large margin of error, so that basically any scales which can weigh a small enough amount is very likely to be "good enough"?

    In my experience, keeping things within a 10% margin of error is overkill.
    Last edited by Ole; 12-09-2006 at 03:43 PM. Click to view previous post history. Reason: Spellling aghain
    -- Ole Tjugen, Luddite Elitist
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  5. #15
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    Quote Originally Posted by wilsonneal View Post
    I bought an Ohaus on eBay. Looked great in the picture. Description was 'excellent'. It's basically a $30 paper weight. Needs service.
    Just curious: what was the problem with it? They look kind of foolproof, but I am no expert on scales...
    “Do your work, then step back. The only path to serenity.” - Lao Tzu

  6. #16
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    Quote Originally Posted by Jerevan View Post
    Just curious: what was the problem with it? They look kind of foolproof, but I am no expert on scales...
    If I calibrate the scale with a known weight, and then weigh another item with a known weight to test it, the second item doesn't weigh the correct amount. And if I recalibrate with the second item and go back to the first, or to a third item with a known weight, again the scale is 'off'.

    It's not at all consistent.

    If anyone has suggestions on what to do with it besides sending it into Ohaus for overhaul, I am all ears.

    N

  7. #17
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    Thanks Neal, I've never thought of it that way - I will have to check mine in the same manner, just to be sure. I also bought mine secondhand.
    “Do your work, then step back. The only path to serenity.” - Lao Tzu

  8. #18

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    I used to measure powders at the post office, then I almost got arrested! That's when I switched to liquid concentrates.

  9. #19
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    And to the practised user, the beam doesn't have to settle down for most measurements. One can judge the center of its swing quite well, especially when the beam has some inertia and consequently a fairly long period to the swings, and some degree of damping of the motion due to the size of it and the consequent air drag.
    Gadget Gainer

  10. #20
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    I already had a letter scale accurate to 1 gram so I bought a cheap digital 0.1g accuracy scale. Weigh large stuff on the letter scale and small, more precise, amounts on the pocket scale.

    Cheers, Bob.

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