Weston Master Universal Light Meter

Discussion in 'Lighting Equipment' started by lobalobo, Dec 12, 2014.

  1. When I purchased a Crown Graphic it came with Weston Master Universal Light Meter, Model 715, manufactured in 1939, I've learned. I've used it with the Crown Graphic, but too infrequently to tell whether missed exposure was my error or the meter's. This afternoon, I pulled out a compact point-and-shoot, set it to manual and compared the compact's (spot) reading with the Weston's. If the compact's reading is correct, the Weston would underexpose by almost 2 stops in the test I ran. If it's consistently off by 2 stops, that's easy to fix, of course, as I'll just quarter the ISO setting. But I wonder whether there might be something I'm missing, or whether the meter is just not working. Anyone else use an old meter such as this and notice a tendency to underexpose? Hope I can get it to work; a lot of fun to use old meter with an old camera. Thanks.
     
  2. Note that the Weston meter is calibrated in "Weston" film speeds, rather than ASA/ISO.
    Set the meter to the next speed lower than the ISO speed (e.g., ISO 100, set to Weston 80).
    Copy of the manual here.
    Also note that the Weston meters have a wide (30 degree) angle of acceptance, so your readings may differ from those of a narrower angle meter system.
     
  3. Much as I love using old equipment, I've had a number of Weston and other old exposure meters over the years, and I often found them disagreeing with a modern digital meter, and with each other. The sensitivity of the selenium sensors seems to change over time. Perhaps you can calibrate it consistently against a known accurate meter but I never had much luck with them.
     
  4. Expect to find that old selenium-cell meters lose not only sensitivity (i.e. they read low) but also linearity (i.e. the measuring error is different in bright and dim light). Simply use your compact to take measurements in bright and dim light, metering from a large object (an 18% gray card would give you a direct exposure reading, a white card is fine for comparison purposes). If your Weston is always out by the same amount (e.g. 2 stops), you can of course adjust the film speed setting appropriately. If the error is non-linear, put the Weston on the shelf!
     
  5. Thanks to all. Had a chance to test this morning and the errors do seem linear. I shoot almost exclusively Provia 100 in the Crown Graphic, and I find that from bright to moderate light (in a bluish-gray sky and reflected from a bluish gray poster indoors) the Weston set to emulsion speed of 32 matches the reading from the compact camera (I tested two actually) set at ISO 100. Not sure the linearity will hold in dim light, but I don't have a fast enough lens for the Crown Graphic to shoot in dim light anyway.

    Thus, I have rescued my Weston meter, I believe, though, having done so it has occurred to me that the good compact digital camera I already have, set to manual, with spot meter and whole-sensor meter (along with histogram) available, will do a quicker better job. May have to give up on the nostalgia (sigh).
     
  6. I have them old meters but never use them. They are not much better than my guess.
     
  7. Interesting, at least to me, that my Weston meter seems now to be well calibrated at emulsion 32 for ISO 100--which is almost two stops fast (or a bit less if Weston 100 is equal to ISO 80 as one poster suggested). Most of the posts suggested that these old meters would become insensitive. Curious as to how mine spent the last 75 years becoming more sensitive.
     
  8. Curious as to how mine spent the last 75 years becoming more sensitive.
    Since this obviously cannot happen, I presume that a series resistor inside your meter has gone down. Either way, if your meter is delivering stable and dependable results (with a tweak to the speed setting), there's no reason not to use it!
     
  9. "I presume that a series resistor inside your meter has gone down." - There's no series resistor in any Weston Selenium meter that I've had apart. The Se cell is directly coupled to the meter coil, and range changing is done purely mechanically by means of the pinholed mask in front of the cell.
    An easy way to check the accuracy of a Weston meter is to point it at something that gives a full deflection on the low-light range. If the same reading isn't consistently got on the high range, then the cell is degraded and the meter needs fixing, or probably more economically, throwing away and a replacement bought.
    The difference between Weston speeds and ASA/ISO is only 1/3rd stop, so it's not really that much of an issue compared to the general vaguaries of taking a wide-angle reflected light reading.
    FWIW I've found that Weston II and III model meters have the most long-lived Selenium cells. The Weston III being the first one to be calibrated in ASA speeds, and therefore it would be my choice if I really had to use a Weston meter. Mind you I'd also want the incident light kit that was available for this meter.
     
  10. An easy way to check the accuracy of a Weston meter is to point it at something that gives a full deflection on the low-light range. If the same reading isn't consistently got on the high range, then the cell is degraded.​
    Thanks, but not sure what this means. My process is this: not owning a true light meter, I've tested both in outdoor and indoor light the metering of two different Panasonic compact cameras and a light meter app on my Android phone. Set at ISO 100, all three devices agree exactly and these agree with the Weston set to emulsion 32. So the Weston does seem reliable, but it is a curiosity that it is reading as if it is oversensitive. As I mentioned, the posts above suggest that this isn't possible, but I'm telling you that it is happening. Perhaps the answer is that the mechanical dial slipped sometime in the last 3/4 century. Don't know.
     
  11. "Thanks, but not sure what this means." - I'm not sure how I can explain it any better.
    All the Weston meters I've come across that have gone bad (several dozen I estimate) lose sensitivity at the high end of the scale. i.e. they become non-linear and inaccurate. An easy check for this common fault is to find a brightness level that full-scales the meter on its low range - usually an indication of 50 on older meters, 10 on the model V and later. Flip the range and check the reading on the High scale. If it doesn't read the same as the low scale, or very close, then the cell has gone bad and the meter is useless. Double check with readings of 25 and 13. Both scales should agree quite closely.
    I've never seen a Weston where the reading has gone high though. What I have seen are meters where a previous owner has tried to compensate for a bad cell by drilling more holes in the perforated mask! Or maybe the cell in your old meter has been changed for a newer one. The newer cells are more sensitive and aren't interchangeable with those in older meters. Unfortunately the newer cells have a very limited life as well.
    Edit. There's a difference in colour between old and new cells. The original cells fitted up to and including the model III are brownish in colour. From the model IV onwards the cells have a bluish-grey appearance. The colour can be seen by looking through the "fly's-eye" lens of the meter. As I said, the later bluish cells are rubbish and will almost certainly degrade over a few years.
     

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