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  1. #21

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    Quote Originally Posted by tbeaman View Post
    Just to toss something into the pot, I recently acquired a well-used 45 CT-1 and was surprised to discover in testing with a flash meter that it didn't seem to throw out any more light than my Canon 199a or Sunpak 422d. I'm not sure why that is (use of alkaline batteries?), or how likely it is, but it's something to look out for I suppose.
    That's interesting. What is the rated or advertised GNs for the the 3 flashes. Did the test results for the Canon and Sunpak match their rated GNs (or at least consistent with the relative rating of the 2 flashes)? Assuming a valid test, my first thought might be a worn out (or aged) flash tube or capacitor.
    "Far more critical than what we know or do not know is what we do not want to know." - Eric Hoffer

  2. #22

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    If you test any flash unit against any other, with all of them in some sort of auto mode, it would be a sign of a bad flash if it didn't produce the same output as any other unit.

  3. #23
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    Quote Originally Posted by tbeaman View Post
    Just to toss something into the pot, I recently acquired a well-used 45 CT-1 and was surprised to discover in testing with a flash meter that it didn't seem to throw out any more light than my Canon 199a or Sunpak 422d. I'm not sure why that is (use of alkaline batteries?), or how likely it is, but it's something to look out for I suppose.
    What method and conditions did you use to test it ? how far was it away from the flash meter ? was the 45CT1 on manual full power ? how did you calculate the guide number ?
    Ben

  4. #24
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    Quote Originally Posted by Q.G. View Post
    If you test any flash unit against any other, with all of them in some sort of auto mode, it would be a sign of a bad flash if it didn't produce the same output as any other unit.
    You can't test the guide number in the computer mode because in that mode it gives the correct exposure by altering the flash duration and the duration could be 1/60,000 sec and flash meters don't sync. at those speeds.
    Ben

  5. #25

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    Quote Originally Posted by benjiboy View Post
    You can't test the guide number in the computer mode because in that mode it gives the correct exposure by altering the flash duration
    True. But that doesn't mean that it could be why the 'test' gave the same results for different units.


    Quote Originally Posted by benjiboy View Post
    and the duration could be 1/60,000 sec and flash meters don't sync. at those speeds.
    They do.

  6. #26

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    Quote Originally Posted by Q.G. View Post
    If you test any flash unit against any other, with all of them in some sort of auto mode, it would be a sign of a bad flash if it didn't produce the same output as any other unit.
    Who do you think I am, Gomer Pyle?

    Attached is the patented SuperFlash™ arrangement that I was testing. The main purpose of the test was to see if the wireless triggers I'd just purchased work (they do!), and also to see how much juice this thing could kick out in combination, with and without an umbrella (to see what kind of options I can get with 4x5 portrait set-ups). Since it was necessary to fire each flash individually as well, I took readings then too.

    All four flashes were set to full manual power, and were metered with a Quantum Calcu-Flash II from about four feet away. I didn't take notes, but I think it was about f16 at 100 iso for each flash. The Canon and the two Sunpaks are all rated at GN 100 (feet), while the Metz is 120.

    Now, I'm sure someone will ask about the diffuser on the Metz. Removing it didn't seem to make any difference. However, this whole thing made me curious, so I just stood the Metz next to one of the Sunpaks and the meter a measured four feet away. The readings are the same as I remember (actually f18), but it looks like removing the diffuser is now consistently giving an extra 2/3rds of a stop extra light compared to the Sunpak (so, f22).

    Therefore, it looks like they perform against each other like they should after all, but that both underperform compared to their stated ratings by almost exactly one stop (calculator tells me they should have been f25 and f30), meaning my Metz rates at an actual GN of 88, and the Sunpak a GN of 72.

    So I'm not sure if that accounts for everything, but it looks like I might be Gomer Pyle after all.
    Attached Thumbnails Attached Thumbnails DSCN5021-apug.jpg  

  7. #27
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    Quote Originally Posted by tbeaman View Post
    Therefore, it looks like they perform against each other like they should after all, but that both underperform compared to their stated ratings by almost exactly one stop (calculator tells me they should have been f25 and f30), meaning my Metz rates at an actual GN of 88, and the Sunpak a GN of 72.
    A number of us, who use different brands of flash units, have found that the manufacturer stated guide numbers all seem to be about 1EV optimistic, compared to what we measure with pro grade flash meters from Minolta or Sekonic.

  8. #28

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    True enough, and that's well known, but Metz has a reputation for being not quite so 'optimistic' with their ratings.

    Also, I was a little off with the stated ratings. I don't know where I got that GN 120 from, but the Metz is actually rated at GN 148. That's almost a two stop difference, so I think mine is definitely underperforming. mgb74, maybe you're right about a tired capacitor.

    In the end, it's of no real concern to me, and it doesn't negatively affect my impression of Metz and their products. Merely, it serves to remind those interested in purchasing used equipment that inspection and testing is valuable, and when possible, the price that something commands should reflect it's real value. In this case, I only paid $15, so that holds true here. In fact, I'd say it was still a bargain!
    Last edited by tbeaman; 06-30-2010 at 08:14 PM. Click to view previous post history.

  9. #29
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    Almost all manufacturers' guide numbers depend at least partially on there being at least some reflection off adjacent walls, ceilings or floors.

    If you take your flash meter measurements from 10 feet in a room with an 8 foot ceiling painted in a light colour, you will get readings much closer to the manufacturers' predictions.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  10. #30

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    Quote Originally Posted by MattKing View Post
    If you take your flash meter measurements from 10 feet in a room with an 8 foot ceiling painted in a light colour, you will get readings much closer to the manufacturers' predictions.
    You're right. Placing the two units up on top of a seven foot tall bookshelf in the corner of the room, then measuring from nine feet away gives a GN of 81 and 117 for the Sunpak and Metz, respectively. A pretty 'optimistic' way of rating them, but that's two-thirds of a stop under the manufacturer's rating for both and therefore well within the accepted tolerances.

    I forgot that the cheaper manufacturers tend to make their flashes a little more directional so that they can rate higher, and therefore compete better with the more professional units. That said, the Sunpak is supposed to cover as wide as a 28mm field of view on 135.
    Last edited by tbeaman; 06-30-2010 at 08:35 PM. Click to view previous post history.

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