"derating" semi-debunked

Discussion in 'Lighting Equipment' started by ellis_vener_photography, Jan 4, 2004.

  1. Timber writes:
    ...we de-rated our flash units by 25% because we don’t believe that manufacturers are being, well, accurate with their specifications of power in watt seconds. This means that if we look at a 1200ws pack, we are going to rate it at 900ws.
    How do manufacturers probably “work the numbers? Oh, they probably do a meter reading from the very center of the light spread. In the center, the very center, there is some unevenness wherein there is likely a hot spot. Instead of taking a reading 1/ 3 out of the center, the manufacturer probably uses the hot spot to “represent” what the power rating of the light is. To see this unevenness, take a flash light and shine it on a wall. Flashlights create obvious hotspots.

    first of all watt-seconds is a measure of potential electrical energy and has only the loosest of connections with actual levels of light produced by an electronic flash unit. I have a roughly 18 year old Balcar A2400 pack which I use with the Balcar "U" heads. This combination puts out twice the amount of light of the the Norman P2000X pack and Norman LH-2400 heads the Balcar replaced. I have a couple of Elinchrom heads I had modified to work with Balcar packs, the Elinchrom/Balcar combination puts out 1.5 x the light the Norman pack and head combination did. I also had a Speedotron Blackline 102A head which I used with the Norman pack (i had an adapter cable made for this purpose.) The Speedtron/Norman combination was 2x brighter than the Norman/Norman combination. I tested with bare tubes, standard reflectors, an umbrella, with the light turned away from the meter and bounced into a large white surface and also with the same softbox (a Plume Wafer 100). All of the heads and packs had recently been serviced and had new flash tubes. I also had at one point a pair of elinchrom EL1000 monolights. These 1000 watt second monolights put out as much light as the Norman P2000X /LH2400 combination when the Norman pack was set for full output. Furthermore the elinchrom monolights were within a couple of tenths of a stop in measured output as Elinchrom's literature said they would be. All of the test were conducted in the same set up and studio over a two day period. As many variables as possible were eliminated.
    My point is you cannot just say "we don’t believe that manufacturers are being, well, accurate with their specifications of power in watt seconds" as a flat, all encompassing statement. My testing show that a large factor in the efficiency of turning energy (watt-seconds) into light (lumen- seconds) has to do with the efficiency of the head design and flash tube design.
    But on the other hand it is clear that some manufacturers actively skew their results, or at least report it in their literature to make their lights look better. They do this by publishing numbers measured with a narrow angle reflector being used, or as Timber points out only measuring the hot spot. (I eliminated this as a factor in my tests by measuring the light using a large range of reflectors and light modifiers) , But the better brands: Profoto, Elinchrom, Balcar, Dyna-Lite, Speedotron, Broncolor, Comet, maybe Hensel -- do not take this route. Perhaps other manufacturers are also as honest but I haven't tested them. As a general rule I would be suspicious of any make that makes claims of "effective watt-seconds" or does not specify the reflector being used.
  2. On an electronic flash; the capacitance of the condenser and the DC voltage across it determine the energy in joules; ie watt-seconds. The "hokey-ness" of marketing specs come into play; when one adds reflectors; to bump the numbers up.
  3. As a flash unit ages; the high voltage condensor ages and many times will drop in capacitance; and the energy in joules; ie watt-seconds drops. Reforming the condensor; or replacing it will bump up the energy stored. An older condensor will often be leaky; and will self discharge fast; due to internal leakage. This shunted current often makes the condensor run warm; and quickens the aging process. A shorted condensor can explode; or thrown chips of metal from ones test leads; if one starts to play around with them; and causes a direct short. Leave the testing of high voltage caps to people who use the proper safety methods; to insure you wont loose your eyes; etc.
  4. Very intersting info from Ellis. I seem to remember that Elinchrom (until recently at least) produced their guide Nos. by testing with wide angle reflectors rather than standard and because of this they understated their real-world performance figures.
    I also remember mentioning to Chris Whittle, Elinchrom's UK boss man, that the performance was better than I expected on their 2,400J pack and he said that this was largely due to their very heavy connecting cable.
    I'm not sure that output performance is even very important today, as ISO settings can usually be adjusted by a stop on digital with very little quality loss and because there are corresponding improvements to film grain too.
    What is important is the range of adjustability, and the ability to adjust output steplessly rather than with 'click' settings. This is more important with digital than with film. Colour and output consistency is also very important - good reasons for sticking with the leading makes!
    Coming back to the original post, some years ago I carried out similar tests with a few on-camera flashes and found that not one of them came within 50% of the advertised guide No, unless they were used at their maximum zoom settings - and even then, they usually fell short of their promises.
  5. Regarding Ellis quote: "But on the other hand it is clear that some manufacturers
    actively skew their results, or at least report it in their literature to make their lights
    look better. They do this by publishing numbers measured with a narrow angle
    reflector being used, or as Timber points out only measuring the hot spot."

    I didn't want to get into a manufacturer vs. manufacturer fight. I didn't want to call
    everyone dishonest about their ratings, but rather to hint that some are fooling with
    their numbers in some fashion; I wanted to level the playing field so that my
    recommendations are conservative. I wanted to place some doubt in the mind of the
    buyer that all watt seconds are perfectly equal, too. But even with all this hub-bub,
    the buyer has to make a decision! I didn't want to leave the reader with a spiral of
    confusion, I took a stand and created a concrete beginning for a standard. So, I took
    some of the air out of the ratings of everyone.

    Ellis is saying that manufacturers skew their results; I agree. Ellis is saying that there
    are efficient designs that put out more light: I agree. And there are ways to make
    the system put out more light by adding a few custom touches to the pack system,

    I am preparing another post, a Part 3 which will take about these "efficiency factors".
    More efficient heads/packs cost more, so even here nothing is free, not even "bonus
  6. I've been following these power recommendation discussions with interest but think we need some actual data. It has been the one missing from these threads (and they have been very interesting to read Timber, Ellis, Brooks and everyone else who has contributed)

    So I just set up one of my new Elinchrom Style 300s mono's with a 16cm reflector (90 degrees). Measuring several time at 10' with a seconic L-358 set to 100ASA I was constantly at f-stop 10. And that is nice.

    I then removed the reflector and repeated the test several times and was surpried to get reading of f-stop 9.

    From reading the previous post I feel that these are good numbers to be getting from a 300Ws unit.

    Anyone else like to contribute some actual measured values?

  7. I remember Chimeras doing something similar to this although I may be wrong since, I can't seem to find it on Chimera's website, they basically did some measurements of different units through their softboxes, something like that which is what's been proposed here would be an interesting series of tests, all done in the same room, with the same calibrated meter, same light modifiers/approx light modifiers since the same reflectors probably would not interchange between manufacturers, same distance, with the tests done by unbiased photographers/electrical engineers.

    I'm sure the manufacturers have done their own tests which may or may not jibe with the numbers put out by their marketing dept, hopefully somebody w/access to the various tests could put together a test of the main players(although I don't think that this will put a dent in the Profoto/Elinchrom level type strobes as it will in others) which could cut through all the confusion.
  8. Well you see, we have an Elinchrom fan who has concurred on my measurements.
  9. Ellis is saying that manufacturers skew their results; - Timber B.
    That is not exactly what i said. i said that some manufacturers may be skewing their results. The only way to resolve this will be to test as much gear as possible in as unifrom way as possible with a standard methodology and the same meter , and similar reflectors from the manufacturer and with the same non OEM light modifiers.
    And i still stand by my statement that since we cannot judge a flash system's output (light) by a simple consideration of watt-second capacity, talking about "de-rating" is equally meaningless.
  10. "Meaningless-ness" doesn't help people who are in the market for buying a flash unit
    package. They need a ballpark figure. No one is going to assemble all the
    equipment, delete all the variables, then test for exact results. It isn't necessary. The
    range of LEAST EFFICIENT TO MOST EFFICIENT for any given watt seconds is 1.5 stops.
    This is a wide variance; but that is life in the flash unit jungles.

    The most efficient systems are Elinchrom, Balcar.
    Second in line are Photogenic, Speedotron
    Lastly is Norman.

    Now, even if Norman is least efficient, perhaps 1/2 as much real output as the others,
    Norman when bought USED is about 1/2 as much as the others! And, all you have to
    do to make Norman more efficient is to put a 9" chrome reflector on it: you will get at
    least .6 f stops more out of it!

    Arguing that we CAN'T DO SOMETHING is for the intellectual set in the ivy towers.
    Today, we need to make a buying decision. Physics has set the output of capacitors;
    physics has arranged "inverse square" rules. We can go very far by interpolation in
    using these rules of physics.

    There is no way that manufacturers are going to label their units for true light output
    and paste this on the outside of the pack. The only thing that is reasonable is that
    they put "watt seconds" on the packs because the packs switch power, not light. It
    doesn't become light until the electrons pass the pack, go up the cord and ignite the
    gases inside of the tube. Therefore, the manufacturers are correct and have a legal
    defense for assigning "watt seconds" to the pack's exterior.

    It is then left up to the photographer to decide the efficiency of the cord and the
    head/tube design. I have some rules to make that decision. Look for it in Part 3.
  11. 'No one is going to assemble all the equipment, delete all the variables, then test for exact results. It isn't necessary.'................Why not? Chimera has already done something like this, although it may not have been their intent to produce the kind of results we're discussing here, I disagree with you, I don't see why a test like this couldn't be done, we get together to compare cameras, I don't see why we couldn't get together and compare strobes, whether or not it's necessary, I would suggest that if such a test could be arranged that even you would want toknow the results?

    It's right after New Years and I've got no wish to get into a flame war, but I am entitled to my opinion, so I'm going to express it, people are making decisions right now on what to buy based on discussions like these, they've asked for help, there's some disagreement between us on the very points we're discussing, that's good for the people making the what can be a very dificult decision regarding what may be for some folks a one time purchase if they don't have much money.

    We've been discussing power, I've mentioned WS out of habit, I'm not an electrical engineer, but I don't have to be one to realize that the bottom line is light output, that's what these strobes are for, putting out light, to say that it's not necessary to measure that isn't going to work. THAT WHY WE GET THESE STROBES IN THE FIRST PLACE,.... LIGHT....and then we measure that LIGHT with a LIGHT METER.

    This is all opinion, the folks looking at these discussions can consider with whatever scrutiny what's been discussed and take it for what's it worth, maybe one of the photographers who happen to be engineers can also SHED SOME LIGHT ON THE SUBJECT.
  12. OMT, regarding the experience of those involved in the discussion, the folks just getting into strobe/studio photography may need info that's not necessary for us, within a frame of reference that is different than ours, in fact that's what this forum is for.

    You can't say the day won't come when among other things, an accurate number regarding light output will be among the specs given out by a strobe maker, some day that'll be exactly what one of them does, and then the other manufacturers will have to follow suit.
  13. It's the marketers jobs to differenciate these strobes. They can't be all the same.
    They must be designed differently to provide a niche advantage for each product.
    One product may be inefficient, but it could be sold cheaply as a simple product. All
    these products have not been "equalized" in the last century. Light power is not the
    end all be all of a pack system, there are other matters to consider: is it a
    transformer unit or a capacitor multiplier unit? What is its recycle speed? Does it
    have a "beauty reflector" available? Will the tube withstand impact? Will the unit do
    220volts and 110 volts?

    Don't lose sleep over wishing that a consumer group will decend from the heavens to
    save photographers! I think the best that we can hope for is that the most efficient
    system manufacturer will try to tout his more efficient specs against other brands, and
    place this into a chart. Nonetheless, the variance will be about 1.5 stops after all the
    testing is done. This is what I see and hear.
  14. Let me answer it another way, in the working world of photography: If I need f11 at
    ASA100 at 10' to take a picture of a person, I want to be able to know a reasonable
    setting or pack to use for the situation. Now I know, from my charts, that if I have 3
    different systems in my car, that all I have to do is select the one that says "600ws"
    and I will have my f11 with a normal reflector. Maybe I will even have the ability to get
    a f16 out of it because it is the most efficient system in my car trunk. You know, it is
    a Balcar or Elinchrom system. At any rate, I am not going to be disappointed. I flick
    the switch to 600ws (down rated to 450ws in my system) and my meter will be at least
    f11. Now, if I am 'wrong', and I get a f16 because I picked-up the Elinchron from my
    trunk, all I do is flick the switch on the Elinchron to 1/2 power, and like magic, I have
    my f11.

    I think it should be a given that any photographer with several systems will get to
    know the power quirks of each system. He will memorize the differences. But if he
    doesn't, he will be able to get his f11 even though he has a bad memory!
  15. 'Don't lose sleep over wishing that a consumer group will decend from the heavens to save photographers!'.........................that was not my suggestion, nor is it my mindset regarding this issue.

    'It's the marketers jobs to differenciate these strobes'......good, bad, or indifferent, the marketers job is to sell, or he doens't eat, he isn't paid to tell truth, or to inform, he is there to creat attention, interest, desire, and action.

    It was never my suggestion, nor did I ever imply that we all need to be 'spoon fed', I don't, I've got exactly what I need in terms of lighting gear, and for the lowest price that I could've possibly paid for the gear, I got exactly what I've wanted, I have a White Lightning 1800, 2 profoto packs, I've been completely satisfied with my strobes, going back around 15yrs, I've never had a malfunction,hopefully, and without sounding presumptous, my input is not for me but for those who need it/want it, where I can save them some money and needless mistakes, we have this and other forums for an in depth scrutiny of all the aspects of the performance of a strobe and there have been numerous threads in addition to this one dealing with this.

    The issue of how you know that x-manufacturers strobe will give you x-F-stop, at x-distance, at x-power, is fine, for you, I would disagree with you in that you seem to marginalize/discount the idea of a real world test of the strobes of the major playors in terms of pure light output, I think it's something we need which would be of benefit to the folks just testing the waters(stobes/studio photography), I think everyone is aware of the other considerations as we've discussed in this thread and in others.

    You've come up with some figures, but some of the figures aren't telling us/at least no me the whole story, and I would suggest that what would be valid for everybody is a test with a well documented method, this brings us to a test to verify what we've all been talking about, what size room, and what color walls were you dealing with? What light modifier are we talking about? When you talk about F11, with what meter, calibrated by whom? How many pops did you take/was each pop consistent to with x-amount to verify what you got?

    What I'm saying if I haven't said it clearly enough is that if you're going to throw numbers around, then is should be as the result of a well documented test conducted by yourself or else what does it mean? A lot of what you've said is anecdotal, for example you say here............................................'Now I know, from my charts, that if I have 3 different systems in my car, that all I have to do is select the one that says "600ws" and I will have my f11 with a normal reflector.'.....................what charts? Compiled how? F11 measured by what/and calibrated by whom.

    What's better that a discussion like that is a real test conducted by academics qualified to do it, if you say 'they won't do it' or 'it isn't necessary' it doesn't give what you say any more validity without a well documented method of how you came about your results.

    This would also help somebody who gets the same pack, so that you could hold up its individual performance to an expected standard, we do this with lenses, I don't see why this can't/won't eventually come to pass with strobes, I think it's a good idea, and while I certainly wasn't the first to bring it up, hopefully by talking about it, I'll help keep the idea alive.
  16. Products are changing all the time. Yet, the variance of the least efficient to most
    efficient light head/pack/mono light is 1 1/2 stops. That is quite a spread. It is
    possible to look at the design and to count up the variables that make the head or
    pack more efficient. You can SEE why it is so. Want one? The least efficient system
    uses gray buff reflectors. The more efficient systems come with shiney chrome like
    reflectors. Well, there it is right there, it is in the chrome! This difference could mean
    .6 f stop more light! Is this fair to compare gray buff to chrome? No. These are
    apples and oranges. But that is what the manufacturer put together in his package!
    Gray buff diffuses the light more! Chrome doesn't! Apples and Oranges!

    If you were needing a ballpark idea of power requirements to do a group picture, you
    need a ball park idea, plus alittle extra buffer in case you are wrong. You need a
    starting point. You do not need to be a scientist to make this decision. You don't
    want to be a testing lab. You need an experienced opinion. Well, I think you can see
    here that there is respect for Elinchrom, Balcar for having efficient systems, for
    example. OK, so what does that mean in numbers? Feeling confused? Yep.

    Take advantage of my experience. If you need to bounce off a portable strobe off a
    pink pastel wall or 12' ceiling, you are going to lose 3 stops. You will need 6x more
    power or a power setting 3 stops higher. Now, maybe you want to be exact, and we
    could find that the true setting is 3.22 f stops more. Well, you will find this all out
    when you meter. The idea then is to have alittle more power available to get you out
    of jams. But do you really need to bring along 9600ws? Do you need to spend $3600
    on a pack system for this up coming job? You need a ball park rating to get you
    started. And, you may need to have an idea what f stop you should be using as well.

    Most pros can do the calculations in their head, and come within 1/2 stop before they
    even meter. Experienced wedding photographers who use bounce and multiple lights
    are often placed into these fast paced predicaments. Perhaps the wedding
    photographers know more about bounced light!

    You notice that an avalanche of disagreeing opinion is not hitting photo.net after my
    post. The posts are seeking to clarify portrait style, table top distances and ideas
    about the cumulative testing of all equipment on the market.

    Don't lose sleep over 1/3 of an f stop you think you are missing!

  17. I pretty much have said all I have to say on this, and will end my participation in this thread with the satisfaction that what was discussed probably provided some useful info and counterpoint for using strobes......................Ciao
  18. Take advantage of my experience. If you need to bounce off a portable strobe off a pink pastel wall or 12' ceiling, You are going to lose 3 stops. You will need 6x more power or a power setting 3 stops higher.
    1 stop = 2x light, 2 stops = 4 x as much light, 3 stops = 8x as much light.
    Not 6x, 8x.

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