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Thread: Holy crap! mirrors on DT40 pros vs CT6215, wow!

  1. #11
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    You lost me at "coating".

  2. #12
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    Sorry guys, I didn't mean the hijack my own thread... There's nothing "wrong" with Bill's reply, he was quite helpful and if I was new I would have thanked him for the information... The tone just tickled some really bad memories... or more accurately a long sequence of bad memories... half the reason I post here so much is I want to keep other people from experiencing some of the problems I've had to overcome. I have no obligation to the laser industry, in storage I have well over a quarter million dollars spent on busted laser gear... this is how I gained my "chops"...

    In response to the suggestions I'll be doing a full test on these and other scanners with all the "edumacation and schienctificism" I can put up with... I was planning on doing it anyways but the last 6215 photos tickled me in a way few things do... and really... you don't need to be a rocket scientist to figure out what these pictures tell you! And just in case it isn't clear, I do not sell DT's and have nothing to do with them..

    I guess I took it as a "given" that everyone already knew the CT's were fine scanners and had no need for defending and just pointed out that the el-cheaper DT's were interestingly nice... Plus saying "that's just how it is" really doesn't fly with me. I know we can do better and jian has quite "proven" that it doesn't have to be expensive.

    The primary reason to go with Cambridges is actually longevity and scanangles... The 6215 has a very wide area, the 6800's are nominally
    rated at 0.5V per degree (40 degrees) but can be overdriven by adjusting
    the AGC and then compensating by adjusting the linearity. As long as the AGC lines stay below 11V you can "safely" drive the scanheads.

    As we only recently got our DT-40 pro's we have just started tuning them...
    The AGC feedback levels is a bit janky, but the coil design gives us enough bite to let us drive to wider angles than a 6800, the placement of the diodes internally prevent super wide movement like a 6215...


    Here we have "muted" the amp and are tuning the AGC to calibrate the POS. Note the 37 degree offcenter... At +/-5V on the POS, we see +37 degrees and -35 degrees...

    In terms of resonant frequency, we're still in the middle of tests, but I'm seeing some interesting information from them... I'll post more on those later. As you can see this forum is somewhat political about half-baked reports and tests

    P.S. I do know for a fact that if the chinese galvos had the EXACT same mirror as the 6215 there'd be a lot of people up in arms about the cheap mirrors... And honestly if I hadn't taken the time to stare at these I would have been right up there with them...

    [added]

    So you guys know, if I hadn't been examining the mirrors specifically I wouldn't have noticed it at all...
    See, they look quite fine if you're normally staring at them... Its when a light source is behind the optic that you notice...
    Last edited by yaddatrance; 03-31-2007 at 22:21.

  3. #13
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    Hey yadda , you got a bit steamed up and blew off ..we have all been there ... I am sure WB done it at some point unless hes superhuman ........ and you got good reason to feel a tad wound up with that amount of kit AWOL.
    Its a strange old mix in here eh ! especially in the size of walletts ... but the levelling field is the love of lasers !
    Look forward to yuo future reports
    PAUL
    In the beginning there was none. Then came the light - #1 UKLEM - 2007
    BUY UK LEGAL LASER POINTER :: NEW - Blue 460nm Laser Pointers

  4. #14
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    Hi Yadda,

    (Sorry, but I don't know how to make this forum "quote" -- maybe I don't have a setting made correct in my profile). Anyway...

    YADDA WROTE:
    Dear Bill, don't you dare patronize me.

    WILLIAM BENNER REPLIES:
    Hey man, I wasn't trying to patronize you or anyone else. But your post did come across as Cambridge-bashing -- at least that's the way I read it. Even the title comes across this way. Then, the main thrust of your post was about the coating of the mirrors, but you only presented one single sample of each scanner type. That's hardly enough to gather meaningful statistics...

    My only goal was to point out to people that -- sometimes, sh*t happens. I am sure that there are LD2000 systems that we ship that have a loose screw, or missing cable, or something like that. It happens with all companies... Likewise, my point was that I am sure sh*t happens with Cambridge mirror supplier, and with everyone's mirror suppliers.

    Next, I asked you to do further statistics -- try multiple wavelengths, and try multiple scanners and mirrors. If the results of such an analysis support your initial conclusion, then great. If not, well, then we will all have some better information. That's all...

    Regarding your reference to "that's just how it is", I don't think I ever said that or indicated that, did I?

    And regarding DT40s, yes, I will agree that Jian did a good job. In fact, a few days ago I wrote to him about how he can improve his product for the whole industry, based on the experience that I had with them at the last FLEM.

    So, my recommendation to you is (as if I am entitled to make one...), cool your pipes man!! Maybe take a swig of whiskey before replying to posts. It's not that big of a deal man!! You are reacting way to harshly to an email that was basically stating that my experience with Cambridge mirrors did not reflect your own, and asking you to do additional tests to improve the quality of the data you supplied...

    William Benner

    PS: If everyone is patient, I will post a picture or two showing our scanner bench, and how we do testing of scanners, including mirror resonances. It's a lot more sophisticated than you might think.

  5. #15
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    I think everyone here can learn a lot from this thread if we can all play nice.
    "Gravity its not just a good idea its the law"

  6. #16
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    I am in the bottom of the learning curve compared to most on the forum here. Most have on-hand experience dealing with electronics and technical aspects of this HOBBY of mine and others.It is a hobby for me......not a way for me to make a living while others perform on at jobs using their lasers. I appreciate the truth {read tag on my posts} no matter if it hurts or not. I try to look at the issues that are with lasers as just a part of it. You learn from mistakes or from others. I can't spend $20K for a really nice set up....so I will make the best of what I have now. There are enough issues with it to keep me busy for some time to come. I guess that what I am trying to say is that the truth about a product is better than a spec sheet from a manu. Personal outcome from private tests are more value to me.....real world usage. Some of the simplest things in life are the best. So I will continue to learn as the curve gets steeper and hopefully not blow too many things up beyond repair. In the mean time I will be watching,listening,and trying not to fry anything around here.
    Last edited by MechEng3; 04-01-2007 at 09:59.
    You are the only one that can make your dreams come true....and the only one that can stop them...A.M. Dietrich

  7. #17
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    Hi Mech,

    Thanks for the posts. I am sure everyone wants the truth here, and as far as I am concerned, the truth should never "hurt" But in this case, the truth can't be found by examining one piece of equipment, if that equipment is made in lot of thousands...

    For example, when Frito Lay is conducting process control over the salt level in their potato chips, they don't just pick a single potato chip and call it a day!! If they did, how would Frito Lay know that the potato chip they picked wasn't the only perfect one out of a bad batch? Or how would they know if they picked the only bad one out of a good batch? Also, the saltiness-testing is not done by someone putting it into their mouth, but rather with sophisticated equipment. In order for Frito Lay to know, to any level of certainty, the quality of a batch of chips, they need to sample a meaningful number of the chips, and then perform sophisticated analysis on them.

    In my articles on audience scanning, I talk about how the human eye is a horrible radiometer. It is possible (and quite easy) to look at something with your eye and make an incorrect judgment call. (For example, this happens often when looking at the two light beams emitting from a PCAOM, and stating that they look to be the same power level.)

    Just because you can see purple light through a mirror at zero degrees, doesn't mean it won't reflect the prescribed visible wavelength range with a high degree of reflectivity at the correct angle. And just because you can't see purple light through it, doesn't mean it reflects better. As one intuitive example of this, metalic coatings don't reflect as well as dielectric coatings, but you can't see light through metallic coatings...

    When someone makes a statement of any kind, I don't think it is unreasonable to ask for them to back it up with additional data. Such a request should not be interpreted as an insult of a personal affront. After all, there have been plenty of times when people have asked me for additional information about my postings. When called upon to provide additional data, I do hope that my own responses have been informative, and not off-putting, but I can’t make any guarantees of this because everyone has a bad day...

    Best regards,

    William Benner

  8. #18
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    Actually, the more items a maker makes, the greater the practise, efficiency, habit, and the less deviation occurs between samples. This fact is the entire basis of mass production, intensive farming, and any major industry. So it should be that a limited number of samples tells the story about a large batch. The larger the batch, the more unlikely it is that a rogue item is picked. So, it is far more reasonable to assume that a single sample represents all items in a large batch than in a small hand built production run. Scanners might be largely hand built, but mirrors are almost certainly not. Coatings are always done in as large a batch as possible because it's so expensive to set up the coating process.

    Incidentally, the WideMove mirrors are 'enhanced aluminium' coated. Not sure what that means exactly, my guess is a non-metal coating to protect them, and possibly done for a limited amount of extra reflection. Anyway, they do pass some light through them. A 150 mW 532 nm beam shows as a fiercely bright spot emerging from the ground rear surface even when optimally set to 45 degrees. Gold leaf is fairly well known to pass light too, it appears green when white light is viewed through it. I wish I could say I'd seen that myself, but gold is expensive, and I haven't had a lot of it around...


    Edit:
    One more thought: If a scanner mirror is made to be better than 99% efficient at optimum angle for broadband light, which is essential for RGB systems unless you go to the extra expense of making three specific multilayer coatings for each of the three prime colours, shouldn't a dielectric mirror be much more opaque to all visible light? I just looked through a Newport mirror (one of eight 1/4 wave flat 1/2" round ones I got lucky with on eBay) rated for >99% R from 0~45 degrees. I held it up to an incandescent filament lamp and turned it through most of its angular range while holding it as close to my eye as possible. Purple light came though, which dropped evenly as I went from perpendicular to near parallel for plane to light axis, and the low end red of the filament appeared more strongly. Whether that was a contrast with the fading violet end, or an actual rise in IR end transmission, I don't know, probably both. Anyway, based on that observation, I'd not be concerned with the CT6215's mirrors if I had some. If I can see a bit of violet through a >99% broadband dielectric even at specified angles, I'd not worry about it if the mirror was specified 'only' for >97%. On the other hand, either I got VERY lucky (which is likely as Edmund want over a hundred bucks for a mirror like that), or there could be a chance for dramatic reduction in costs if each small scan mirror were cut from a single coated plate of glass. I also tried a blue/violet LED through that mirror. Transmitted light looked dramatic, but that light was a small quantity. Sure I can see it, but can't see any noticeable reduction from the reflected light compared with the direct light. Less seems to be lost from transmission that a cheaper metallised mirror would lose by absorption. If the DT40's are shipped with ANY kind of decent dielectric mirror, that should be better that a 95% aluminium mirror, no matter what it looks like, so long as there aren't any weird dropouts at important wavelengths.

    Edit_2: I found some thin gold in a reflector lamp, having remembered where it is. Light passes through it. Not much though, it's like that foul colour Microsoft called teal, a kind of depressed cyan.
    Last edited by The_Doctor; 04-01-2007 at 11:59.

  9. #19
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    You must have missed some of the earlier threads where the DT's were
    bashed soley because they are not cambridges... This thread was meant
    as a counterpoint to those threads...

    Quote Originally Posted by Pangolin View Post
    Hi Yadda,
    (Sorry, but I don't know how to make this forum "quote" -- maybe I don't have a setting made correct in my profile). Anyway...
    I always click on "Reply" on the lower right side of the specific post...
    that autoquotes things, and then I manually add specific stand and end
    quote tags...

    WILLIAM BENNER REPLIES:
    Hey man, I wasn't trying to patronize you or anyone else. But your post did come across as Cambridge-bashing -- at least that's the way I read it. Even the title comes across this way. Then, the main thrust of your post was about the coating of the mirrors, but you only presented one single sample of each scanner type. That's hardly enough to gather meaningful statistics...

    My only goal was to point out to people that -- sometimes, sh*t happens. I am sure that there are LD2000 systems that we ship that have a loose screw, or missing cable, or something like that. It happens with all companies... Likewise, my point was that I am sure sh*t happens with Cambridge mirror supplier, and with everyone's mirror suppliers.
    When I originally read your original post, I read the undercurrent of "sh*t happens" as "that's just how it is"... and I read the "HR" stuff as patronization... though as I read it now, it was probably meant to be humorous chiding, I am definitely guilty of taking things too seriously and missing jokes... and darn it, the word "gullible" WAS in the dictionary.
    And if my overly expensive belgian optics on my HR was only 99.9% reflective I'd be quite miffed! Darn it I paid double for that extra 0.05%!!! (mental note: do not look at the HR, repeat, do NOT look at the HR)

    (That was another one of my lessons learned, if you want a better beams you don't have to crank a tube up to get more power, up to a point you can just buy nicer optics... the tradeoff is tuning and finding the sweetspot is a pain... For some reason nobody seems to like selling nicer optics, I literally had to beg!)

    I'll put up in my defense, most people have a hard time getting even one CT set, much less a roomful and I did run around cracking cases open to see if that one was just a fluke... And as I am an "end user" customer, not a reseller or distributor... I have a right to be miffed, though to be honest, I was far more amused than miffed (though maybe a little sad)...

    Obviously, since you (a very reputable manufacturer) felt the need to jump to the defense of another very reputable manufacturer, you could see there was some sort of problem with the optics as presented by the photos... I assure you that on the units I have here, in person, the effect is a lot more dramatic. As you pointed out, we did buy all the 6215s in one batch so it could've been a bad optics week at camtech... but as someone who actually specs out optics, I personally think they just let themselves play a little loose with the tolerances. When you coat optics, it's still enough of an art that they have to test each sheet, and compare to the tolerances the customer sets out.

    I'm quite positive that at 45 degrees it meets their specifications, however these are 6215s and as you pointed out they were optimized to go wider!

    Next, I asked you to do further statistics -- try multiple wavelengths, and try multiple scanners and mirrors. If the results of such an analysis support your initial conclusion, then great. If not, well, then we will all have some better information. That's all...

    Regarding your reference to "that's just how it is", I don't think I ever said that or indicated that, did I?

    And regarding DT40s, yes, I will agree that Jian did a good job. In fact, a few days ago I wrote to him about how he can improve his product for the whole industry, based on the experience that I had with them at the last FLEM.

    So, my recommendation to you is (as if I am entitled to make one...), cool your pipes man!! Maybe take a swig of whiskey before replying to posts. It's not that big of a deal man!! You are reacting way to harshly to an email that was basically stating that my experience with Cambridge mirrors did not reflect your own, and asking you to do additional tests to improve the quality of the data you supplied...

    William Benner

    PS: If everyone is patient, I will post a picture or two showing our scanner bench, and how we do testing of scanners, including mirror resonances. It's a lot more sophisticated than you might think.
    Heh, whiskey, us dignified californians drink Pinot with our cheese...

    I would love too see your bench! Nobody ever showed me how its supposed to be done, so I just hook up a sweep function generator set at low volts but higher current to the raw galvo while FFTing the position sensor and slowly spin up until I see resonance, mark it and move up till we find the second point, caulk it as good enough and set the notch filters.

  10. #20
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    Quote Originally Posted by The_Doctor View Post
    Incidentally, the WideMove mirrors are 'enhanced aluminium' coated. Not sure what that means exactly
    Generally that's short for "UV enhanced aluminum"... most mirrors are bad
    in the UV and deep blue range...

    P.S. So how do you guys think I should pick colors? take a white tube and
    prism it? PCAOM? Can I get away with an RGB diode whitelight?

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