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Archive 2011 · Thyristor Technology
  
 
Zenon Char
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p.1 #1 · p.1 #1 · Thyristor Technology


I am interested in learning more about this. I recently purchased a Metz flash but decided to start a mew thread. I was having some trouble with my Metz because I was adjusting the flash exposure compensation and later found out you can not do that in Auto (Thyristor) mode. The operator manual was incorrect regarding this.

So my question now is very low light events. Even though I know now I cannot use FEC the Metz still has a warning system that tells you when the camera settings are outside the flashes operating parameters. So if I'm in a very dark venue and want to shoot at ISO 3200 or 6400, 1.4 aperture and 1/60 shutter speed it will warn me but allow me to take the shot and some people/objects will be overexposed. I took a shot with the above settings without the flash and the exposure was very dark.

In ETTL I know my Canon 580 will output far less power than the lowest manual setting of 1/128. I have not tested the Metz for this in ETTL mode yet.

So what is Thyristor doing? Is it the limits of the technology itself or the Metz design that does not allow to power down enough with the settings I mentioned. I had to go to 1600 ISO and F4 to make it happy.

Hopefully Metz ETTL will do the trick. It think it will but I currently don't have it to test it. I don't mind having to flip it over to ETTL when needed but the Auto ISO 1600 shots came out great. The consistency really surprised me. I had heard about it but did not really believe it.

Also I had read in the day when there was less technology you had to use a set aperture for Thyristor regardless of the manufacturer.



Dec 24, 2011 at 09:21 PM
brett maxwell
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p.1 #2 · p.1 #2 · Thyristor Technology


There's probably just a minimum power it CAN output. I've run into this using an SB800 direct on TTL at high ISO and large aperture, even though in TTL it can go lower than the 1/128 available in manual, it still wasn't low enough. The solution was putting a 3 stop ND gel on the flash. I would think the same should work with a thyristor.


Dec 25, 2011 at 12:08 AM
Zenon Char
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p.1 #3 · p.1 #3 · Thyristor Technology


Thanks


Dec 25, 2011 at 01:21 AM
BrianO
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p.1 #4 · p.1 #4 · Thyristor Technology


Not directly related to your question, but related to "Thyristor Technology" --

Someone asked a question on another thread, and from the question and some of the responses I realized that many people don't know what a thyristor is and what it does. Many people seem to be under the impression that the automatic flash sensor built into the flash is the thyristor. It's not. The thyristor is the switch that cuts off the flash under the control of the autosensor (or the manual power setting), but it is not the sensor itself.

Most newer flashes don't even use a thyristor; they use a functionally similar but structurally different technology called an IGBT (Insulated Gate Bi-Polar Transistor).

One way to think about thyrsitors and IGBTs is to think of a light switch: I flip the switch in my bedroom off when I've had enough light, but that doesn't mean I'm a light switch. I just activate the switch. Similarly, the autosensor "flips the switch" (the thyristor or IGBT) when it receives enough light, but that doesn't mean the autosensor is a thyristor/IGBT. It just activates the thyristor/IGBT.



Dec 25, 2011 at 07:33 AM
ukphotographer
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p.1 #5 · p.1 #5 · Thyristor Technology


Zenon Char wrote:
I am interested in learning more about this. I recently purchased a Metz flash but decided to start a mew thread. I was having some trouble with my Metz because I was adjusting the flash exposure compensation and later found out you can not do that in Auto (Thyristor) mode. The operator manual was incorrect regarding this.


In the 'olden' days if you set f8 on your flash as the 'correct' exposure level, (or the yellow, blue or red setting) - then FEC happened by adjusting your aperture away from f8. The sensor didn't change anything, nor what value it provided.

Regardless of the aperture values set, the auto settings (yellow, blue, red) were fixed levels. Only the ISO changed the aperture you would need to set for the correct level at each setting, so providing you could remember what (film) ISO value you were using your flash just did it's thing with you intelligently adjusting aperture.

You just need to think occasionally.



Dec 25, 2011 at 12:23 PM
Zenon Char
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p.1 #6 · p.1 #6 · Thyristor Technology


Thanks everyone. Interesting information.


Dec 25, 2011 at 02:38 PM
Zenon Char
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p.1 #7 · p.1 #7 · Thyristor Technology


brett maxwell wrote:
There's probably just a minimum power it CAN output. I've run into this using an SB800 direct on TTL at high ISO and large aperture, even though in TTL it can go lower than the 1/128 available in manual, it still wasn't low enough. The solution was putting a 3 stop ND gel on the flash. I would think the same should work with a thyristor.


Not the road I wanted to take. I purchased it to spend less time screwing around with the flash. Auto is extremely accurate but I have yet to test ETTL at high ISO. I have found Metz ETTL more accurate than my 580. We will see.



Dec 25, 2011 at 04:56 PM
hugowolf
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p.1 #8 · p.1 #8 · Thyristor Technology


I think optimistically you could rate a 580ex at 80 Ws, and probably more realistically at about 60 Ws. Either way you are down to about 0.5 Ws at 1/128 power and somewhere in the region of candle power and a flash duration of 29 žs.

If you want lower lighting than this, then you may be better looking at a small shoe-mountable LED panel.

Or you could look for a candle to hot shoe adaptor, although I have heard that the cheaper Chinese knock offs of these donít transmit ETTL information, so you'd be manual only.

Brian A



Dec 25, 2011 at 05:41 PM
cgardner
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p.1 #9 · p.1 #9 · Thyristor Technology


The main difference between a Thyristor style flash like a Vivitar 285HV and a modern digital camera TTL flash is how the exposure calculation is made. On a digital camera with TTL flash the amount of flash power needed is computed via the pre-flash and the flash it told before the shutter is fully presses how much flash is needed. When ISO is cranked up to the point where the background (and foreground) are exposed more or less normally the pre-flash metering (which on Canon compares ambient and pre-flash) will conclude very little or no flash is needed. A Thyristor flash like the Vivitar 285HV does the metering in the flash in real time. The shutter is pressed, the flash goes off, the sensor cell meters it and when it sees it reach a threshold it cuts power to the flash tube.

When overexposure occurs with flash at high ISOs it is because there are physical limits to how fast the flash tube can be fired then quenched. The flash simply can't turn itself off flash enough to prevent overexposure of the foreground. You found that limit by trial and error to be f/4 and ISO 1600 and you just need to learn to work within it and change your flash strategies accordingly, in effect finding ways to make the flash less efficient.

In that situation to cut flash output I'd suggest using card style diffusers to split the path and bounce most of the light off the ceiling and only some forward, and adding a CTO filter to the flash which will both cut output and correct for the flash foreground.

I also would suggest using manual flash power and distance to control the foreground exposure for the simple reason it is more predictable. Since the limit you are up against is minimum flash duration put the flash on minimum power with the diffuser and CTO filter at the ISO and aperture you want to shoot at and dod some tests to find out what distance the foreground is correctly exposed. That will tell you your minimum shooting distance (restricted by min flash duration) for either manual flash or TTL. Then do testing and find out what aperture setting is needed for various other distances you typically shoot at at events, such as 8ft.

For the most consistent results find the camera settings / flash power needed with your gear from a baseline distance, set the flash zoom manually and adjust flash power as you change shooting distance. I use that manual technique with my Canon 580ex flashes whenever I find the ETTL exposure control isn't producing predictable results. I switch to manual power, find the power level needed for the distance I'm shooting, and stay at that distance. My DIY diffusers are attached to a vertical flash head, which is automatically zoomed to 50mm by the flash so there's no variable of flash zoom. My baseline shooting distance is 8ft. If for example I'm shooting at 1/4 power from 8ft I know from the inverse-square law that if I move out to 11 or 16 feet for wider shots I'll need to boost power from 1/4 to 1/2 or 1/1, respectively to adjust the foreground exposure lit with flash while keeping the background exposure consistent with the same aperture/shutter/ISO setting.




Dec 26, 2011 at 01:43 PM
wilt
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p.1 #10 · p.1 #10 · Thyristor Technology


A thyristor shunts the electricity from going to the flash tube and redirects that electrical energy BACK to the storage capacitor, thereby saving battery power and speeding up the recycle time when full output to the flash tube does not take place.




Dec 27, 2011 at 04:09 AM
 

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BrianO
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p.1 #11 · p.1 #11 · Thyristor Technology


cgardner wrote:
The main difference between a Thyristor style flash like a Vivitar 285HV and a modern digital camera TTL flash is how the exposure calculation is made. On a digital camera with TTL flash the amount of flash power needed is computed via the pre-flash and the flash it told before the shutter is fully presses how much flash is needed.


While the above information about how and when the metering is done is correct, it has nothing to do with whether the flash has a thyristor or not as I said above and as Wilt correctly states as well when he says...

wilt wrote:
A thyristor shunts the electricity from going to the flash tube and redirects that electrical energy BACK to the storage capacitor, thereby saving battery power and speeding up the recycle time when full output to the flash tube does not take place.


The reason a Canon 580EX, for example, is commanded based on a reading of the preflash when it's on a DSLR is because the sensor doesn't reflect light the way film does, and so OTF TTL metering (off-the-film through-the-lens) cannot work. Instead, the meter reads the preflash before the shutter opens revealing the sensor. If you mount a 580EX on a film-based body, then it will be commanded "in real time" as the exposure is taking place. So it's not about "the main difference between a Thyristor style flash like a Vivitar 285HV and a modern digital camera TTL flash," it's about the difference between a film camera and a digital camera.

Canon could have used a thyrisor to quench the flash on its Speedlites, but uses an IGBT instead; it's a newer technology.



Dec 27, 2011 at 05:36 AM
cgardner
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p.1 #12 · p.1 #12 · Thyristor Technology


Brian you are quoting out of context and editorializing and moderating about the advice of others again based on your own narrow interpretation of the question. You say I'm correct but just don't understand the context of the information I'm trying to convey because you can't get past your point of view....

Although I didn't quote the OP I was responding to his last statement where he said... " I had read in the day when there was less technology .... " which is why I referenced the Vivitar 285HV to explain the differences, not with respect to the narrow topic of thyristors but in practical usage of auto thyristor type flashes vs. camera TTL control.

"The difference between thyristor style like a Vivitar 285HV and a modern digital camera is how the exposure calculation is made...." With older Thyristor flashes like that one the exposure calculation was made entirely in the flash as a real time feedback loop independent of any camera control vs. today's digital cameras where pre-flash read and flash output controlled by the results of the camera with today's digital cameras.

So to clarify I was pointing out meter was done on flash vs. camera as the main difference between today and "when there was less technology".

A thyristor doesn't "shunt the electricity .... BACK to the capacitor" it more accurately simply switches off the flow of current from the capacitor to the flash tube which preserves the charge remaining in the capacitor.

With a flash the gap between the electrodes of the xenon flash tube act as the "ON" switch. To fire the flash a charge is sent to a ring, wire or shield around the flash tube which changes the state of the xenon in the tube enough to make it conduct a charge between the electrodes creating a "short circuit" across the electrodes which is what actually unleashes the charge from the capacitors through the open gate of the Thyristor to energize the xenon into a plasma state. A "thyristor style" speedlight signals the thyristor gate to close when it sees sufficient light, stopping the flow to the capacitor. The gate of the thyristor must then be reset to the open position for the next exposure.

Very early flash designs prior to the introduction of semi-conductor based Thyristors switching flash power was controlled by banking capacitors because there was no "OFF" switch. A flash with four capacitors could be banked to fire at Full power (all 4), 1/2 power (2 of 4) or 1/4 power (1 of 4). The trigger circuit would energize the flash tube and make the xenon conductive, closing the circuit and firing the flash until all the current in the connected capacitors was depleted.

The semi-conductor Thyristor technology added the "off" switch which allowed self-contained automatic metering on the flash and multiple flashes per capacitor charge. The auto sensor on the Vivitar flashes consisted of a simple sensor with ND filters which are placed over it. The ND filters clicked in place over the sensor would transmit less light vs. when no filter was over the sensor, which would cause the flash to stay on longer before the metering circuit triggered the closing of the Thyristor gate.

As for practical usage and comparison of flash control methodology (flash metering control vs. camera metering control)?

I used pairs of Vivitar Thyristor flashes since the early 70's, first with a pair of model 263 and then when switching to digital in 2000 a pair of 285HVs. In 2005, after using the 285HVs for a year on my Canon 20D I switched to a pair of 580ex.

The simple averaging on-the-flash metering on the Vivitar worked quite well with negative film for single flash use because negative film has about a 2 stop latitude for overexposure. So you could just err on the side of over-exposure and a good print could be made. Outdoors I'd set the camera at f/11 @ 1/250th and the flash on the "f/8" color code for ISO 100, shoot into the shadow side and get flash fill that was slightly under the ambient.

The auto mode didn't work with dual flash because the light of one flash would affect the output of the other. Since I use a pair of flashes as fill and key most of the time, most of the time I used my Vivitars in their manual power mode.

When switching to digital manual power mode on the Vivitars offered the same precise control it had with film but I found that in "auto thyristor" mode simple averaging metering cell on the flash didn't work a well because digital requires more careful exposure control for the highlights. The fact the flash sensor was metering the FOV similar to a 50mm lens created exposure variables when I used zoom lenses. I found it was was cumbersome to use the Vivitars in auto mode on a digital camera. While in theory you would set the lens to an f/stop corresponding to the color code on the flash sensor control ring such as f/8, in practice the metering wouldn't correctly read the scene requiring adjustment of the actual f/stop to obtain correctly exposed highlights.

Switching to the 580ex allowed me to utilize the zone based evaluative metering of my 20D in ETTL mode, or when more advantageous switch to M mode. It also freed me from the ball and chain of the sync limit outdoors, which was actually my main motivation for making the switch from the Vivitars.

Learning to use Canon ETTL flash effectively was an acquired skill. First it was necessary to understand how the camera metering of ambient and flash works on in the various modes and what the limitations are. I tested all 18 combinations of ambient and flash metering on my 20D because I was curious which, if any, produced the best results. The test results are here: http://photo.nova.org/Canon/TTL/ I concluded that evaluative ambient and evaluative flash metering did the best job overall and have used that combination with good results.

Part of my learning curve was how the flash operated at the higher ISOs possible with digital cameras. I discovered, as the OP did, that the limitation is a physical one: the minimum flash duration. As the OP discovered it is possible to raise the ISO to the point where the flash can't trigger the flash then quench it quick enough to avoid underexposure. In terms of getting good results understanding strategies to work around that limitation are more important IMHO than whether or not the physical limitation of the flash is the result of it utilizing Thyristor or IGBT switching circuit.



Dec 27, 2011 at 01:13 PM
BrianO
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p.1 #13 · p.1 #13 · Thyristor Technology


cgardner wrote:
Brian you are quoting out of context and editorializing about the advice of others again base on your own narrow interpretation of the question.


No, I'm just pointing out your (common) imprecise use of words. If you had said "The difference between older automomatic flashes like a Vivitar 285HV and a modern digital camera is how the exposure calculation is made...." I wouldn't have said anything.

You're repeating your error when you write in your last post "With older Thyristor flashes like that one the exposure calculation was made entirely in the flash..."

Once again, that has nothing to do with the presence of a thyristor. You should have said ""With older automatic flashes like that one, the exposure calculation was made entirely in the flash..."

Of couse I don't expect you to change. I'm sure you'll go on cutting and pasting the same long-winded posts into every thread that you always do, even when it has little to do with the actual topic at hand, and when the information includes mistakes you'll get all offended when someone points out the error -- for the benefit of those who actually want to learn something, not for you -- and you'll get all righteous and indignant and try to weasel out of it by claiming just what you done here; that I simply don't understand what you're really saying.

Well, I do understand what you're saying, and part of it is right and part of it is wrong. Get over it.



Dec 27, 2011 at 04:55 PM
cgardner
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p.1 #14 · p.1 #14 · Thyristor Technology


Brian....

What you don't get is that it's not your job to moderate the forum and limit the range of discussion. If I want to paint beyond lines you seem to define in threads "Once again, that has nothing to do with the presence of a thyristor. " that's something you should respect as my right as a participant. You don't moderate or set the rules for my behavior here, or decide what is out of order. That's Fred's job last I checked.

I never cut and paste I just type fast.... If the replies seem repetitive to regulars like you it is because the same basic questions get repeated. As for my use of the language most people seem to understand the point I make...

I have no problem with you correcting factual errors but please stop the editorials based on my use of grammar.



Dec 27, 2011 at 05:36 PM
dmacmillan
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p.1 #15 · p.1 #15 · Thyristor Technology


cgardner wrote:
Brian....
What you don't get is that it's not your job to moderate the forum and limit the range of discussion.

Neither is it yours. Your doing the very thing of which you accuse Brian, you're just too self absorbed to realize it.



Dec 27, 2011 at 08:43 PM
BrianO
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p.1 #16 · p.1 #16 · Thyristor Technology


cgardner wrote:
What you don't get is that it's not your job to moderate the forum and limit the range of discussion. ...I have no problem with you correcting factual errors but please stop the editorials based on my use of grammar.


In this case, it was a factual error, intended or not. Your post gave the impression that it's the thyristor that makes the difference between metering in the different flashes, and it's not; it's the built-in autosensor versus the in-camera sensor. If you put a 580EX II in auto mode it works just like a Vivitar 285HV as far as metering goes, but there's no thyristor in a 580EX II; it uses an IGBT instead. I believe the same is true of a Quantum Trio in auto mode.



Dec 27, 2011 at 09:07 PM
cordellwillis
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p.1 #17 · p.1 #17 · Thyristor Technology


I have to say that dmacmillan has a point.

Please make peace and lets get back to the actual subject instead of whatever this discussion is. Make use of the "HIDE ME" button if needed.



Dec 28, 2011 at 02:13 AM
hugowolf
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p.1 #18 · p.1 #18 · Thyristor Technology


cgardner wrote:
What you don't get is that it's not your job to moderate the forum and limit the range of discussion.


cordellwillis wrote:
I have to say that dmacmillan has a point.

Indeed. I canít see what Chuck doesnít see in the irony of his comments. But I am fairly new here, so perhaps I am missing something.



Dec 28, 2011 at 04:48 AM
Zenon Char
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p.1 #19 · p.1 #19 · Thyristor Technology


Thanks everyone for all your input. This helped and made sense. At least now I know why it is doing that.

"When overexposure occurs with flash at high ISOs it is because there are physical limits to how fast the flash tube can be fired then quenched. The flash simply can't turn itself off flash enough to prevent overexposure of the foreground. You found that limit by trial and error to be f/4 and ISO 1600 and you just need to learn to work within it and change your flash strategies accordingly, in effect finding ways to make the flash less efficient".

Metz USA told Auto mode was never designed to be adjusted using FEC. More that likely the cutoff time has something to do with it. Surprisingly adjusting the FEC will work and make and exposure adjustment. Only thing is if you are outside the flashes exposure perimeters it locks up both the flashes and on camera FEC adjustments.



Dec 29, 2011 at 07:57 AM
Zenon Char
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p.1 #20 · p.1 #20 · Thyristor Technology


Forgot to add this put me at ease. I don't have the flash back yet so I was a little concerned. If I need a higher ISO, etc I can just flip it over the ETTL. Since it pre-determines the flash output during the pre-flash stage it would make sense it can handle that much better. It should work just like my 580 flashes.


Dec 29, 2011 at 08:07 AM
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