starcentral
Veteran
Anyone run through the quick skinny on the difference, advantage, pros/cons, etc.. ?
Thanks,
Thanks,
HMI: magnetic vs electronic
- Thread starter starcentral
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Cool Lights
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Magnetic Pros
- Quieter than Electronic due to use of sine wave and lower frequency drive on the output
- Less circuitry inside in general means less possibilities for things to go wrong
Magnetic Cons
- Must pay attention to flicker calculations as the 50 and 60 hz magnetic ballasts each have their own "safe" shutter speeds/frame rates.
- Transformer needed in a magnetic is heavy so the ballast in general will be heavier than the equivalent wattage electronic
Electronic Pros
- When running on a "flicker free" setting you are more likely to not have to pay attention to flicker shutter speed for normal frame rates (i.e. 24 to 30 fps)
- The higher the output drive frequency, the higher frame rate you can run for slo mo work. For example, an electronic ballast with a 300hz output driving capability allows you to do more frames per second
- In general lighter than the equivalent wattage magnetic ballast--no heavy transformer needed as the circuitry does all the work
Electronic Cons
- Is noisier than a magnetic. The noise emanates from the bulb and is related to resonance set up in the glass envelope by the type of wave of the ballast as well as the frequency. In other words, the higher the frequency output drive in general the more noisy they it can be. Square wave vs. sine wave is the other determining factor in noise.
- More complex circuitry inside means more to go wrong and also requires a qualified technician to fix should there be an issue
The main takeaway from this for most is that the electronic ballast is best to use when frame rate / shutter speed is such that it's necessary to use on and magnetic ballast is used when sound is most important. Its not often that both sound and high frame rate or weird shutter speed are important.
Since sound isn't often recorded on set at high frame rates (used for slo mo), then the normally louder electronic ballast with its "bulb noise" is more advantageous. Of course if you're doing higher frame rates for projection at the same high frame rate, and sound is important then you have to use other methods to make sure the bulb noise isn't recorded.
If I think of any more I'll edit it later.
- Quieter than Electronic due to use of sine wave and lower frequency drive on the output
- Less circuitry inside in general means less possibilities for things to go wrong
Magnetic Cons
- Must pay attention to flicker calculations as the 50 and 60 hz magnetic ballasts each have their own "safe" shutter speeds/frame rates.
- Transformer needed in a magnetic is heavy so the ballast in general will be heavier than the equivalent wattage electronic
Electronic Pros
- When running on a "flicker free" setting you are more likely to not have to pay attention to flicker shutter speed for normal frame rates (i.e. 24 to 30 fps)
- The higher the output drive frequency, the higher frame rate you can run for slo mo work. For example, an electronic ballast with a 300hz output driving capability allows you to do more frames per second
- In general lighter than the equivalent wattage magnetic ballast--no heavy transformer needed as the circuitry does all the work
Electronic Cons
- Is noisier than a magnetic. The noise emanates from the bulb and is related to resonance set up in the glass envelope by the type of wave of the ballast as well as the frequency. In other words, the higher the frequency output drive in general the more noisy they it can be. Square wave vs. sine wave is the other determining factor in noise.
- More complex circuitry inside means more to go wrong and also requires a qualified technician to fix should there be an issue
The main takeaway from this for most is that the electronic ballast is best to use when frame rate / shutter speed is such that it's necessary to use on and magnetic ballast is used when sound is most important. Its not often that both sound and high frame rate or weird shutter speed are important.
Since sound isn't often recorded on set at high frame rates (used for slo mo), then the normally louder electronic ballast with its "bulb noise" is more advantageous. Of course if you're doing higher frame rates for projection at the same high frame rate, and sound is important then you have to use other methods to make sure the bulb noise isn't recorded.
If I think of any more I'll edit it later.
Last edited:
starcentral
Veteran
Thanks Richard, what about life-span. If I'm looking to get a used HMI what would I need to know? Also is it true that some balasts can be used to drive the heads of other brands/makes?
Cool Lights
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Yes some brands do drive other brands of hmi head. I don't know all the different brands though and which work with which. That will require some research. Some use the same cables as well. The 7 pin Veam connector that Arri uses is a very commonly used one now. About lifespan, I would think the magnetics have a longer life in general because of the less active components. Hard to wear out a transformer (which is the main component) but it does happen.
Patryk_Rebisz
Veteran
Just to add a bit more info.
Transformer inside Mag ballast will wear out over time and get loud (sometimes very loud) - something to look out for when buying a used HMI kit.
Noise produced by the bulb when driven by Elect ballast is usually louder when dealing with double ended bulb as opposed to single ended bulb.
Transformer inside Mag ballast will wear out over time and get loud (sometimes very loud) - something to look out for when buying a used HMI kit.
Noise produced by the bulb when driven by Elect ballast is usually louder when dealing with double ended bulb as opposed to single ended bulb.
Cool Lights
DVXuser Sponsor
Good points on the transformer aging. Nothing's ever perfect. Just have to use whichever tool is best for each situation.
Never noticed that before on the double ended because I never use them.
Never noticed that before on the double ended because I never use them.
Adam J McKay
Veteran
This is a pretty informative thread. Good to know.