does using led lights (on dimmed settings) on a cmos camcorder = banding ?

L

lt-cartman

Member
hi all just came across this thread where the following post was

http://www.dvxuser.com/V6/showthread.php?242438-LED-the-Z96-or-ALZO-790

the post stated the following regarding these 2 led lights the Z96 or ALZO 790?

Also, beware dimming ANY of these LED lights, if you're using a CMOS camcorder. Dimmed LEDs = nasty scrolling bands in your footage.

I have a canon hfs 10 which has a CMOS sensor and I'm very interested in getting a comer 1800 led light for it. my question is as follows

Has anyone with a canon HF S10 used a Comer led video light and dimmed it - if so was there scrolling bands as stated above due to the cmos sensor? or is this scrolling bands only evident with cheaper led lights?

thanks in advance for your help.

Toolman
 
Wouldn't be surprised. I think LED lights (esp. the less expensive ones) usually are dimmed by having an intermittent output, so what you'd effectively wind up with is a bunch of partial exposures. You could always just tape on a couple ND gels and flip them down when you need them, not like you have to worry about heat melting the adhesive.
 
thanks Moseph - to every one else has anyone used the comer 1800 or 900 light with the canon hfs10. If led is not an option whats the next best on camera lighting option (similar priced to comer 1800 i.e. £200

thanks
 
Not all LEDs will cause the banding when dimmed. The Yongnuo yn160 definitely does. The z96 doesn't. You really have to try the specific light you're interested in, at all dim levels, to know.
 
thanks Barry goood to know unfortunatly i am buying it over the net so i wont get a chance to try it out - so has anyone on the forums used the comer 1800 with a canon hfs10 thnaks in advance

Toolman
 
That banding effect is caused by the way the driver controls the bightness (dimming) of the led(s) in the lamp. Leds are fed a constant current through them as not to go overboard on the maximum allowed current. The dimming on the problem leds ( the ones that have the banding issues) are being controlled by the driver that is the PWM type or Pulse Width Modulation. The PWM driver really is the problem as it "pulses the led's on-off cycle duration to achieve the dimming effect. The longer the on cycle, the brighter the led(s) get. Problem is that most, if not all, led lamp makers, do not specify the type (PWM or nonPWM) type of the controller driver used in their design. The issue of banding really is not apparent on 30 fps ( frames per second) shutter speed capture but at specific higher speeds, notably 60 and higher. Led lamp makers did not take that in consideration but I am sure that they are all aware of that and most likely will change the configuration to fix the problem on their next production run.I have seen many complain about that with cheap and sometimes expensive led units. The driver necessary is the constant DC current type that varies the current flow and not the cycling of it. I have also seen the flickering effect when the battery voltage level is at a specific low point ( minimum threshold) of the lamp. This can be accomplished by putting in a dead battery with the others in order to lower the voltage. Somewhere on youtube has just that demonstration to something like led strobing or strobe effect. Banding is a serious issue and cannot be fixed in post or almost impossible.
 
I have seen this at weddings. Sometimes they line the wall curtains with LED's placed on the floor and only a few of them give the climbing band while the rest are fine.. Guess those are the ones that are slightly dimmed.
 
Hi Norman99 thanks for the detailed reason for the banding bars. - PS what non led on camera light would you recommend (similar specks to the comer 1800)

Does anyone know the main manufacturing website for the comer lights so i can email them about the dimmer circuitry
 
Leds don't have to be dimmed in order to exhibit the banding issue.Some have it on the midway setting and others on the high and anywhere in between. It depends on the driver circuitry design which varies from manufacturer to manufacturer and at the specific shutter speed (fps) of the camera settings. The el-cheapo led units that have dimmers on them are the ones to watch out for. I am not saying that they all have that problem but it seems that even the more expensive ones (and I am not going to name any brand) have the bug. I know that Comer is a very good and popular one, powerful and versatile, but I never saw or heard of any issues with that one. I don't think you can get far with any manufacturer circuitry schematics/specs/type as that is not relevant information necessary to the end user and also very confidential info. Electronic jargon is a language in itself. At this time we can only go by other user's experiences with various led units out there. I would make sure that the store/source of my purchase has a return policy or exchange after I try the lamp at various settings with different camera shutter speeds to verify. Also to mention is that not all PWM designs will have banding. Some have a dual circuitry (hybrid) that is designed just for that. Please don't ask me where to get them or which lights have them. I don't know. I just read up on them in the past during my research era, and were not mentioned in use for video applications. Read reviews, check out youtube for strobing/banding/horizontal lines etc. As a non led light to recommend... plenty out there. Lowell, Bescor, Frezzi, Anton Bauer to name a few. Why would you want to go to the non-led route ? Comer is the one I recommend, Taky in lacolor has excellent service and will answer all your questions.
 
Hi Norman Thanks for your continued info. I will let you know how i get on with my search. thanks again to all in the forum :)

Toolman
 
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