Flash Duty Cycle

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defunktlemon

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jason
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Hi - Just joined the sit so big hello to all - Newby question please.
Actually, this is something someone recently tried to explain to me but I don't think I fully understand and feel a little dumb. I have uploaded an image of the explanation to make it easier to understand my problem.
So, for instance, If I am running a production line and taking images of the product every cycle period, I can change exposure time (ET) to get lighter or darker images and the Flash Duty Cycle (FDC) to stop my LED / Light Source from overheating. In the image you will see that the FDC at 100% gives a cycle time of 1250m/s, in which presumably I would be able to capture 100% well lit images at whatever ET I have set as 100% light would be given to all images at say 50m/s exposure.
At 10% FDC there would only be 125m/s within the 1250m/s total cycle time that I could capture frames in. So, if my ET is set to 25m/s or m/s then I would get good images, 5 images at 25m/s and 25 images at 5m/s. If I set the ET to 50m/s then I would get two good images but the third would only have 50% light and so be dimmer than it should be.
After the 10% of the total time is up, 125m/s I would then have to wait 1125m/s until the next cycle begins and I can capture images again.

This is a bit confusing for me and I'm not too sure I'm right, to be honest.

FDT.JPG
 
Welcome to TP :)

Can you first explain the subject and situation, what equipment you are using, and what your perceived problem is? The answer shouldn't be difficult from there but the information so far is confusing and even a bit contradictory ;)
 
What Richard said. Let's start with: is this a flash or a continuous LED lightsource?

Make / model?
 
Hi thanks.
I'm not sure what the equipment specifications are and not sure it really matters either. As far as I'm aware it is using a Basler camera and is being lit with a white LED. I'm afraid that is all I know. Picture (no pun intended) a production line of goods coming down a production line and being photographed in series, in a line, then the images run through a machine vision application / program. I really only wish to know how to work out what the correct percentage of Flash Duty Cycle should be with a given Exposure Time, as I was told that if these are set incorrectly with one another then one / or some of the series of images could come out black somewhere down the line. Hope that makes more sense.
 
The light source is a flashing LED, as it's a cheaper version of LED so can't stay on continuously.
 
It's pretty simple, the lower the flash power is set, the "quicker" it fires, the quicker it recharges, and the less hot it gets. But, because it's putting out less light, your camera settings will have to be different for a "correct" exposure compared to if it were putting out 100% of what it can.

I'm pretty certain that by "FDC" you're actually meaning flash duration (how long the light is on). And unless you are shooting something moving the duration itself shouldn't be a concern.

If you actually do mean Duty Cycle then there should also be corresponding "rest times" between cycles (which should/would be shorter for lower power settings)
 
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defunktlemon said:
Hi thanks.
I'm not sure what the equipment specifications are and not sure it really matters either...
Click to expand...
Well IMHO, that's where you'd be completely wrong. There's hundreds of active members who can give very detailed advice about 'ordinary' flashguns or studio heads. There's a handful who will have experience of LED lighting, and probably less than that who could give accurate advice on this kit, which appears to be a very specialised piece of kit which is unlike anything most photographers would have experience of.
 
The unknown nature of the equipment makes advice difficult.
 
defunktlemon said:
yes, I mean Flash Duty Cycle when I say FDC, not flash duration.
Click to expand...
Then you have mixed information, wrong information, or a lack of information.
m/s is meters per second but I assumed you meant millisecond.
The fastest DSLR's out there can only fire at a rate of 10/11 fps (~100ms per image) There's no way your getting 25 images w/in the 10% 125ms... you're not even getting two.
Duty cycle is how long and how many repetitions are possible before damaging the equipment. Duty cycles (total limit/time and recovery periods) seldom vary but the number of uses may (i.e. 10 at 10% or 1 at 100% and then cool-down). Depends on what the limiting factor is. Only the manufacturer can tell you what the duty cycle limitations are. (They are not only "time." If they were then the time would be greater for lower power settings/work load)
I've never seen an LED with a duty cycle limit (but my experience is limited with them).

The only way what you seem to be saying makes any sense at all is if you're doing stroboscopic photography/video. In which case your exposure time isn't relevant.
 
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OK, it seems I am being too ambiguous and confusing. I'm sorry for causing that and will try to get some better hardware details and figures to you all, though you do seem to be on track with your response so far sk66. So, apologies for the confusion and please allow me a bit of time to become more accurate in my description. thanks
 
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