actinglight

<p>Just a quick noteregarding pelse length. I strictly believe - the best way is not to set the pulse length to any fixed value, but to make it variable. For instance - menu driven. If you'll be able to set by menu any desirable pulse length 1/1000000 or 3/10000, or 2/100, etc - what is the reason to care about X-sync speed? Just select preferable value and make a shot :) Agree? By the way I probably can't imagine other technology exept of LED able to regulate pulse duration is such wide range.<br />Regarding doubling the current. Yes, you're right. After reaching the nominal current value dependence of light output is not linear. Actualy douling the nominal current increases the light output at appriximately 60% only</p>

<p>Please pardon me for mistyping and missed zero. Flash contain 8x10W LEDs. Their nominal current is 1A (each) and maximal allowed is 2A. At my unit each of them takes near 1.5A at pulse. Regarding self-capacitance and pulse duration. Thank you for your advise. I agree - the exact length of light pulse duration need to be measuared well. At current I have only data based on measurement of current made by oscillograph. As you've pointed, due to self-capacity their could be an extra illumination for some time and exact lighting characteristics on short pulses could be not as well. Maybe you can point me to equipment able to do such measurements?<br />Regarding transmition lines I can completely agree. An impendance here is a critical issue. Because of impendance of each LED chip is low, it is easy to loose a lot of power on poor designed transmition lines. Need to say - it was a huge issue at first prototypes. We've made a lot of efforts to find low-impendance power supply and to design transmittion lines well, because even each extra millimeter of conductors counts here. And design of contacts between parts of transmitting lines was a true nightmare. <br /><br> Thank you a lot for advise<br />Leonid</p>

<p>Dear Joe,<br />Regarding LED lifetime. The manufacturer of LED's I'm using guaranties their lifetime to be 50000 hours of coninuous work. Value above 10000 hours is a typical for LEDs. I definitely haven't tested my LEDfr so long, because it means above a year of continuous work :) Nevertheless after 4 months of intense use I have no signs of their degradation. Heat seems not be an issue for pulse mode. Where are several LED chips are placed into the lighting head, and each chip takes only a bit above 1W. Also pulses are short. So power dissipation is going during relatively short time. Well designed cooling system allows LEDs to return to normal temperature between pulses. I've got signs of overheating in case of continuous work within several seconds. Just for this reason upper limit for pulse duration was set to 1 second. <br />Regarding pulse length. I completely agree - sometimes bullet looks a bit blured. From my point of view the main reason for this is rather small focus depth (apt 7.1 is not good for close-up shots). Measurement of current indicates pulse length is close enough to value I'm setting by menu. But I think I should measure the length of light pulse itself<br> Best regards,<br> Leonid</p>

<p>Dear Walker Angell,<br> Thank you for your response and warm words. One of my nearest plans is to make a special macro-head for my flash. It promise to be highly configurable.<br />Regarding camera settings, I'll indicate settings for some samples here.<br> 1. Pulse duration 1/10000 sec. Camera settings: ISO 800, apt. 7.1. Due to no TTL support - camera exposure set to sync value (1/100 sec).<br> <img src="http://d6d2h4gfvy8t8.cloudfront.net/18199248-md.jpg" alt="" width="680" height="453" /><br> 2. Pulse duration 1/50000 sec. Camera settings: ISO 400, apt. 7.1<br> <img src="http://d6d2h4gfvy8t8.cloudfront.net/18196645-md.jpg" alt="" width="680" height="453" /></p> <p>3. Pulse duration 1/1000000 sec. Camera settings: ISO 1600, apt 7.1<br> <img src="http://d6d2h4gfvy8t8.cloudfront.net/18199253-lg.jpg" alt="" width="1024" height="683" /></p> <p>4. Strobe mode. Pulse length: 1/1000000 sec, interval between pulses set to 3/10000 sec. Camera settings: ISO 1600, apt 11<br> <img src="http://d6d2h4gfvy8t8.cloudfront.net/18199252-md.jpg" alt="" width="680" height="453" /></p> <p>Best regards,<br> Leonid</p>

<p>Dear Wayne, realy a good question and I'm not sure I have right answer for now. I just can give only a few digits. Each pulse gives me 10000 lumens. It is somehow similar to usage of continuous light with 1000W halogen lamp. And in case of using of "ideal" camera allowing to set any desirable exposure, how would look like pictures taken with exposure 1/1000000 sec? Because my current prototype is not a ready to use commercial product I haven't made full set of measurements. For now I can only say pulse duration 1/500 sec gives enough lite for portraits at ISO 100, apperture 5.6, taken from 3 meters. And pulse duration 1/1000000 gives enough light to make pictures at ISO 800, apperture 9-11, with distance from flash to object near 50 cm. Moreover, I've discovered heavy light loss due to dissipation and definitely need to improve construction of lighting head to avoid it. Think determination of guid will have a sense only after construction will be finalized</p>

<p>My unit is dissipating 125W. LEDs in use gives 100 lumens per watt. The key reason of using capacitors for pulse lamps is not the energy itself, but high voltage. Typical value for xenon pulse lamp is 300V. If you have 4 accumulators giving near 10V, you need to riise voltage 30 times. But the current will drop accordingly. So to get 1A at 300V you need to get the current of 30A at 10V. No one of portable accumulators could give such value. So, it is neccesary to collect necessary charge for a relatively long time. And capacitors are placed just for this reason. If you can get a high-load power supply giving 300V, you probably could remove capacitors and use this power supply directly. Unlike pulse lams LEDs are working at lower voltage. In case of parallel connection it is possible to keep voltage as low as 12V. So, 4 3.7V accumulators could give necessary volage easely. Because some modern accumulators are designed to give high current, it is possible to get necessary energy without capacitors. </p>

<p>Thank for responses. Let me give some answers:<br />1. Dear Charles, LED's doesn't require any capacitors, so zero recharge time is realy possible. The device I have assembled indicates it clearly. I've got above 100 pulses in a row in strobe mode at full power even if interbal between pulses was setup to as low as 1/1000000 sec. As well I've got complete support of camera row in serial mode at full flash power<br />2. Dear Matt, I can somehow agree. Device I've assembled can give near 10000 lumens (such as 1000W hallogen lamp), and it is below the value given by pulse lamp. But it seems to be enough to make the device useful. At pulse length 1/500 sec I have enough light for portraits and at pulse length I have enough lite for commercial quality pictures of relatively small scenes. But in general I can agree - LEDs are not as bright as pulse lamps<br />3. Dear Henry. Overheating realy could be a big issue for pulse lamp working with high frequency. And typical value for them is near 1000 HZ max because at higher frequency it could form a kind of short circuit due to ramaining plasm. LEDs are free of this issue, and cooling quickly enough</p>