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Archive 2012 · Continous equivelent of flash - Power
  
 
Beni
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p.1 #1 · Continous equivelent of flash - Power


Hi,

Looking for the (plug in) LED or fluorescent equivalent of a D1 500 used about 15" from the subject (repro studio) without any modifiers. I need as much power as possible in as small a package as possible because an LED modifier the size of a softbox will have the soft output of a softbox and we need much more contrastier than that. Problem is I don't know how to convert power from one system to the other so I don't even have a baseline for what I want.

Help?



Jul 30, 2012 at 05:50 PM
RDKirk
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p.1 #2 · Continous equivelent of flash - Power


There isn't a good equation to use. The LEDs will be rated in lumens or an incandescent watt-equivalent (and I've seen them vary wildly between brands of LEDs with the same real wattage).

Electronic flash will be rated in the watt-seconds capacity of the capacitors (which may or may not exactly represent the actual output) or more rarely the more accurate lumen-seconds with the standard reflector. This figure will be what the light output would be if the flash lasted a full second.

So you could figure what you'd want your working shutter speed to be and divide the electronic flash watt-seconds or lumen-seconds (preferably) by that amount to arrive at a rough lumen or watt level the continuous light must reach for that shutter speed (note that the electronic flash is always giving you a very short shutter speed equivalent).

The obvious problem is that the common measurement is "watts" and that is wildly inconsistent for both LEDs and electronic flash units. If you find a flash unit providing its lumen-second rating, you'll have a bit more to go on.

I do recall back in my early days working in a studio with a total of 10,000 watts of incandescent light that a 1,000 watt beauty light still left me with ASA (now ISO) 400 exposures of around 1/60 and f/5.6.



Jul 30, 2012 at 09:04 PM
markd61
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p.1 #3 · Continous equivelent of flash - Power


You mention that you need contrasty light. That means you need a smaller light source which lends itself to LED light sources well as they are very directional.

LED sources that are large are striving to provide the soft light that works around their native directional nature while also offering greater output.

There are quite powerful small LED lamps that may work for you depending on what shutter speed you need.



Jul 31, 2012 at 04:18 PM
Beni
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p.1 #4 · Continous equivelent of flash - Power


1/125 at f16 iso 80 at about 25cm distance.


Jul 31, 2012 at 04:24 PM
visualist
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p.1 #5 · Continous equivelent of flash - Power


Beni wrote:
1/125 at f16 iso 80 at about 25cm distance.


O_o, you have sooo no chance with these settings. If you choose two out of three maybe.

Oto a Speedlight should do the trick, too.



Jul 31, 2012 at 06:26 PM
 

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RDKirk
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p.1 #6 · Continous equivelent of flash - Power


There are quite powerful small LED lamps that may work for you depending on what shutter speed you need.

Is that "powerful" relative to small LEDs or "powerful" relative to electronic flash? How many lumens are you talking about? I consider about 7500 lumens (500 watts for incandescent) "powerful" for a photographic continuous light source.



Jul 31, 2012 at 08:21 PM
cgardner
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p.1 #7 · Continous equivelent of flash - Power


What exactly do you mean by "repro studio"?

To me repro (duction) implies copying flat object like books where the convention for lighting is lights on opposite sides at 45 angles.

Is that what you are trying to do with LEDs? If not what exacly are you photographing?

Also contrast in an image is a function lighting ratio vs. sensor range. The reason crossed 45 lights are used for copy work is that configuration creates flat even light on flat objects. For max contrast (no shadow detail) you'd want one small source off axis with no ambient or bounced spill fill.

Do you have an L-358 meter? The manual has a chart for converting EV readings @ ISO 100 into Lux and Footcandle readings.









Jul 31, 2012 at 09:57 PM
Beni
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p.1 #8 · Continous equivelent of flash - Power


visualist wrote:
O_o, you have sooo no chance with these settings. If you choose two out of three maybe.

Oto a Speedlight should do the trick, too.


At the moment we are using a Profoto D1 500 on about 2/3 of full power, a speedlite wouldn't come close I'm afraid. I thought that the LED's wouldn't manage but wanted to confirm so that I can remove them from consideration.



Aug 01, 2012 at 06:30 AM
Roland W
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p.1 #9 · Continous equivelent of flash - Power


You never made is clear what is wrong with your Profoto D1. With no modifier on it, it should provide a fairly contrasty light, and there is no practical way you can match or improve on the power output for your exposure over a strobe, except going towards a more powerful strobe.

If you want more contrast, you need the source to appear smaller to the subject. One way might be to move the D1 further away from the subject, and then focus its light toward the subject to keep a similar exposure. With the D1, you may need to add the dome accessory to allow the light to be properly focused, and then add a reflector like the standard 7 inch reflector, set to focus the light into a beam. Or, if your D1 is not bright enough when pulled back and focused, go for a higher power strobe. Profoto has heads up to 2400 watt seconds.

If you are lacking contrast in your current setup with it that close, it could be the wide beam of the D1 with no modifier reflecting off off other surfaces in the area of the shot, and acting like fill light. A real Profoto snoot, or an improvised way to limit spill and only allow a narrow beam to reach the subject may increase contrast.

And as others have mentioned, most copy type of photography goes for balanced dual lighting from two light sources angled in from two sides to lower specular reflections and fill shadows in, with an effect of making the lighting look like very low constrast. But without knowing what you are really trying to do, it is hard to advise. In any case if you want similar lighting level to your 500 watt second D1 strobe, you need to stay with a strobe, because there is no way any continuous light can match it unless you can take your exposure up to many seconds.



Aug 01, 2012 at 01:00 PM
visualist
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p.1 #10 · Continous equivelent of flash - Power


Roland W wrote:
there is no way any continuous light can match it unless you can take your exposure up to many seconds.


One or two, maybe three 5000W Follow-Spots will do it.

But since we have no idea what we're actually talking about it's a rather mute point.
When i started shooting small products, all i had were two SB24. Bare and at short range they put out a lot of light, but i'd have to dig into my archive to give exact numbers. 1/125 @f16 doensn't sound totally unrealistic with 25cm distance, but i honestly wouldn't vouch for that, since this was around 2003i'sh. The products also were only a cpl of cm large and verry similar. Add to this a crashed raid and it would be faster for me to set up a test shoot, then searching around.



Aug 01, 2012 at 02:35 PM





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