Does 200W/s is sufficient to power up large modifiers?

[danielyamseng]

Does 200W/s lights is sufficient to power up a full body softboxes (5' or larger) and octaboxes (5' or larger) ?

[picturecrazy]

The answer is... it depends!

It depends on how far away from your subject the lights are.

It depends on if you are competing against the sun or are shooting under controlled studio-like conditions

It depends on whether you NEED to shoot at F/16 ISO100 or are ok with F/5.6, or ISO400.

It also depends on your shooting style.

For me, 200w/s would be MORE than enough for me under controlled conditions.

[danielyamseng]

The answer is... it depends!

It depends on how far away from your subject the lights are.

It depends on if you are competing against the sun or are shooting under controlled studio-like conditions

It depends on whether you NEED to shoot at F/16 ISO100 or are ok with F/5.6, or ISO400.

It also depends on your shooting style.

For me, 200w/s would be MORE than enough for me under controlled conditions.
picturecrazy, let say the subject to light distance is 3-6 feets in studio at F/8 or smaller ISO 100 ?

Could you explain a bit on 'more than enough in a controlled environment'?Then what's an examples of uncontrolled environment?
Is that mean a light >200W/s is for outdoor shooting to overpower the sun? Otherwise in as studio I still can use 200W/s at f8 ISO100 ?

Then if that's the case why some studio use light >200W/s i.e 600w/s and still not enough for potraiture shooting?

Is it related to higher W/s to freeze the movement ( i.e for high fashion shooting)?

Please advice because I want to use a high power light but turn to min all the time.

[Wilt]

It is not the amount of w-s that determines usability in a softbox...I have put a head on a 500 w-s power pack, on one of two channels (thereby putting no more than 250 w-s into the head) then switched the unit down to 1/4 power (250...125...62) then used the variator dial to reduced further (down to about 37 w-s)

The Alien Bee AB400 is truly a 160 w-s light (overinflated naming!) Buff web site says that unit into an AB softbox results in f/11- f/16, so it could achieve the f/8 you mentioned, as the basis of assessing the ability of a 200 w-s light to allow you to shoot at that setting.

[apersson850]

[nitpicking mode on]
It's not W/s, ws, w-s, w/s or anything else but just Ws.
[nitpicking mode off]

[Wilt]

[nitpicking mode on]
It's not W/s, ws, w-s, w/s or anything else but just Ws.
[nitpicking mode off]

Well if you truly wanted to be picky, the term is 'Watt seconds' with a space between the two words, so 'Ws' is unfortunately incorrect, too! bw!

[TMR Design]

Does 200W/s lights is sufficient to power up a full body softboxes (5' or larger) and octaboxes (5' or larger) ?

As a main light source, knowing you'll be using large modifiers with 2 layers of diffusion and pulled back enough for a full body shot, using ISO 100 and looking for f/8-f/11, I personally would be looking at a 400 Watt second strobe rather than 200. I'm not saying you wouldn't be able to get f/8 but I don't think it leaves you much leeway and depending on the distance between the light source and the subject it might just cut it or perhaps not cut it. 400 Watt seconds would give you those smaller apertures as well as the ability to turn down the power to get those wider apertures when needed or desired. Additionally, you can always use an ND gel on a modifier but if you don't have enough power you're screwed.

[vadim_c]

Does 200W/s lights is sufficient to power up a full body softboxes (5' or larger) and octaboxes (5' or larger) ?
You do not light the modifiers, you light the subject and the modifiers just shape the light. Going from here you can draw the following conclusion:
Since the impact of the light modifiers of the same type is approximately the same, i.e. your 5' softbox will absorb as much light as 3' it does not matter how big the softbox is. However one tends to move a very large modifier further away from the subject that gives an impression that the large modifiers require more light.
The bottom line it is the distance from the subject to the flash tube that dictates the power of light not its size.

[RandyMN]

Pretty funny debating watt second abbreviations or even nit-picking about it.

Oopps, is nit-picking cirrect? Oh no! Can I say Oopps?

Is my punctuation correct?

[RandyMN]

:lol:Shoot, I mispelled a word? Or is it mispelt?:lol:

Is it correct to use the :lol: at the beginning?

[vadim_c]

Pretty funny debating watt second abbreviations or even nit-picking about it.

Oopps, is nit-picking cirrect? Oh no! Can I say Oopps?

Is my punctuation correct?

Your sarcasm in inappropriate since there is a huge difference between W/S and WS.

W/S has no scientific meaning as Watt already contains the time factor (J/S does have meaning)

WS (or W*S) means the total ammount of light energy emitted during one actuation so light sources with low light intensity but long duration are not necessarily weaker than lights with hight intensity but short duration.

[eduardofrances]

Does 200W/s lights is sufficient to power up a full body softboxes (5' or larger) and octaboxes (5' or larger) ?
As others have said, the answer is "it depends" at which distance from the subject will you be using it? I can tell you that a 48x36 softbox modifying a 200ws monolight at full power with a distance of 1.5 meters approx from the subject gives you f/11, put more distance and you will loose exposure.

Sincerely: for a large modifier like the 5' octa I would seriously recommend a minimum of 500ws/600ws monolight or more power if possible.

[Wilt]

Your sarcasm in inappropriate since there is a huge difference between W/S and WS.

W/S has no scientific meaning as Watt already contains the time factor (J/S does have meaning)

WS (or W*S) means the total ammount of light energy emitted during one actuation so light sources with low light intensity but long duration are not necessarily weaker than lights with hight intensity but short duration.

You defined the mechanical definition of Power = Work / time.
A Watt as a unit of electrical power, Power = Volts * current (P= V*I)...it has not unit of time... Watt = volt * amp.

The Watt second is Power * time = Volt * Amp * Time.
By convention the Watt second is a unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second. Watt second = Power * time

The absurdity under debate is whether or not the 'Watt second' (W s) or the 'Watt-second' (W-s) is the right expression of the abbreviation (I care not which is right). Clearly the Watts per second (W/s) is the wrong expression.

[apersson850]

Users of Anglo-American units often find these things difficult.

Everyday users of the SI system of course has an advantage, especially when they happen to be graduate engineers in electrical enginering, like myself.

This is of course nitpicking, but I say that half humoristically, half seriously. But some people want to learn more things than just how to illuminate a subject. If you don't care about knowing, just skip the rest of this post.

Otherwise:

It's indeed Ws. Units in the SI system aren't written with multiplier symbols (W*s) unless necessary to avoid ambiguity. These cases are very rare, so implied multiplication is used in almost every case. They aren't written with any spaces either. But multiply and divide symbols, just like parantheses, can be used if you feel it will make things more clear. The unit for thermal capacity, J/kgK, may be easier to understand if you write it as J/(kg*K). It's Joule per kilogram and Kelvin.

It's also Ws, not WS. Units in the SI system that are named after people are written with upper case letters. In this case, James Watt has given name to the unit for power, so it's W, not w. But seconds is a unit not named after anyone particular, so it's s, not S. The unit S also exists. It's named after Werner von Siemens and is the unit for conductivity (the reciprocal of resistance).

Watt is the unit for power. The nature of the power is irrelevant. It must not be electrical. A gasoline engine capable of delivering 136 horsepowers at 6000 revolutions per minute is capable of 100 kW at 100r/s, for example.
The definition of 1 W is actually 1 kg*m²/s³.
Volt (V) is defined as kg*m²/(A*m³) and ampere is a base unit, so it's just A. Multiply the two and you get the definition for W.

[[godfather]]

Whooaa!! Physics Class...

[vadim_c]

You defined the mechanical definition of Power = Work / time.
A Watt as a unit of electrical power, Power = Volts * current (P= V*I)...it has not unit of time... Watt = volt * amp.


There is no electrical or mechanical power there is just power. It is perfectly correct to define power of a combustion engine in kW (although most people prefer horse power which is equal to 0.75 kW). It is also correct (althought very unusual ) to express the power of an electic bulb in horse powers)

At the end it is all the same - electical energy comes from mechanical movement of electrons.

As for the power which is exressed in (V * I) having no unit of time it is also incorrect as the definition of electrical current unit ( I in your example ) is a certain ammount or electical elementary charges that pass through a conductor in a certain ammount of time.


We can go deeper if you want but it is probably boring on a photography forum.

[apersson850]

As I said: If you care, then read it. Otherwise, don't bother.

The funniest thing with the unit for power, Watt, is that it was that same James Watt who came up with the unit horsepower. He wanted to rate his steam engines in a unit people easily could understand and compare to what a horse could do.

[qtfsniper]

http://farm4.static.flickr.com/3424/3192435737_6d81f4bb88.jpg

[vadim_c]

As I said: If you care, then read it. Otherwise, don't bother.

The funniest thing with the unit for power, Watt, is that it was that same James Watt who came up with the unit horsepower. He wanted to rate his steam engines in a unit people easily could understand and compare to what a horse could do.
He should have picked up a little stronger horse so 1HP would be equal to i kW :-)

[TMR Design]

I'm not knowledgeable enough in this area to participate in this aspect of the discussion, so I'll stick to the original question and information surrounding that question.

In a real world test I just fired my Elinchrom 600RX (600 Watt seconds) into an Elinchrom 53" Octa. The Octa had both layers of diffusion mounted. The room is approximately 14 ft. wide x 17 ft. long x 8 ft. high. The floor is wood, the walls are middle gray and the ceiling is white.

At half power (300 Watt seconds), with a Sekonic L-758DR positioned 3 feet from the front of the forward diffusion material, at ISO 100, I got a reading of f/16. That translates to 150 Watt seconds producing f/11. Obviously working a ISO 200 will give you an extra stop, and pulling the Octa further back will drop the level.

Using these numbers as a working reference you see that if you had 200 Watt seconds you would get the numbers you're looking for, but as I previously indicated, you might be hard pressed to get those numbers with the modifier pulled further back or if you wanted to see f/8 across two people or from top to bottom when feathered.

I would still opt for 400+ Watt seconds if I wanted to play it safe.

[RandyMN]

My Quantum is 200 'watt seconds' and even without using a diffuser I feel it is vastly underpowered for anything further than about six feet away at f/8.

This would be using either an ISO of 100 or 200.

My 400 'watt second' light is much better and my 600 is great!

I agree, play it safe and use 400 if you have the choice. If forced to use 200 then plan to stay within 6 feet at about f8. With a 5 foot softbox I'd cut an f-stop off that and I probbaly would not use a 7 foot or larger with 200 'watt seconds'.

[Hermes]

I'm not knowledgeable enough in this area to participate in this aspect of the discussion, so I'll stick to the original question and information surrounding that question.

In a real world test I just fired my Elinchrom 600RX (600 Watt seconds) into an Elinchrom 53" Octa. The Octa had both layers of diffusion mounted. The room is approximately 14 ft. wide x 17 ft. long x 8 ft. high. The floor is wood, the walls are middle gray and the ceiling is white.

At half power (300 Watt seconds), with a Sekonic L-758DR positioned 3 feet from the front of the forward diffusion material, at ISO 100, I got a reading of f/16. That translates to 150 Watt seconds producing f/11. Obviously working a ISO 200 will give you an extra stop, and pulling the Octa further back will drop the level.

Using these numbers as a working reference you see that if you had 200 Watt seconds you would get the numbers you're looking for, but as I previously indicated, you might be hard pressed to get those numbers with the modifier pulled further back or if you wanted to see f/8 across two people or from top to bottom when feathered.

I would still opt for 400+ Watt seconds if I wanted to play it safe.

My experience is similar.

200Ws should get you f/11 and perhaps even f/16 if you're like me and tend to use your lights close-in, but you'll be working at or near the max limit of your strobes' output. Once you start adding gels & grids, this will suffer even more.

Bottom line, if working regularly at f/11+ is important to you, go for at least 400ws (though I can say that it is incredibly rare to need to go above f/11 for studio work unless you plan on doing macro or product photography and are prepared to suffer the diffraction)

[Wilt]

There is no electrical or mechanical power there is just power. It is perfectly correct to define power of a combustion engine in kW (although most people prefer horse power which is equal to 0.75 kW). It is also correct (althought very unusual ) to express the power of an electic bulb in horse powers)

At the end it is all the same - electical energy comes from mechanical movement of electrons.

As for the power which is exressed in (V * I) having no unit of time it is also incorrect as the definition of electrical current unit ( I in your example ) is a certain ammount or electical elementary charges that pass through a conductor in a certain ammount of time.


We can go deeper if you want but it is probably boring on a photography forum.

The electrical engineers of the world would be very sorry to hear that their branch of physics and engineering does not exist.

http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/elepow.html

[bobbyz]

Using AB800 at 1/2 power and 5' photoflex octobox with both diffusion panels, I get f8 at 8-10 feet.

[apersson850]

Wilt, you aren't insisting on this, I hope? Nobody is questioning that electrical power is measured in Watt. It's just that all sorts of power is measured in Watt, so in that context there's no difference between electrical and mechanical environments.

[Wilt]

Wilt, you aren't insisting on this, I hope? Nobody is questioning that electrical power is measured in Watt. It's just that all sorts of power is measured in Watt, so in that context there's no difference between electrical and mechanical environments.

No, not insisting upon anything. Particularly not the definition of Watt, but question the insistence that there is only a single definition of "power" when there are two formulae, one for mechanics and the other for electrical.

[apersson850]

But there aren't. I gave you the definitions in post #14 above. They are all the same, when you take the definitions apart.

[fivegallon]

He should have picked up a little stronger horse so 1HP would be equal to i kW :-)

I don't care who you are, that right there is funny!! :lol:

[eduardofrances]

Instead of winding up into a long discussion about physics, in the end what matters the most is what the lightmeter readings say, and I get almost the same readings that Robert has kindly posted.

I think that in order to keep this on topic and help the OP with his question let's stick with the flash meter readings and examples and let the explanation behind the WS rating for another thread.

[abdul10000]

If I cut the distance of light to subject by half does that reduce my exposure by 1 stop? For example, if the light is at 10ft and I bring it closer to 5ft, will that reduce my exposure from f16 to f11?

[SkipD]

If I cut the distance of light to subject by half does that reduce my exposure by 1 stop? For example, if the light is at 10ft and I bring it closer to 5ft, will that reduce my exposure from f16 to f11?That would be fairly accurate for a small light source.

If you are using a large umbrella or softbox, however, then there would be much less change in exposure when moving the lights.

The inverse square law (which your assumption is derived from) truly applies only to a point source of light.

[abdul10000]

That would be fairly accurate for a small light source.

If you are using a large umbrella or softbox, however, then there would be much less change in exposure when moving the lights.

The inverse square law (which your assumption is derived from) truly applies only to a point source of light.

Thanks, can a 7" reflector be considered a point source?

http://www.alienbees.com/specs.html
Assuming so, Alienbee's specifications link states that using the B1600 (640ws) with a 7" reflector at 10ft and iso100 gives f22 exposure. Which means if the light was to be brought closer to the subject (more like 2.5ft which is the normal distance with portrait hard lighting) the exposure will go down to f64.

Using a light with a 5 stop range the exposure can be increased to a maximum f11. With a 6 stop range the exposure will go up to f8. Sounds like 600Ws is a little too much power for hard lighting, especially if the goal is to achieve f4-5.6?

[alan_potter]

With apologies for continuing the off-topic part of the discussion, why Ws and not Joules?

regards,
/alan

[bobbyz]

Thanks, can a 7" reflector be considered a point source?

http://www.alienbees.com/specs.html
Assuming so, Alienbee's specifications link states that using the B1600 (640ws) with a 7" reflector at 10ft and iso100 gives f22 exposure. Which means if the light was to be brought closer to the subject (more like 2.5ft which is the normal distance with portrait hard lighting) the exposure will go down to f64.

Using a light with a 5 stop range the exposure can be increased to a maximum f11. With a 6 stop range the exposure will go up to f8. Sounds like 600Ws is a little too much power for hard lighting, especially if the goal is to achieve f4-5.6?

If you need AB1600 and want to shoot at f4-f5.6, you should check out X1600. It is like Ab1600 and AB400 in a single light. There is a switch to go to lower power mode. That way you can go to really low power so that you can shoot at f2.8 and ISO100 if you need to.

[SkipD]

Thanks, can a 7" reflector be considered a point source?

http://www.alienbees.com/specs.html
Assuming so, Alienbee's specifications link states that using the B1600 (640ws) with a 7" reflector at 10ft and iso100 gives f22 exposure. Which means if the light was to be brought closer to the subject (more like 2.5ft which is the normal distance with portrait hard lighting) the exposure will go down to f64.

Using a light with a 5 stop range the exposure can be increased to a maximum f11. With a 6 stop range the exposure will go up to f8. Sounds like 600Ws is a little too much power for hard lighting, especially if the goal is to achieve f4-5.6?No, light from a 7" reflector does not act like a point source of light would (relative to the inverse square law). It is closer to acting like a point source of light, though, than light coming through a 30"x60" softbox would be.

You really need a light meter which can measure light from flash sources rather than trying to do math to establish your exposure settings. I highly recommend the Sekonic L-358, used in incident mode, for the purpose.

Your last paragraph is quite confusing. I don't quite know what you're getting at. If you can explain your thoughts better, maybe we can help with an answer.

[ebann]

With apologies for continuing the off-topic part of the discussion, why Ws and not Joules?

regards,
/alan

Here... enjoy and let's be done with it! :lol:

1 joule is equal to:
1×107 ergs (exactly)
6.24150974×1018 eV (electronvolts)
0.2390 cal (gram calories or small calories)
2.3901×10−4 kcal (kilocalories, kilogram calories, large calories or food calories)
9.4782×10−4 BTU (British thermal unit)
0.7376 ft·lbf (foot-pound force)
23.7 ft·pdl (foot-poundals)
2.7778×10−7 kilowatt-hour
2.7778×10−4 watt-hour
9.8692×10−3 litre-atmosphere
1×10−44 Foe (exactly)
Units defined in terms of the joule include:
1 thermochemical calorie = 4.184 J
1 International Table calorie = 4.1868 J
1 watt hour = 3600 J
1 kilowatt hour = 3.6 × 106 J (or 3.6 MJ)
1 ton TNT exploding = 4.184 GJ
Useful to remember:
1 joule = 1 newton × 1 metre = 1 watt × 1 second

[abdul10000]

If you need AB1600 and want to shoot at f4-f5.6, you should check out X1600. It is like Ab1600 and AB400 in a single light. There is a switch to go to lower power mode. That way you can go to really low power so that you can shoot at f2.8 and ISO100 if you need to.

Yes! that one interesting mono, how does it achieve that with two capacitors in one mono?

[abdul10000]

No, light from a 7" reflector does not act like a point source of light would (relative to the inverse square law). It is closer to acting like a point source of light, though, than light coming through a 30"x60" softbox would be.

You really need a light meter which can measure light from flash sources rather than trying to do math to establish your exposure settings. I highly recommend the Sekonic L-358, used in incident mode, for the purpose.

Your last paragraph is quite confusing. I don't quite know what you're getting at. If you can explain your thoughts better, maybe we can help with an answer.


Sorry I just realized that I was not detailed enough. Regarding the last paragraph, what I meant is that if you dial a 5 stop 600ws mono to its lowest power range it will give you f11 exposure at 2.5ft and iso100. Using a 6 f stop mono at its lowest setting will give f8.

Of course as you pointed out a 7" reflector is not exactly a light source so those f stop figures are most likely wrong. Probably the real f stops are a little higher.

[danielyamseng]

Sorry I just realized that I was not detailed enough. Regarding the last paragraph, what I meant is that if you dial a 5 stop 600ws mono to its lowest power range it will give you f11 exposure at 2.5ft and iso100. Using a 6 f stop mono at its lowest setting will give f8.

Of course as you pointed out a 7" reflector is not exactly a light source so those f stop figures are most likely wrong. Probably the real f stops are a little higher.
abdul10000, 600w at it's lowest setting still yeild f11 at 2.5ft at ISO100? At 50ws(min power), it's still able to produce such a result? What if a fullbody softbox and Octabox was used?

[Wilt]

The light is a virtual 'point source' from a 7" reflector if the distance between the object and the source is more than about 3x the diameter of the source, if I remember correctly; the farther away, the more it becomes a virtual point source. Also the 7" reflector does not behave like a true point source because its light is not all emitted in all directions, but it is somewhat 'focused' in its directionality. For short distances relative to the size of the source, lights may not strictly follow the Inverse Square principle. Inverse Square is generally applicable to lamps used in shallow reflectors, but not when deep reflectors are used, and is not applicable to the illumination provided by a spotlight'. Focused beams, like theatrical spots, also do not obey the Inverse Square principle. A softbox is not a point source because the distance to the subject is 'small' in proportion to it's size.

[phr0ze]

I'm getting .215hps out of my AB400. Should I be concerned?

[shooterman]

I'm getting .215hps out of my AB400. Should I be concerned?
I'd start feeding that horse some oats if I were you.

[bobbyz]

Yes! that one interesting mono, how does it achieve that with two capacitors in one mono?

capacitor bank switch from what I understand.

[ebann]

I'd start feeding that horse some oats if I were you.

bw!

[abdul10000]

abdul10000, 600w at it's lowest setting still yeild f11 at 2.5ft at ISO100? At 50ws(min power), it's still able to produce such a result? What if a fullbody softbox and Octabox was used?


Check this out:

http://www.alienbees.com/specs.html

The AlienBees B1600 (640Ws) with 1) 7" reflector 2) at a distance of 10ft from the flash meter 3) at iso100 4) powered at full power provides an exposure at f22.

Since the B1600 is a 5 stop power range monolight if you dail it to lowest power level 1/16 or 40Ws and do the same test you will get an exposure of f5.6.

Now To simplify my next example assume a 7" inch reflector acts as a "point source". In this second example keep all settings from the previous example and only change the light distance to 2.5ft from the light meter. Since the light is now closer by 2, exposure will move down from f5.6 to f11.

As others have pointed out a reflector in not technically a "point source" so my guess is that the exposure would be higher than f11, perhaps as high as f8. So for hard light application, a 640Ws unit seems too much. A 160Ws monolight would be 2 stops lower so it can provide f5.6 exposure at its lowest power setting or perhaps f4.

Hope this helps and if I did get anything wrong please correct me.

[Wilt]

Check this out:

http://www.alienbees.com/specs.html

The AlienBees B1600 (640Ws) with 1) 7" reflector 2) at a distance of 10ft from the flash meter 3) at iso100 4) powered at full power provides an exposure at f22.

Since the B1600 is a 5 stop power range monolight if you dail it to lowest power level 1/16 or 40Ws and do the same test you will get an exposure of f5.6.

Now To simplify my next example assume a 7" inch reflector acts as a source light. In this second example keep all settings from the previous example and only change the light distance to 2.5ft from the light meter. Since the light is now is closer by 2, exposure will move down from f5.6 to f11.

As others have pointed out a reflector in not technically a "light source" so my guess is that the exposure would be lower than f11, perhaps as low as f16. So for hard light use a 640Ws unit seems too much. A 160Ws monolight would be 2 stops lower so it can provide f5.6 exposure at its lowest power setting.

Hope this helps and if I did get anything wrong please correct me.

'Point source' is the term to use, not 'light source'

Since Inverse Square does not apply when really close to a not-point source, then the f/5.6 at 10' does not geometrically increase in intensity as you get closer. So rather than f/11 at 5' (per Inveserve Square) it might result in f/8 instead...you said f/16, which is creating more than a geometric lost with distance, not less.

[abdul10000]

'Point source' is the term to use, not 'light source'

Since Inverse Square does not apply when really close to a not-point source, then the f/5.6 at 10' does not geometrically increase in intensity as you get closer. So rather than f/11 at 5' (per Inveserve Square) it might result in f/8 instead...you said f/16, which is creating more than a geometric lost with distance, not less.

thanks for the correction, I amended my post. By the way my example is about bringing the light closer to 2.5' not 5'.

Is the bare bulb the best example of a point source?

[Wilt]

thanks for the correction, I amended my post. By the way my example is about bringing the light closer to 2.5' not 5'.

Is the bare bulb the best example of a point source?

Going from 5 to 2.5' with a 3' softbox would be similar in practice to going from 10' to 5' with a 6' softbox, so the actual distances matter only in relationship to the light source size. In any event, with a 7" reflector the light is probably acting closer to a point source even at 2.5' (4x diameter).

Bare tube is probably the best approximation to a 'point source'.

(BTW as an aside, in the film days there were some specialized enlargers available that had true point source designs for maximum contrastiness and detail definition -- vs. the many condensor light source elnargers which were improvements over low contrast diffusion source enlargers but still not as good as pricey true point source designs)

[apersson850]

...why Ws and not Joules?I wondered that too. Perhaps some tradition among light manufacturers?