Lens Diaries Go Now
Glamour, Beauty, Nude, Models, Photographers

*    |  Register  


 
Go Back   Garage Glamour™ > Garage Glamour™ Main Forums > Main Community Forum
 

Main Community Forum General Modeling & Photography Forum
Adult posts prohibited!>>Please Read Our GUIDELINES before posting!

Reply
 
LinkBack Thread Tools Display Modes
True WS vs Effective WS ... What????
Old 02-01-2007, 01:14 PM   #1 (permalink)
Free Member

 
R_Fredrick_Smith's Avatar
 
Join Date: Jun 2003
Member GG#: 35872
Location: Dallas/Fort Worth Area
Posts: 3,660
Comments: 41

R_Fredrick_Smith is offline IP: 76.186.138.153
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

There has been a lot of discussion lately about different ways of measuring how powerful a flash system really is. Some manufacturers use the term "Effective WS" as well as True WS. Some people say that this is just marketing hype. Is it? What is the purpose of these two terms and what do they really mean?

This post is not about giving an answer, but rather exploring what is being talked about and perhaps leading everyone to a better understanding of the difficult nature of comparing how powerful two flash systems really are. In that light, I'm simply presenting a link to an interesting article about how one rates the powers of flash. It is a bit on the technical side, but nevertheless will give you a good idea about the fundamental facts in the question.

http://doug.kerr.home.att.net/pumpki...ash_Output.pdf

One interesting pull quote from the article is this:

Quote:
Accordingly, two units having the same watt-second rating can deliver
substantially different luminous energy levels. Some authorities have
suggested that the conversion efficiencies of typical studio flash units
fall in the range 15-50 lm-s per W-s (a variation of over 3:1!).
Efficiencies on the order of 40 lm-s per W-s are common with modern
units.
Anyway, read it over and then post your questions, responses, ideas, etc. and we can discuss the issue.

But don't use this thread to bash any products or get into other issues other than just the issue of comparing the relative power of a system to light a scene, as that will dilute and defeat the purpose of the thread, in my view.


In other words this thread is about discussing a technical issue of how flash system powers should be rated and what the ratings mean. So that may lead us to discuss Guide numbers, WS, lumens, etc.

Cheers,
rfs.
__________________

"The map is not the Territory"
  View Public Profile Send a private message to R_Fredrick_Smith Visit R_Fredrick_Smith's homepage! Find More Posts by R_Fredrick_Smith
 
Re: True WS vs Effective WS ... What????
Old 02-01-2007, 01:45 PM   #2 (permalink)
Lifetime Amateur

 
jford's Avatar
 
Join Date: Nov 2002
Member GG#: 35246
Location: Indiana, PA
Posts: 2,726
Comments: 7

jford is online now IP: 144.80.193.138
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Here you go again, spoiling a good discussion with facts.

Jeez
__________________
"Keeping shooting will do more for the excellence of your photography than most any camera will!" JimmyD, PGS Extraordinaire.
  View Public Profile Send a private message to jford Visit jford's homepage! Find More Posts by jford
 
Re: True WS vs Effective WS ... What????
Old 02-01-2007, 03:48 PM   #3 (permalink)
Lifetime Photographer
 
Join Date: Nov 2002
Member GG#: 35218
Location: Metro Atlanta
Posts: 717
Comments: 0

Doug_Lester is offline IP: 66.32.156.230
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Since I purchased my first studio type flash unit in about 1974, I have never known the watt seconds of either that first one or any later unit, including the lights I shoot with now. There are too many factors, including design, which can reduce a light's output. I've always been intrested in one and only one measure of a flash unit's output. What is the f-stop at 10 feet indoors and a 100 ISO? That tells me all I need to know and pretty much removes any promotional hype by the manufacturer.
__________________
Every normal man must be tempted at times to spit on his hands, hoist the black flag, and begin to slit throats.
--HL Mencken
  View Public Profile Send a private message to Doug_Lester Visit Doug_Lester's homepage! Find More Posts by Doug_Lester
 
Re: True WS vs Effective WS ... What????
Old 02-01-2007, 04:33 PM   #4 (permalink)
Free Member

 
R_Fredrick_Smith's Avatar
 
Join Date: Jun 2003
Member GG#: 35872
Location: Dallas/Fort Worth Area
Posts: 3,660
Comments: 41

R_Fredrick_Smith is offline IP: 76.186.138.153
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Quote:
Originally Posted by Doug_Lester View Post
I've always been interested in one and only one measure of a flash unit's output. What is the f-stop at 10 feet indoors and a 100 ISO? That tells me all I need to know and pretty much removes any promotional hype by the manufacturer.
Basically what you're talking about, then is comparing guide numbers. This can also end up being very misleading. To be accurate, all things about the angle of the reflector on the flash and the reflectivity of the environment have to be known for each flash in the comparison. If either of these bits of information is missing from one or both of the products being compared, then we can't know which flash is more powerful.

What often happens in competitive comparisons, is that one group will give the GN based on an unstated angle of coverage of the flash in question. So suppose one flash head gives a 80% angle of coverage and the other 50% angle of coverage, but both show the same guide number. Which is the more powerful flash?

Unless we know all the facts and do the test ourselves, we wouldn't know if these unknowns exist. Another example would be that group 1 publishes a GN for 80% coverage and group 2 publishes a GN for 80% and the published GNs are the same, but group 1 does their GN testing in a small all white walled studio and group 2 does their test in a small all black walled studio. Then which unit is more powerful if they both advertise the same GN?

So what I'm saying is, that unless we have full disclosure of the method of testing the GN, we can't know which unit is the more powerful until we test them ourselves.

In an ideal world, we would have a central testing organization that would test all flashes and give us a GN value that had real meaning because all would be subjected to the exact same testing conditions.

Cheers,
rfs
__________________

"The map is not the Territory"
  View Public Profile Send a private message to R_Fredrick_Smith Visit R_Fredrick_Smith's homepage! Find More Posts by R_Fredrick_Smith
 
Re: True WS vs Effective WS ... What????
Old 02-01-2007, 10:12 PM   #5 (permalink)
Free Member

 
johnrieger's Avatar
 
Join Date: Nov 2002
Member GG#: 35294
Location: Kansas City
Posts: 33
Comments: 0

johnrieger is offline IP: 24.2.23.245
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

For as long as I can remember - I don't think watt seconds have ever been an accurate way to compare one strobe to another. Manufacturers don't rate things the same & the light output all depends on which reflector is being used. I might be showing my age - but a long time ago Calumet Photo used to test the light output from each strobe head in a softbox at a set distance & list the f/stop obtained in their catalog. It was a great way to compare power packs & light heads from different manufacturers ( and even the same manufacturer). It would be nice if someone did that now.

John
  View Public Profile Send a private message to johnrieger Visit johnrieger's homepage! Find More Posts by johnrieger
 
Re: True WS vs Effective WS ... What????
Old 02-01-2007, 10:24 PM   #6 (permalink)
Free Member
 
Join Date: Mar 2006
Member GG#: 50494
Location: Torrance
Posts: 25
Comments: 0

coffee_mon is offline IP: 66.27.204.184
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

I've liked using lumen's as the standard for light output, this is what I've used for years on measured light levels in working spaces.

I would like to see an industry standard for measuring these lights. I would think a specified volume [sealed testing room] of a specified color with the flash ran as a bare bulb, no modeling light and any reflective surface masked to give any increase of the output of the system. Yes a standard would be needed for the measuring device as well [sekonic,gossen].

I've seen too many misleading statements on lighting, stereos, car HP and I'm sure the list can go on forever.

Mike
  View Public Profile Send a private message to coffee_mon Find More Posts by coffee_mon
 
Re: True WS vs Effective WS ... What????
Old 02-01-2007, 10:34 PM   #7 (permalink)
Free Member

 
DavidsStudio's Avatar
 
Join Date: Aug 2006
Member GG#: 54108
Location: Austin
Posts: 111
Comments: 0
Send a message via AIM to DavidsStudio

DavidsStudio is offline IP: 66.25.130.63
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Watts and watt-seconds have no direct relationship to the amount of light a unit puts out. Light output is measured in lumens. When you compare units, lumens are the critical numbers to compare. A 360 watt-second unit from one manufacturer could put out more or less lumens than a 360 watt-second unit from another manufacturer. The difference is due to the efficiency of the units design.

There is a good site that describes it a bit more. Site

Best

David
  View Public Profile Send a private message to DavidsStudio Visit DavidsStudio's homepage! Find More Posts by DavidsStudio
 
Re: True WS vs Effective WS ... What????
Old 02-02-2007, 12:27 AM   #8 (permalink)
Free Member
 
Join Date: Jan 2005
Member GG#: 41850
Location: Cleveland
Posts: 46
Comments: 1
Send a message via AIM to DannyZ

DannyZ is offline IP: 129.22.60.147
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Quote:
Originally Posted by DavidsStudio View Post
Watts and watt-seconds have no direct relationship to the amount of light a unit puts out. Light output is measured in lumens. When you compare units, lumens are the critical numbers to compare. A 360 watt-second unit from one manufacturer could put out more or less lumens than a 360 watt-second unit from another manufacturer. The difference is due to the efficiency of the units design.

There is a good site that describes it a bit more. Site

Best

David
You are correct sir, and while some of the design elements are electric, others aren't and can vary the efficiency based on your light modifier.

For example, a really efficient design could have a highly-polished reflector around the strobe's bulb to increase the lumens put out for a given amount of watt-seconds.

If the reflector is removed/changed, the efficiency will likely go down.

Rarely is glamour photography shot bare-bulb with a reflector. As soon as the reflector is replaced with a softbox (non-silver lined), the efficiency will go down to a level characteristic of most strobes with that actual watt-second rating in that particular softbox.

So one needs to keep in mind what light modifiers will be used to gauge how much power is needed.
  View Public Profile Send a private message to DannyZ Visit DannyZ's homepage! Find More Posts by DannyZ
 
Re: True WS vs Effective WS ... What????
Old 02-02-2007, 12:54 AM   #9 (permalink)
Free Member
 
Join Date: Jul 2006
Member GG#: 53796
Location: Wellington
Posts: 12
Comments: 0

dagwell is offline IP: 69.172.252.164
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Too bad most manufacturers don't give us the lumen-second output of their strobes. Then we could make fair comparisons.

On the other hand, I'd be surprised if the efficiency variation between modern strobes is as wide as the paper states. In fact, even the paper's author doesn't seem to believe that wide range.
  View Public Profile Send a private message to dagwell Find More Posts by dagwell
 
The problem as I see it.
Old 02-02-2007, 02:53 AM   #10 (permalink)
Free Member
 
Join Date: Sep 2003
Member GG#: 36812
Location: Saginaw
Posts: 320
Comments: 0

j4m3z is offline IP: 24.247.246.73
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Guide numbers can be fudged with reflectors and routinely are. Even Canon uses the guide number reflector trick by naming and placing first the guide number at the longest zoom. Hence the GN for the 580ex is 58 meters (190') *@105mm zoom*. It would be comparing apples to oranges to the Sunpak 120j which has a GN of 40 meters (120') but there is no zoom on a 120j and the standard reflector covers 28mm. Then if you go back to the 580ex and dig deeper you'll notice the GN drops to 42 m (138') at 50mm where, with the proper reflector, the 120j jumps to 150'. Hard to tell which has more power? It should be. Obfuscation gives someone a leg up.

Enter Wattseconds. You can't fudge a wattsecond. A tech can open up your pack or monolight and tell you haw many joules your equipment can store in the capacitors and presumeably dump in the flash tube. If the mfr lies it'll get out pretty quick and their reputation will be sunk. It would be false advertising. Sure there's a difference in light output due to efficiency but at least we know about that and are free to discuss it and it's impact on different manufacturers. While the differences are up to "3:1" I'd like to know what standard deviation is. See, that 3:1 is the range not the norm, in fact it's the least norm. Very few data points if not only 2 will match up with the 3:1 difference. In the end we're left with a measurement of stored power and not light output.

Enter Effective Wattseconds. Great, wtf is that? It's a unit of measure a manufacturer is free to define for themselves. For on mfr it might be 17.5lms per ws today, maybe 15 tomorrow, maybe 10 at another manufaturer. Either way, I see it as another obfuscation. I know it claims to account for the inconsistencies in effiency but it's more like saying there are problems with defining flash power in term of X so we'll define it in terms of Y but call it XY so it looks more like X. Naturally one wonders what is Y? Oh, Y is 17.5 * Z! It's all crystal clear now. You might as well say it's one quabillionth the light coming out of Osiris's crown when he comes to reclaim the throne of Egypt. It's using a similar terms only basing it on an arbitrary formula and coincidentailly (I'm sure) it makes them look better by direct comparison. Only instead of comparing apples to oranges (like you would ws to ws from competing mfrs) your comparing apples to roof shingles packaged in fruit boxes. If that wasn't bad enough the main proponent of effective ws claims 2.5x greater light output than an actual ws. If the entire range is light output difference due to effeciency is 3:1 how on earth can these lights be 2.5x (2.5:1) more effecient per ws than the "average light"? It's possible but extremely improbable. But all this could be solved if everyone used lms as their unit of measure! Yeah, but they don't. This is my own point of view on the issue and I've decided to disregard effective ws and generally distrust ANY manufacturer that uses them (there is more than one).
__________________
-James Mullineaux
www.jmxphoto.com
www.aaaarrrgggggg.com My Photography Blog
  View Public Profile Send a private message to j4m3z Visit j4m3z's homepage! Find More Posts by j4m3z
 
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How do I get a true black background? lvthunder Tech Talk Forum 12 01-02-2008 10:06 PM
Yes it's true, I wouldn't miss it... rolandogomez Main Community Forum 0 02-16-2006 02:26 AM
Which is the more effective image? icuphotography Main Community Forum 24 11-20-2005 02:34 AM
Well if you see me at an NBA game, yes it's true... rolandogomez Main Community Forum 11 10-28-2005 04:43 PM

Sponsors


New To Site? Need Help? Photographer & Model Links
All times are GMT -5. The time now is 10:49 PM.

© 1999-2017 Garage Glamour™




Search Engine Friendly URLs by vBSEO 3.2.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93