Speed light power

The godox ring that will hold the flash is a Bowen's Mount and will fit in any soft box that accepts Bowens.

 

I think it's a pretty good value at 299 and you can go bear ball with it you can put the fresnel lens on it you can put barn doors on it.

 

You can go with the godox brand or you can go with the flashpoint which is just rebranded by Adorama camera but it's basically The Identical same thing.

 

Especially in my situation I don't need TTL and all that fancy stuff I just need Power and Light.

Guide Number (GN) is like a car's horse power or mileage or stereo output power. Depending how you measure, you can get different results.

This has been a problem since the 1960s when I got into photography.

 

If you measure the flash with a flash meter in different environments, you will get different results.

• A small 10x10 WHITE room (floor, walls, ceiling).
  
• A small 10x10 room with creame walls, popcorn ceiling, brown carpet.
  
• A hall, carpet floor
   
  
• Outdoors on grass
  

Each of these will give you a different reading.

• The manufacturer likely will use the first, as it will give the highest reading, and thus the highest GN. Even light not aimed at the subject/meter will bounce back and hit the subject/meter, giving the max reading.
  
• Shoot outdoor on grass and you are at least 1 stop down, because there is nothing to reflect the light back on the subject.
  
• So you will likely not match the manufacturer's GN spec, because you are not shooting in that max reflection room.
  

And you need to READ the details of the spec, to see if they are playing games, to get a higher GN.

• If they spec at ISO 200, than at the standard ISO 100.
  
• If they spec at 5ft, rather than the standard 10ft.
  
• If they spec at 10 feet rather than 10 meters, for the people that use metric.
   
  
• If they use the tele zoom setting, rather than 50mm/standard lens zoom setting.
   
  
  • Then how do you compare to a flash that does not have an adjustable zoom, where the flash angle could be a normal lens or a wide angle lens?
    
  • And what is the flash angle for a normal lens?
    

So to sum up, use a flash meter and build your knowledge level based on experience with your equipment and shooting style.

"This has been a problem since the1960s when I got into photography."

 

Maker's wildly inflated guide numbers are the problem. I doubt that even a small fully white room would give the GN quoted by the manufacturer. A length of white drainage pipe maybe.

 

Makers' Guide Numbers are probably the next most pernicious hyperbole after 'The cheque is in the post' and 'Best cooked from frozen'.

 

Anyway, you only get taken in by the lie for a short time before automatically knocking a stop off the stated GN, or buying a flashmeter.

 

"And you need to READ the details of the spec, to see if they are playing games, to get a higher GN."

 

- I'm pretty sure there's an ISO specification for measuring Guide Numbers, which I'm not going to pay 50 Euros to view, but I believe the standard measuring distance is 2.5 metres = 8' 2.5".

 

"And what is the flash angle for a normal lens?"

 

- Easily worked out. A 'normal' lens has a focal length equal to the diagonal of the format, which gives it a diagonal angle of just over 53 degrees. This equals a horizontal AoV between 39 and 45 degrees for common aspect ratios.

My first "professional" flash was a Strobonar 700. Honeywell advertised a guide number of 80 @ ASA 25 (f/4@20 feet). However, my initial tests using transparency films, was that it was off by at least one stop. I couldn't afford a flash meter at the time, but figured that transparency film couldn't be fooled by the printer. What you shot, was what you got, and I adjusted exposure to compensate, knowing that print film could be "fixed" by the printer. A couple of years later, I found a Wein WP500, which revealed the ugly truth, Honeywell was guilty of hyped advertising! :eek: :eek: Was I surprised?

 

The Honeywells gave a nice warm light, which brides liked, despite the adage that pale skin was in.

The limiting factors in flash power are the voltage, typically 450 VDC or less, and physical size of the capacitors. The power, in joules, is V^2 * C (in farads). An electrolytic capacitor which holds 100 joules (watt-seconds) at 450 VDC is about the size of one of these new, skinny Coke cans. Electrolytic capacitors are used because they have a large capacitance in a small size and weight.They also have high internal impedance, which stretches out their discharge time (less reciprocity effect). Really powerful flash units, used for aerial reconnaissance are often oil-filled, and run at up to about 10,000 VDC, and have flash duration in the millionths of a second.

 

The guide number is the most useful data regarding use, but depends on how well the light is focused, and has little bearing on the total power of the unit. A soft box spreads the light over such a large area, the effective guide number almost vanishes. My first pro flash was a Graphlex Stroboflash IV, 400 Joules, with a pack weighing about 9 pounds. It produced about as much light (integrated, intensity x time) as an AG-1 flash bulb.

 

Since the OP is using a large Westcott soft box, a mono flash would be a better choice than a "speed" light, designed to fit on a camera shoe, and generally less expensive. If you don't need a lot of frills, you can expect to pay about $1 per joule. One or more 250 Joule units would be a good place to start. You'll spend a lot more for a Broncolor or Profoto flash, but get a constant color temperature at any power setting.

 

Be sure to budget for a portable flash meter too ($350 or so). TTL flash takes more time to set up and is less reliable than the old-fashioned method.

"The power, in joules, is V^2 * C (in farads)."

 

- The energy in Joules is 0.5C*V^2.