In the process of preparing for a project I discovered something about the three Yongnuo YN560 flash units I own.
The published Guide Number (GN58 at 105mm) does not match my experience. This makes it difficult to accurately expose a scene using the manufacturer supplied information.
As you already know, this model of flash is completely manual. There is no TTL capability, nor is there any built-in RF triggering (at least in the series one and two versions I own).
Someone measured the output of a more recent model Yongnuo flash and shared their results. They concluded that their measurements proved the factory Guide Numbers were accurate.
Who am I to doubt? So I followed carefully what was measured, set the camera and flash to the appropriate settings, and the image was... *sad clown sounds*... two stops under-exposed.
Huh. What had I done wrong?
If you've followed me over the years, you already know the importance I place on sorting things out "in the real world." Forget the marketing lies. Forget what someone claims to have measured, particularly if things aren't adding up correctly. Somethings they can be wrong. Or I should say, in the earlier days of Chinese manufacturing and sales, mostly wrong. And sometimes there are significant differences in systems of measurement and/or understanding.
So what would the real Guide Number of my flash units be?
To sort it all out I took a Sony A7 and A6000, mounted up a couple old manual focus Nikkor lenses, grabbed a tape measure and set out to find the answer.
Here is the simple formula for determining Guide Numbers -Guide Number = Distance (meters or feet) X Aperture
Test Setup -
- Sony A7 (following values set to M1 on the mode dial for future use in the field)
- ISO 100
- 1/125th sec shutter speed
- Daylight white balance
- Nikon Nikkor 24mm f/2.8
- Nikon Micro-Nikkor 55mm f/3.5
- Subject exactly 1 meter from the sensor plane
As you will see I made things as easy as possible to calculate GN's at various flash power settings by setting the distance to 1 meter. 1 times anything is still just anything. In this case the Guide Number is simply the Aperture (anything).
Guide Number = 1 meter Distance X Aperture
At each aperture setting (f/2 through f/22) I carefully noted the flash power output that gave the best range of tones from highlight down through and into deep shadows by looking at the image histogram.
Using 1/125th of a second and 100ISO, mapping flash power (FP) settings to Guide Number to distance, here is the matrix I came up with. As you can see, at 1 meter, the Guide Number in my case is the same as the aperture.In my system of Sony cameras, camera settings, Nikon manual focus lenses, and Yongnuo flash I found that the Full Power Guide Number is 22 at all flash zoom settings except 100mm where the Guide Number is a whopping 24. I found these GN's are valid for all three of my Yongnuo YN560 units. There is no variation between them.
- Distance = 1 meter
- GN2, f/2, FP 1/128
- GN3, f/2.8, FP 1/64
- GN4, f/4, FP 1/32
- GN6, f/5.6, FP 1/16
- GN8, f/8, FP 1/8
- GN11, f/11, FP 1/4
- GN16, f/16, FP 1/2
- GN22, f22, FP 1 (full pop)
- Distance = 2 meters
- GN4, f/2, FP 1/32
- GN6, f/2.8, FP 1/16
- GN8, f/4, FP 1/8
- GN11, f/5.6, FP 1/4
- GN16, f/8, FP 1/2
- GN22, f/11, FP 1 (full pop)
- Distance = 3 meters
- GN6, f/2, FP 1/16
- GN8, f/2.8, FP 1/8
- GN11, f/4, FP 1/4
- GN16, f/5.6, FP 1/2
- GN22, f/8, FP 1 (full pop)
To see how this works, let's say I have a subject 3 meters away and I would like to hit it with the correct amount of flash power with a lens aperture of f/4. Looking at the matrix I see I need to set the flash (FP) to 1/4. This is exactly how it reads on the back of the flash, so I don't have to think any further about it. Hit the shutter release et voila, a perfect exposure.
Now let's say I have a subject that is 2 meters away and I am using a polarizing filter (to knock reflections off certain subject surfaces). Let's say I would like to use an aperture of f/2. Looking at the table I see the flash power setting would be 1/32. Then taking into consideration that polarizing filters grab approximately two stops of light I see that I need to go from the GN of 4 to a GN of 8, where the flash is now set to 1/8 power. Hit the shutter release et voila, a perfect exposure.
Let's do one more calculation, shall we. Let's say we have a subject three meters away, want to use f/5.6 _and_ we have a polarizing filter. We start with a GN of 16. Then we need to account for the polarizing filter which is another two stops. A GN of 22 won't cut it as it's only good for one more stop. So, we need two flash units at 3 meters set to a GN of 22 (full pop) to give the subject enough light. Hit the shutter release et voila, a perfect exposure.
You might question why go through all the trouble? After-all, for a mere 500Euro/USD you can get a camera manufacturers own fully integrated flash system. Valid question, right?
A valid response is I'm a Cheap Old Slob. Being retired and living on a fixed income can do that to a guy. Further, I come from a time where these kinds of mental gymnastics were required and not optional. Balancing ISO (ASA back in the day) against shutter speed, flash output, and lens aperture was simply part of the act of making a photograph.
Here's what I paid (approximately) -
- 50Euro each for two new Yongnuo YN560II flash units
- 40Euro used for a third series 1 flash
- 30Euro on a pair of cheap flash stands
- 15Euro for a pair of shoot-thru umbrellas
- 8Euro for a silver bounce umbrella
- 15Euro for a three flash cold bracket
- 20Euro for an RF (FM band) trigger with two remote receivers.
For less than 230Euro/USD I now have a fairly flexible fully GN verified three light system. This, where just one Sony/Nikon/Canon flash would cost over twice that much.
I hope to be able to share results from an upcoming project. It would be fun show what's possible while on a fixed Cheap Old Slob income.
