3 Things Photographers Get Wrong About Flash

If you’re diving into using strobes for the first time or if you are still learning how to use additive lighting in your photography, then definitely check out these three misconceptions that many photographers have about shooting with flash.

Coming to you from Pye Jirsa of SLR Lounge and Adorama TV is a quick educational video on some of the biggest obstacles when tackling flash photography as a beginner. Pye does a great job of relaying how each of these issues works and the misconception behind the thought process versus the reality. Let’s dive into one of these explanations a little more in depth, and I’ll share how I learned to quantify the inverse square law in a way that may be more intuitive.

As the video explains, when we take a light that is a certain distance from the subject (for example let’s say one meter or about three feet) and pull the light back to double the distance (now at two meters or about six feet), the light that is hitting our subject is not halved but is actually reduced to a 1/4 of the amount of light. This is the inverse square law. This also works in a similar way if we take our light and move it closer to the subject (decrease the distance by half): we then have four times the amount of light on the subject. This is the explanation of the inverse square law that we are used to, but it’s not a great way to understand how light works in a real world scenario when we might want to change the lighting to actually be 1/2 as powerful instead of 1/4. This is why we should all know how our f-stops work, as they describe exactly how our light power works and it gives us our formula to use, too!

Let’s say I have a multiple light set-up where everything else is perfect, but my key light is metering at f/11 and I need it at f/8, a one-stop difference or half the power of f/11. If we move that light the current distance multiplied by 1.4 (as in f/1.0 to f/1.4 is one stop or half the amount of light), then you have brought that light down in power to f/8. If we needed the key light instead to be at f/5.6 then we would simply double the original distance (for example, f/1.0 to f/2.0 is two stops difference), and therefore, we've calculated that we would have to multiply the distance by two. We are in fact substituting our f-stop for the multiple of our original distance to quickly change the power of the light. 

Next time, if you’re doing portraits outside, and your subject is a little too bright, then try pulling your light back by the original distance multiplied by 1.4. For example, if your original distance is 3 meters, then you will try to move your light back to about 4.2 meters from your subject. If you think more in terms of imperial measurement, then if your light is 10 feet from your subject you would multiply that distance by 1.4 and move the light to about 14 feet away from the subject. This will reduce the amount of light hitting your subject by one stop just like if you were closing down your aperture from f/1.0 to f/1.4. 

Let us know if you learned a bit more about flash from Pye and Adorama from their video or if you’d like to add to the top things photographers get wrong about flash.

Log in or register to post comments

21 Comments

Benoit Pigeon's picture

Third point is not complete. I am glad that finally t.1 is viewed like it is, but there is a lot you can do with Hyper Sync to obtain the same or very similar results as well.

Brook Brown's picture

“Hyper Sync” refers to long flash durations as a method for using flash at shutter speeds that exceed the cameras flash sync speed. You certainly won’t be freezing motion with the flash using this technology. I don’t see your point.

When it comes to freezing motion with flash, the t.1 speed is only relevant for shutter speeds at or below the camera’s flash sync speed.

Karim Hosein's picture

Hypersync has several issues; gradation, rolling shutter, limited power, & limited usability (strobe-camera combinations).

Hypersync relies on the t.5 time, and the actual shutter speed, (meaning the speed at which the shutter moves, versus exposure time, meaning the duration for which the sensor is exposed).

If freezing motion is the goal, then X-sync exposure times at low strobe power levels is the preferred method. Using HSS or Hypersync is only for balancing strobe with ambient light when exposure times need to be slower than X-sync times, (a.k.a., the actual shutter speed).

Now there is something which most photographers get wrong. Shutter speed is how fast your shutter moves, and determines the X-sync speed on focal plane shutters, and shortest exposure time on leaf shutters. Exposure time is what affects the exposure.

Benoit Pigeon's picture

I don't agree with this entirely. Broncolor RFS2.2 has it dialed very well and barely has any banding. I have tested with various packs and Siros as well at many shutters. Power is not really an issue if you use a lower end (longer duration) but powerful 1600ws TopasA2.
Compared to t.1 using a Grafit, you can shoot either technique and achieve the same result. The advantage I currently find with t.1 is multi exposure on a single frame.

Karim Hosein's picture

ME: «…limited usability (strobe-camera combinations).»
YOU: «Broncolor RFS2.2 has it dialed very well….»

ME: «…several issues; gradation….»
YOU: «…and barely has any banding.»

ME: «… limited power, & limited usability (strobe-camera combinations).»
YOU: « Power is not really an issue if you use a lower end …powerful 1600ws TopasA2.»

We agree. …Except you ignore the rolling shutter issue and the freezing motion issue.

Benoit Pigeon's picture

What do you use for Hyper Sync? I had too many issues with Pocket Wizard, I totally stopped using mine.

Benoit Pigeon's picture

I can't locate the series of tests I did to evaluate t.1 and Hyper Sync so I will do another similar test later this coming week depending on my schedule. This image only illustrates t.1.

Karim Hosein's picture

In these images, the exposure time is longer than the X-sync time, and can be taken using any flash, HSS and Hypersync not necessary. For reduced flash power, typically the output of the flash is abruptly cut after t.5, t.75, t.875, etc. (Some strobes use reduced voltage, but that complicates things).

HSS is for exposure times less than X-sync time, and is done by a series of flashes at less than full power, to allow exposure of the entire sensor as the slit passes over.

Hypersync is also for exposure times shorter than X-sync, but requires t.5 to be much longer than the X-sync time. This typically only happens on very powerful studio strobes (as you have been using), or poor quality hot shoe strobes.

Hypersync relies on the strobe being triggered at full power before the leading shutter starts moving, so that by the time the sensor starts to be exposed, the flash power has already diminished below t.5, so that the light power decay over time is not too severe for the remaining exposure time. (But there still is a decay, hence, gradation).

I, myself, never use hypersync, and don't ever recall using HSS, as the need for flash below X-sync time has not occurred for me yet.

Benoit Pigeon's picture

Speedlights will probably not do the above especially the one on the left and at f9. I would have to see it done to give it a thought. Speedlights generally require less power for short duration while strobes work the opposite way and most strobes are not capable of short duration.

HSS is pulse and can only make use of half the power of the unit. By default it will limit the output affecting the result. I don't know if HSS can fire three times on a single capture as in three groups of pulses, at least I have never seen any example of this. But you could probably use 3 units with a delay for each and achieve that result.

Hyper Sync can be used at any power level the pack or monolight can produce and is not limited to full power. The shutter speed needed for a set aperture will dictate how much power is needed.

Strobe units (not speedlights) that are capable of very short duration (T.1) do need full power in order to achieve the shortest flash duration it can (lower setting), but even at half power they can deliver durations that are not needed for most applications. They are not suited for Hyper Sync.

Karim Hosein's picture

First off all, stop conflating terms. A strobe is a flash, a flash is a strobe. A Speedlight™ is (or was) a trademark of Nikon branded hot shoe strobes/flashes.

The first picture can be done with a hot shoe flash. I have several capable of multi-bursts. It is not a problem. However, when I said that they can be done with any flash, what I meant was that no special HSS ability or pre-curtain trigger (Hypersync) necessary. (Wait…. Didn't I say that? I did).

Secondly, HSS is firing the flash (at low power) several times over the duration of the X-sync time, simulating a pulse of continuous light, and typically produces much less than half the power output of light.

Hypersync can typically only be used at full power, because, for most strobes, anything less than full power means that the discharge curve will be truncated. Some flashes reduce power by using less voltage, but this also means that the discharge curve extends for less time.

The discharge has to last for longer than the X-sync time, (and has to start prior to the leading curtain trigger), regardless of the exposure time required, (but it's indeed based on the speed of the shutter curtains).

HSS, invented by Olympus, is a workaround, (for fill-flash at shorter than X-sync times), and Hypersync, invented by Pocket Wizard, (I think) is a hack, (for a lack of HSS in the strobe/camera combination of choice).

All strobes are better at freezing action at lower power settings that higher. At lower power settings, the discharge is cut earlier, resulting in a shorter time of output exposure.

It matters not if it is a studio strobe or hot shoe strobe. It matters not if it is 200Ws, or 1600Ws. It matters not if it is GN 60m @ 105mm or GN 18m @ 105mm. Lower power settings cuts the light output early, reducing the exposure time.

This does not affect t.5 nor t.1 specifications, as those are based on the output curve of an uninterrupted, full power, discharge.

T.1 is the time it takes for light output to fall to 10% of the maximum level, where's t.5 is the time it takes to fall to 50% of the maximum level. If the flash is set to ¼ power, the output will be cut long before t.5 arrives.

Benoit Pigeon's picture

So I have done some test tonight, this time using the track and HotWheel car with HyperSync and I can confirm what you say when shooting the car at 1/8000. It's not as clean, definitely not as sharp as the t.1. I did not notice rolling or any trails. However I had to use much higher ISO for the Hyper Sync.
The set up with the miniature car is to me a very extreme case. It took a clip with my phone and compared the car speed with a timer and it takes less than half second for it to travel the full loop.
In actuality, I use Hyper Sync for full size race cars at night to reach 1/400s to 1/500s with my lights. For other applications, I can cover t.1 with no issue. I therefore don't need extremely fast shutter speed with Hyper Sync, but I assumed it would probably give similar results to t.1. There is only limited info in Hyper Sync out there beside over powering the sun for portraiture. In the future I'll test with a different reflector and set up differently to bring my light closer to see what I get from less ISO. And yes, I do believe Pocket Wizard Wizard came up with it but they are in my opinion not the best at it.

Chris Edwards's picture

Having used flash for quite a while now, I didn't think I'd pick up anything here; I was wrong. Thanks for the video.

Brook Brown's picture

If you’ve been using flash “for quite a while” and learned anything from this video, you really need to check this out:

https://strobist.blogspot.com/2006/03/lighting-101.html?m=1

David Love's picture

Anyone else notice the never ending slider moves and not be able to focus on anything but that? Just me? Okay.

Karim Hosein's picture

I do not know where it is that MOST photographers get these wrong. The first and third thing is not even flash 101, but remedial flash 86.

As for the second thing, I do know that quite a great deal of photographers get that one wrong, and maybe MOST. Aside from that, this should be, “Three (out of many) things beginners ought to learn…,” and not, “Three things most photographers get wrong….”

Karim Hosein's picture

Here are twelve tips for strobe photography, and things which a fair amount of photographers seem to occasionally get wrong.

https://www.quora.com/What-are-some-photo-tips-for-Speedlite/answer/Top-...

Brook Brown's picture

Isn’t light falloff a much more important consequence of the inverse square law than the one mentioned here?

Karim Hosein's picture

I would not say, “much more important,” but I might say, “just as relevant.”

There are far more than three things which flash photography students need to learn.

Tom Manuccia's picture

IMHO, your discussion of the idealized inverse square law makes it seem more accurate than is in real world applications. Specifically, the inverse square law is only applicable if the light is coming from a point source. In contrast, if the size of the light source is similar to, or larger than the distance between it and the subject, the rate of fall-off with increasing distance will be slower than inverse square, possibly, a lot slower. If you don’t believe this, get out your flash meter and take readings at different distances from the front of a large, doubly diffused soft box, and plot the results.

Karim Hosein's picture

«…the inverse square law is only applicable if….»
«…if the size of the light source is similar to, or larger than the distance between it and the subject….»
Correct.

…But even with a 56 inch, doubly diffused soft box, the inverse square law comes back into play once it is significantly further away than 56 inches.

Where the inverse square law really breaks down is with parallel rays, but how often do we see that? We come close with a parabolic, shiny reflector, and the light source at just the right point. That is the real place where we consistently need to do actual light meter readings when we move the light.

Eckhardt Kriel's picture

Super useful info and a good reminder of some key points. Thanks for keeping it Simple!!