Flash Test for twin NX1000 Synchronization

A simple way to get an idea about how well a pair of Samsung NX1000 cameras synchronizes is to use the “Flash Test.” This test will also allow you to decide which camera will be the right (R) and which will be the left (L). It will also help you understand how flash synchronization is achieved and what can go wrong.

 

First, look at this timeline (click to enlarge) of flash use for twin cameras with mechanical “focal plane” shutters (which is what the NX1000 has).

 

In these cameras there is a mechanical shutter and the flash fires only when the shutter is fully open. The shutter has two curtains, the front and the back, that travel vertically (in the NX1000). The time needed for the shutter (front curtain) to open determines the “flash synchronization speed” which is the fastest camera speed for which flash can be used. For the NX1000 this speed is 1/160s. This is about equal to the speed that it takes for the front curtain to open, exposing the entire sensor to light.

 

 

At instant 0 the camera receives the signal to fire the shutter. There is a very short delay (known as “shutter lag”) and the shutter starts to open at instant 1. The shutter is fully open at instant 2. After a very short delay, the signal is given to fire the flash (3A if the flash is fired at the start of the exposure). If the shutter speed is slower than the flash synchronization speed, then the shutter will remain open until 4, to satisfy the exposure. Then the second curtain will start to move (shutter starts to close) and at 5 the shutter is fully closed and the exposure ends.

 

This is the timeline for the camera firing the flash. If there is a second camera involved (as it is in stereo) then the question is, when the flash in camera #1 fires, what is the status of the shutter in camera #2?  When camera #1 fires the flash, what does camera #2 sees? (Camera #1 always sees the full flash exposure since it triggers the flash).

 

There are three possibilities, as seen in this figure:

• A: The shutter of camera #2 is also fully open the camera sees the entire flash exposure.
• B: Camera #2 is “slower” (has larger shutter lag) so when the flash fires, the shutter is partially open. In this case, camera #2 will see a partial flash exposure.
• C: If there is a large lag difference between the two cameras, it is possible that when camera 1 fires the flash, the second camera’s shutter is still closed. In this case, camera #2 sees no flash exposure (image is dark).

 

Based in these concepts, here is how the flash test works:

 

Flash Test

 

Step 0: First, make sure that both cameras have the latest firmware (1.15). It has been reported that this helps improve synchronization. Connect the cameras (their remote plugs), using a method of your choice.

 

Step 1: Put both cameras in Manual mode (M) and 1/160 speed. The f-stop and ISO are not important. I use f4 and 100 ISO.

 

Step 2: Put the flash on camera #1, fire the cameras (the flash should fire) and note what camera #2 sees (camera #1 fires the flash so it sees the entire flash burst). There are three possibilities for camera #2: F: Camera #2 sees the full flash exposure, P: Camera #2 sees a partial flash exposure, N: Camera #2 sees no flash (misses the flash exposure).

 

Step 3: Switch the flash to camera #2 and note what camera #1 sees.

 

Possible outcomes of this test:

 

• A. Both cameras see the entire flash exposure, no matter which camera fires the flash. This is as good as it gets. I estimate the synchronization of this camera pair to be in the order of 1ms (1/1000s) or better.

• B. One camera consistently sees a partial flash. This camera is “slower” (has longer shutter lag), so when the flash fires, the "slower" camera's shutter is not fully open. An estimate for the synchronization of this pair is 5ms (1/200) or better (often closer to 1/500), which is still acceptable for me.

•  C. One camera consistently misses the flash. In this case the synchronization is worse than 5ms (1/200). This is a situation that I do not see very often (I think I only saw it on one pair, but that was before checking the firmware on each camera). In this case, I will try to find another pair.

The picture above shows situation B. The right camera fired the flash. When the flash fired, the left camera's shutter was not fully open, so part of the image is dark.  (This picture also shows that in the NX1000 the shutter travels vertically, and opens from bottom to top.) Here is an estimate of the mis-synchronization of this pair:  The time it takes for the shutter to open is at least 1/160s (6.25ms). Probably it is a bit shorter, let's say 5ms. About 2/5 of the shutter has not opened yet. So, a rough estimate is that the two cameras are off by 2ms or 1/500s. That's not bad at all for most shooting. (PS. This is a stereo pair but the cameras are side by side aiming close so the stereo base is excessive, do not try to freeview it.)  

 

The figure below is a variation of the previous one, applied for the NX1000 pair and summarizes the test and possible outcomes when using flash with the twin camera pair. In this figure I recommend starting the test at 1/100 but I have found little difference vs. doing it at full flash synchronization speed (1/160).

Designate R and L cameras: If one camera is slower than the other, make the slower camera fire the flash (for me, this will be the R camera). If the slower camera fires the flash, the flash will be seen by both cameras. So this test can also determine which camera should be the R and which should be the L. In the pair with the partial exposure above, the left camera is slower (shows partial flash exposure) so it should be the one firing the flash (which for me will be the R camera). When this camera was firing the flash, I was getting 100% flash success.

Our of curiosity, I wondered if I could capture a picture showing a band of light and dark top and bottom. This would be the case if the front curtain is opening while the back curtain is closing. For that to happen, the shutter speed must be higher than 1/160. In the example below, the right camera is set at 1/160s to fire the flash but the left camera is set at 1/1000. At this fast shutter speed, the back curtain starts to close before the front is fully open and the flash froze the action while both shutters are in motion. (PS. This is also a stereo pair with a normal stereo base, so it can be freeviewed)

 

Final Note: If flash exposures are important, they could be improved using the “Magic Flash”. This is a device made by Rob Crockett. See: http://ledametrix.com/magicflash/user.html

 

The Magic flash can guarantee flash synchronization as long as there is an overlap in the time the two camera shutters are open (so use 1/125 shutter speed, or slower - do not use 1/160).

 

I have found the Magic Flash to be useful with other Samsung NX cameras which do not show as good synchronization as the NX1000. Also, for other digital cameras (Panasonic, for example) that do not show good synchronization, due to “flash induced shutter delay.”

Flash with the Samsung NX1000 twin camera rig

[Last Update: July 20, 2017]

Flash use was a pleasant surprise with this rig because… it works!!

I am often asked: “How do I turn the Flash On in these cameras?”

 

Answer: You do not. The two basic principles of flash use with a pair of twin NX1000 cameras are:

1. Use a non-dedicated flash and attach it or connect it to one camera.
2. Make sure that the shutter speed is less or equal to 1/160s.

If these two conditions are met, then the flash should fire.

 

Here is the rest of the story:

 

1. Use a simple (non-dedicated) flash.  If you use a dedicated flash, i.e. a flash recognized by the camera, then the camera firing this flash will be delayed (I call this “flash induced delay”), and synchronization will be lost. If you really want to use a dedicated flash (like the small flash that comes with the camera), you can use two flashes, one on each camera. Then the “flash induced delay” should be the same and you might get OK results. I do not recommend using two flashes (one on each camera). It is confusing and the shadows can be strange. Just use a simple flash, not recognized by the camera.

 

2. There is no camera flash setting to turn on. The camera will fire any flash attached to it, as long as the shutter speed is 1/160 or less (this is the flash synchronization speed). If the speed is faster than 1/160  (for example, 1/200) then the flash will not fire. Nothing will happen. If the flash is 1/160 or slower (for example, 1/100) then the flash will fire.

 

There is no indication by the camera that a flash is attached to it. It is as if the camera is totally unaware of the existence of the flash and this is a good thing because I believe it makes flash synchronization possible. Often, when the camera detects the presence of a flash, the shutter firing is delayed and synchronization is lost. That's the case with the Panasonic micro 4/3 cameras and synchronized flash with these cameras is problematic.

 

Note: Any vintage or modern flash should work with these cameras. If using a vintage flash, make sure that the flash voltage is safe (older units use high voltages that might damage a modern digital camera). There have been reports that some flash units are not fired by the NX1000 camera. The only flash I have found not to work is the Nishin i40. I do not know why this is happening but if you put the camera at 1/160 (or slower) and the flash does not fire, then you might have found another unit that does not work.

Physical Connections

For the flash to fire, the center contact of the flash must connect to the center contact of the camera. The extra contacts (on flash or camera) are used for flash dedicated functions and are not used here. They are usually not a problem.

There might be some issues with the physical connection, depending on how the cameras are supported. Some flashes hit the mount (the Werner body mount, for example, see below) and not make good contact with the camera.

In this case you might need a flash adapter that simply raises the flash higher while maintaining the center contact. Any flash adapters or flash accessories can be used with this camera rig. I show one in the picture above. I get these from ebay.

When I use on-camera flash, I always attach it to the right camera, which is the natural choice for the z-mounting configuration. There is also the possibility of using a flash off camera, connected either with a cable or wirelessly. In this case, you have to worry about how the cable or wireless receiver attaches to the camera.

Flash Exposure

 

So, you have a flash connected and fired by one camera. How do you control the exposure? This is a general flash question, not specific to the Samsung NX1000 twin rig. But a lot of people are not familiar with flash use so I will review the basic concepts.

Flash exposure is controlled by:

• The flash (it controls the amount of light emitted by the flash) and 

• The camera (it controls the exposure of flash and ambient light). Ambient light is any light in the scene, not coming from the flash.

There is nothing new about that, this is how flash always worked, even when using a 1950s Stereo Realist. The main difference between film cameras and digital cameras, when it comes to flash exposure, is that with film cameras the ISO (speed of the film) is fixed and cannot be changed from one picture to the next. With digital cameras the ISO is an extra variable and can be changed at will.

The question is, how do you set the flash and how do you set the camera to get good exposures?

 

Camera settings

There are three camera settings that affect exposure:

• Shutter Speed
• Aperture
• ISO (fixed with film cameras, variable with digital cameras)

 

Because flash duration is very short, the camera shutter speed has no effect on flash exposure. Flash exposure is only affected by the aperture and the ISO setting.

 

I recommend that you fix the ISO when using flash so it is not an extra variable. You can use for example ISO = 100 or 400. If you fix the ISO, only the aperture will affect the flash exposure. Then use the shutter speed to control ambient exposure. For example, you can use ISO = 100, f = 5.6 and get good exposure with flash. Then if you use 1/160 shutter speed (the fastest possible), you will minimize the amount of ambient light. If you use a slower speed, you will admit more ambient light.

 

The NX1000 camera can be used in one of these settings:

• P (Program): camera sets both aperture and shutter speed to satisfy exposure.
• S (Shutter Priority): you fix the shutter speed and the camera selects the aperture to satisfy the exposure.
• A (Aperture Priority): you fix the aperture and the camera selects the shutter speed to satisfy the exposure.

In any of these settings (P, S, A) you can override the camera’s choices by using the exposure compensation. Setting exposure compensation to +1 results in the camera overexposing by one f-stop. Setting it at -1 results in the camera underexposing by one f-stop, etc.

• M (Manual): you set both the shutter speed and the aperture. With the ISO fixed, the camera makes no choices and you have full control of the exposure.

 

In addition to these 4 basic modes, the ISO is set independently, either in AUTO (the camera decides what value to use, to satisfy the exposure) or at any fixed value (100, 200, 400, etc.)

When using flash, my personal recommendation is set the cameras in Manual mode. This is the easiest to understand and gives you full control of the exposure. Fix the ISO (set it at a fixed value, not AUTO), set the shutter speed at some value of 1/160 or slower. Then, the aperture would be the only variable that affects flash exposure. Change the f-stop to get good flash exposures. If needed, tweak the ISO. Only change the shutter speed if you want to balance flash and existing light.

 

It is also possible to use S, A, or P modes, but be careful. The camera will select settings for the ambient exposure, without taking flash into account, which will most likely lead to overexposure. You might need to use Exposure Compensation to reduce ambient exposure to balance with flash. It is a matter of trial and error.

 

One interesting camera setting when using flash is the Framing Mode:

 

This is normally OFF. When the ambient exposure is dark (this happens when using flash, for example, with settings that give good flash exposure, in which case the camera only shows the ambient exposure) the display will be dark, or even totally black, so you will not be able to frame your subject. By turning this setting ON, the display brightness is constant regardless of the camera settings, so you can frame the shot better.

 

 

I like to have the framing mode ON in one camera and OFF in the other. In the picture above it is turned ON on the right camera. The settings for this picture (Manual Mode, f4.0 1/69 ISO 200) result in a picture underexposed by about 3 f-stops. The left camera shows the correct (ambient) exposure while the right camera is brighter, to allow for better framing.

 

By using a different setting on each camera I can frame the picture and still have an idea of what the ambient exposure will be, when I use flash. Best of both words and possible with stereo photography!

 

White Balance?

How about the white balance setting when using flash? Some people recommend using the "daylight setting" instead of "Auto Balance." That's because the light from the flash has a daylight balance. I have tried both and don't see much difference. But like exposure, maybe it is better to specify the color balance, instead of leaving it up to the camera to decide.
 

Flash Exposure - Guide Number

Flash units have controls that adjust the light output from the flash. All flashes can be fired at full power. This is the most light that can come out of the flash. A larger, more powerful, flash, emits more light.

There a quantity that measures the maximum amount of light that a flash can emit. This is the Guide Number (GN). You can read more about the Guide Number, here: https://en.wikipedia.org/wiki/Guide_number

The guide number is defined as: GN = f-stop x distance
It is expressed as a distance @ given ISO. For example, 20m @ 100 ISO.

Here is how you can use the GN: Say a flash has GN = 20. You have the camera set at f4 @ 100 ISO. From the definition: GN = 20 = f4 x distance. Solving for distance = 5m. So, if an object is at 5 meters from the camera, it will receive the correct exposure. You can do this the reverse way. Say, an object is at 10m from the camera. What f-stop should we use to get good exposure?  Solving for the f-stop, we get f = 2.

In some flashes (usually older) there is a Table in the back, showing how to set the f-stop with distance. This is the Guide Number, expressed as a Table. Here is one example:

This flash has a GN of 20m @ 100 ISO. I drew the lines at ISO 100 and f4. You can see that if the camera is set at f4 then the object distance for good exposure is 5m (16 ft). Reversely, if an object is at 5m, then the camera should be set at f4 for good exposure. Other combinations are possible too. The Table is basically a graphical expression of the Guide Number.

Note: This flash also has two Auto modes, discussed below.

Flash Exposure Control: Manual - Auto - TTL

The Guide Number, discussed above, expresses the full power of the flash. But flash is often used at less than full power. Most flash units usually have 3 exposure-related modes, that control the amount of light emitted from the flash:

 

• Manual: The flash outputs a fixed amount of light. This can be the full power of the flash or a fraction of it (1/2, 1/4, ... 1/64) if the flash has this capability.

 

• Automatic: The flash has a sensor that detects the light reflected from the scene and stops the flash output when the exposure is satisfied. Usually, there is a choice of f-stops (for a given ISO). You select a given Auto mode (f-stop at, say, 100 ISO) and then set the camera at this ISO and f-stop. The flash will then control the exposure. Ambient light can be controlled by changing the shutter speed (at or below 1/160). I find this useful. For example, I set the flash at, say f5.6 AUTO mode, the camera at f5.6 and then the exposure is controlled by the flash and it is good for different subject distances or when I bounce the flash.

Example: The Metz 20 C-2 flash shown above has two Auto modes, marked f2.8 and f5.6. Here is how to use the flash in these settings: At 2.8 set the camera at f2.8. The camera will stop the flash when exposure is satisfied. There is a limit of distance that this works. To find this limit, draw a line from 2.8 until it meets the ISO 100 line and read the distance above. This gives 7m or 23ft. Another way to figure this is to divide the GN by the f-stop: 20/2.8 ~ 7m. What this means is that the flash can only illuminate objects as far as 7m. Same concepts apply for the 5.6 setting. Note that these calculations apply for ISO 100. If you use ISO 400, then double the f-stop setting, so the 2.8 becomes 5.6 and the 5.6 becomes 11.

Note: The auto setting does not work well if you take the flash off the camera, unless if the flash sensor can remain on the camera (this is an accessory or an option in more advanced units).

 

Unfortunately, even though Auto mode was common in older flashes, modern units tend to omit it because they have replaced it with more dedicated modes (TTL, see below). But these modes are not useful for our stereo camera rig.

 

• TTL (Through the Lens): The flash communicates with the camera. This mode is not useful here because you should not use a dedicated flash.

 

My recommendation: For successful flash photography set the camera in manual mode (M) and fix the ISO. Set the flash in manual mode. Set the shutter speed at some value at or below 1/160. Then control the flash exposure using the f-stop and/or the flash output. Control the ambient light (if any) using the shutter speed. Use trial and error (take one picture, judge the exposure, make adjustments, take another picture, repeat). That’s the best starting point.

For Best Results: In general, direct on camera flash is the worst way to use the flash. One exception is for fill-flash, outdoors, etc. Try to bounce the flash, use off-camera flash, or multiple flashes. Balance ambient light if possible or desirable. For bounce flash, a lot of power is lost. That is not a big problem today, even when using compact units with digital cameras: Use the widest possible f-stop and a higher ISO value. Experiment! Trial and error. Shoot, adjust, repeat.

 

Flash Units that work with the twin Samsung NX1000 rig

 

Depending on their size, I classify flashes in 3 groups:

Large: Usually used for studio work or by professionals for weddings, etc. They are large powerful units (GN of 70m @ 100 ISO, or higher) used off camera, and usually have external power packs. I used a Quantum Qflash and now I use a Bolt (Chinese made) VB-22 flash.

 

Medium: They typically take 4x AA batteries, are of average size, and can attach to the camera’s flash shoe. Typical guide numbers: 25-50m @ ISO 100. They are usually heavy, often weighing over 1 lb (with batteries) or 500g. This is the most popular compact flash size, and there are many choices in this group. You can get a new unit made in China for $50 or so. These units usually offer:

• Variable Manual mode
• Option to be used in (optical) slave mode.
• Bounce flash

An example of a simple Chinese-made unit (Bolt VD-410) is shown above. This is a non-dedicated unit with variable manual mode, optical slave mode, and bounce head. The controls on the back are simple and controlled by buttons or dials. They are more advanced/expensive units, offering a few more features like zoom head and LCD displays. Some of these units are dedicated to specific cameras, but that does not matter here as long as the unit can be used with non-dedicated controls (manual mode, etc.)

You can also buy older used units by Nikon, Metz, etc. with similar, or more features (AUTO mode, stroboscopic mode, zoom head), for about the same price ($50-$100). Some of these units are already 30 years old. They cost a lot of money (typically $300 or more) when new. The built quality is excellent and they should easily last for another 30 years. Again, the fact that these units are dedicated to Nikon or other cameras, does no matter, as long as they have controls for manual or AUTO use.

Here is one of my favorite vintage flash units, the Metz 54 MZ-3.It has a standard form, bounce head, LCD display. It has all kinds of modes, manual of variable output, auto, slave, stroboscopic. It has a little rotary wheel that allows you to select settings quickly. Also, it has a secondary flash head in the front for when using bounce (it can be turned off). It also takes different modules for different cameras. You only need the manual one with one contact, but any others will work too. It is a nice unit, but I find it too heavy for every day carry.

So, what is it going to be? A new Chinese flash or an older Nikon, Metz, etc.? The choice is yours.

 

Small/Compact: These units take 2x AA or 2x AAA batteries (or a single or two lithium batteries) are lightweight and compact and are better suited for casual use or travel. Typical Guide Numbers are 10-20m @ ISO 100. Their weight can be as low as 100g. These are the units that I usually carry, because I like to travel light. You can even have two of these and use one on the camera and the other as slave flash.  Some favorite units are shown here:

• Nikon SB30: A nice compact & light weight (it only weighs 100g with a battery, which is approximately the weight of a pair of Samsung batteries), loaded with features:

- Sticks up so it is not blocked by the Werner mount (no adapters needed)
- Guide number of 16m @ 100ISO
- 4 Auto modes (2,8, 4, 5.6, 8 @ 100 ISO)
- 3 manual modes (1/1, 1/8, 1/32)
- Exposure compensation +1/2, –1/2
- Exposure confirmation (when used in Auto)
- Optical slave (at full power)
- Everything is controlled by dials, so very easy to set and see at a glance, after you become familiar with it. Also, very rubust (dials don’t fall out, labels do not rub off).
- Wide angle diffuser build-in (retracts or extends in place).
- Infrared filter build-in (this is useful if using on-camera flash, to trigger slave flashes, and you do not want the SB30 to contribute to the exposure).
- Runs on one CR123A lithium battery. This for some people is a disadvantage, as it is not easily available. The battery however is tiny, about the weigh t of a AAA, but a lot smaller, and more powerful - you can buy these for ~$1.50 each.
- Tilting flash head, so it could be used for macro, for example with the Panasonic 3D lens.

The only thing missing is manual firing (it is strange that you cannot fire the flash manually). You can find these on ebay.... Expect to pay around $40.This little guy is a keeper. You can download the instructions here: https://cdn-10.nikon-cdn.com/pdf/manuals/Speedlights/SB-30.pdf

 

• Sunpak PF20XD: Very nice unit, runs on 2x AAA, has Manual and Auto modes and also can be used as slave. No bounce. This is not made any more and it is not easy to find. The picture below shows the back of this flash and how the controls are laid out. I like this layout because I prefer dials over LCD displays. The only thing I do not like is that the sliding switch that selects slave or on-camera use is not easily accessible.

• Metz 20 C-2: Nice compact unit runs on 2x AA. Has two Auto settings (no variable manual, only full power). The head can bounce up and I use this feature often (I also use a white card to bounce flash forward, see picture below).
  
  It is also available under the “Bolt” name (Bolt VS-210) and it is made in China. I use this flash quite a bit, to bounce the light off the ceiling. It works well in the Auto mode where I do not have to worry about changing the settings of the camera or flash. I just fix the f-stop of the camera and shoot.

 

 

• FlashQ Q20: This is an interesting unit, a dream come true in some respects. It runs on 2x AA batteries, weighs only 110g, has variable manual mode (also Video mode – constant variable light) and bounce up head. It also has a slave mode. The big attraction is that it can be separated from the base and fired as a radio slave. Both the bounce and the off-camera flash are useful for better flash pictures. While any flash can be used off-camera using a wireless flash trigger, the attraction here is that the trigger is built into the flash design and it is very small.

 

This now has be come my to-go unit and I am still evaluating it. For more information, see this web page: https://www.lightpixlabs.com/pages/flashq

And watch these videos:

https://www.youtube.com/watch?v=9oTlGA4gdA4

https://www.youtube.com/watch?v=7XH82qmX4yQ

Slave Flash

Slave flash is attractive because you can position the flashes at will, fill shadows, modify the scene, and do this without any wires, everything controlled from one flash. Most units discussed here can be used as slave flashes. But there are also dedicated slave flashes. One unit that I like is the one shown below. It goes with different names, like "Mini Slave Wide" by Morris, and (recent incarnation) Holga 006S. Some older units work on 2xAAA batteries (I prefer these because they are smaller and lighter) but most recent units work on 2xAA.

Part of the attraction for me is that the head is like "Bare Head" type, meaning it is not modified but spreads over a wide area. Also, you can remove the top (it unscrews) and easily modify the light, install filters (the Holga unit comes with a set of filters).

One drawback of this unit (and others) is that slave mode only works on full power, so there is no control to reduce the light. You can cover the head with tissue paper as a way to reduce the exposure.

Two examples of pictures where I used slave flash:

The top one as taken by looking down at the slave flash.The bottom one was taken with a slave flash inside the shoe. In both cases the slave was triggered by a on-camera flash.

Flash Synchronization
 

One subject not addressed here is how the flash synchronizes with the pair of cameras? This is of course a very important question for stereo photography. I am addressing this topic in this blog: http://drt3d.blogspot.com/2017/07/flash-test-for-twin-nx1000.html