Rear Curtain

Using Nikon's Built-in Flash In Different Metering Modes

Almost all consumer level DSLRs and some of the pro level DSLRs come with the built-in flash. Professional photographers who shoot wedding, fashion, commercial portrait, or other special events do not rely on built-in flash to illuminate their subject. But, you don't have to use flash only when there is not sufficient natural light. It can also be used as a fill light to remove shadows or to add a catch light to the subject's eye. One of the best thing about the built-in flash is, you don't have to carry around an extra equipment and is always available on your camera, as long as the camera has sufficient battery power to charge and fire the flash. It can be put to use instantly whenever you want and doesn’t require any sophisticated setup. However, you need to understand few basics settings of your camera and should be comfortable navigating through the menu settings and the buttons on the camera.

Use of camera's built-in flash and its effect on the picture is determined by various settings on the camera, but most importantly, which metering mode you are currently using and what exposure mode you are on play a bigger role. Let's recap these camera metering modes briefly and then we can discuss about the steps we would be following in order to use on-camera flash. Since I wrote the blog about camera metering (in more detail) almost 9 years ago, Nikon has added a new metering mode; Highlight-Weighted Metering, which we will be discussing in the section below.

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Understanding Flash Sync Modes - Which Sync Mode Should You Use?

Nikon DSLR cameras come with the five different shutter sync modes to work with the flash. Not all the exposure modes (S, A, P or M) come with the same flash sync modes but they are available in a slightly different variation depending on which exposure modes you are on. You might want to check your camera manual to find out which sync mode is available in which exposure mode. To change the flash sync mode in your camera, you can hold down the flash button (usually on the front left side of the camera body near the built-in pop-up flash unit) and rotate the main command dial. When I was first learning about these different types of sync modes, they sounded very confusing to me. After reading lots of articles and doing lots of practice on my camera and flash, I got the hang of it. If you are new to flash photography, I am sure it sounds confusing at the beginning. It is simple concept to understand yet confusing sometimes but let me explain them briefly and as clearly as I can. And if you already know about these modes and experimenting a lot with the flash, this might be a topic of interest to you as well.

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1. Front Curtain Sync (Normal Sync) - In this mode, camera fires the flash as soon as the front shutter curtain (or first curtain) has been fully raised. It means camera fires the flash as soon as the window for the exposure is opened. Sometimes, it is also called firing the flash at the beginning of the exposure. When your camera is set to the Front curtain sync mode, the slowest (minimum) shutter speed it uses is 1/60th of a second (default to most of the DSLRs which you can change later by going into Flash shutter Speed menu inside the Custom Menu). This shutter speed is also called "Flash Shutter Speed". If your subject is in a low light condition, flash would be the only light for the exposure since the faster shutter speed cuts the ambient light. But if you are shooting with the Normal sync in a bright day light in an Aperture priority mode, your camera will try to use the fastest (maximum) shutter speed defined in "Sync Speed" which is usually 1/250th of a second. If you need a faster shutter speed than the sync speed, you will have to setup an Auto FP High Speed Sync which allows to sync your flash up-to 1/8000th of a second.

Front Curtain Normal Sync

Front Curtain Normal Sync

Normally, you should use the Front Curtain Sync when your subject is in a dark condition and flash is the only source of light and you don't care too much about the background. It is also widely used for standard studio setup where your only source of light is the flash light or the studio strobe.

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2. Red-eye Sync with Front Curtain - Have you ever noticed a red-eye effect while shooting a portrait? Usually, red-eye is caused by the light from the flash reflecting off the back of your subject's retina. When you are shooting close and with a straight flash, pop-up flash for example, it is very likely that you get the red-eye effect. And if your subject is in dark, red-eye gets worse because of the increased size of the subject's pupils (pupils get bigger to be able to see in the dark).

When you use the red-eye sync mode, depending on which flash system you are working with, camera will try to overcome the issue with a different technique. If you are using an external flash unit, camera fires series of quick light pulse just before the shutter opens. And if you are using a built-in pop-up flash, red-eye reduction is accomplished by illuminating camera's red-eye lamp, which is very bright and might be annoying to the subject. The best way to reduce the red-eye effect is by moving the flash unit away from the camera by using cords or wireless technology.

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3. Slow Sync - Slow Sync mode allows you to use the flash to expose your main subject while getting the ambient light to expose the background or surroundings. The standard Slow Sync mode is the front curtain sync mode in which camera fires the flash at the beginning of the exposure and then keeps the shutter open for the ambient light exposure. Normal Slow Sync or Front Slow sync is used mainly when your subject is stationary. For example, if your subject is standing still in front of a building at night, you want to use the normal slow sync to illuminate the subject with the flash and then the shutter will be opened for the ambient exposure to illuminate the background.

Slow Sync Flash Photography

Slow Sync Flash Photography

If your subject moves during the exposure, you will get the motion blur due to the long exposure.

Using Slow Sync Normal Flash (ball was moving from the right to the left)

Using Slow Sync Normal Flash (ball was moving from the right to the left)

In this mode, since the flash is fired at the beginning of the exposure, it freezes the subject initially but if the subject starts moving while the shutter is still open to capture the ambient light, it produces a motion blur after subject is initially being frozen. Sometimes this can produce an interesting picture with the motion blur but it could be a distraction as well. So, you have to be really careful while using this mode for a moving subject.

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4. Slow+Red-eye Reduction Sync - This is a slight variation on the Red-eye reduction sync we discussed earlier. In this mode, flash fires at the beginning of the exposure freezing your subject and keep the shutter open for the ambient exposure. Since this mode is similar to the Normal Sync where flash fires as soon as the shutter is opened, red-eye reduction sync works exactly same as the previous case.

You should use this mode when you want to use on-camera pop-up flash to illuminate the subject and keep the background lit with the slower shutter speed by capturing the ambient light. The problem with this mode can be similar to that of slow sync mode where if subject moves right after the flash is fired, you get the motion blur due to the longer exposure setting (shutter is kept opened after the flash is fired for the exposure).

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5. Slow+Rear Sync - This mode works exactly as the Slow sync mode except that the flash is fired at the end of the exposure just before the rear curtain (or second curtain) is closed rather than at the beginning. In this mode, the front curtain is opened first and the camera sensor starts collecting the ambient light and then just before the rear curtain begins to close, the flash fires. In this mode, the term "Slow" refers to the longer shutter speed and the "Rear" refers to the flash firing before the rear curtain closes.

Using Slow Sync with Rear curtain (ball was moving from the right to the left)

Using Slow Sync with Rear curtain (ball was moving from the right to the left)

This mode is widely used to include the motion blur as an effect rather than a distraction. For example, if you are taking a picture of a moving car (driving forward) using this mode, the shutter opens for the exposure and the car movement creates a blur effect but at the end just before the rear curtain is closed, flash will be fired to freeze the car motion. In this example, the motion blur seems natural giving the sense that car is moving forward leaving nice light trail behind. If we use the normal slow sync in the same scenario, the motion blur occurred at the front of the moving car making it as a distraction (also giving the sense that car is moving backward even though it is moving forward).

When you are using Slow Sync modes, it's best to dial down the flash power to balance the ambient exposure (you can see the ball is little overexposed in both of the examples above). You can test with -1 flash power and do some test shot and then adjust the flash power accordingly for proper balance between the flash and the ambient.

Note : This mode is only available in an Aperture Priority Mode (A) or the Program Mode (P) because these are the only modes where camera controls the shutter speed. But if you are using the Shutter Priority Mode (S) or the Manual Mode (M), you set the shutter speed and the camera can't adjust it independently and hence camera only uses a Rear Sync mode where camera still fires the flash at the end of the exposure just before the rear curtain is closed creating a nice trail effect in a moving subject.

Which Sync Mode should you use?

The most popular and the widely used sync modes are the Normal Sync mode and the Slow+Rear Sync mode. If you do not want the ambient light to contribute to the overall exposure of your photograph but want to expose the subject using the flash light, you should use the Normal Sync mode. And if you want to use the ambient light to expose for the background and the surrounding and illuminate your subject by using the flash light, you should use the Slow+Rear Sync mode. You can also use the Slow+Rear mode if you want to create a motion blur effect on the moving subject. While using Slow+Rear mode, even if motion blur gets produced without your intent, most of the time it gives a nice effect on the photograph rather than being a distraction. Red-Eye reduction methods are rarely used and their effect can be easily corrected during post-processing.

What Is Flash Shutter Speed?

This post is a part of our Q&A section. If you want to submit your question, please use the form in the Contact page.

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Dinesh (Mumbai, India) asked : I read your post about flash sync speed and got confused about flash sync speed and flash shutter speed. I went through Nikon D90 manual but couldn’t be satisfied with the explanation they gave. Can you please tell me the difference between flash sync speed and flash shutter speed?

If you already read my post about flash sync speed as you have mentioned in your question, I will skip that part and jump right into your question about what is flash shutter speed and when should we use it?

Flash shutter speed represents the minimum (slowest) shutter speed your camera will use when the flash is set to normal sync mode. Sometimes it’s also referred as a “studio sync” speed. Many photographers especially studio photographers have used sync speed of 1/60th of sec which has become somewhat standard. However, some photographers like to shoot in a different shutter speed. If you would like to eliminate as much ambient light as possible, you should go with the higher value such as 1/200th of sec or 1/250th of sec shutter speed. But if you want to capture ambient light (using rear curtain slow sync), you can start with 1/60th of sec and decrease the speed as you need.

There is no standard or correct sync speed, but if you are shooting under normal light inside studio or outdoor, default flash shutter speed, which is 1/60th of sec can be best choice and then you can manipulate your speed depending upon whether you want to capture the ambient light or avoid it. And if you want to change the default value in your camera settings, it is fairly an easy setup. If you are using Nikon D90, you have to go to CSM (Custom Setting Menu) and go to the Bracketing/flash and choose option e1. But if you are using D200, D300, D700 and other higher D-series like D2 or D3, you have to navigate through CSM and go to option e2.

Auto FP High Speed Sync Mode

Flash photography is a very exciting topic and confusing too at the same time. It offers variety of techniques to produce excellent photographs, but also requires you to learn its technical terms, understand those techniques and apply them properly. Earlier, we discussed about different types of flash sync modes and when should we use them. Today, we are going to discuss about another flash technique/mode, Auto FP High Speed Sync mode. But before jumping right into the topic, let’s discuss about what is the flash sync speed and how does it work?

What is Flash Sync Speed?

Flash sync speed represents the fastest shutter speed any camera can use with a flash. Different camera offers different flash sync speed, and over the time, flash sync speed has been increased significantly due to advancement of technology in digital world. Nikon D90 has a sync speed of 1/200th sec, whereas D7000, D300s and D700 offer 1/250th sec to 1/300th sec. Similarly, Nikon D3X and D3S have a sync speed of 1/250th sec. When you are using a built-in flash unit or an external flash unit, you can’t use a shutter speed faster than the camera’s flash sync speed. It is as simple as that. If you need to use a flash light beyond the flash sync speed, you need to use a feature called Auto FP High-speed sync. This situation may arise when you are shooting in a bright daylight and need to use a flash as a catch light or fill light for the shadows. When you use flash in such condition, you would need to use a shutter speed faster than the flash sync speed to compensate the exposure from the flash light.

After this brief intro to flash sync speed, let’s get into today’s topic, Auto FP High Speed Sync. FP stands for focal plane and it represents the type of shutter used in DSLRs camera. A focal plane shutter is two precisely timed curtains that move vertically between the lens and the camera sensor allowing or disallowing the lights hitting the sensor. The reason to use two precisely timed shutter curtains is to increase the performance of the shutter speed. The shutter speed is determined by the timing between the start of the first curtain opening and the start of the second curtain closing. This is important to understand that the entire sensor will be exposed to the light (the condition where the first curtain completely opens before the second curtain begins to close) for the duration of the shutter speed that matches the flash sync speed, also called maximum normal flash sync speed.

When you are using a faster shutter speed than the normal flash sync speed, the second curtain (also called rear curtain) starts closing before the first curtain (also called front curtain) is completely opened; thus never exposing the entire sensor to the light at any one time. If you keep increasing the shutter speed higher and higher, this will result in a very narrow 'slit' of light that travels across the sensor. And in this case, if there is not enough ambient light, you will get a dark area at the bottom of the picture. This is because when the camera takes a picture, image is recorded upside down on the focal plane, and as the second curtain already started closing before the first curtain completely opens, sensor will not get enough light to brighten the top part of the image which is actually a bottom area of the subject. To overcome this issue, Nikon developed a technique called Auto FP High Speed Sync Mode (not available in all models of DSLR). Auto means camera will automatically use high speed sync whenever it’s needed, or otherwise it will use normal standard sync speed. In a normal flash sync mode, the flash is fired at once with its full power. But in case of FP High speed sync mode, flash is divided into burst of flashes and fires continuously throughout the travel time of small window which travels across the camera sensor. And because of that reason, when you are using very fast shutter speed like 1/8000th sec for example, you will have to consider the power of the flash unit as the flash power is stretched more for narrower slits and it may not be able to brighten the picture or subject area.

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Different camera has a different menu option to setup Auto FP High Speed Sync mode. If you are using Nikon D90, you can go to the CSM menu and go into the option e5 to set Auto FP ON, and if you are using D700, you can go to e1 to enable High speed sync mode.

Here is what Nikon says about Auto FP High Speed Sync Mode

Auto FP High Speed Sync is a flash mode used for fill-flash photography under brightly lit conditions. It will fill in and open up shadowed areas in order to portray the greatest detail in subjects. It's also ideal when using wide aperture lenses, and because it allows fast shutter speeds up to fastest shutter speeds on compatible Nikon D-SLRs. It is often used for action-stopping sports photography. And for portraits, you can open up your lenses to their full aperture in order to isolate your subject against a blurred background without overexposing the image.

When Auto FP High Speed Sync is selected, the flash will fire for the duration of the shutter curtain's travel, thus syncing with the camera's shutter speed when that speed is set higher than the camera's normal sync speed.

The loss of a flash power is the trade-off when you are using a flash in a High speed sync mode.