The main characteristics to take into account are:
The flashes (shoe flashes, other than the studio strobe lights that are also flashes) work with AA batteries. As strobe lights progress, they are the lower end of the totem when it comes to energy, so every spare piece you can put together is useful. The output power of a flash is generally given as its guide number. The guide number, when divided by the number f of the aperture setting, gives you the distance that the light will travel in a combination of iso and zoom. However, many companies cheat by setting the flash at its highest zoom level (below) to make the number appear higher. To compare apples to apples, make sure that the zoom setting is the same in all the flashes, or look at a review in which the power was measured with a light meter (for example, in speedlights.net).
Think of the power output as you would with the maximum aperture in a lens. The more you have, the more you can do with it, but the bigger and more expensive it becomes.
Tilt / turn
Tilt and turn allow you to place the flash head in a different orientation to the body. This becomes important for two reasons. When you use a flash in the camera, the method of going to dissipate the light and make the flash look nice is to bounce, where the flash head points toward a reflective surface (usually a ceiling or a wall). This softens the light. However, to choose the direction of the light, you must choose the bounce surface; the inclination and the turn determine your freedom to do that. The complete 360 ° turn gives you total freedom; The 270 ° turn eliminates 25% of your options and, depending on how you turn in vertical orientation, you could eliminate 50%.
The second reason why you rotate is important is if you are going to use an optical trigger system to use the flash off camera. Typically, the sensor is in the body and should point towards the optical master unit (for example, the flash popped out of the camera or other light in the configuration). If it has a full turn, the head can always point to where it wants the light to go while the sensor in the body is facing the camera.
Zooming the head of the flash simply means that the flash tube on the head can move back and forth so that the extension of the light matches the field of view of the lens you are using. You can use this function outside the camera to adjust the focus of the beam. The longer the zoom setting is, the further behind the head is the light, the more focused the beam is and the farther the light can travel.
TTL, M and Auto modes
TTL means "through the lens" measurement. It is an automated way to configure the output power of the flash. The camera tells the flash to send a "pre-burst" flash of a known brightness level; measure it and then adjust the flash power according to the results and the power limits of the flash. Just like using any automatic mode based on the measurement on the body of the camera, it adjusts quickly and easily, but it may not be perfect and you must mark in compensation. Usually, he uses it for run event situations where he moves through different lighting situations in which he can only have a fleeting shot opportunity, and the speed is more than that. important that accuracy or consistency.
Because there is flash / camera communication involved, TTL is proprietary and will be system specific. If you want this function, you should look for a flash that is compatible with the camera system you are using.
Also keep in mind that movie-age flashes do not normally work in TTL with digital SLR cameras; The algorithms based on the reflectance of the film to calculate the correct exposure of the flash had to be modified for the digital sensors. OEM digital era flashes can usually switch between film and digital TTL, but movie-age flashes, obviously, only work accurately for the movie.
SUBWAY, like M in the camera, is the full manual mode, where you can directly configure the output power of the flash as a proportion of its total power. Relationships are usually given in complete stops (1, 1/2, 1/4, 1/8, etc., etc.). And, just like using M in a camera, you use this to achieve shot-to-shot consistency and control precision. It is most commonly used in study situations where lighting is controlled and is unlikely to change rapidly without the possibility of re-taking it. The wider the range of settings, the more control you have over the flash output. The power of 1/128, for example, can be very useful when working near the macro or product work due to the law of the inverse square. M also becomes very important as the only way to control the output power of the flash if you are using manual solo radio triggers for off-camera flash.
Car It's a different way to automate the light / energy output of the flash that does not require TTL communication with the camera, so it can be found in older and manual film-era third-party flashes. A sensor is used in the flash (usually an autotimer) to cut off the flash output at the right time. You may need to enter the aperture and iso settings used for shooting in the flash.
High speed flash / focal plane
Most system cameras use focal plane shutters these days. The speed of your shutter is determined by the size of the space between the first and second curtains as you sweep the sensor. At a certain shutter speed, that gap becomes smaller than the sensor itself. And because most flash bursts will be much faster than the shutter speed, if you increase the shutter speed, the curtains will cover parts of the sensor when the flash fires, and you will get black bars at the top and / or lower part of the frame. The magic shutter speed depends on the body and is known as the "maximum synchronization speed" of the camera (usually around 1 / 200s for most digital SLRs).
High-speed synchronization (HSS, also known as "focal plane" synchronization or FP) overcomes this limitation, but requires patented communication between the flash and the camera's shoe, so, as a TTL, it has to find a flash that is compatible with the camera system in which you are using. Also, Nikon and Fuji entry-level bodies can not do it. The camera tells the flash to press and act as a continuous light source during the exposure. However, the cost of rapid pulsation is a loss of power of approximately two stops.
This is often used when creating fill-in flash for portrait work with shallow depth of field in bright sunlight. In Sunny-16 conditions, (iso 100, f / 16, 1 / 100s), if you want to use a larger aperture, you must increase the shutter speed. You can also use ND filters instead of HSS. But the HSS can also be used to freeze motion at high shutter speeds if there is a lot of ambient light.
The Strobist form of studio lighting with flashes off camera is widespread, and can be bitten by the error. So, consider how many ways a flash allows you to shoot when you're do not in the shoe. The following characteristics to consider are:
- PC synchronization port (Protor-Compur) [typically only on higher-end flashes]
- 1/8 "(or 3.5 mm) minijack sync port, such as headphone jacks [3rd party only]
- Owner wireless slave mode (TTL) [Canon: wireless eTTL; Nikon: CLS]
- "Silly" optical slave mode [Nikon: SU-4 mode; 3rd party “optical slave” modes]
- built-in radio receiver [typically only works within a specific (same-brand) radio triggering sytem]
The main distinctions here are how many signals are communicated from the camera to the flash (full shoe protocol or just the synchronization signal) and the mechanism by which they communicate (radio, optics, cable).
For example, PC and 1/8 "jacks can be used with cables to fire only manually, or as a way to connect a manual radio trigger without using the hot shoe. They can be tied with a TTL cable for complete communication and, of course, can be connected to some optical / radio triggers or synchronization connector adapters (that is, a way to add a synchronization port if your flash or camera does not have one).
When an activation system is labeled "TTL", not only does it mean that TTL can be performed through the system, but that most of the shoe signaling protocol can be used. These systems allow you to control the flash remotely as if it were in the hot shoe (possibly with some exceptions of functions). However, activation systems that are "manual only" can only cause the flash to fire in synchronization with the exposure being made.
Optical The firing systems use light to communicate. The patented optical systems with TTL / HSS capability convert the shoe protocol into light signals; Generic "only" manual systems only use one sensor in the flash to detect when another flash has been fired as the moment of shooting. The optical systems are limited by the "line of sight" (the sensor has to "see" the master signal) and the ambient lighting conditions (the more light there is, the more the signal can be exceeded).
Radio The shot is not hampered by line of sight or ambient lighting conditions and has better range and reliability. However, most triggers, especially those that are integrated, are designed only to work within a specific system. It is incredibly rare that triggers work through brands or systems. Additional triggers can give you more flexibility of choice, but built-in triggers will often add more features (for example, power / zoom control for manual-only flashes) and are more convenient, as you do not need to remember to bring them along triggers and extra batteries for them.
In addition, like all other activation systems, the amount of communication may vary: some are synchronization signals (manual only), others allow synchronization and remote control of power, HSS or tail synchronization, and some mimic patented RF or optical systems. Consider how much communication you want or may want in the future. And also consider, if you are getting a built-in RF trigger, what upgrade paths are available.
Radio triggers tend to be part of a specific system. In general, pairing triggers made by different manufacturers can not be combined, even if they all work in the 2.4GHz bandwidth. And it is worth looking at what a system can offer in terms of future expansion.
Yongnuo, for example, has three separate activation systems, mostly incompatible, that do not allow you to mix your super cheap manual equipment with your TTL / HSS equipment. And they only offer flashes. And they only support TTL for Canon and Nikon, and you can not mix the two.
If you ever plan to add or move to cameras without a mirror, or you may need to share your lights with a different system shooter, or you need more power than a flash can provide, this could be problematic. And in the Yongnuo system, starting with a totally inexpensive manual configuration and then deciding to add a TTL / HSS capable light requires buying back all its triggers and flashes. Also, if you are used to remote power, TTL and HSS via the flashes, not having the same in a combination of flashes and studio flashes can be frustrating.
You may want to see and see if a lighting / activation system supports it with options larger than those of a flash, if you can mix TTL and manual equipment, and whether or not it offers cross-system support. There are many systems that offer one or the other or both (for example, Cactus V6, Jinbei / Orlit RT, Phottix Odin II, Nissin Air, Profoto Air). The Godox X system is currently one of the favorites because it offers cross-system lights and larger lights with lights at prices similar to those of Yongnuo, as well as lights with lithium lights.
Battery Port / Lithium-ion battery
The flashes mainly use four AA's. In intensive use, AA batteries may need to be replaced several times, so an external battery may be useful. In addition, a larger energy source can reduce recycling time (but carries a higher risk of overheating).
There are some flashes now on the market that use a lithium-ion battery pack instead of AA batteries. This reduces battery management for multiple lights, and works as an external battery pack (increases capacity, reduces recycling time) without the hassle of cables and an additional unit.
You have your eye on that super cheap Yongnuo, right? While it may make sense, just understand what you are doing by going with the lowest price tag. The quality of construction, the consistency of the copy and the quality of the components are probably more variable than with OEM. It is likely that the support, the guarantee and the resale value are of a much lower quality. And the compatibility with the future / backward is likely to be lower.
Most third-party manufacturers reverse engineer the hotshoe communication protocol, and as a result, while the flash can work very well with a current camera model, it may not work as well with a future or older model, or, let's say, a movie body with what is ostensibly the same flash protocol. To solve this problem, some third party flashes can update their firmware, but most of the super cheap manuals (YN-660, Godox TT600, etc.) can not.