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Canon Macro Ring Lite MR-14EX by Markus Ehrenfried
When you like macro photography, you will pretty soon discover that you're in constant trouble due to low light. Under extreme closeup conditions the depth of field (DOF) is in the order of millimeters and less. Have e.g. a look at the DOF table in my Canon 100mm Macro Lens review. To gain DOF you have to stop down the lens. This leaves two options: you can use faster film or you have to use slower shutter speeds. I try to use ISO 100 print film whenever possible. For macro photography (nature photography in general) I wouldn't go beyond ISO 400. But even with an ISO 400 film you need a lot of light to stop down to f/16 or f/22 and maintain shutter speeds of 1/90s and faster. Of course you ask back now: Why don't you use a tripod?? Indeed, a tripod would allow me to stop down as far as I want and use very long exposure times, as it will prevent camera shake. But there are two reasons why the use of a tripod often doesn't help either:
As a general rule, one should at least use the reciprocal of the focal length in seconds as shutter speed when handholding the camera. With a 100mm lens this would indicate shutter speeds of 1/100s and shorter. 1/90s would already be very much at the edge, 1/125s would be much safer and with 1/180s or 1/250s you can be pretty sure to get a sharp picture. To achieve shutter speeds like that you often have to shoot at apertures like f/2.8 which means DOF of less than 1mm at 1:1 magnification. The tinyest movement will bring your subject outside this thin slice of space which is in focus! Macro photography means constantly making tradeoffs between motion blur (shutter speed), depth of field (f-stop) and film grain (ISO speed). Sooner or later you'll give up and accept that more light is what you need, an insight at which Johann Wolfgang von Goethe arrived really late in his life. What you need is flash.
Macro Ring Flash If you try to use a single, hot-shoe mounted flash unit, you will discover that it casts ugly, hard shadows onto your subject. This effect is e.g. known from using flash indoors: if you take a picture of a person standing close to a wall, you will get shadows which can look very disturbing. To prevent this you have to use either indirect flash light (point the flash tube e.g. towards the ceiling and use the light reflected from there) or use more than one flash tube. You'll pretty soon arrive at a complicated studio flash setup with several flash tubes distributed across the room. Flash photography is difficult! In macro photography the problems are similar. One single, point like light source will not give you the results you want. You'll have to use more than one flash tube or use reflectors or diffusors. One way to prevent hard shadows is to use a ring flash. The Canon Macro Ring Lite MR-14EX discussed here utilizes two flash tubes shaped like ring segments.
This ring mounts directly on the 100mm Macro lens. It does this in such a stupid way that it is both impossible to use filters (not even a small UV filter as protection of the lens front element!) and to put on the lens cover. Perhaps it is unfair to mention this right at the beginning of this review (as this product is apart from this design flaw close to perfection!) but it really annoyes me each time I use the flash unit. The front element of this expensive lens is totaly unprotected! To put on the cover one has to remove the ring flash from the lens and then it will dangle from the spiral cord which connects it to the hot-shoe mounted control unit! :-(( As the light is emitted from the two ring segments you can take flash pictures without casting any shade onto your subject. People often complain that this produces a 'flat' lighting, meaning that there is no shade. But this is exactely what this type of flash unit is designed for. To my experience the lighting is quite suitable for insects and plants. It is possible to rotate the flash ring freely on the lens. You are not restricted to the left-right setup of the two flash tubes, you can rotate them by 90 deg. to bring them in up-down position or in any position in between. That is important if you decide to fire only one of the two tubes or fire them with different intensity to give your light some direction. One matter of personal taste is if you like the reflection of the flash tubes on whatever is reflecting in your picture, like e.g. rain drops, eyes of insects, etc. In the picture below you can clearly see the reflection of the two flash tubes as ( ) pattern on the ladybug. It is also possible to fire the flash tubes idependendly: in this case you would get either a ( or a ). Once you know what you look for you'll realize the telltale reflections of the used flash setup in many professional macro photos. But would you have realized if I hadn't mentioned it?
E-TTL: Evaluative Through The Lens Flash Metering The real elegance of this macro flash system is its sophisticated flash metering system. It uses so-called E-TTL flash metering. This system works remarkeably well. NK Guy explaines on his webpage photonotes.org the technical details. The principle is simple: when you press the shutter, the camera first fires a pre-flash of known intensity, measures how much light is reflected from your subject and calculates from that the flash power which is necessary to correctly expose your subject. How does it know what your subject is? It simply looks at the active focussing point and weights the exposure with the light reflected from that area. This is about the only real mistake you can make: NEVER use the old lock-focus-and-recompose technique. If you e.g. focus on your subject, lock focus and then recompose in a way that the active focusing point is somewhere on the background, the background will be correctly exposed (and your subject will probably be overexposed, depending on the distance). So simply don't do that. Apart from that the system is almost foolproof and I'm not going to mention in this context that Canon sells most of these devices not to nature photographers but -- guess -- to dentist (!!) who use it to document their work. It's really as simple as that: attach the flash control unit to the hot-shoe of your E-TTL capable Canon EOS (not all EOS cameras have this feature, only the so-called type A bodies, have a look at the list on photonotes.org!!), mount the ring flash on your macro lens and switch the flash unit on. You will get perfectly exposed pictures as long as you remember two simple rules:
On the back of the flash control unit is a green light which confirms that the picture is not underexposed by lighting up for about two seconds after exposure. Keep in mind: it doesn't confirm correct exposure, your picture could still be overexposed but I myself up to now never managed to get an overexposed picture with the MR-14EX.
Maximum X-Sync Speed and High Speed Synchronization in FP mode Every camera has a maximum X-sync speed which typically is much much slower than the fastest shutter speed your camera offers. My camera, the simple EOS 300, has a maximum shutter speed of 1/2000s but the X-sync speed is only 1/90s which is painfully slow. The shutter of my Canon EOS consists of two shutter curtains, made of a very lightweight material, probably some magnesium alloy. When I press the shutter button, the first curtain opens and exposes the film surface to the light falling through the lens for e.g. 1/60s. Then the second shutter curtain follows the first one and closes the shutter again. The shutter curtains are fast moving, light weight mechanical objects but when you go to shorter and shorter shutter speeds they are no longer fast enough for the sequence (i) first curtain opens, (ii) shutter is open for a certain time, (iii) second curtain closes the shutter again. Going to higher shutter speeds, the curtains will follow closer and closer and at a certain point the second curtains already starts to close the shutter before the first curtain travelled all the way across the film plane. The curtains form together sort of a slit which slides across the film plane. The higher the shutter speed is, the narrower this slit will become. If you e.g. take a picture at 1/1000s, each area of the film is exposed for 1/1000s but as the shutter is never fully open not the whole film plane is exposed at the same 1/1000 second! And this is exactely the problem. Imagine you fire a flash with a shutter speed of 1/1000s. The maximum flash duration of the MR-14EX is 1.4 Milliseconds. This is much shorter than the two curtains need to travel across the film plane. Therefore this flash burst will only expose part of the film: the part where the shutter is open at that respective time. The rest of the negative will be underexposed. The maximum X-Sync speed is the highest shutter speed where the shutter is fully open at the same time. At this shutter speed the flash burst can expose the whole film surface, above this shutter speed it will only expose part of it. This is a serious limitation. Imagine you want to take a picture of a person outside with fill flash. The ambient light forces you to stop down so far that you get to a shutter speed below the maximum X-Sync speed. This often forces you to use small apertures (giving you more depth of field than you probably like for a portrait). To deal with this high speed synchronization was invented. It is usually called FP mode, often refered to as 'fast pulse' mode but in fact 'FP' comes from 'focal plane' mode. But pulsing the light fast is exactely what it does. We said that one flash burst will only expose a certain part of the film area when shutter speeds above the maximum X-Sync speed are used. The solution simply is to fire not only one flash burst but a fast series of flash pulses in a way that the flash is always 'on' for the time the slit formed by the two shutter curtains needs to travel across the focal plane. When used for fill flash this is really great: you can select shutter speeds up to the maximum shutter speed of your camera (e.g. 1/2000s at my EOS 300) and therefore use every aperture you want. You are no longer forced to stop down if you don't want. The price you pay is that FP mode reduces the range of the flash significantly. That is easy to understand: there is a certain amount of charge on the capacitor you discharge over the flash tube(s). If you use the whole energy in one shot you get maximum light output. But this is only possible up to the maximum X-Sync speed. If the flash unit fires a series of flash pulses it has to distribute the energy and each of these flashes will of course be weaker. Don't underestimate this effect: At X-Sync speed the MR-14EX has a guide number of 14.0 [ISO100/m]. This corresponds to 1/90s on my camera. If I go one step further to 1/125s the guide number reduces already to 7.9 [ISO100/m], at 1/500s it is only 4.9 [ISO100/m] anymore and at the maximum shutter speed of my camera, at 1/2000s, it's down to 2.4 [ISO100/m]!!
High Speed Flash doesn't freeze motion! It is a widespread misunderstanding that high speed flash helps to freeze motion. Admittedly it sounds like doing that. Many photographers think they will freeze motion at the timescale of 1/2000s if they force shutter speeds like that in FP mode. But this is not true. Remember that not the whole film area is exposed at the same 1/2000 second! Only a tiny slit is exposed at the same time, the area above and below are exposed for different 1/2000s. It takes the shutter much longer to travel across the whole focal plane than 1/2000s: actually, the highest X-sync speed of your camera gives you a hint about the shutter curtain speed which is exactely the limitation for that! High speed synchronization works by simulating a longer duration of the flash burst by firing many flash pulses. My EOS 300 has, as mentioned before, only 1/90s maximum X-Sync speed. When taking a picture without flash with my 100mm Macro lens, 1/90s is really on the border. With a little bit luck and a steady hand I can get a sharp picture, but it's always risky. Usually I select something between 1/180s and 1/350s when handholding the camera. Does this mean I will always risk to get unsharp pictures due to camera shake when I use flash at 1/90s? Absolutely no! The reason is, that the flash burst itself is much shorter than 1/90s. According to the technical data in the instruction booklet of the MR-14EX, the normal flashpulse (non-FP mode) lasts 1.4 Milliseconds. This corresponds to roughly 1/700s which is of course absolutely safe with a 100mm lens! From this point of view high speed syncronization in FP mode can be counterproductive as it makes the (stroboscopic) light puls longer! This is only exactely true, if the flash is the only light source. Imagine for instance, the ambient light would be as bright as the flash, then your picture would be formed by one half from the flash light and by the other half from the ambient light. In this case the 1/90s could become problematic as you could produce 'ghost images' by camera shake or movement of the subject: one image from the flash, the second one from the ambient light. I never had this problem as I use the flash always in a way that the flash intensity is much stronger than the ambient light.
Black backgrounds If the flash intensity is much stronger than the ambient light, everything outside the flash range will be underexposed, i.e. black. John Shaw askes in his wonderful book 'Closeups in Nature' the question: "How often do you look at flowers, insects, or other closeup subjects at night with a flashlight?" -- Of course, he has a point. But backgrounds are often a problem in macro photography. I have some perfectly exposed and really sharp pictures, taken under ambient light conditions, which are ruined by a distracting and 'restless' background. In this case I indeed prefer a black background which emphasizes the main motive.
But it doesn't hurt to pay a bit more attention to backgrounds. I found that it often is possible to find a point of view where a leaf or something else is nearby, preventing the background from being completely black. One just has to be aware of the problem. I still use a film camera, not a digital SLR, and therefore I cannot see the result instantly. But with some experience it is not really a problem to know what I have to expect under certain exposure conditions.
Flash in Manual Mode Usually I use Manual (M) Mode when I work with flash. I disable FP mode on the flash unit to prevent the flash control unit using high speed syncronization. I use 1/90s shutter speed and select an aperture which gives me the amount of DOF I need. That's the elegance of the E-TTL flash metering system: E-TTL will mix in exactely the necessary amount of light to expose the subject perfectly. At X-Sync speed the flash has it's highest guide number of 14 [ISO100/m] which makes it possible to use it even at the smallest aperture my 100mm macro lens offers, which is f/32. At 1:1 magnification this delivers approx. 4mm depth of field, which is a lot in extreme closeups! In fact, most often I use f/22 as the sharpness decreases due to diffraction (although I have to admit that it probably is my textbook knowledge of optics which makes me see that...).
Flash in Av Mode Av Mode (aperture priority) is in a certain sense the 'fill-flash mode'. It meters the ambient light and chooses the appropriate shutter speed, according to the aperture selected by the photographer. You can e.g. select f/16 and the camera will choose a shutter speed of 1/20s. It meters in the same way as if you wouldn't have a flash unit at all. But when you press the shutter it mixes in the amount of light necessary to expose your subject correctly (again it looks for the active focusing point, so do not lock focus and recompose!). It works very similar to the slow syncronization modes used for night exposures: it fires a flash for the subject in the foreground but leaves the shutter open long enough to get in some of the background. That's why I called it fill flash. In Av mode I usually try to make use of the ambient light and select of course the aperture depending on the depth of field I want to have. Therefore I usually switch on FP mode on the flash unit: with ambient light of similar brightness as the fill flash light I want to use higher shutter speeds to avoid 'ghost images'.
Batteries The MR-14EX requires four size-AA batteries. Rechargeable NiMH batteries work perfectly and are a pretty cheap solution. If you use the high capacity 2300 mAh accumulators they will last for a very long day. As the internal resistance of these NiMH batteries is much lower than the resistance of 'normal' single use alkaline batteries the flash recharges much faster after firing. With fresh batteries you'll be ready for the next exposure within 1 to 4 seconds!
References [1] Canon Tech report on the 100mm Macro Lens and MR-14EX Macro Ring Lite
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