The design of the cameras is a bit varying, especially across brands, and the AF assist LED can be located differently in different camera models or brands, but the number of possible locations is quite limited and I have so far not seen any camera where the LED can be placed optimally so well that it actually works without problems. The AF assist light LED is always blocked by the lens or the left/right hand holding the camera, regardless which camera we look at.
This is a problem even if the camera is on a tripod. The level of problem also depends on the subject to camera distance and the camera model. This is the case even with the lens hood removed, some lenses are just too large in diameter, or too long, so they block the light completely or partially. Sometimes only half the AF area, or even less than that can be used, the rest is blocked by the lens. This problem severely limits the ability of image composition, and the problem can become quite serious if you want to use AF areas which end up totally out of the light beam.
Another problem with the built-in AF assist solution is that their range can be very limited, depending on camera and the age of the camera. LED technology evolved quite a lot the last years, and today we can have small and very bright LEDs with low power demands, but typically older cameras have quite weak LEDs.
The video below demonstrates both the problem and the possible solution.
The solution is fairly simple
A separate and external AF light, which turns on and off by the AF assist light of the camera. This unit can be used on almost any camera, not only the Nikon Z6 and Z7, as long as it has an AF assists LED built-in the body. The brand, size or the format of the camera does not make any difference; it can be used on small, as well as large cameras, DSLRs as well as mirrorless cameras. The light beam emitted is bright green, just like it is commonly used in mirrorless cameras.
The circular green light beam provides a bright area in a large part of the image area, allowing you to compose the image and place the focus freely in a much larger part of the image than before. The light is strong and the camera will normally focus quickly and accurately, without racking, or hunting.
The light is switched off immediately when the camera switches the internal AF assist light off. This means that the exposure is not affected by the AF assist beam extender device. The green light will be switched off before the actual exposure, so the beam will not be visible in the actual image and will not contribute with any light for the image. It will also not affect the white balance measurements.
The range is about 8-10 meters, depending on the type of battery and the level of charge. This range is measured on a Nikon Z7 with the 24-70/4 S lens on it. Other cameras and lenses may give other results. Note that the range will degrade as the battery gets used and discharged.
The used battery is a common 23A type, which is a small but powerful 12V battery. Battery capacity is dependent the type and brand of the battery. Maximum current use of the device is 22mA. This means that the capacity is good for about 30 minutes to 2 hours of continuous light, depending on battery. This will normally be enough for quite a large number of shots, depending on the speed at which your camera and lens can acquire focus. Remember that focusing normally should not require more than 1-2 seconds, at least not with the Nikon Z7 and the 24-70/4 S lens, so even in the worst case, one battery should last for about one thousand images. Of course, if you are using better quality batteries this number will increase several times.
There is an on/off switch on the device. Use it if you store the device or if you don’t intend to use it over a longer period. The current consumption is basically zero when the device is in the dark, but it is totally zero only if it is switched off, so it is better to switch it off when not in use. The light is on only for the duration the camera requires for focusing, and this is when the device actually is using the battery.
The flexible attachment solution provides a liberty to place the device on almost any other device, be that a flash, a camera or even a radio trigger. The adhesive putty supplied with the device can be used for many years over and over again, allowing the attachment and removal of the device and the sensor many times. It does not need any treatment, should not be mixed with oil or water or any other liquid. If it feels dried out it should be massaged between your fingers until it feels right. It is non-toxic and will not cause damage to the surface of the cameras, the flashes or other devices. It does not leave stain and can be easily removed. When stored, it can be put between two plastic sheets or a small plastic bag to protect it from dust.
This device will be available soon, solving some of the problems related to using mirrorless cameras in low light conditions, such as it is common in studio conditions or other situations where the available light is low. It will increase the focus speed even in situations where focus is possible, but slow due to the low light. If the camera detects such situation and activates the built-in AF light then this device will take over and will provide the necessary AF assist light.
Note that the video above shows a prototype of the device. The final product will be slightly smaller, but will have the same range, using the same battery as in the working prototype.
A final note
This device is now available. Check this post for more details:
https://adapting-camera.blogspot.com/2019/03/the-external-auto-focus-assist-light-is.html
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