The one thing that makes or breaks a captured image – is absolutely sharp focus. This goes for all genres of photography but it is very true for wildlife photography. At the best of times it is a challenge to obtain sharp focus particularly when using longer focal length lenses. You may have all of your lens techniques correct, but you seem to miss the vital focus point that you intended. The depth of focus of a 600mm f/4 lens for instance, particularly at shorter shooting distances, is minimal. You want the pupil of the eye of a subject (like a bird) to be in optimal sharp focus but on processing the image you find the feathers just in front of the eye or slightly behind the eye displaying the sharpest focus. The image is great, but not quite perfect!
Need for AF Micro-adjustment
Individually there is nothing wrong with the camera body or the lens. However, due to the combination of small tolerances in each, the particular camera body and particular lens does not focus optimally at the focus plane. Fortunately camera manufacturers have catered for this eventuality by having an “autofocus micro-adjusment” (AFMA) option in their menus. This gives you the ability to move the plane of focus slightly forwards or backwards for that particular body/lens combination. Many even give you the option of making the adjustment at the shortest and longest ends of zoom lenses. The issue is how much adjustment you need and how do you measure this.
There are a variety of methods to do this – generally manually checking the focus of a target image at various autofocusing micro-adjustment settings. This can be a painstaking procedure, which years back I used to often give up on and leave the default setting of zero as is. In my instance I usually had three camera bodies and about 5 lenses, of which 4 were zooms. I also had to cater for a 1.4x and a 2x converter on some of them. This entailed doing the manual check 0n 13 combinations per camera body. Multiply that by 3 bodies and you’ve got 39 tests to carry out. Each one entails capturing images at various settings. You just end up “goggle-eyed” and still have, what can be regarded as, subjective results.
Manual or Semi-manual solutions
I did try processes that had very detailed targets which showed whether the camera/lens combination was focussing in front or behind where it should be. This still entailed looking at countless images to see which had best focus. It used to drive me crazy. It also needed very precise positioning of the “target” – at times necessitating looking through “keyholes” to align the camera with the target. Just added to the frustration.
Automated software solution
Most fortunately, I stumbled upon an automated process that not only makes the whole operation relatively painless but also produces much more consistent and objective results. This software is called FoCal By Reikan Technology. http://www.reikanfocal.com
The basis of this system is that you set up a target image (see below), then set up/aim your camera/lens at the centre of the target. Connect your camera to your laptop, start the software and the process is then automated to find the optimum AFMA setting.
The first step in the process is to set up your target image. The application download includes a folder which contains two files. One is a 600dpi png file and the other in pdf format. The images are about 27cm by 19,5 cm. I happened to have a 3 cm thick perspex block which I used for the backing. Also printed the image on quite thick posterboard so that it had enough strength to keep flat. I trimmed the printed image, without in any way affecting the “target” to fit my piece of thick perspex. I would suggest any backing, but it must be sturdy. In my case I attached an old spare lens foot to the bottom of the perspex backing and also attached a quick release plate. This made mounting the target on a tripod very easy at any time. You can print a larger target, like A3 size, but then you must “tell” the app that you are using a larger size print and not the standard. There is an indication on the target image where you must measure and then input that value into FoCal’s settings. If you do something like this, then whenever you want to do any calibration you just have to attach the backed target image to a tripod head, assuming it has a quick release clamp, and you are ready to go. The printed target image can also be stuck to a wall, but have found that the tripod option is better.
The next part of the set up is to mount the camera body and lens to be calibrated on another tripod and align the centre of the lens with the centre of the target image. This is where Focal makes life so much easier. Whilst it is pretty easy to take a measurement from the floor to the centre of the lens and then make sure that the centre of the target is the same, it is not absolutely necessary to have them exactly the same. I tried some other systems where this step was so critical that you even had to peer through small holes to check the alignment. Obviously good alignment may give better results, but FoCal makes this much easier. Just ensure that the target image is horizontally level and vertically upright. Most ballheads and/or tripods have spirit levels where you can easily check the level.
Make sure the camera is level (if you have one, use the level indicator in your viewfinder) and that your centre focus point is over the centre of the target image. Again, even if this is slightly off FoCal still does the job.
The downloaded software also includes a detailed user manual and a set up check list. There is even an automated target check that you can use when you start the software to determine the AFMA. This is a handy feature as it checks all your settings and the target distance (see below).
Printed and mounted target on a tripod. The target is held firmly in place on the backing with some duct tape. I did try Prestick® but that did not work too well.
Note: All my experience with FoCal has been with Canon cameras. This will work equally as well with Nikon DSLR’s.
The user manual takes you through all the set up of the necessary camera settings. I will list the key ones. I put the camera on Aperture Priority shooting mode and it is recommended that you use the largest aperture that the lens has. Focal does however remind you whilst doing your calibration if you have not used the largest aperture setting. You must use single point AF. Also don’t disable any AF, particularly Spot, metering modes. Use One Shot AF mode – not AI Servo AF.
The two other important things you must do – keep the viewfinder closed and turn off Image stabilisation on the lens, if it is an IS lens.
Gives you an idea of the overall setup. However, the camera must be connected via the (USB) cable to your laptop and the distance from camera to target depends on the lens focal length. This is a 600mm lens and it should be about 12 meters from the target. This is just for illustration purposes.
You need to find a place where you can set up which gives you the space and the ability to have your laptop in a handy position. I am fortunate the have an outside upstairs deck which is about 12 meters long and my digital workshop has a door opening onto the end of the deck. I am easily able to position my camera inside with the laptop on a desk next to it and the camera facing to the target outside. I can easily move the target nearer or further from the camera. Only issue is the light. I need a day with constant light (no moving clouds).
Now to the interesting magic of the FoCal software.
The automated AF Micro-adjustment
Start the FoCal application on your laptop and connect the camera to your laptop via the USB cable and turn the camera on. The software will recognise the camera body and the lens that is attached.
The software has a target distance tool. You can either specify the focal length or the software will automatically give you the recommended distance for the actual lens you have attached to the camera. You can click on the “Target Setup” button. This will check if all the settings and the target is correct.
This is now where the automated process of the FoCal software really comes into its own. The user guide clearly takes you through the steps of using the software. In effect you now click on the ” Start button” and FoCal will now start to automatically determine the correct AFMA setting and it will set the determined number in your camera menu system. With some camera bodies, like my Canon EOS 1DX Mark III, you still need to manually change the AFMA settings as the program advances through its sequence. It is quite eerie as you hear a voice telling you to set your “Auto focus microadjustment setting” to +20 or +10 or -10 or -20. Unless the setting is already set to a number different from the default zero it will do the first test setting using zero. As each image is taken of the target FoCal starts to plot the results on a graph.
This is an actual plot of a Canon EOS 1DX Mark III with a Canon EF 600mm f/4L IS II USM lens. The focus fit quality is shown as excellent and it is clear that the required AFMA setting is +8. This means that the focus has been moved slightly further back of where the camera had been focusing if it had been left at the default zero setting.
This is an actual plot of a Canon EOS 5DsR with a 70-200mm f/2.8L IS III USM lens at 200mm. The required AFMA was -3. A slightly earlier version of Focal was used. The focus consistency at the required AFMA in this case turned out to be 99.7%
I used to detest every time I had to determine the optimal AFMA for any camera/lens combination. With the automated processing of FoCal it is a breeze and, in fact, I rather enjoy doing AFMA. It also gives you a lot of reassurance that you are not just doing it subjectively by looking at the focus of an image . The graph clearly shows what the lens is doing. The application also gives you a lot of information about your lens and camera as each test is done. A sixteen page PDF document can be saved for each test – with a myriad of info.
I use the Pro version of FoCal which gives you the added ability to check sharpness at various apertures, focus consistency and even dust analysis.
FoCal has made a huge difference to calibrating any camera/lens combination I use and now feel very confident that I am getting the best sharpness that the camera and lens can deliver. As a professional nature photographer I am often asked what piece of software has made a big difference to the quality of your images. FoCal certainly is right up there with the best.
Disclaimer: FoCal and the respective icons are the registered trademarks of Reikan Technology Ltd. John Bryant and Photo Images of Africa disclaims any and all rights in those marks. John Bryant or Photo Images of Africa has no proprietary interest in or connection with Reikan Technology Ltd.