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. There is an indication on the target image where you must measure and then input that value into FoCal’s settings. 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. This made mounting the target on a tripod very easy at any time. In my case I attached an old spare lens foot to the bottom of the perspex backing and also attached a quick release plate. I would suggest any backing, but it must be sturdy. I trimmed the printed image, without in any way affecting the “target” to fit my piece of thick perspex. Also printed the image on quite thick posterboard so that it had enough strength to keep flat. I happened to have a 3 cm thick perspex block which I used for the backing. One is a 600dpi png file and the other in pdf format. The application download includes a folder which contains two files. The first step in the process is to set up your target image. Connect your camera to your laptop, start the software and the process is then automated to find the optimum AFMA setting. 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. This software is called FoCal By Reikan Technology. 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. It also needed very precise positioning of the “target” – at times necessitating looking through “keyholes” to align the camera with the target. This still entailed looking at countless images to see which had best focus. 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. You just end up “goggle-eyed” and still have, what can be regarded as, subjective results. Each one entails capturing images at various settings. Multiply that by 3 bodies and you’ve got 39 tests to carry out. This entailed doing the manual check 0n 13 combinations per camera body. I also had to cater for a 1.4x and a 2x converter on some of them. In my instance I usually had three camera bodies and about 5 lenses, of which 4 were zooms. 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. There are a variety of methods to do this – generally manually checking the focus of a target image at various autofocusing micro-adjustment settings. The issue is how much adjustment you need and how do you measure this. Many even give you the option of making the adjustment at the shortest and longest ends of zoom lenses. This gives you the ability to move the plane of focus slightly forwards or backwards for that particular body/lens combination. Fortunately camera manufacturers have catered for this eventuality by having an “autofocus micro-adjusment” (AFMA) option in their menus. 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. Individually there is nothing wrong with the camera body or the lens. The image is great, but not quite perfect! Need for AF Micro-adjustment 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 depth of focus of a 600mm f/4 lens for instance, particularly at shorter shooting distances, is minimal. You may have all of your lens techniques correct, but you seem to miss the vital focus point that you intended. At the best of times it is a challenge to obtain sharp focus particularly when using longer focal length lenses. This goes for all genres of photography but it is very true for wildlife photography. The one thing that makes or breaks a captured image – is absolutely sharp focus.
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