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Manual Focus vs. Autofocus

Nowadays, photographers have numerous technical mechanisms available to help them achieve a perfect picture. One of these is the auto focus (AF), which sets the focus for the subject automatically. However, when very large focal lengths are involved, which is also the case with digiscoping, this function is pushed to its limits.

© Dr. Jörg Kretzschmar

Auto focus

Even if a camera lens is used when digiscoping, it is still rather difficult to use the auto focus. The sharpness of the images that are shot using the auto focus depends on the quality of the camera and the contrast of the subject. The auto focus doesn’t always display the part of the image you want in focus. It can also only compensate for shots that are out of focus to a minimum degree. This means that rough focusing still needs to be carried out with the spotting scope/binoculars. However, the auto focus function is even pushed to its limits with telephoto lenses, due to the large focal lengths and the accompanying small focus depth.
Magic Lantern firmware offers a technical mechanism to help in this case (which can be used with selected cameras). Its focus peaking function makes it easy to perform manual focusing using contour lines that have been inserted optically in the live image in a contrasting color.
Eine technische Hilfestellung bietet hier die Firmware Magic Lantern (auf ausgewählten Kameras anwendbar). Die sogenannte Fokus Peaking Funktion erleichtert hier manuelles Scharfstellen durch optisch ins Livebild eingeblendete und farblich abgesetzte Konturlinien.

Image stabilization also plays a key role in achieving optimum picture sharpness. A good support or a stable tripod including a tripod head is the main requirement for producing high-quality digiscoping shots. There are two image stabilization options offered. One is located in the optics, i.e. the camera’s lens, while the other is in the housing, on the camera’s sensor. The image stabilizer in the objective lens is a function that offsets minimal movement using movable lenses, thus preventing images from going out of focus due to vibration. On the other hand, the stabilizer in the camera offsets vibrations by the sensor being mounted mechanically. The sensor-based image stabilizer operates regardless of the lens being used, which is a major benefit when combined with the TLS APO adapter. This is precisely the technology that, for instance, makes the Olympus system camera OM-D E-M5 very useful for digiscoping. In contrast to this, the digital image stabilizer offsets out-of-focus images purely by reducing the megapixels, which, in turn, has an adverse impact on image quality.