I have received this lens today, I haven't fitted it to the Mobius yet but I have connected the ribbon cable and set it up in webcam mode on my laptop. Could someone please point me to a tutorial on how to focus this lens.
Each unique lens has its own “built in” amount of depth of field. This is especially true of the fixed focus primary lenses which we are all familiar with from our dash cams. Fixed aperture varifocal lenses such as the one featured in this thread are different in that the depth of field varies as you zoom the focal length. (I'll talk more about this later.)
Hyperfocal distance is a
function of the lens' depth of field but is dependent upon WHERE you've focused the lens.
Hyperfocal distance can sometimes be a complicated and confusing subject but at its simplest,
hyperfocal distance is the focusing distance that gives your images the greatest
depth of field. For example, consider a landscape where you want everything — foreground and background — to appear sharp. If you focus on the foreground, the background will appear blurry in the image. And if you focus on the background, the foreground will look out of focus. The solution is to focus at a particular point
between the foreground and the background, which makes both the foreground and the background elements of the scene appear reasonably sharp. This focusing point is called the hyperfocal distance. If you focus at the hyperfocal distance, your photo will be sharp from
half that point out to infinity. So, if your hyperfocal distance for a given aperture and focal length is ten feet, everything from five feet all the way until the horizon
should appear sharp. (although sharpness will drop off at greater distances outside the available depth of field with these types of lenses, especially at the longer focal lengths.)
As the illustration I've created attempts to demonstrate, the basic idea here is to determine (approximately) how much depth of field you've got to work with (the green box) and then move the hyperfocal distance forward and backward until you get the results you are after. So, you are essentially moving the green box forward towards the horizon (infinity) or closer to the camera (foreground). For normal everyday photography or video one might just focus on the particular object one is interested in and not worry so much about things nearer or farther away being out of focus. For dash cam work however, the depth of field available to us with each lens is vital, so adjusting for the optimal hyperfocal distance when focusing these varifocal lenses becomes more critical.
From my experience with both the 2.8-12mm ƒ/1.4 varifocal and this 6-22mm ƒ/1.6 varifocal, when using these lenses for dash camera work, finding the optimal point of focus can be a bit of a challenge and can require some trial and error. There have been times when I thought I had the lens perfectly focused only to later discover after a day's shooting that cars either near or far were not quite as in focus as I wanted them or expected them to be. This is partly the result of lots of experimentation with these lenses that require constant refocusing. Once you find a permanent focal length setting that you are happy with for dash cam purposes, you can basically set it and forget it.
One reason finding optimal focus can be a challenge is that every time you change the focal length of the lens, even slightly (zooming) you are changing the amount of depth of field available to you. The depth of field you thought you had last time might not be the depth of field you've got now. This is partly because these varifocal lenses have a fixed aperture. As you zoom the lens this fixed aperture becomes a “
relative aperture” according to the amount of zoom applied because you've got the same sized hole (the aperture) in relation to either the wide angle or telephoto capability of the lens. So, the fixed ƒ/1.6 aperture when the lens is set to “6mm” will be different (
relatively smaller) when the lens is zoomed out to 22mm. Also, as you zoom in, your hyperfocal distance moves farther and farther away and you need to compensate for this too.
Many high end DSLR and professional cinema zoom lenses have automatic irises that adjust the lens opening (aperture) according to the amount of zoom applied and the amount of exposure required. These CCTV M12 zoom lenses on the other hand are entirely manual and have fixed apertures that stay the same regardless of how you adjust the focal range, thus the depth of field will change as you zoom in and out and the exposure settings may even need to be adjusted.
Sometimes there is a grey area between the theory of hyperfocal distance and the actual practice out in the field, especially when attempting to use these CCTV lenses designed for static surveillance conditions in the challenging and dynamic environments that dash cams operate in. So, the bottom line here is to have a basic grasp of the concepts outlined here and then experiment with focusing until you find out what works best for your particular installation and driving conditions. You may find that you really want the sharpest imagery of cars way out ahead of you or you may want to optimize for cars directly in front of you in traffic. Maybe you want to try for the best compromise? (This 6-22mm lens happens to have excellent depth of field characteristics which is one of its more appealing features for dash cam use because it can actually work relatively well capturing good detail in the foreground AND as a sharply focused telephoto.)
Once you become more familiar with exactly how this lens performs you can find and select the sweet spot that works best for you. A bit of trial and error here will be your friend.