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Right after the question of ‘what X should I buy?’ comes ‘how do you manually focus your lenses?’ in popularity. Unfortunately, it’s not possible to dismiss everything under the sufficiency banner; contrary to the trends in image quality, we’ve gone the opposite direction away from sufficiency. There used to be a time when viewfinders were actually very good for acquiring focus manually; there was no choice because there was simply no other way to focus, either. That required a few things: firstly, a focusing screen with adequate coarseness (sometimes also referred to as ‘snap’); the same distance between flange and focusing screen and flange and imaging plane; adequate magnification, and fast lenses – to compensate for the coarseness of the focusing screen making it somewhat dark. Looking through the viewfinder of an F2 or a Hasselblad is a revelation compared to the drinking straws of modern finders. It seems we barely have the latter these days. So what can we do?

The obvious answer would be to use a camera with an EVF or live view off the LCD, since both approaches eliminate almost all of the issues – you see actual depth of field, can magnify, and use aids like peaking. But holding a camera at arms’ length or mounting it on a tripod isn’t always practical, which rules out the LCD; and EVF cameras are probably the future, but for the moment there seem to be some practical implementation issues*. In the meantime, we still need a solution to be able to access the great range of manual focus legacy lenses out there, and others that will never be designed for AF – such as the Zeiss Otuses.

*Basically, the technology exists but for one reason or other no manufacturer has built one that’s ‘right’ yet. Those which are usable have small sensors that compromise image quality; those with large sensors suffer from file compression or lag or excessive bulk.

There are actually quite a few reasons why you’d want to use manual focus even if your system is AF capable – these mostly centre around precision. In order to understand why, we need to understand a bit about how AF works. Whilst AF can determine distance to a target and move the lens accordingly, it has to do so either via phase detection or contrast detection. The latter assumes that the highest contrast image is achieved when the image is in focus; this looks for the highest spatial contrast within the box and racks the lens helicoid back and forth until a maximum is hit. This may not necessarily correspond with the intended subject being in focus if it’s lower contrast than the background – being backlit, for instance.

Phase detection splits light from the subject through two paths and calculates the phase angle between them; if in focus, the phase angle should be zero. The lens is moved accordingly; no racking back and forth is required because the camera knows in which direction the image is out of phase, and can turn the lens directly there accordingly. The problem here is if your subject is not planar, then the camera doesn’t know which part of the subject underlying the AF box is your intended focal plane: think about a face in profile that occupies perhaps 5% of the frame. Which part of the face is focused on? Most of the time, this is a non issue because the distance covered by the area under focus box is much less than the depth of field of the lens. Those of you who use fast telephotos will know this isn’t the case: in a headshot, there’s a very clear difference between focusing on the iris and the eyelashes even though the camera will report either one in focus without having moved the AF point. And it’s visible and only gets worse with higher resolution cameras.

To complicate things further there’s also field curvature – this is where the plane of focus isn’t flat but curved; an AF array can only be made accurate for one point in the curved plane unless you can tune each individual AF point, or only use the centre one. And we haven’t even started talking about focus shift when stopping down yet – suffice to say that it isn’t always covered by increase in depth of field for all lenses. There are some that are notorious for this such as the Leica 35/1.4 Summilux ASPH (pre FLE); Zeiss ZM 1.5/50 C Sonnar, and in my experience, the worst of the lot – the Nikon PCE 24/3.5 which has both focus shift AND extreme field curvature.

In an ideal world, then manual focus is very much WYSIWYG – but only providing you are actually seeing what you’re getting. The trouble is that with an SLR of any kind, you need to have an identical distance from mount flange to focusing screen and sensor plane across the entire plane for critical focus; this is almost impossible to achieve to the level of precision required for the D810 and 5DS class of cameras. It requires both flatness for planarity, shimming of the focusing screen for distance, and mirror angle for parallax in one of the axes (the other is not easily adjustable). To make things worse, such shims are not easily available, modern mirror box designs appear to be fixed and lack adjustable mirrors** and the service centres look at you like you’re from Mars if you ask them to align your mirror and focusing screen. (It’s easier with medium format because everything is larger but the tolerances stay identical.) So whilst you can make a serious improvement on things by changing your modern matte slow-AF-kit-lens-friendly focusing screen for one that’s designed for manual focus, it will only help to a degree.

**The Nikon D750, for instance, lacks the eccentric mirror adjustment screws accessible through the mirror box that all previous cameras had. It displayed the best out-of-the-box mirror alignment I’ve seen yet, but it still wasn’t perfect.

It’s also worth remembering that there’s a tradeoff between brightness, coarseness and ability to discern between faster apertures and focal planes – the coarser a finder is, the darker it will be, but the better it will be able to show accurate depth of field at larger apertures. This is because it is not gathering light that spills off-axis (i.e. comes from out of focus areas). Modern focusing screens are very good at gathering light and consequently very bright, but they’re also unable to show depth of field much less than about f4 – you’ll notice that the bokeh of an f1.4 lens appears much more pronounced in the final image than in the finder.

The best kinds of focusing screens are those that have both a split image (line up continuous lines to be in focus) and micro prism collar (little pyramids that dissolve when you’re in focus) – this allows you to work on both images that have line detail and irregular textures. Effectively, both split the image into two paths; if it’s in focus, the distance between the two paths is the same, and you see no break in the image. If not, it’s obvious the image has been broken up. The Nikon K3 is probably the best modern version; Canon also makes the Ec-A and Ec-L with various types of split prisms. None of these natively fit modern cameras, and so must be modified; focusingscreen.com has a variety of options. However…they are not ideal, as frequently they will require filing or trimming to fit, and you of course run the risk of scratching the very fragile surface. On top of that, the thicknesses do not match the original screens – I suspect this is because they have to add material around the edges – and sometimes the thickness is too much to be adjusted for by shimming. Canon screens are much thicker than Nikon screens, for instance, and there isn’t always enough adjustment latitude; you may also need to file the thickness of the edge of the screen where it sits in the wire carrier.

In the past, I have fitted every one of my DSLRs with a manual-focus aid screen – whether by modifying a screen myself or using a third party product. The D810 will probably be the last camera that I bother with simply because we have now reached the point where such screens are not accurate enough to reliably and consistently focus lenses like the Otuses wide open, no matter how well calibrated and adjusted the installation. At best, I can hit focus in the centre about 50% of the time with the 55mm, 20% or less with the 85mm, and not at all at the edges because of the geometry of optics. Undoubtedly this is because the focusing screens show depth of field somewhere between f2 and f2.8, and that just isn’t enough for a lens that slices the world into planes at f1.4. Combine that with the risk of slipping and damaging something inside the mirror box, and it’s not really a recommended option.

Top: Zacuto Z-Finder Pro 2.5x and mount; bottom: Kinotehnik LCDVF

More interesting are the LCD magnifiers I’ve been using instead: the Zacuto Pro and Kinotehnik LCDVF models. Both were designed for DSLR cinematographers – the underlying theory being that of easy viewing of the LCD when filming. They’re equally good for live-view stills shooters, and of course are much more stable than holding the camera at arms’ length since you now have a third point of contact with your face and the ability to brace the whole setup. Both are available in a variety of fitments to match the aspect ratios of various cameras. Neither is good for eyeglass wearers because of the eyecups; I have to use contact lenses to not make a mess of my glasses and be able to see the whole frame at a glance. The Zacuto is available in 2.5x and 3x magnification; the Kinotehnik offers 2-2.2x magnification. I find 3x to be too much because the resolution of the LCD is simply insufficient; 2.5x is nice for size but adds little extra detail or ability to discern critical focus over 2x.

All are a massive improvement over the optical finder and bare LCD; it actually takes you a little while to get over the fact that you can now accurately see and focus on any point in the frame without having to remember how much to turn the focusing ring to compensate for off-axis parallax. I find my hit rate is somewhere in the 70-80% range across the frame, which is much, much better than using the optical finder. A little focus bracketing takes care of the rest. Of course all is not perfect: for most DSLRs, there are significant compromises involved in using LV to shoot. This manifests as slowness to get into LV, image lag in low light, long blackout time between successive frames, no image when shooting bursts, and of course terrible battery life. They weren’t designed as mirrorless cameras, and it shows. Sadly, it seems none of the mirrorless cameras quite get it right either – the only serious full frame contender suffers from image quality compromises through shutter shock and/or compression.

As far as the actual products themselves go, I’m on the fence. The Zacuto is clearly the better built of the two, being thick gauge plastic and machined aluminium – it really feels solid. Unfortunately it’s also nearly three times more expensive and the bulkier of the two, requires mounting via the tripod hole (kiss your L bracket or vertical grip goodbye, and remember your spanners) and is very fiddly to remove. On top of that, it’s not very ergonomic: there are a lot of bits that poke at your hands. I also suspect the mount points will wear down to the point of looseness after a while – mine are showing some signs of abrasion already. It also has built in diopter adjustment, better optics and an (uncleanable) anti-fog eyepiece, which the Kinotehnik does not.

What the Kinotehnik loses to the Zacuto, it makes up for in convenience and price. It mounts either via a sticky frame that adheres to your LCD, or clips on (to the existing LCD protector brackets on the D800/D810), and then the finder itself sticks to it via magnets. This makes it easily removable for reviewing images or navigating menus; I find it extremely useful when teaching because I can easily show my students what I shot. It is thinner gauge plastic with some very visible seam lines, doesn’t sit that securely (I suspect this is why a neck lanyard is provided) and the eyepiece is neither anti-fog nor does it contain diopter adjustment. It is just a little more low profile and streamlined, though.

I actually think there’s a case for both (at least until a better alternative comes along) – the Zacuto is best when you’re either always going to be using MF lenses, don’t need to show somebody else your LCD, and if you don’t need a vertical grip. If you want something that can be quickly removed, or you need to use a vertical grip or you’re switching between AF and MF lenses (the optical finder still has a clear advantage for AF lenses), then the Kinotehnik is a better choice. My one hesitation with the Kinotehnik is that customer service seems to be utterly nonexistent – several emails to try and purchase additional mounting frames have gone ignored, and there’s no way to get them otherwise in Malaysia.

It seems to me that we are currently in a transition phase: there is still a clear advantage for optical finders and DSLRs in some situations, but those are rapidly shrinking. I don’t think AF is the way to go for all applications; most of the time it takes me so long to get precisely the right focal plane with AF that I’m faster with MF and one of the LCD magnifiers. Yet we’re not quite there with EVFs, either – ironically though, it’s the rest of the hardware that’s holding things up. In the meantime, at least there are workarounds. I’d highly encourage giving one of them a try; you’ll probably find manual focus a lot easier than you imagine. MT

Zacuto and Kinotehnik finders are available here from B&H.

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