AF-H: A New Focusing Mode for Hyperfocal Distance

March 13, 2008 | Mark Goldstein | Photography Blog | Comment |

Hyperfocal DistanceIn his first article for PhotographyBLOG, Zoltan Arva-Toth takes the bold step of proposing an entirely new auto-focus mode for digital cameras…

Update 1: As this has created a lot of interest, we’ll be contacting the camera manufacturers soon to ask for their input.
Update 2: Kodak, Carl Zeiss, Olympus and DxO Labs have now provided their feedback - see the end of the article.

It is no secret to anyone with a basic knowledge of photography that most modern cameras offer two main focusing modes, manual focus (MF) and autofocus (AF). Autofocus may come in several flavours, including AF-S (called one-shot AF by Canon) for stationary subjects, AF-C (AI Servo) for moving ones – especially useful if your subject is moving toward or away from you – and an intelligent AF-A (AI Focus) mode, which detects if the subject is in motion or not, and acts accordingly.

In manual focus mode, one of the things you can do is set the lens to the hyperfocal distance, which will depend on the actual focal length of the lens and the f-stop you pick. At this setting, everything between infinity and the near limit of the depth of field pertaining to the hyperfocal distance will be in focus. This comes in very handy when you strive to attain the greatest possible depth of field at a given aperture setting. With dedicated manual-focus lenses, this is easily done, for these lenses tend to have a proper distance scale complete with depth-of-field marks. Once you have decided on the f-stop you want to use, you consult the DoF marks belonging to this f-stop and turn the focus ring until the right mark is at the infinity sign. If your lens has a distance scale but no DoF marks, things get a little more complicated, as you have to either calculate or look up the hyperfocal distance for the given focal length and f-stop. But it’s still manageable.

The real problem comes when you have a lens with no distance scale. This, unfortunately, applies to most modern autofocus lenses, i.e. the ones you are most likely to use. In fact, it’s hard to set most AF lenses to the hyperfocal distance regardless of whether they have a distance scale or not, because the manual focus ring tends to have a lot less „travel” between the close-focus point and infinity than on dedicated MF lenses. I have a lens on which there are literally just a couple of millimetres between the 1m mark and infinity. No matter if you know the hyperfocal distance or not, you cannot accurately set it, which can be very frustrating at times.

But hey, aren’t we now living in the 21st century? These new lenses all communicate with the camera body. They transmit focal length and distance information, while the body tells them about the working aperture chosen either by the photographer or the camera’s electronics. So everything that is needed to calculate the hyperfocal distance is at the CPU’s disposal, as is the AF motor that can propel the lens into the specific setting.

Therefore I can see no obstacle to the inclusion of a new autofocus mode, in which the camera would set the hyperfocal distance on the lens, based upon the f-stop and the lens’ focal length (current focal length for zooms). This mode could be called HF or AF-H, and be accessible via the same dial or menu as the current MF, AF-S, AF-C and AF-A modes. The hyperfocal distance could be calculated and set by the camera either every time the aperture and/or the focal length changes, or upon a half-press of the shutter release button. The former may prove a bit power-hungry and irritating in practice, but would also ready the camera for shooting well in advance of releasing the shutter, so I would make this customisable.

Of course, this mode would mostly make sense when shooting wide to normal lenses, not telephotos. But with those lenses, it would make our lives a lot easier. This mode would not have to be limited to SLR cameras. It could be included in compacts too. In fact, it could greatly improve the responsiveness of digital compacts, provided it is implemented in the former way, thus bypassing the two-stage shutter release routine. This focusing mode could transform any sluggish compact into a highly responsive street photography tool, for instance. Sure, you’d need to mind your backgrounds, because they would also be sharply rendered, but that seems like a small compromise for a potentially major improvement in operating speed.

If you like this idea, express your support for it in the Comments section below.

What the manufacturers have to say…

“1° Computing the hyperfocal distance from the aperture and the focal distance is very easy indeed. Since the lens can communicate with the camera body, it would be very simple to automatically set the focus to the hyperfocal distance. This is only a hardware problem. Actually, an old camera as the Canon EOS 850 had a “depth of field mode” where it was possible to specify the furthest and closest point at focus, and the camera determined the aperture. This is quite the same problem, viewed from a different angle.

2° A software solution is not a well posed problem, since we cannot determine the object distance from a single shot and cannot change the focusing distance adequately. In a further future, we can think of having different types of lenses that could provide an estimate of the distance (see for instance the work done at Stanford University, see for instance http://youtube.com/watch?v=9H7yx31yslM ). In this case, it is possible to change the focus a posteriori. In a short term, DxO Labs also integrates its technology in embedded systems and also controls the autofocus, and the answer is then in 1° again.

DxO Labs

“Thanks for the information. Yes, the AF-H autofocus mode might be an interesting feature for AF (D)SLR-cameras.
Because we do not offer any AF camera model and most of our current lenses are of MF type (except Sony ZA lenses), we cannot comment the technical feasibility in future products.
This is definitively a subject for camera developers and manufacturers, e.g. our partner Sony.

Best Regards

Bertram Hönlinger - Carl Zeiss

“At Kodak, we don’t comment on specific future development. Of course, we’re always open to new ideas and will continue to listen to our users to help provide guidance on which features are most compelling and interesting to them. To the extent this feature helps users to easily take better pictures it is interesting, but we can’t comment on whether we would look to implement it without more user insight and feedback.

Kodak

“No comment. Many companies may be working on this kind of approach but they would never talk about it or comment just in case there is a conflict of influence.

Olympus



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