Street Fusion By Terry Cioni

Sunday, February 28, 2016

Some Thoughts On Auto Focus

Auto Focus

One of the most significant advances in modern digital cameras is the auto focus system. It is often the biggest challenge for new users to set-up, understand, and work with, and get useable results.

Most of the so called enthusiast digital single lens reflex cameras have nine or more focus points some of them cross type sensors meaning they are more likely to achieve autofocus because they can focus on both vertical and horizontal detail.

The problem is when you let the camera make the choice of which point to use to focus on an object it may not be your intended subject. Popular AF features are auto focus face detect, and continuous auto focus with focus subject tracking. From my experience when using all the AF points the camera/lens will focus on the closest subject in the frame and that will be the point of absolute focus as determined by the camera's AF system and not the photographer.

The more expensive the DSLR the faster and more complex the auto focus system, allowing sports photographers to never miss the peak action shot. Most of these DSLR cameras can shoot 6 to 12 frames a second while continuously focusing on the 'selected subject'. Anticipating peak action is no longer a requirement of the good sports shooters of days gone by.

The Camera Multi-point AF selected the lamp post and buttons as they are closest to the camera. The subject is out of Focus as I was shooting at F4 which limits depth of field (focus)!

For every day use and/or day to day shooting I strongly recommend starting with the (single) centre AF point locking the focus on the subject - keep the shutter release button half pressed - recompose if necessary and shoot. The centre point is usually a cross type sensor which makes it fast and accurate. I want to add that with all but the most expensive DSLR cameras the Auto Focus depending on the light can be both slow and inaccurate so managing how it is used is critical.

This method of using the AF system is akin to how it was done with manual focus film cameras. The split screen or focus fresnel point was always in the centre - focus and recompose was a given. In short you take control of the auto focus and decide what will be the point of focus - not the cameras AF system.

Understanding depth of field (focus) can't be ignored - also knowing what factors effect depth of field (focus) are important to understanding focus be it auto or manual focus. Not the subject of these thoughts, but knowing depth of field is always greatest behind the point of focus will help your composition skills.

Finally the reason Nikon and Canon continue to own the professional camera market is the speed of their DSLR cameras especially as it relates to Auto Focus. The broad spectrum of the most modern mirrorless cameras just can’t keep up when it comes to AF tracking - I would be kind in saying that most of them are not even a distant second to the likes of the pro Nikon and Canon bodies and lenses. Take a Sony A7RM2 mirrorless camera with Sony’s very latest 70-200 F2.8 lens to an NHL hockey game and shoot beside a Nikon D4s and the AF speed difference gets apparent very quickly.

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Thursday, February 25, 2016

Auto ISO, TAv, Aperture Priority - Auto ISO

Auto ISO In Digital Photography

Often requested is the ability to use Auto ISO in full manual exposure mode which to the mind of many sounds counter intuitive. Often added to that request is the ability to use the exposure compensation function (hopefully a top dial).

Ricoh/Pentax saw the value of this approach and created a fifth mode called 'TAv' on their cameras which does pretty much as I have described.

Here is how auto ISO manual exposure mode works, the shooter sets the F stop and Shutter speed hopefully based on what they are shooting and the camera choses the appropriate ISO keeping the exposure correctly set for the lighting conditions, ideally the low and high ISO values can be limited in the camera. Rule #1 with ISO - is the lower the better the resulting image - but digital (high) ISO has come along way in recent years.

Manual Exposure - Auto ISO

OK, where do I use this technique, I am an avid street shooter, my subjects are moving and I am moving as I am shooting, depth of field (focus) is important as often the Auto Focus is not fast enough to be totally accurate and falls short (out of focus images). This is why so called "Zone Focus" (a front to back zone of acceptable focus - a Google search will give you the fine detail) is popular among street shooters - depth of field (focus) is king on the street. Prior to auto focus (a film Leica as a good example) it was the zone focus technique with the lens aperture set to F8 usually with a wide-angle lens (wide-angle lenses have greater depth of field). Because of subject and camera movement a fast shutter speed is also required. Unfortunately most (not all) modern auto focus camera lenses no longer have depth of field scales engraved on them making zone focusing next to impossible.

Often I choose a fast shutter speed somewhere between 1/640 - 1/800 of second. Because of depth of field (focus) considerations related to AF speed if shooting full frame F8 if shooting APS-C F5.6 or m4/3 F4. Please note; each of those sensor sizes yield different amounts of DOF given the same point of focus. The camera is changing ISO as the light changes correcting exposure. This gives me complete control and I don't have to worry about exposure settings as I shoot. The cameras I like the best give me the ability to set the ISO ranges say between 200 to 3200 ISO, you get the idea. Unfortunately some camera OEMs haven’t implemented Manual Exposure, Auto ISO, and access to Exposure Compensation and that is not understanding the benefits of digital cameras - and they should talk to a few real shooters.

The other option I often see requested is the ability shoot in Aperture Priority mode (the favourite mode among most serious shooters) with Auto ISO but, and this is important, is the ability to set the minimum shutter speed up to a 1/500 of second or higher (at least for my purposes). Of course because the camera is in Aperture Priority mode the shooter would have access to Exposure Compensation. I haven’t tried this personally but I will. These techniques certainly go beyond street photography your imagination being the limit.

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