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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