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Using Auto-ISO


Using Auto-ISO

by Rico Pfirstinger

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Thanks to continuous firmware updates, all Fujifilm X-Mount cameras will eventually use the same Auto-ISO paradigm. This “new” feature is actually based on the original custom Auto-ISO function in the classic X100. Since the Auto-ISO section in my book Mastering the Fujifilm X-E1 and X-Pro1 is still describing the previous (and not so popular) Auto-ISO version, this X-Pert Corner column also serves as a free update for my loyal readers.

Auto-ISO Parameters

How do you make the most out of the improved Auto-ISO feature? First, let’s see how it works:

Instead of automatically using a minimum shutter speed (MSS) based on the focal length (FL) setting of your lens, the new Auto-ISO lets you choose and set any MSS between 1/4s and 1/500s (or 1/125s in the X-A1 and X-M1). That’s quite a range! For the record: The MSS formula for the previous Auto-ISO version used to be MSS = 1 / [FL x 1.5], with exceptions for very long lenses and lenses and active image stabilization.

In addition to setting your own minimum shutter speed, you can now also set the default sensitivity and the maximum sensitivity. These two sensitivity parameters define your Auto-ISO range: The camera will never pick an ISO setting that is lower than the default sensitivity, and it will never exceed the maximum sensitivity setting. Within these limits, it will always try to meet the set minimum shutter speed requirements, and in order to do so, it will automatically increase the ISO value.

Auto-ISO and Exposure Modes

How does Auto-ISO work in concert with your camera’s four PASM exposure modes? Let’s have a look:

  • In mode P (program mode), the camera automatically selects the appropriate aperture and shutter speed. It will always try to expose at least as fast as the set minimal shutter speed (MSS). However, before it automatically increases the ISO value beyond the default sensitivity setting, the camera will open the aperture to its maximum setting, so there’s a fair chance that your aperture will always be wide open under low light conditions, especially when you select a faster MSS. If you want to avoid this, either choose a higher Auto-ISO default sensitivity setting or switch to A mode (aperture priority).
  • In mode A (aperture priority mode), the camera will always expose with your pre-selected aperture setting. It will also try to keep the shutter speed above the MSS setting, and in order to achieve this, it will pick higher ISO values as appropriate—until the ISO reaches your maximum sensitivity limit. If this limit is still insufficient to guarantee a correct exposure, the camera will pick a slower shutter speed (below the MSS setting) in order to correctly expose the image. This means that the maximum sensitivity setting takes precedence over the minimum shutter speed setting. Of course, this rule also applies to P mode.
  • In mode S (shutter priority mode), you pre-select a shutter speed using the shutter speed dial, so the MSS setting in the Auto-ISO menu becomes irrelevant. The camera will always use the shutter speed set on the shutter speed dial, and it will open the aperture to its maximum before it automatically increases the ISO value. Again, this may be problematic for some users (especially those using fast prime lenses with very little depth-of-field). Possible remedies are either selecting a higher default sensitivity setting or using the camera in manual mode (M).
  • In mode M (manual exposure mode), you pre-select both shutter speed and aperture, and the camera’s Auto-ISO will automatically pick a suitable ISO value—as far as this is possible given your Auto-ISO default sensitivity and maximum sensitivity limits. If the correct ISO value isn’t to be found between those two limits, the resulting underexposure or overexposure is displayed in the viewfinder’s exposure compensation scale. In order to correct the over- or underexposure, pick different aperture or shutter speed settings until the exposure compensation scale hones in at “zero”.

Mode M does not allow using the exposure compensation dial to bias the camera’s exposure in either direction when Auto-ISO is engaged. This feature may be part of a future firmware update. However, this addition has become much less pressing, because you can now just as well shoot in mode A (aperture priority) and set a minimum shutter speed of your choice. In A mode, the exposure compensation dial is always fully functional.

Auto-ISO and Custom Shooting Profiles

To quickly switch between different Auto-ISO configurations that include different minimum shutter speed settings, it’s possible to store a custom Auto-ISO configuration in each of the custom shooting profiles (C1 – C7) of your X-E1, X-Pro1 or X-E2.

For example, you could save MSS settings of 1/30s, 1/60s, 1/125s, 1/250s and 1/500s in your custom profiles 1-5, then quickly access them by either using the Q menu or an Fn button. Yep, that really works!

Of course, this feature would be even more convenient if your camera allowed assigning labels to custom profiles (like “1/500s Action” instead of “C5”). I made sure that Fuji knows about this, so there’s a fair chance that labels for custom shooting profiles may become available in the future. Click here to read my X-Pert Corner column on Custom Shooting Profiles and the Quick Menu.

Auto-ISO and Auto-DR

What about using Auto-ISO in concert with Auto-DR? Simple: DR takes precedence. So when your camera operates with Auto-DR and Auto-ISO, and it decides that (for example) DR200% is the way to go, it will increase the ISO value as needed—as long it doesn’t exceed the maximum sensitivity set by you, the user.

X-E2 Full-Size Samples

The full-size SOOC JPEG sample images in this column belong to a series of shots I took with a production X-E2, featuring XF lenses with the latest firmware. The Lens Modulation Optimizer (LMO) was set to ON, sharpening and noise reduction operate at factory defaults. Feel free to check out these and more unedited full-size images on Flickr by clicking here. In Flickr, you can also view the complete EXIF data (including Fujifilm maker notes) by selecting the EXIF option offered in the menu.

For your convenience, here’s a TOC with links to my previous X-PERT CORNER articles:

Rico Pfirstinger studied communications and has been working as journalist, publicist, and photographer since the mid-80s. He has written a number of books on topics as diverse as Adobe PageMaker and sled dogs, and produced a beautiful book of photographs titled Huskies in Action (German version). He has spent time working as the head of a department with the German Burda-Publishing Company and served as chief editor for a winter sports website. After eight years as a freelance film critic and entertainment writer in Los Angeles, Rico now lives in Germany and devotes his time to digital photography and compact camera systems. His book “Mastering the FUJIFILM X-Pro1” (Kindle Edition) (Apple iBook Store) (German version) is available on Amazon and offers a plethora of tips, secrets and background information on successfully using Fuji’s X-Pro1 and X-E1 system cameras, lenses and key accessories.