It’s interesting that we know without a shadow of a doubt when auto ISO was first used. Auto ISO was not used on any SLRs simply because ISO could only be changed by removing the film and replacing it with a faster film!
Does it really matter what ISO setting I use for wildlife photos?
Yes, the ISO setting matters for wildlife photos. It determines the sensitivity of your camera’s image sensor to light and affects the quality and noise level of your wildlife photos.
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Should I use aperture priority for wildlife photography?
What you Gain by Using Auto ISO
Auto ISO adds to the advantages of the exposure modes used in DSLR and mirrorless cameras. For instance, using auto ISO with Aperture Priority retains the advantages of
- Control of depth of field
- Good bokeh
- Deeper area in sharp focus
- Always correctly exposed photos
while extending them over a wider range of lighting conditions by raising the ISO once the shutter speed drops to a level where sharpness is lost.
So this improves the functionality of Aperture Priority which is already the exposure mode most used by wildlife photographers. It is therefore recommended that you should use auto ISO with Aperture Priority for your Wildlife photography. As well as the photographic effects, It also reduces the attention you need to pay to monitoring shutter speed and allows you to change and adjust more rapidly.
How Auto ISO works
To set up auto ISO you need to set some parameters which define how the camera reacts to changes. This varies between camera manufacturers but in principle, the camera needs three things to decide what change to make to keep your photo exposed.
- Base ISO – this is the ISO setting at which the camera begins shooting
- ISO Limit – this is the maximum ISO the camera should use to achieve the correct exposure and is linked to the image quality deterioration caused by too high ISO
- Minimum shutter speed – this is the shutter speed below which the camera should compensate for a lack of exposure by increasing the ISO rather than decreasing the shutter speed which could decrease sharpness as a result of camera shake or subject movement
Some cameras have an auto setting for this which reads the lens focal length and sets the minimum shutter speed according to the reciprocal of focal length rule.
What You Loose by Using Auto ISO
The reluctance to use auto ISO Is based on the well-known fact that increasing the ISO increases the noise in the image and can decrease the dynamic range. However, there have been vast changes in camera and post-processing technology which have increased the usable ISO and we have most likely not kept up with this in our perceptions.
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Choosing the ISO Limit
The question then is what should you limit it to, which is very complicated, taking us to things like ISO invariance and real and simulated ISO and their effect on noise and dynamic range. There’s also photon, front end, and rear end noise that are interrelated and can make it better to lighten a photo in post-processing rather than in the camera by boosting the ISO.
There is an article that the author, Spencer Cox, claims to be a simplified description for amateurs online which runs to 1 7000 words if you want to try and understand it.
I would suggest that the easiest way is to do some test shooting over a range of ISO settings and judge for yourself what you see as the limit for different subjects and conditions.
Be like the vast majority of wildlife photographers and do most of your shooting with auto ISO probably best with Aperture priority.