Choosing between ISO and shutter speed - What is fast enough?

Left: Antilles hummingbird & juvenile black tern.  Right:  Juvenile Bonaparte's gull

Today's cameras are a far cry from the cameras of old, even going back only 10 years.  There are a multitude of differences, including sensor resolution, processing speed, electronic noise level, and vibration-mitigation technology.

The two images on the left were taken with a Nikon D500, which came out in 2016.  Both lenses used had VR (~4 stops compensation).  The right image was taken with a Z6iii, which has built-in VR (~8 stops compensation).  Also, the D500 is a crop-sensor camera (1.5x crop factor) while the Z6iii, which came out in 2024, is a full-frame camera.

OK - so, why tell me that?  

It comes down to electronic noise.  Electronic noise in a digital image causes reduced definition; details get eroded.  Noise is affected by numerous variables; photographers want to keep noise levels down to maximize details.  The counter to capturing details has to do with blur, specifically the kind that comes from subject movement.  Camera motion has been significantly mitigated with anti-vibration technology, so the real culprit here is subject motion.

Higher ISOs mean more electronic noise, thus reducing image quality, while slower shutter speeds cause motion blur that does the same thing in a different way.  Ideally, you want the lowest ISO possible for the best shutter speed to produce the clearest image.

There is no one solution, one perfect camera setting, that will solve all your definition-related issues.  However, there are things to keep in mind.  Consider these points below:

• The smaller the sensor (DX vs FX), the greater the noise at any given ISO.  Full-frame cameras typically produce better images at any given ISO than crop-sensor cameras.  Consider shooting with a full-frame camera if you tend to need higher shutter speeds.  The cost is losing that extra magnification that comes with a full-frame body.
• Stronger lighting allows faster shutter speeds to be achieved without sacrificing ISO.  Light, cloudy days offer good lighting with little harsh shadow.  Sunny days, if you point your shadow towards your subject, provide excellent shutter speeds, but the price is that your angle to the subject is very narrow without inducing shadow.
• Lenses with a low minimum aperture provide faster shutter speeds, but these lenses are usually out of the reach of many.  A 500 mm f/5.6 lens may cost $5000, but a 500 mm f/4 lens will cost upward of $15,000.
• Modern cameras boast better noise levels than older camera technology, all else being equal.  Also, older equipment may not have the best anti-shake technology, meaning that you need faster shutter speeds to reduce blur caused by the operator's motion.  Keeping up with technology changes can be expensive.
• Higher pixel counts are a mixed blessing.  Pixels are crammed closer together and the wells that create them are smaller, meaning more noise.  However, the greater resolution has the advantage of allowing more cropping, less extrapolation, and averaging out noise.  Higher pixel counts will tend to produce better images regarding noise than lower pixel count cameras, assuming you aren't doing significant cropping.

The bottom line on everything comes to personal satisfaction with your results.  Take your equipment and play with ISO and shutter speed settings in a situation where your valuable shots won't be at risk because you were using the wrong settings.  Photograph creatures you would normally ignore - house sparrows, starlings, squirrels, and the like.  You will have to find the right settings for your personal taste.  The nature of the light will have a big impact on this too, so doing it once won't give you the whole picture.  

As with most things, knowing your equipment and how to compensate for any situation will go a long way to improving your photography.  Be patient, and have fun.

Thanks for reading.

Eric Svendsen     www.ericspix.com