ISO and depth of field compared - from a spring flower

Spring crocuses photographed with different ISOs and apertures.
Who doesn't love spring?  The allure of new life coupled with a more friendly sun brings hope to those suffering the doldrums of winter.  With a zip in my step which had been absent for the last several months I remembered my camera and began once again capturing the world around me. 

The crocuses in my front yard became the focus of my attention.  I had lots of pictures of this purple harbinger of spring, and getting a few more was not likely to improve my collection.  No, it was time to play with the camera's settings.  So, with my new-old toy I began the process of playing and exploring.

ISO is greatly misunderstood.  Although it is a miraculous tool on the one hand it penalizes the user by reducing the quality of the image, especially when taken to the extreme.  I find there is usually a happy medium between shutter speed and ISO settings where the time interval is fast enough to prevent blur and the ISO is low enough to ensure no significant noise.  Finding that balance takes a bit of practice but is well worth the endeavour.

The image on the left was taken with an ISO of 80, the camera's lowest setting.  There is no electronic noise visible in the image.  The photo on the right was shot with an ISO of 25,600 - that is 8-1/3 stops beyond 80.  To put that into perspective, the sensor needs about 322 times more light at the lower value to make the exact same exposure at the higher value.  This phenomenal superpower comes with a cost though.  Notice the insets and specifically the bottom panel; those purple, white, and black blotches are the result of electronic noise.  As ISO increases, so does noise, and at some point it has a deleterious effect on the image.

The other thing to be taken from the photos is that they were shot at different apertures.  The left image used an aperture of f/4.3 - wide open for the given focal length of the lens.  There is some depth of field but it is modest at best.  You can see how the background gets softer as distance increases from the camera.  The grass behind the back crocuses is a good example.

The right image was shot at f/11.  Using such a high ISO necessitated it to reduce the amount of light coming into the camera.  The effect of the small aperture was to obtain a greater depth of field.  You can see that the background crocuses are much sharper than their counterparts, although that is somewhat mitigated by the electronic noise.  The grass behind them is somewhat blurry, but much less than the other.

One of the joys of photography is learning about the interrelated aspects of things like aperture and ISO.  It turns out the relationships become much more convoluted when you bring other factors such as shutter speed, technology, and sensor size.  So much to learn!

Thanks for reading.  www.ericspix.com   Eric Svendsen

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