I was just as excited as anyone when I got my first prime lens. After years of kit lenses with variable apertures where I was often stuck with f5.6+ and higher than ideal ISOs, f1.8 seemed amazing.
The first photo I took of my son laughing with all that cinematic bokeh behind him made me feel like my photography had taken a bit step forward.
People spend lots of money for lenses that open even further – to f1.4, f1.2, or even f0.95.
The idea of letting in that much light seems amazing for low light situations, keeping photos clearer and less noisy. Right?
The downsides of shooting quite so wide open…
There are compositions where wide apertures make sense, for sure.
And some modern and high-end lenses are still really sharp wide open.
But a lot of lenses sharpen up a fair bit when stopped down, and conversely are a bit soft wide open. Both of the prime lenses I’ve started with (35mm and 50mm) for instance are appreciably sharper when stopped down to f2.8 instead of f1.8.
They don’t look bad wide open, but for shots where I really want to maximize the detail, f1.8 isn’t ideal.
There’s a lot of debate to be had there, a lot of exceptions and “yeah but what about this lens?!”
Another concept that I’ve come to see as I build my skills is that cameras can struggle to autofocus as quickly or accurately if the aperture becomes too wide. Seems like when that much light floods the sensor it can be tougher to distinguish a subject.
But there’s one more aspect to focusing that is directly affected by the aperture as well, and that’s of course how shallow the depth of field becomes.
Depending on your distance to the subject, even f1.8 can cause issues like the nose being in focus but not the ears, or parts of the hair being in focus and other sections not. That becomes more severe at f1.4 and especially at f1.2.
That can mean that, as expensive and exciting as an f1.2 lens seems, it can also be less reliable. That’s for portraits, sure, but especially for wider shots like street photography or straight up landscape photography.
For shooting video as well, those kinds of super-wide apertures can wash out so much of the background the viewers can lose context about where the subject even is.
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