Why Fast Primes Might Be Hurting Your Portrait Sessions

A shallow depth of field ruins more portraits than a small aperture ever does. That claim runs against nearly everything you've been told about what makes a serious portrait setup, and it's worth sitting with before you spend money on another fast prime.

The case for reaching for a zoom over a prime comes from Martin Castein, who has shot weddings and portrait sessions professionally and argues that a 24-70mm f/2.8 suits far more shooters than they'd like to admit. Castein doesn't pretend the zoom matches an 85mm f/1.2 for background blur. His point is that most photographers overemphasize that blur while ignoring everything else that actually builds a portrait, starting with the person in front of the lens.

The heart of the argument is your subject's experience. When you shoot with a prime and want a tighter frame, you stop, step in, find your composition, and start again. None of those pauses feel long to you. Castein flips the perspective and asks what the subject sees: someone breaking the flow, then repositioning, then asking them to pose differently for a full-length shot when they'd have been better off just continuing what they were doing. Every move resets their rhythm and their confidence, and you're forcing them to process a new scenario each time.

Distance carries a second cost that Castein thinks portrait shooters underrate. When you step in for a close-up with a 50mm, you're moving into someone's personal space, and that changes how they respond to you. A zoom lets you plant your working distance, say the equivalent of where you'd stand at 50mm, and stay there. Because your position holds steady, your perspective holds steady, so you can pull to 24mm for a wide frame without distorting features. The trap is moving closer as you widen, which is exactly what warps a face. That means being deliberate about focal length while you keep talking and keep the session moving.

There's a broader shift worth connecting here. Camera makers have leaned hard into the f/1.2 and f/1.4 prime as the mark of a professional, and the pricing reflects that positioning. What Castein describes is a return to thinking about a lens as a working tool inside a live interaction rather than a spec sheet you win. The zoom-first approach fits new or nervous subjects especially well, since anyone still learning to be photographed benefits most from an operator who never breaks the flow. If your subjects are relaxed pros who thrive on a slow, deliberate pace, a prime workflow costs you far less. Knowing which situation you're in tells you which tool earns its place in the bag.

Castein isn't anti-prime. He uses primes for portraiture constantly, and he suggests supplementing them into a shoot alongside the zoom, grabbing your safe frames first and then switching over to build skill wide open once the pressure is off. He also raises the question you should ask every time you crush the background: is that blur making the picture better, or is it erasing context you actually wanted? Watch the video above for his full breakdown of working distance and why he leans on the zoom for most studio work.