X-T20 and 18-55mm F2.8-4 question

Started 3 months ago | Questions thread
OP villebon Senior Member • Posts: 2,225
Re: X-T20 dials, auto lever, aperture ring

Jeff Biscuits wrote:

As you say, setting the aperture ring to A and the shutter speed dial to A (and yes, it is the shutter speed dial, I can’t see any use of the term “mode dial” in the manual—that would be for PASM-style cameras) puts you into program mode.

In program mode, the camera makes decisions about how to balance aperture and shutter speed (and ISO, if you’re also using auto ISO). If left to its own devices, it’ll stick to a single version of what’s called a “program line”, so for any given exposure value it’ll choose the same combination of shutter speed and aperture.

However, the dial will give you control over “program shift”, which moves the camera onto a different program line. So effectively you’re telling it “I’d like a shorter exposure” or “I’d like a smaller aperture” or whatever. But that doesn’t mean you’re directly controlling aperture: you’re just shifting the program line. The smallest apertures may not be on an available program line because the camera knows that they cause diffraction and will avoid them.

Program shift is not aperture control. If you want to control aperture directly, use the aperture ring.

The accepted answer on this Stack Exchange page explains program lines and includes a couple of program line charts: https://photo.stackexchange.com/questions/18665/how-do-dslrs-figure-out-what-aperture-to-select-in-p-mode

Finally a name for it.  Turning the Rear Command Dial in Program Mode gets you into the Shift Program mode. Fine. That's all I wanted to know.


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