How can I keep an angled poster photo sharp across the whole surface when shooting handheld?

Question

I’m photographing posters and large signs outdoors with a Sony A7 III and a 24–240mm lens. Sometimes I shoot slightly from the side to avoid reflections in glass or for a more stylized look, but then only part of the poster looks really sharp.

If I stop down in Aperture Priority to get more depth of field, the shutter speed gets slower and I see blur from camera shake. If I use a wider aperture or Auto mode, shutter speed is better but sharpness falls off across the poster.

What’s the best handheld approach to get the whole poster as sharp as possible when shooting at a slight angle? Would raising ISO, changing distance/focal length, image stabilization, extra light, or a tripod be the right solution?

user95237 · Accepted Answer

Options

No additional equipment methods

Stand further away and use the zoom to frame the subject(s). At a given aperture, a longer focal length "lens" will provide, in absolute terms, a deeper depth of field. In terms of linear perspective this is a change to the station point. This will also have the effect of reducing linear perspecive distortion in the picture because a more distant station point makes angle between the flat subject and the lens axis closer to a right angle.*
In manual mode, set the aperture small enough to provide adequate depth of field + raise the shutter speed fast enough to reduce motion blur + and increase the ISO high enough to provide an adequate exposure. Higher ISO's may generate more noise than is acceptable for your use. Or it may not.

Additional equipment methods

In aperture priority mode, use a tripod.
In aperture priority mode, use external light sources under your control.
Swap out the lens for a tilt shift lens. Rotate the lens so that it provides front swing instead of front tilt. Adjust the angle of swing and aperture to capture the receding subject plane in acceptable focus.

Remarks

Making the picture you want will often require tradeoffs. Often one of those is additional work (e.g. using a tripod). Another common tradeoff is money (e.g. tripod, lights, tilt-shift lens). If the picture matters enough, then the work is worth it. If it doesn't matter enough, then it isn't.

Sometimes making the picture you want means exploring similar but different pictures (e.g. changing the station point). Personally, if I am trying to make a picture in "street style" I will use high ISO as a natural part of what I am trying to capture.

Often, making the picture you want will involve social risk (e.g. what will people think of me using a tripod in public, the creepiness of taking pictures across a busy street with a long lens**). For me, this is the hardest part.

Footnotes

*You could also use a shorter focal length (wider angle) "lens" from the same distant station point and then crop in to the subject of interest. The loss of absolute resolution might or might not be acceptable for your needs.

**Using a tripod for long lens shots across a busy street is probably less creepy than hand holding because it's slower and more obvious. This makes it less likely for people to assume you are trying to get away with something. And it gives people time to ask questions as you go about your business.