One important correction to keep in mind when trying to capture a flat surface is the Plane-of-Focus on the subject, relevant to your camera sensor. The image below is an important example of that and I discuss it in more detail below. This technique will greatly improved your documentary-style photo skills!
When you shoot onto a flat surface and you want to capture the surface – and other detail that projects in front of and behind that surface – you first have to get parallel to that surface – that is, your camera sensor or film plane, not you. You can have the camera mounted on a tripod and be standing a considerable distance away and trip the shutter remotely. The key here is to think planes that are parallel to each other. Those two planes are the subject and camera sensor. Aligning them is a touch tricky and takes practice.
The above and below screen grabs offer more than enough information for you to decipher the challenges of getting a decently sharp photograph: wide open aperture, slow shutter speed and a ISO setting that’s as high as I want to go. Above, you can see the key data: f-stop, shutter speed and ISO, as well as the specs to which I saved the image after processing the raw file. Shown below is information about the camera and lens, if you’d like to know what I shot with.
For the shot – and because I was in a museum – there were a couple of factors restricting the ability to get an easy capture: lower lighting, no tripod, limited space to name a few. I was practically sitting on the floor and using my eye to focus across the flat surface of the rudder. If you tilt the top of your camera in towards the rudder, the bottom of the camera, naturally, pulls away, and one section of the rudder goes out of focus, as does other elements of the image. And, vice versa. The same applies to the left and right side of the camera.
I didn’t worry too much about the lateral roll (left and right, around the axis of the lens), and if you inspect the image carefully you can tell from the out-of-focus background that I am rolled well to the right! However, the propeller is sharp – it extends well out towards me – as does the planking on the boat (you can see the loss of depth-of-field on the plank lines near the top of the image). I have some crop room if I don’t like the blurred lines of the planks, but I wanted to get the rudder, propeller, and attaching surfaces for the rudder in focus. Therefore, the reference focal point for the image is the plane of the rudder. All of it.
Low light impacted the sharpness of the image due to using a slow shutter speed. I added a bunch of sharpening and grain and tints and vignette, to name just a few of the after effects applied in Photoshop. I can see knocking out the background of this image and having a bit of fun in Photoshop or Affinity Photo, for sure.