When I take a photo, I sometimes have an aspect ratio in mind, as a creative choice. For example, I wouldn't use a widescreen aspect ratio for a portrait. As another example, if I'm shooting a landscape, and I have some junk in the immediate foreground that would distract from the view, a widescreen may work better to crop that out. But if the thing in the foreground adds to rather than distracts from the photo, a 3:2 aspect ratio may work better, to include it in the photo.
But these are specific cases. Most of the time, though, I have no specific opinion regarding what aspect ratio to use. In those cases, should I use the aspect ratio of the camera sensor (3:2), or the aspect ratio of my monitors (widescreen)? Should the aspect ratio of the camera drive my photography, or the aspect ratio of the monitors?
To put it differently, what default aspect ratio would you suggest when I don't have an opinion one way or the other?
When I view photos, I always prefer using the entire area of the screen to display the photo, even if the photo ends up going off the edge of the screen and being cropped along one dimension (like Lightroom’s Fill view mode). I don’t like letterboxing (like Lightroom’s Fit mode), because that means that that some of the space on the monitor is being wasted, and the photo is being displayed at a smaller size than it could and therefore loses its punch. I want to make use of every inch of screen space to display my photo.
My camera, the Sony NEX-5R, lets me shoot photos at 3:2 (native) or 16:9. When I set 16:9, the preview is cropped. Note that it doesn't display the entire image with a border around the part that it will retain. Rather, it shows only the part that fits the chosen aspect ratio. This camera has no viewfinder (whether OVF or EVF).
I shoot RAW, and opening the RAW in Lightroom shows the cropped image, but I can undo the crop because the information is still there in the RAW.
My monitors are all 16:10 (but I may buy a 16:9 monitor). Taking a step back from the detail of 16:10 vs 16:9, the point is that I use only widescreen monitors.
So, given that I want to end up with widescreen photos, in cases where I have no opinion regarding what aspect ratio to use as a creative choice, do I set my camera to widescreen? Crop in post? Don't crop at all? In more detail:
Option 1: Forget about the aspect ratio of the sensor. If you want to display photos full-screen on a widescreen monitor, use a widescreen aspect ratio while shooting photos. Get things right in-camera, and don't worry about wasting a few pixels (2MP of 16MP). Instead get the composition right.
The preview will match the aspect ratio of the final photo. A more accurate preview is better, right? This should let me compose a better picture if I can see the final result.
This goes for the review as well.
Option 2: Shoot at the native aspect ratio of the camera, and crop it in Lightroom or iPhoto to 16:10 to match your monitor.
This is good in that I can do the cropping on a 30-inch monitor rather than a 3-inch screen, so that I can actually see what I am cropping out, can try various options and see what works well, and I'm in no hurry. On a 3-inch screen, I'm effectively doing things blindly and hoping it turns out well.
This is bad in that I'm not getting things right in camera.
This is good in that I can crop to the exact aspect ratio of my monitor (16:10) in post, but my camera doesn't let me shoot at this aspect ratio (I have to go with 16:9).
This is good because I might realize after taking a photo that a different aspect would have worked better for that particular photo.
Option 3: Don't crop at all. Leave it to the photo viewer to effectively crop the photo while displaying it, like Lightroom's Fill view mode.
This is bad in the sense that the photo viewer either letterboxes (ugh) or chops off the top and bottom part of the photo to fit it onto a widescreen monitor, whereas if I had done it myself, I could have done a better job deciding what part to crop (perhaps only the bottom part, if it's noisy -- full of objects that distract from the composition). Basically, I can exercise creative control if I do the crop myself.
This is good because if I buy a monitor with a different aspect ratio one year, or five years, down the line, keeping all the data will let me display the photo best on that monitor. If the sensor is 3:2, and I crop it to 16:9 in-camera or in post, but 3:2 monitors make a comeback five years from now, I'd have painted myself into a corner.
As a general question, should my goal as a photographer be to get things right in-camera, or preserve as much data as possible to give myself flexibility later? These two goals are in conflict here.
Footnote: I shoot in RAW, so the data is not actually lost when I set my camera to shoot 16:9. I can, in theory, go back and undo or modify the crop later. But realistically, if I buy a 4:3 or 3:2 monitor five years from now, I'm not going to go redo the crop for thousands of photos, so for all practical purposes, the data is lost if I set my camera to use a non-native aspect ratio.