Photographers Tend to Deal with Too Much Crop
Cropping an image can be a blessing and a curse. By cutting off some part from around the edges, you can help improve framing and create a more focused composition. But cropping can't solve everything, and it will cost you a portion of the resolution you paid for when you bought your camera sensor. You see, cropping cuts both ways, if you'll pardon the pun.
Cropping gives us an opportunity, in some limited sense, to recompose photographs after they have been shot. Does a pesky tree branch intrude into the frame, one you didn't see at the time because you were focused so much on your subject? No worries. By cropping off that edge of the frame, you can get rid of the distraction and create a more tightly cropped, more impactful image. Or perhaps your subject just doesn't seem to stand out enough what with all that space around it, or perhaps you wished you could have zoomed in just a bit more, and cropping lets you compose the image you wish you could have in the field if you had a longer lens or more time. There are countless reasons to justify cropping an image after the fact.
Sometimes, we don't even wait until later to crop. Most Nikon full-frame FX-format cameras allow the user to shoot in cropped mode in order to use DX-format lenses without the attendant vignetting that would otherwise occur. The image circle for DX lenses is designed to cover a smaller sensor but by using only the central portion of a full-frame sensor, the area used will more closely match the intended area. Many professional cameras will let you shoot in a cropped aspect ratio to facilitate higher frame rates. Smaller files take less time for the camera to process and offload. Sometimes, we might shoot cropped for the simple reason that we don't really need large images for this application. Or at least we don't think we will.
Thankfully, contrary to some rumors out there, the new Nikon FTZ adapter to let you use traditional F-mount lenses on your new Z-mount body doesn't have any effect on resolution and has nothing to do with cropping. F-mount lenses are designed to focus a particular distance away, and the FTZ merely realigns the mirrorless camera sensor to be the required distance from the lens flange.
But however you crop, the process isn't free. It will cost you some of the pixels you started with, having been cut off from one side or another. And the magnitude of the cost may surprise you if you've never thought about it. Assuming you maintain the standard 2:3 aspect ratio, cropping from one side also forces you to crop from an adjacent side as well. You'll end up trimming down both height and width if you crop either if you keep the relative dimensions consistent. And with loss in both dimensions, the total portion sacrificed when you crop will be a product of how much you cut off along each axis. Cut down an image to just seventy-five percent of its original width forces you to do likewise to the height. Multiplying the loss in each dimension together will leave you with just fifty-six percent of the original area in the cropped image. And that in turn comes from using just fifty-six percent of the original pixels on your sensor to form the image. The remainder will have gone unused, having been cut off in the crop.
You probably bought your new, expensive camera because it has a resolution that far exceeded that of your old camera. It makes sense to want to get something for your money, after all. Cool camera. But most likely, also a better camera. Progress, and all that. Every time I buy an upgraded camera, I can't help thinking that I can now afford to sacrifice a few megapixels if it means getting better images through cropping. Maybe that's true, and maybe it isn't. It's a judgement call, I guess.
But sometimes I think people let their overflowing pixel counts lead them into bad habits. I suppose it's another form of the "I can fix it later in Photoshop" syndrome. Except that some bodies now let you crop images in-camera, so you don't even have to wait for an image to download to your computer to crop it. Cropping has become easy, and perhaps just a tad too normal and common. Back when megapixel counts were lower, each one counted for more. Today, losing a few for a good cause can seem an acceptable tradeoff.
But just as it's always been, your best option is to get the framing right when you shoot it as opposed to fixing it later, regardless of how soon after you do the deed. Remember, although we may be able to debate the relative cost of cropping from one side, no technology yet devised can tack on more image area on the other side if you indeed pointed the camera slightly the wrong way. I mean, no matter how worthwhile cropping may be in any given circumstance or situation, it only solves half the problem of framing. It can remove unwanted areas, but we can't yet add on wanted but unrecorded areas. Cut the top off of the waterfall? Too bad. You can crop the bottom closer if you think it will help, but that won't do anything to help save the top of the falls. It wasn't left on the cutting room floor; it was left behind in the field. If you saw it at all, your camera didn't. I suppose there is "content aware fill," but I hardly think that counts.
For me at least, cropping remains a tool of last resort, not a regular part of how I approach things. It's a judgement call, as I say, but you might give it some thought.