One of my favorite Lightroom features is lens correction, which can correct vignetting, chromatic aberration and distortion. I find this really useful because my lenses are not pro-grade and suffer from these issues. With lens correction, my photos look like they are from more expensive lenses. :)
I used to assume that I ought to apply lens correction to all my images. However, I found out that sometimes, it's better not to use lens correction (or to choose which issues to correct for).
I recently took a portrait of my family and some family friends. I used a Tamron 17-50 VC at 17mm, which exhibits very noticeable complex distortion (the middle of the image bulges). Here's what the distortion pattern looks like:
Notice that the middle of the closet door bulges, but the top and bottom do not. This is one of the weaknesses of this otherwise great lens.
Anyway, back to the portrait that I took. Here's the image without lens correction:
Here's the image with lens correction:
If you look at the "corrected" image, the faces of the people at the edges look more distorted (and less flattering) than those of the uncorrected image. Take a closer look at my son's face, which appears skewed in the corrected image.
So in this case, I chose not to apply the lens correction.
Fortunately, Lightroom also allows not just turning lens correction on or off completely, but also selectively applying the lens correction to correct vignetting, chromatic aberration or distortion or any combination of those issues. You can also select the degree of correction of each issue.
Rather than thinking about it as "how much correction" to apply, I would think about it as "which projection/distortion best fits the image". The out-of-camera distortion, the fully corrected (stereographic) image, and even the spectrum between them, are just a tiny part of the space of all possible projections of the 3D scene into the 2D image.
ReplyDeleteThis is most evident when working with ultrawide and fisheye lenses. For these, often the best-looking projection/distortion is something like the Panini projection of Hugin, or Fisheye-Hemi, which are very different from both in-camera and fully-corrected stereographic (for one, they're not radially symmetric: horizontal and vertical are stretched differently).
So in principle, we pick the projection that looks best, regardless of the lens' native projection. Of course, one you stray away from native, you pay in effort and resolution.
As you demonstrate, 17mm on DX is wide enough for the corners-stretched-away effect of the standard stereographic projection to start showing up, so the Tamron lens's slight barrel distortion actually looks better; but this is just luck and may still be far from optimal. It would be interesting to try reprojecting this image into, say, Hugin's "Panini General" and see if it looks better.
Hi Opt. Thanks for your very informative comment. I don't have much experience using ultrawide lenses and wasn't even aware of the different possible projections. I'm glad I learned something new thanks to you. What software do you use to try other projections?
ReplyDeleteBest regards,
Mic
Mic, ultrawide is tremendous fun, you ought to try it out! It does make one very much aware of projections, since distortions become enormous and inevitable (a large chunk of a sphere is just too different from a flat plane).
ReplyDeleteFor software, I use the open-source Hugin (http://hugin.sourceforge.net), which is primarily a panorama stitching tool, but works great if you just load one image and then "stitch" it into your projection of choice. Hugin has a nice preview window that lets you experiment with different projections and the effect of shifting/rotation (which is often dramatic). Hugin does take a bit of getting used to, but is very powerful.
The "real" (stereographic) ultrawide lenses are big and expensive; it takes a lot of glass to optically stretch out the corners enough to get a stereographic projection, and this is often not the right projection for the job anyway, as discussed above. So I use a fisheye (the Samyang/Pro-Optic/Bower 8mm f/3.5, $300) and post-process it. The Samyang has a native projection that's somewhere between stereographic (regular ultrawide) and typical fisheye. Since some of the useful projections, such as the aforementioned Panini, are also somewhere between stereographic and fisheye, the Samyang may actually be *better* (in terms of resolution loss when you reproject) than both true ultrawides and more expensive fisheyes like the Nikon 10.5mm f/2.8 ($700) fisheye.
Very cool Opt. I had been thinking of getting a wide lens as my next lens but was wondering how often I would use it. Perhaps I'll see how useful it can be after checking out Hugin. Already, my curiosity has been piqued by your post and the flickr pool of amazing Hugin images. Much thanks!
ReplyDeleteBest regards,
Mic
I guess you mean taking panoramas with a moderately-wide lens like the Tamron at 17mm, and then stitching it and playing around with it in Hugin? Yes, that's a great idea. The catch is that it's very hard to stitch good panoramas of moving or close scenes, so you're pretty much limited to landscape and large architecture); with people and closeup.
ReplyDeleteIn particular, you need a real fisheye lens to do one of my favorite kid photography tricks. Say you're at the zoo and your kid is staring at the elephant with a wide-eyed fascinated look. To capture the moment, you'd like to capture the expression together with the subject of the fascination, the elephant. You can't do that with a normal lens; the most you can do is step far off to the side and capture the elephant and the kid's profile, losing most of the expression and also making the face too small. But with a fisheye you can bring the camera up close to the kid, about 45 degrees off from the kid-to-elephant line, and pointing off to the side (perpendicularly to the kid-elephant line). This gets you a frame with the kid's face (big and from a good angle) on one side, and the elephant (shrunk down) on the other -- just what you wanted for the family album.
Then, tame down the distortions in Hugin.
BTW, for this trick you don't even need to stoop down to stare through the viewfinder -- just hold the camera in the right place and roughly right orientation, and snap (so if your kid is leaning on the zoo fence, you can reach your arm through the fence). Since the fisheye has plenty of spare FOV coverage, Hugin will let you "rotate" the frame to fine-tune the orientation in post-processing (this is the 3D sphere version of cropping).
All that said, you're right, a fisheye or ultrawide isn't something you'll be using a lot; but when it works, it works wonders. My walk-around lens kit is a normal zoom, a 50mm prime and the Samyang 8mm fisheye, and while the fisheye gets maybe 3% of the shutter count, I rarely leave without it and rarely return without having used it.
Hmm. I didn't even thinking about simulating an ultrawide angle by stitching several wide angle shots. I might try that though.
ReplyDeleteWith a toddler and a baby, we rarely travel and I don't have a lot of time for personal photo projects, so I wondered how often I would get to use an ultrawide lens, much less a fisheye. However, you brought up an interesting way to use an ultrawide for capturing a family photo. What I'll do first is try a cheap 35mm film fisheye camera to see how often I use it. If it proves very useful, then I plan to get either the Samyang 8mm or a Sigma 8-16.
It looks like you have a lot of experience with ultrawides. If you would like to share or discuss some of your ultrawide or other photos, perhaps you could email me at info AT betterfamilyphotos.com so we can discuss a guest post! I'm sure many readers would appreciate that.
Best regards,
Mic
Thanks for the invitation, Mic. For now I'd rather just lurk in the shadows and make the occasional typo...
ReplyDeleteA very interesting and informative discussion, I must give the Hugin software a try, thanks for the info Opt.
ReplyDeleteIn the above discussion, every time I wrote, "stereographic", I meant "rectilinear", of course. Sorry for the confusion...
ReplyDelete