2/19/2023 0 Comments Ptlens vs dxo viewpointfilm days) distortion correction was a first priority. It’s well known among lens designers (I’m not one, but I read their textbooks and journals) that when designing a lens correcting distortion often reduces resolution. well, it had better be a lot higher, or it’s a fool’s argument. Distortion correction generally improves the look of a photograph and a small sacrifice in resolution isn’t too important with today’s cameras and lenses, even in the corners.īut when someone wants to argue that they buy a lens with high distortion because it has higher resolution and distortion is easy to fix in post. Landscape photographers making large prints, though, would be interested in MTF50. Since MTF20 probably is a more important measurement of resolution for small prints and online jpgs, this would probably correlate more with what most people would see in an image. I reran the numbers for MTF20 which decreased in the center from 1552 to 1450 LP/IH (93.5%), on the edges it dropped from 1015 to 838 (83%), and in the corners from 1005 LP / IF to 837 LP / IF (83%) which is more like what I expected. Actually I was a bit surprised, expecting more decrease in the corners and less in the center. The far sides from an average of 556 to 477 (86%), while the corners decreased from an average of 539 to 460 (85%). The center MTF50 dropped from 1068 LP/IH to 939 (88% as sharp) after distortion correction. The numbers are a bit hard to read, so I’ll summarize. I measured the autocorrected version as carefully as I could and barrel distortion had been reduced from 4.2% to 0.5%. Photoshop does a really nice job of correcting the image. Image Correctionīelow are the original and corrected shots. I’m presenting data from one lens here, but I did another for completeness. Then I loaded the correction profiles for the Canon 5D Mk II and 24-105 and did an auto distortion correction, saving that as a TIFF.įinally, I compared the corrected and uncorrected versions in Imatest. ![]() So I took the RAW file to Photoshop, turned off every single sharpening and modifying tool and converted it to TIFF. We usually run Imatest only on RAW files, but that would make it impossible to correct the image. I mention this only as a preemptive strike because I’m 100% certain some Fanboy is going to be saying, “Roger said the Canon 24-105 has the worst barrel distortion of any lens.” It doesn’t, not by a long shot, but it has plenty for this test. I chose it simply because we already had Imatest set up at 24mm and because I feel our Imatest setup is a bit less accurate wider than 16mm. It has a large amount of barrel distortion at 24mm (over 4%). I used the Canon 24-105 f/4 IS for this test. That has me a bit behind on my real job, so please excuse that this isn’t an exhaustive test of 30 different lenses. I hate when that happens, especially when I’ve already spent two days playing with the Canon 24-70 f/4 IS and taking it apart. ![]() I had to go do some testing and gather some actual facts. I won’t waste my time with you anymore.”īeing that I was out there using my real name and all, the comment left me no choice. Now, if I were hanging out on a forum under my anonymous handle of LensGuruGod1 I could have used proper Internet etiquette and replied, “If you weren’t an awful photographer you’d already know that. Yesterday, unfortunately, someone asked me to tell him exactly how much resolution you actually lose?ĭon’t you just hate it when someone interrupts your Rant of Absolute Knowledge by asking for facts? What a buzz kill. There is no way you can shift that many pixels around and not decrease resolution. But every tool, whether in-camera or in your post-processing program, that modifies an image is a trade off of sorts. But when combined, they become false.ĭistortion correction is a wonderful tool. ![]() Unfortunately, way too often, the complete statement goes like this: “I got it because it has such high resolution. Yes, it has a lot of distortion, but that’s easy to correct in post.” That’s two totally true statements. I hear this about 20 times a day and it’s true: “Yes, it has a lot of distortion, but that’s easy to correct in post.” It’s a totally true statement.
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