Category Archives: Equipment

Equipment, Software, Technique, Tests

A Test: Correcting Lens Distortion in Post-Processing

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Earlier this weekend I read a forum thread about the Canon EF 50mm f/1.4 lens, of which I have a copy. The thread lamented the barrel distortion of this lens (which I don’t really find to be that big of an issue) and continued with posts suggesting alternatives including software correction in the post-processing phase. One response to this proposal was that software correction would degrade the  image and would therefore be unacceptable.

That theory seemed sound and I have believed this to be true in the past, but I decided to test this idea for myself. Using an old photograph taken with this lens, I cropped a small section from one of the far corners – the worst part of the frame and, according to some, subject to a lot of softness and distortion on full-frame bodies like my Canon 5D. To make things a bit more challenging I used a photograph that included a bunch of dried california grasses – full of very fine details and high contrast.

I converted the original RAW file using ACR (Adobe Camera RAW) with no sharpening. In Photoshop I cropped to a section of reasonable size for web presentation, using that section from one of the corners of the image. Then I made a duplicate of the cropped section of the image.

In one of the two versions of the crop I used the LensfixCI plugin to correct for the slight barrel distortion of the EF 50mm f/1.4 lens. This $29 plugin* includes a database of many lenses, and also keeps a smaller databases of your lenses. It uses EXIF data to identify the lens (and focal length with zooms) used to take the photo and automatically applies optimum distortion corrections from its database. It takes me about 10 seconds to select the plugin and apply its changes.

* (I have left the reference to this plugin that I used when I did the test several years ago, even though I no longer use it. Today I simply use the built-in correction in Lightroom or ACR, where I apply lens- based corrections by default in virtually all cases.)

Next I used my normal sharpening methods on both images, inspecting the results and making adjustments as I applied them. In the end, as would typically be the case, I used slightly different sharpening settings for the two images – but that reflects the normal way of operating. Finally, I took the two images and placed them side by side in the single high quality jpg file that follows.

Barrel Distortion Correction
Barrel Distortion Correction

(NOTE: The version shown above on this page may have been downsized for formatting purposes, which limits the amount of detail that is visible. Click the image to view it at its original size, or follow this direct link to the original image.)

I have a darned hard time seeing any difference in sharpness, contrast, or color that might have been introduced by the correction process. If a difference is visible a) it is almost impossible to say which version is better, and b) the difference is almost certainly completely insignificant in an actual print. (Keep in mind that these are 100% crops of the worst part of the frame in the far corner – and that the area shown here would be a very tiny section of a full print that would be something like five feet/60″ wide.)

After doing this test, I’m not really concerned at all about any negative effects of using this method of correcting lens distortions, and today I simply allow ACR or Lightroom to automatically correct for such lens characteristics by default. And whatever the tiny negative effect on sharpness we might imagine to produce, it is far outweighed by the ability to straighten lines and so forth when necessary.

(Anyone care to guess which half contains the “corrected” version of the crop? Feel free to post a comment and an explanation of what you (think you) see… ;-)

(This 2007 post was slightly updated on 1/5/2013)

G Dan Mitchell is a California photographer and visual opportunist. His book, “California’s Fall Color: A Photographer’s Guide to Autumn in the Sierra” is available from Heyday Books and Amazon.

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Equipment, Ideas

The “Best” Camera?

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Recently I’ve seen an upswing in the number of “which camera is best” posts in some of the online forums I follow – perhaps due to a minor Gear Lust epidemic after announcements of new cameras by Nikon and Canon and others?

I posted a reply to one question about whether it would be better to purchase a Canon 40D or 5D and my response got some supportive responses – so I’m posting it here:

The 5D can produce better image quality than the 40D (unless some miracle is revealed when the camera is available for actual testing) because it has a) greater MP dimensions, b) larger photosites.

That said, the question remains whether the “betterness” is a) noticable, b) significant, c) worth the cost.

(Selecting one camera over another because it is “better” is kind of like buying one car instead of another because it is faster. Let’s say one can go 120 mph and the other can go 125 mph. I suppose that 125 mph is “better” than 120 mph, but what if you never drive faster than 70 mph…)

A crop sensor 10 MP DSLR can produce outstanding image quality. With good technique (oh yeah, and inspiration…) you can get photographs that will reproduce at quite large print sizes. (I sold 16 x 24 inch prints of photos made on a 350D.) If you aren’t going to print this large or if you will mostly distribute electronically, frankly there is little to be gained from FF. (And, yes, I’m a full frame camera user: 5D plus L lenses.) You’d probably see more difference in your photography by taking the money you saved by getting the 40D and investing in good lenses, tripod, filters, etc.

By the way, it also remains to be seen how much difference the extra two bits makes in actual images.

So, yes, the 5D is “better” than the 40D (OK, not if you need a fast burst rate…) on the basis of image quality. However, the 40D – or even the excellent 400D – could be a “better camera” for a particular user.

My point is not so much about the specific comparison between the Canon 5D and the newly-announced 40D. It is more about what it means to look for the “best” camera.

I believe that “best” is a very subjective concept here. The important question is not “which camera is best?” but, rather, “which camera is best for [the kind of photography I do]?” The answer would be quite different for each of the following:

  • Professional photographer doing studio portrait/product photography.
  • Photojournalist shooting professional sports.
  • Landscape photographer shooting while hiking/backpacking. (Hmmm… that sounds familiar, somehow… ;-)
  • Serious photographer shooting wildlife with long lenses.
  • Serious, experienced amateur shooting a variety of subjects and making letter-size prints.
  • Casual amateur shooting family events for electronic sharing and small prints.
  • Beginner with no previous SLR photography experience, unsure of where/how interest will lead.

I’m not going to make specific recommendations, with one exception. If you are new to this DSLR stuff, please don’t listen to those people telling you to immediately invest thousands in pro-level lenses and bodies… that are appropriate for their photography. Start small; a Canon 400D/XTi with the kit lens (or the equivalent from Nikon, Sony, Pentax, et al) is a far more appropriate place to begin. Take a lot of photographs; explore and learn – before long you will begin to understand what your best camera might actually be.

Commentary, Equipment

Slingshot 200 AW UPdate: Lowepro Earns an A+ For Customer Service!

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As part of an answer to a question posed by a reader last week I wrote:

(One final note on the [Lowepro] Slingshot [200 AW]. I’ve used mine heavily for a year and a half or so and it has generally performed well. However, last week I discovered that one of the main zippers is coming apart where it curves around the “top” of the bag. I’ll have to reserved final judgment until I find out what Lowepro has to say about replacement or repair when I contact them later this month.)

Shortly after I wrote that I emailed the Lowepro customer service department to ask about a repair. “Maury” wrote back immediately with instructions for sending the bag to their service facility in Sebastapol, California for repair. I sent it off last Friday.

Today (only three business days later!) I received a brand new Slingshot 200 AW from Lowepro. Even though I hard removed interior padding and so forth, they sent a full new product package including all accessories and components.

Good work, Lowepro – I’m very impressed!

Commentary, Equipment

Canon or Nikon… Who Wins?

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Here is an informal “scorecard” I recently posted at another site – some thoughts about how new Nikon and Canon products stack up against one another.:

1DSMKIII v. ? – Canon wins until Nikon (or Sony?) announces a very high MP FF body

1DMKII v. D3 – Purely on features, I’d say the Nikon wins. The difference in fps is pretty inconsequential, but the D3 wins on most other counts. Of course, in the real world, both of these cameras are extremely powerful and very well suited to the sort of work they were designed for.

5D v. ? – Canon wins since it is the only company with a FF body in the sub-$3000 (more like mid-$2000) price range. While it lacks the speed of the more expensive cameras, it is extremely well suited to the needs of many photographs for whom image quality is paramount.

D300 v. 40D – A slightly awkward comparison since the prices are significantly different. On features, the D300 beats the 40D. In a sense, the D300 is today’s camera, while the 40D would have been an outstanding product introduction… last year.

A few words of explanation…

1. I don’t really place much stock in which camera/manufacturer “wins” or which product is “best.” I really believe that the determination of “best” has more to do with the photographer’s needs than the intrinsic qualities and features of the products produced by top-tier manufacturers.

2. Any advantage that one manufacturer has over the other is likely to be temporary.

3. All of the cameras included above (and others not mentioned) are excellent products, and all can produce fine photographic results.