Tag Archives: crop

Equipment, Tests

An Example of Corner Performance on the Canon EF 24-105mm f/4 L IS

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Sample24105f16Corner.jpg
I’m taking the opportunity to use the photograph I posted earlier today to illustrate a couple of technical points about equipment and technique. Here is a 100% magnification 400 x 400 pixel crop from the far upper corner of the photograph.

Not much to look at, but that isn’t the point. At this resolution, you are looking at what would be a small section from a print that is four or five feet wide. Before I explain why I think this is important, some technical information about the image: Canon 5D, Canon EF 24-105mm f/4 L IS, 2.5 second exposure, f/16, focus point was on the foreground tree seen in the full image (e.g. – perhaps 50 feet closer than the subject of this test image), IS disabled, tripod, mirror lockup, remote release.

Some doubt the ability of this particular lens to produce sharp images. This sample challenges lens performance in a number of ways: it is a very low contrast image, the crop is from the far corner of the frame, the crop is not in the focus plane of the photograph, at f/16 the effects of diffraction blur should be just visible at this magnification.

With all of that context in mind, this cropped sample represents quite good performance. This section of the image would be very sharp, indeed, in a print at 16″ x 24″.

This photograph is not in the public domain. It may not be used on websites, blogs, or in any other media without explicit advance permission from G Dan Mitchell.

Commentary, Equipment

Canon 50D Announced: Competition is a Good Thing

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News of Canon’s announcement of the new EOS 5D cropped sensor mid-range DSLR is all over the web today – well, at least all over the photographic portion of the web. The new body updates the X0D line from the recent 40D, primarily by updating the 1.6x cropped sensor to 15 megapixels. According to Canon this was done while increasing the performance at high ISOs, keeping the burst rate almost the same as that of the 40D, and maintaining image quality by the use of “gapless microlenses” that can capture more light than would have been the case with older designs. There are other feature updates as well, and it looks like the price will be roughly but not precisely in the same ballpark as that of the 50D… at least once the prices drop a few months after the introduction of the new camera.

What does this mean for the DSLR buyer? The answer is, “It depends.” Continue reading Canon 50D Announced: Competition is a Good Thing →

Equipment, Ideas, Technique

Wide Angle Lenses and Image Stabilization

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I often hear people claim that image-stabilization is only of value on normal to long focal length lenses, and is not useful on wide angle and ultra wide angle lenses.

The photograph posted earlier today was shot handheld on a full frame DSLR at 1/25 second at ISO 800 and 32mm. (32mm on full frame is equivalent to using a 20mm focal length on a 1.6x cropped sensor body.)

I had just finished a session of tripod-based landscape shooting on the summit of this dome, had packed up, and was heading down when the lone hiker crossed the ridgeline below me just as some lovely post-sunset light gently illuminated the landscape. Having no time to set up a tripod – hiker and light would have been gone by then – I dropped everything, pulled the camera with image-stabilized 24-105mm lens from the pack, made some quick seat-of-the-pants exposure calculations, and got of three quick frames before the scene was gone. Without IS I simply would not have gotten a usable version of this photograph – a photograph that has since been licensed for use in a print journal.

Even as one who often shoots from a tripod – and almost always carries one – I have found the notion that IS has no value at shorter focal lengths to be a myth not born out in actual practice.

Equipment, Tests

Sharpness Test Updated

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I have updated my Sharpness and Aperture Selection of Full-Frame DSLRs post to include the corner crops from the same photos used for the center crops that were already there. Here’s the image I added – see the link for full information.