focus | Photocrati

Tilting at Focus

Last week I wrote a bit about the reasons tilt-shift lenses were becoming more popular in the DSLR world. This week I’d like to provide a simple example of using tilt in an image to increase effective depth-of-field, and offer a basic overview of how that’s done.

Tilt dialed in, about three degrees. f/3.5. Focus is near the nearer of the two lens caps. If you look to the left of the table, you'll notice part of a cat tree, note that the upper parts of the cat tree are more in focus than the lower parts.

To demonstrate what a difference this can make, I ran a quick example with and without tilt using the older ::amazon(“B00009XVCD”,”Canon TS-E 24mm f/3.5L”)::. (To make the effect a little more apparent on these small screen samples I focused the image without tilt near the “near” lens cap. Of course, in that image I could have chosen to focus farther into the image–which would have blurred the near image somewhat to reduce the blurring in the far image, but both would have still been out of focus. Both images were taken at f/3.5 with a ::amazon(“B000V5LX00″,”Canon 1Ds Mark III.”):: (more…)

Q and A: How does the Autofocus Adjustment function work–and should I use it?

Question

From reading reviews, I know that some recent DSLRs, like my Pentax K-7, include an Autofocus Adjustment function that allows for modifying the AF system for more accurate focus with certain lenses. Is this function necessary? If so, how does it work? R. Webber

Answer

Yes, an increasing number of high-end DSLRs of several brands include a feature of this type. It allows for instructing the camera to focus slightly more closely, or to a slightly greater distance, than it would do at default. This function would be useful for an older AF lens-especially one that has been banged around-if it is no longer focusing accurately. You may find that it focuses slightly ahead of the subject, or slightly behind it; these issues are called “front focus” and “back focus” and they call for AF Adjustment.

Before using this in-camera feature however, be absolutely certain of the lens’s exact focusing tendencies. (more…)

Mix ’em Up, Part 2: Focus Blending in Photoshop CS4

This is the second of a series of posts on digital darkroom techniques describing digital darkroom techniques that “combine” groups of images towards various ends.

Focus blending is a technique for combining a series of images of the same scene to create a resulting image with a wider depth-of-field. Focus blending is best-known to aficionados of macro photography, as depth-of-field at close distances is almost always razor-thin even at the tiniest apertures. While best known in macro circles, it could benefit any type of photography where it’s impossible or pragmatic to get enough depth-of-field. (more…)

Mix ’em Up, Part 1: Introduction to Combining Images in Photoshop CS4

The advent of digital photography has opened up an array of new techniques for working with and combining multiple images in pursuit of technical perfection. Three of the most popular techniques in this category are panoramic stitching, focus blending, and high-dynamic range imaging.

As of Photoshop CS4, Adobe now includes some level of support for applying all three of these techniques without external tools. In this post, I’ll provide a brief overview of the three techniques and the problems they’re intended to solve. In future posts, I’ll address each of the three techniques individually, provide an example or two, and discuss both Photoshop’s built-in tools for applying those techniques as well as talking about third-party solutions and other alternatives. (more…)