Simulating a Shift Lens: Why and How

Here are 4 pictures illustrating why you might need a shift lens and how you can just substitute a wide-angle lens instead.

When you shoot at an angle, parallel lines appear distorted and only part of the target plane is focused. A tilt lens would cure the focus, but an even better solution would be a shift lens to enable shooting perpendicular to the target.

When you shoot at an angle, parallel lines appear distorted and only part of the target plane is focused. A tilt lens would cure the focus, but an even better solution would be a shift lens to enable shooting perpendicular to the target.

Attempting to shoot perpendicular to the target to improve perspective and focus can result in problems like the camera’s shadow. It can even be impossible to be get a centered perpendicular shot when the target is a tall building.

Attempting to shoot perpendicular to the target to improve perspective and focus can result in problems like the camera’s shadow. It can even be impossible to be get a centered perpendicular shot when the target is a tall building.

I don’t have a shift lens, but I do have a large sensor, wide lens and way more megapixels than necessary. I can simulate a shift lens by using only part of the frame like this and cropping it.

I don’t have a shift lens, but I do have a large sensor, wide lens and way more megapixels than necessary. I can simulate a shift lens by using only part of the frame like this and cropping it.

Here’s the final result.

Here’s the final result.

ADC Designs Including Delta-Sigma

I recently interviewed a candidate who listed having worked in an ADC group at Analog Devices.  Wanting to ask a technical question on a topic he would/should know, I noticed that I wasn’t sure exactly how an ADC works.  So, I thought up three solutions before asking the question, but still wondered how ADC’s work fast enough for applications like audio.  I’m familiar with the ramp and counter method used in microcontrollers from having used them.  The successive approximation method is also a straightforward and fairly good solution, but even that takes 24 cycles for audio quality ADC.  Next, I reinvented multistage subranging ADC as a way to expand flash ADC.  While trying to figure out what my invention was called, I stumbled across another really cool ADC that I would never have thought of.  The operation of most ADC’s can be explained to anyone because they don’t require special knowledge to understand, but delta-sigma ADC’s are completely based on frequency-domain thinking.  Learning about them helped improve my understanding of DSP and control theory.

Here’s a good discussion of various ADC’s:
http://www.analog.com/library/analogDialogue/archives/39-06/architecture.html

Read all 3 parts of this post.  Part 1 helps understand what the modulator does.  Part 2 makes Nyquist simpler than ever before.  Part 3 gives insight into how the noise shaping really works.
http://skywired.net/blog/tutorials/how-delta-sigma-works/

I like this one because it explains how you extract 16 bits of width out of just 64 samples.
http://www.triadsemi.com/2007/01/25/how-to-design-a-16-bit-sigma-delta-analog-to-digital-converter/

And once you understand all that, you’ll appreciate this piece on upsampling in CD players
http://www.simaudio.com/pdf/Upsampling.pdf
but don’t buy one because it’s all overpriced.  Advertising the $1.25 DAC http://www.ti.com/product/pcm1748 in a CD player as “Burr Brown” brand is like restaurants labeling their bacon “applewood smoked”.