Spatial resolution information | Strolls with my Dog

You have obtained a raw file containing the image of a slanted edge captured with good technique. How do you get the Modulation Transfer Function of the camera and lens combination that took it? Download and feast your eyes on open source MTF Mapper version 0.4.16 by Frans van den Bergh.

[Edit, several years later: MTF Mapper has kept improving over time, making it in my opinion the most accurate slanted edge measuring tool available today, used in applications that range from photography to machine vision to the Mars Rover. Did I mention that it is open source?

It now sports a Graphical User Interface which can load raw files and allow the arbitrary selection of individual edges by simply pointing and clicking, making this post largely redundant. The procedure outlined will still work but there are easier ways to accomplish the same task today. To obtain the same result with raw data and version 0.7.38 just install MTF Mapper, set the “Settings/Preferences” tab as follows and leave all else at default:

“Pixel size” is only needed to also show SFR in units of lp/mm and the “Arguments” field only if using an unspecified raw data CFA layout. “Accept” and “File/Open with manual edge selection” your raw files. Follow the instructions to select as many edges as desired. Then in “Data set” open an “annotated” file and shift-click on the chosen edges to see the relative MTF plots.]

The first thing we are going to do is crop the edges and package them into a TIFF file format so that MTF Mapper has an easier time reading them. Let’s use as an example a Nikon D810+85mm:1.8G ISO 64 studio raw capture by DPReview so that you can follow along if you wish. Continue reading How to Get MTF Performance Curves for Your Camera and Lens →

You want to measure how sharp your camera/lens combination is to make sure it lives up to its specs. Or perhaps you’d like to compare how well one lens captures spatial resolution compared to another you own. Or perhaps again you are in the market for new equipment and would like to know what could be expected from the shortlist. Or an old faithful is not looking right and you’d like to check it out. So you decide to do some testing. Where to start?

In the next four articles I will walk you through my methodology based on captures of slanted edge targets:

Continue reading How Sharp are my Camera and Lens? →

Musings about Photography