Niels Noordhoek’s weblog

This simple application just grabs an area of your windows screen and finds the focussing accuracy:

download: Bahtinov grabber (13731)

Cloudy Nights Thread on this tool

It updates 10x per second, so you can also track a live viewing window, or a youtube movie:

An the latest additions:

- the error now has a sign (positive or negative)

- a red ball clearly indicates the direction of the error, indicating in which direction to adjust focus

- the average error of the last 5 seconds is shown, helpful in poor seeing conditions

Works fine for the tele lense. Note that the spacing of the grid is just 1 mm!

Through light pollution and fog, still well visible. Not optimally focussed.

Nikon D90, 200mm F/2.8, 13x 30s, ISO200, 100% crop:

Much harder to image than I expected. Though a nearly full moon (77%) and  a lot of light polution should have been an indication that it would not be easy: 30s exposures, ISO200, 200mm F/2.8 on Kenko Skymemo

around March 6 2009, 2000h UT, when Lulin was closely passing a magnitude 9.7 star (GSC 1383.160)