View Full Version : Star Test

E. von Hoegh
25-Feb-2006, 12:09
I would like to suggest a very simple fairly objective test for LF lenses known as the "star test" I use a 7.5 watt christmas tree or nightlight bulb about 6 inches behind a one millimeter hole drilled in a piece of aluminium or brass sheet. You can put the lamp in a shoebox and tape the bit of metal to one end. Place the artificial star at least 20x the focal length of your lens from your lens and focus it on the ground glass in a darkened room. This will show you quite alot about your lens; coma off axis diffraction rings etc. By replacing the hole with a slit made of two razor blades .5mm apart you can also observe astigmatism. You can also settle once and for all the Dagor focus shift question - all of mine get longer as they are stopped down, it is not a matter of opinion, or how I focus. By all means try the star test,I find it more informative than a resolution chart for lenses 100mm and up

Kevin Crisp
25-Feb-2006, 12:56
Or you could just go use the lenses to take pictures and see if you like the results. Sorry.

E. von Hoegh
25-Feb-2006, 13:32
Mr. Crisp, Thank you .I was worried about making the post too long and got distracted. E.v.H.

25-Feb-2006, 17:27
Mr. E von, have you met Andrew Glover?

25-Feb-2006, 19:35
Sorry, that should have been Herr E. von....