AF Sensitivity and Function

Started Oct 14, 2008 | Discussions thread
Marianne Oelund Veteran Member • Posts: 7,788
Kerry's Experiment #1: Setup

This is the setup and preparation for the AF sensor optics experiment that I have been discussing with Kerry on this thread. This should be performed in the evening, so that the room can be dark to aid in seeing the projected images.

Recommended lens is a 50mm f/1.4 or f/1.8 prime. Good alternatives would be a 35 f/2 (or faster), or an 85 f/1.8 or f/1.4. D-type lenses, with an aperture ring, should be used for this.

Set the lens horizontally on a smooth-top table. It's helpful to have a sheet of paper taped onto the table under the lens, and you may also want to tape some small stops down to the paper, to keep the lens from rolling. Aim the lens toward a bright lamp (use halogen or bare bulb) at least 20' away, and hang a sheet of cardboard, aluminum foil, etc., close in front of the lamp. Make a hole about 3/4 to 1" diameter in the cardboard, and align it so the light shining through the hole strikes the lens. It is best if the light source is at about the same height as the table top.

Cut a sheet of paper about 3" or 4" square, and tape it onto the side of a smooth, square box, such as a kleenex box or a Nikon lens box; this will serve as our projection screen. Set this behind the lens, adjust the lens focus ring to near infinity, set the lens aperture wide open, and align the screen position until you have a nice, sharply focused image of the light source, which will be a very bright spot.

You can now vary the lens aperture, observing the brightness of the projected spot changing as you do so.

We're ready to begin - on to Part 2.

Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow