Lenses Selection and Setup - Part 5

Please Note: This blog post is part of a series of five posts altogether. The posts include: Part 1, Part 2, Part 3, Part 4 and Part 5.

Typical Mistakes

The bewildering variety of optical components, as well as "historical legacy issues" originating from the world of picture tubes, lead to different mistakes when selecting these components. In the following you will find the three most basic misunderstandings:

Incorrect: The lens format and the camera format have to be identical. Correct: The lens format should preferably be larger than the CCD format since optical flaws appear at the rim of the lens.

Incorrect: If the lens format is larger than the CCD format it has to have a larger/smaller focal length. Correct: The focal length exclusively depends on the CCD format, the working distance and the object size.

Incorrect: Extension rings increase/decrease the depth of field. Correct: Extension rings decrease the minimal working distance.

Fixing blurred images

There are two basic reasons for blurred images:

• The lens quality is lower than the quality of modern CCD chips. The Pentax M Series recommended in this white paper has been especially designed to work with modern CCD chips. Wide-angle lenses, however, have weaknesses due to their construction.
• The lens setup is incorrectly arranged. This usually leads to extremely blurred images. In such cases please proceed as follows:

C Mount Lens / CS Mount Camera:

Please check whether a 5 mm extension ring has been screwed between the camera and the lens. The Imaging Source exclusively manufactures CS mount cameras. Each of the cameras is shipped with a 5 mm extension ring.

CS Mount Lens / CS Mount Camera:

If you have accidentally screwed a 5 mm extension ring between the camera and the lens, you will only be able to focus on close objects.

CS Mount Lens / C Mount Camera:

This configuration only allows to focus on very close objects. If this is not your aim, then you have to use a CS mount camera. The Imaging Source exclusively manufactures CS mount cameras.

"Sticking" Extension Rings:

If you previously have used the camera or the lens with a thin extension ring, it often "sticks" to either of them. In such cases you are not able to focus to infinity for no apparent reason.