Lenses Selection and Setup - Part 3
Published on June 16, 2008 by TIS Marketing.
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.
Step 3: How to deal with very small working distances
Especially in the case of small objects, the working distance may be smaller than the selected lenses minimal working distance (MOD). In this case, we decrease the minimal working distance by putting extension rings between the lens and the camera. We will see details at Step 4 (Setup). The following example depicts the selection of an extension ring:
Inspection of a birthmark:
- Object width = 5 mm
- Working distance = 30 mm
- CCD format = 1/4″ (CCD width = 3.2 mm)
In this case the focal length is 14.7 mm and thus we select the H1214-M(KP). Its minimal object distance (MOD) is 0.25 m and thus exceeds considerably the required working distance of 3 cm. The table below indicates the use of a 5 mm extension ring.