ABSTRACT
The inverted telephoto, or retrofocus, lens consists of a negative front lens group and a rear positive lens group. It is characterized by having a long back focal length (BFL) in relation to its effective focal length (EFL). This type of construction is then extensively used in short-focal-length, wide-angle lenses for single-lens reflex (SLR) cameras. Here, a long BFL is required to clear the moving mirror and shutter mechanisms. It is thus important when setting up the merit function in the optimization program to properly limit the minimum allowable back focal length. Figure 8.1 shows an inverted telephoto. The requirements for this lens were that it have a BFL of at least 1.8 F (Laikin 1974). Table 8.1 provides the lens data for Figure 8.1. An inverted telephoto, <italic>f</italic>/3.5. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315222295/bd2ad0d9-a48e-40ac-8986-c51474069cbd/content/fig8_1.tif"/> Inverted <italic>f</italic>/3.5 Telephoto Lens
Surface
Radius
Thickness
Material
Diameter
1
4.5569
0.1000
N-PK51
0.940
2
0.7040
0.8254
0.860
3
0.5900
0.1200
SF1
0.940
4
0.5329
0.5916
0.820
5
3.8106
0.3022
LF5
0.940
6
−2.4206
0.4382
0.940
7
Stop
0.0150
0.647
8
5.0596
0.0695
SF1
0.940
9
0.7648
0.2412
N-LAK21
0.820
10
−1.6496
2.2253
0.820
Distance from front lens to image = 4.928, distortion = 2.39%, lens focal length = 1.181.