An investor's lingering perceptions of a dire market environment may be causing them to view investment opportunities through an overly negative lens, making it less appealing to consider taking on investment risk, no matter how small the returns on perceived " safe " investments.
12.
The telephoto lens configuration combines positive and negative lens groups with the positive at the front, so as to reduce the back focal distance of the lens ( the distance between the back of the lens and the image plane ) to a figure shorter than the focal length.
13.
The inverted telephoto configuration does the reverse, employing one or more negative lens groups at the front to increase the back focal distance of the lens & ndash; possibly to a figure greater than the focal length & ndash; in order to allow for additional optical or mechanical parts to fit behind the lens.
14.
In most cases, two thin lenses are combined, one of which has just so strong a positive aberration ( " under-correction, " vide supra ) as the other a negative; the first must be a positive lens and the second a negative lens; the powers, however : may differ, so that the desired effect of the lens is maintained.