Cambridge World, Item Details: Schneider 28mm F2.8 PC Super-Angilon

Relative density of light The brightness waste to the Bilfeldrand consists of several components. On the one hand the natural Vignettierung causes a brightness waste with the 4th power of the cosine of the angle of vision w. This effect can be changed

by distortion in the picture and by pupils coma. On the other hand curtailments of rays Ganges by lamp holder edges cause an additional brightness waste ( artificial Vignettierung). This can be reduced by fades and disappears as a rule with shading abo

ut two to three screens steps. The curves in the data sheets give(indicate) the resultierenderelative density of light (relation(connection) =Bildmitte) as a function of the angle of vision w. Distortion The distortion is an image mistake which ca

uses a distortion of the picture geometry. A rectangle is returned, e.g., according to sort of the distortion in the form of pillow or in the form of metric ton. Also a reversal of the forerunner with a certain Bidhöhe is possible. The distortion is dep

endent on the image graduation and is covered in the data sheets always to the image plane been careful for the application. Spektrale transmission By the absorption of the glasses and the rest reflections in the lenses surfaces appear bright losses

which are dependent on wavelength. The rest reflections can be decreased by suitable compensation of the lenses surfaces (Bedampfung with thin shifts). The whole transmission ( transmission degree) is represented as a function of the wavelength. Modul

ation transmission function (MTF) The ideal objective has the task to illustrate all coarse and fine structures seeming in an object realistically. This means that the brightness differences given in the object find themselves invariably in the picture

, namely for the most different structures equally. This demand is not already fulfillable for physical reasons severely. It appear in the whole area, from coarse up to the finest structures, more or less big contrast losses. Now this whole structure

area is grasped(registered) numerically by the number of line pairs per millimeter (place frequency R [1 / mm]). The MTF describes the contrast still appearing in the image plane as a function of the number of the line pairs per millimeter. The ab

breviation MTF expresses these circumstances, she comes from the English one: modulation transfer Function (modulation or contrast transmission function). This leads to a Kurvendarstellen how she is to be seen on the left. How evidently, the modulat

ion reproduction for finer structures becomes much worse and sinks for a certain number of line pairs per millimeter on zero. For the sharpness impression not this highest place frequency is authoritative, but a very high contrast reproduction about the w

hole place frequency range, up to the highest place frequency dependent on the application case. Besides, a special MTF curve is valid only for a certain point of view. In general the MTF curves differ for the different picture points, so that one wou

ld need a big number of curves to the description of the whole field of vision . Therefore, one passes over to another representation, with which the modulation for meaningfully selected place frequency about the picture height, going out from the picture

middle, is applied. This representation underlies the data sheets. In addition comes that the rays way becomes asymmetrical in the objective for picture points beyond the middle increasingly. Therefore , the MTF also still depends on the orientation

of the line pairs in the field of vision. Two are selected from the multiplicity of the possible orientations to each other vertical how in the accompanying image explains. The MTF curves valid for both orientations are sketched in the diagrams (tangen

tial) or pulled through ( sagittal) represented. Besides, the modulation transmission function depends on the opposed f-number, the applied image graduation and the weighting of the separate spektralen interests. Therefore , other MTF curves are necess

ary correspondingly to the characteristic of the image goodness. The insensitiveness to graduation changes is a quality criterion also to be considered. With extreme wide corner constructions with big angles of vision should be considered by the jud

gement of the modulation transmission that for physical reasons the modulation goes back in the field of vision for sagittale structures with the cosine, for tangential structures with the third power of the cosine of the angle of vision. The image mak

es clear on the left this at the example limited to conjugation (i.e. perfect) of objective for 20 line pairs per mm and f-number k = to 22 with a wavelength of 546 nm. The modulation is applied as a function of the angle of vision w.