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CE NEN EEE 
DEUS WERDE aee uu dte ARR ASS NRA CNRS NE SUR MES EEE ES St rs sa 
FSA 
In Jena MTF on aerial camera lenses is measured with an 
equipment working by the principle of slit-image analysis. 
This measuring principle is based on the relation between 
slit-spread funotion S (x') and MTF, which is brought 
about by the Fourier transformation and applies to very 
narrow slits: 
400 
J 5 (x!) . o STARR un (1) 
Lo 
M (R') = 
  
In the Jena measurement equipment M (R') is calculated 
with the aid of a mini-computer by using the discrete 
Fourier transformation instead of the integral (1): 
+ N 1/2 - 2TiR* nd x! 
M (R') = | Ax! > SQ 4x) eo (2) 
n = - N 1/2 
allowance being made for the sampling theorem by select- 
ing | 
Ax! = 1/2 Re: 
and 
NL 
(Ry! = threshold frequency of test piece; X' ppt = Scanning 
ralige of slit-spread function) , 
With finitely wide slits, the computing programme enables 
the slit-width influence to be corrected according to the 
formula sin I b'R'/ Tr b'R'! (b!z slit width converted to 
the image side of the test piece). 
Apart from calculating the LZF the computer serves for 
acquiring the measured data in on-line operation and for 
controlling the total measuring process. 
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