I noticed that the effective focal length can be negative for a relay systeem with a real object distance and real image distance.
Based on the lens formula you suspect then a positive focal length.
for f1=80mm, f2=45mm and d=235mm gives an EFL=-32.7m, this is simmular to zemax.
My question is: Is the EFL really negative and how am I supposed to interpret this?
Best answer by Csilla Timar-Fulep
View originalHere it means that the image will be inverted.
+2
Hello,
By definition the Effective Focal Length is the distance from the rear principal plane to the paraxial focal plane. A negative focal length means that the rear principle plane is behind image surface. This is due the intermediate focus, which flips the rays top to bottom.
Best,
Csilla
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