Originally Posted By: taym
I wonder if the f/ (quite higher than 2.8) is also affected by the fresnel lens, and if so, how...

This lens has a quite small front element diameter, with a small lens cap to match. Thus the f-stop range of 4.5-5.6: the opening at the front only lets in that amount of light. Not enough light for f4 or f2.8 etc.

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