Why should I buy a 12-35/f2.8 whenI have a 20/1,7/ Just comfort or...?

If you need a wider angle of view – take Samyang 7.5mm f3.5, if you need portrait range – take Oly 45mm f1.8 or legacy. I see no advantage of 35mm over 20mm and 12mm over 7.5mm.

I have Pana 20mm f1.7 for all-around along with Samyang 7.5mm f3.5 for landscapes and Minolta 85mm f2.0 for portraits. Very simple but powerful gear.

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Yuri Stangrit
http://natalispalette.jimdo.com/new-and-old-camera-lenses-by-yuri-stangrit/