Funny you should say that. Nominal 6x9 is more or less 56 x 81, whence its normal focal length is 100 mm. Slightly longer tessar types were used on 6x9 folders to improve image quality in the corners a little. 35 mm still is 24 x 36, whence its normal focal length is 43 mm. That 35 mm cameras are usually supplied with 50 mm lenses is due to an historical accident.
Originally Posted by 250swb
The two formats have the same aspect ratio, so comparisons between them are easily made. A 90 mm on a 2x3 (nominal 6x9 is actually 2.25" x3.25", usually called 2x3; 6x9 is a lousy metric approximation) is sees the same view as a (90/100)*43 = 39 on 35 mm still. A 180 on 2x3 sees the same view as 1.8 * 43 = 77 on 35 mm still. Short verging on medium tele, I'd say.