Hello,

I watch this

and basically it shows that not only focal lenght has to be multiply by the crop factor, but also the aperture. It is possible to the get real aperture by

focal lenght (on 35mm) / lens diameter = aperture

I calculated it for some pentax lenses and just wonder whether it is correct, because most of the time I did not get the right aperture.

smc PENTAX DA Star 55mm F1.4 SDM

55mm (equiv. 82.5mm)

82.5mm/58mm=1.4224137931034482758620689655172 == 1.4

smc PENTAX DA Star 50-135mm F2.8 ED (IF) SDM

50-135mm (equiv. 75-203mm)

203mm/67mm=3.0298507462686567164179104477612 != 2.8

smc PENTAX DA Star 16-50mm F2.8 ED AL (IF) SDM

16-50mm (equiv. 24-75mm)

75mm/77mm = 0.97402597402597402597402597402597 != 2.8

smc PENTAX DA Star 60-250mm F4 ED (IF) SDM

60-250mm (equiv. 90-375mm)

375mm/67mm = 5.5970149253731343283582089552239 != 4

Thank you in advance.

Mic