D800 Portrait Lens Battle!

Started Sep 30, 2013 | Discussions thread
OP Shotcents Veteran Member • Posts: 4,472
Re: D800 Portrait Lens Battle!

Dear Robert,

I have found a formula to find effective aperture formula here:

Effective Aperture = Lens Aperture x (1 + Magnification)

There is also magnification calculator here:


When I calculate for (Tamron) 90mm focal length, 2.8 f number and 1 meter (about 40 inches) focusuing distance , magnification result is 0.11.

In this case effective aperture=2.8x(1+0.11)=3,10

I am confused how your apperture got f4, because it seems you were not closer than 40 inches acording to your models position.

I may have gotten F4 because I set it there. I'll do a test shortly to see where the values change at various distances.

But I'll tell you that this Tamron 90 VC is a whopper of a lens. For the most part I prefer it to the 85mm 1.8G. But in a light starved space that 1.8 does come in handy as I always want the shutter speed up and the ISO down.


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