06-06-2012, 02:38 PM
[quote name='popo' timestamp='1338992443' post='18709']
I'm using the effective aperture value = physical aperture value * (1 + magnification) as given in the MP-E65 manual. Seems to work well enough for everything I've thrown at it, although of course I can't say it'll be perfect always.
Liveview doesn't help with the "no light" problem of tiny effective apertures (5x mag and f/2.8 = f/17 effective) and the very short working distance meaning you shadow what little ambient light there is.
[/quote]
For all intends and purposes your used formula is fine (and obviously that is why it is used in the MP-E 65mm manual. For longer (focal length) macro lenses it underestimates the effective aperture somewhat. To get more accurate calculations one will need to know the pupil magnification: Effective Aperture = Lens Aperture x (1 + Magnification / Pupil Magnification). This can result in quite larger f-values. Another problem will then be that the pupil magnification changes with focus distance, so per magnification level the pupil magnification value will be different.
I'm using the effective aperture value = physical aperture value * (1 + magnification) as given in the MP-E65 manual. Seems to work well enough for everything I've thrown at it, although of course I can't say it'll be perfect always.
Liveview doesn't help with the "no light" problem of tiny effective apertures (5x mag and f/2.8 = f/17 effective) and the very short working distance meaning you shadow what little ambient light there is.
[/quote]
For all intends and purposes your used formula is fine (and obviously that is why it is used in the MP-E 65mm manual. For longer (focal length) macro lenses it underestimates the effective aperture somewhat. To get more accurate calculations one will need to know the pupil magnification: Effective Aperture = Lens Aperture x (1 + Magnification / Pupil Magnification). This can result in quite larger f-values. Another problem will then be that the pupil magnification changes with focus distance, so per magnification level the pupil magnification value will be different.