Back-focus or Iris issue...?

my Sony EX-1 camera produces a soft/out of focus image whenever I close the iris around or passed f16? the more I close the softer it gets.

at 1st I thought it was a back focus prob, EXCEPT increasing the shutter speed and opening the iris makes a wide shot sharper. ( which is a little confusing since opening the iris is supposed to decrease DOF...)


HELP appreciated. PLEASE ANYBODY.

ps i had firmware upgraded so it is NOT a firmware issue.

thanks!
Matt

http://www.youtube.com/orf
https://sites.google.com/site/orfvideo/list

Its a problem of all lenses .. dont know the science but up around F16 you,ll see this focus problem.. its not your camera.. use ND filters ..

The small chip cameras need to shoot at around f4 or wider to avoid the diffraction. I put an extra ND.6 on the camera to make sure of not stopping down beyond f5.6 at most.

This is not just small sensors it's a standard photographic principle. We learnt this at our mother's knee, always try and expose with an aperture around f5.6 or f4. That's why Sony have given us two ND filters, if you need more (must be a hell of a bright light) then fit them.

Michael Slowe

I'm not sure whether small sensors make it worse or not, they may well do so, but the standard photographic principles still apply. Similarly with depth of field. Less depth the wider the aperture and less depth the longer the focal length of the lens (referred to as 'zoom' in these modern times).

Michael Slowe

I also have a Panasonic HPX250 and use the same ND6 principle of never shooting above f4-5.6. Alan Roberts explains all in his BBC report for the HPX371 amongst others. As mentioned it is physics not the manufacturers that causes the softness.