Re: [OM] ( OM ) lens resolution capability

[Winsor Crosby]

> Hi folks
>
> Wayne Harridge wrote
> >  What seems a bit strange is that the corner resolution is better 
> > than the centre
> >  for many of the tests - I wonder if there is some sort of focus 
> > problem with the
> >  camera (e.g. miiror or screen alignment problem).
> I agree. I think that probably I didn't have the camera and target board
> perfectly parallel.
>
> Also it is **not easy** to read those chart results - not at all.
>
> Later  I read in the instructions (like, when all else fails, read 
> the instructions
> <g>) that a sharper image can be obtained on the screen if one makes a pin-
> hole (as in "very big pin-hole" ) mask and places it over the projector lens.
> Stands to reason - even if the projector lenses ARE designed to be sharpest
> at full aperture, it wouldn't be surprising if a little stopping down improved
> what was projected.
>
> HOWEVER, if it is SO difficult for me to obtain a very sharp image on fine-
> grain 50 ASA slide film when the camera is weighted firmly on the floor and
> the mirror-up & pre-fire aperture routine is done (even if the two-dimensional
> plane subject is slightly off parallel), what chance of getting a sharp image
> with a hand-held camera and a subject that is three-dimensional?
>
> Brian - somewhat puzzled on this topic as usual.
Only macro lenses are designed to have perfectly flat fields.  The 
center and the corners of the film plane have different focus points 
with an ordinary lens, but the center is usually the sharpest.  If 
your best focusing efforts produce sharp corners and soft 
centers(sounds like a chocolate) your focusing system may be off. The 
camera may need servicing to make sure a focused image on the focus 
screen corresponds to sharp center focus on film plane.  The angle of 
the mirror could be off.  And other things I do not know about. It 
would explain the soft slides overall as well if a carefully focused 
viewfinder is producing a focused image in front or in back of the 
film plane.
--
Winsor Crosby
Long Beach, California


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