Re: Konica IR ...!st time, hyperfocal focusing, and Stigmata

["Christina Z. Anderson" <tracez@xxxxxxx>]

Thank you, Clive; I now get it!  I think I must have assumed that
diffraction gets worse the closer you get to wide open, which is the
opposite of the truth.  I have always assumed the smaller the aperture
(larger f-no.) the better the image, really. And, maybe I'm the only one,
but I continually throughout my photographic education (graduating in May)
have mixed up stopping down/opening up etc and the backwardsness of the
f-stop numbers.  I have no problem intuiting it, just verbalizing it.  And,
I seem to always work from the smallest aperture on "down" which is
technically not the correct terminology--you are working from the largest
wide open hole/aperture to the lesser wide open which you call 'stopping
down'.  (by this time everyone on the list is wondering what neophyte they
have here).  So I will use your rule of thumb of 3 stops 'down' from wide
open and that'll  do just fine.  BTW I also checked out your website and
it's great.
Chris
----- Original Message -----
From: Clive Warren <Clive.Warren@xxxxxxxxxxxxx>
> Generally you are correct - although some lens designs break the rule and
> are sharpest wide open - the 203mm Kodak Ektar for example.  Usually,
> stopping a lens down by two stops is good practice if you want the
sharpest
> possible image across the negative.
> Using large format lenses (eg 4x5), some of these lenses need to be
stopped
> down in order for the image circle to cover the negative.
> Generally, diffraction is worse at smaller apertures, the trade off is
> around two stops down from wide open. Any smaller and diffraction effects
> decrease image sharpness.
> The best aperture for shooting infrared for image sharpness is again
> generally two stops down from wide open.  However with infrared film the
> focussing point is different from that using normal film. Stopping down
> further helps to cover any focussing errors with the associated increase
in
> depth of field.
> If you want a rule then stop down three stops from wide open when using
> Infrared Film. However use of the aperture is part of creative photography
> and although you should avoid very small apertures, feel free to
experiment
> and explore in the same way as you would with visible light photography.
> Throw the rules out of the window and delight in the freedom :-)
> All the best,
 Clive   http://www.cocam.co.uk


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