>
> To wit, how are the depth of field indicators on Zuiko lenses calculated?
> Basically, they need to arbitrarily decide on a value for the Circle of
> Confusion. Is this 30 microns for all lenses (I read somewhere that this
> is fairly standard in the 35mm format, but I can't recall the reference
> or estimate its reliability)?
I have some documentation Olympus delivered with a new lens ( 4/200, 1.8/50,
2/85)
. There`s a d.o.f Table inside. Thei are all calculaeded with a circle of
confuion of
a 1/30 mm = 33 microns. 33 microns is 1/1500 of the focal lenth of the standard
lens.
According to literature this ratio is determined by standardization.
But they also give the ratio 1/2000 of the focal lenght to use for higher
demands.
>
> Since the allowable value for the circle of confusion should vary with the
> anticipated enlargement (and to a lesser degree film speed/graininess),
As long as you increase the distance of view with the enlargement of your
pictures (what is what you usually do- have a close look to a big advertisement
poster :-)
There is not too much reason to change the c.o.c.
Exeption, if you make partial enlargements
> would be useful to be able to reestimate d.o.f. for different values of
> the c.o.c. from the lenses as well. Is there a way to interpret e.g. the
> f8 mark as giving the f8 depth of field at 30 microns, but the f16
> indicating the same f8 depth but at ~100 microns?
The formula for calculation of d.o.f gives a linear relationship betwen
aperture mark and
coc. The f16 mark gives F8 at 66 microns, and the f4 mark gives f8 at 16
microns.
>
> Similarly, any tricks for extended lenses (especially with the 14 and 25
> mm rings)? I find that my sense of d.o.f. is almost always off from the
> finished product with my very amateur macro work (mostly with the 90mm f2
> portrait lens which does a decent job pretending to be a macro lens)
In close-up photograpy, d.o.f. is always very limited. There is not too much
help on this.
I use the d.o.f-Button. But give an addition of 2 F-stops to be sure.
E.G. when the d.o.f in the viewfinder seems to be o.k. at f4, I take the shoot
with f8.
Frieder Faig
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