Re: Hyperfocal Chart

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>>What would my depth of field be at f22 - f32 - f45?
>
>
>Boy, wouldn't that be nice?  Mine goes much smaller, too.  But it
>probably won't work.
>
>Smaller apertures give sharper images only up to a point, then
>diffraction effects spoil things. I think F16 and F22 are about it
>for useful apertures.  I have a Bercovitz spreadsheet somewhere that
>calculate this, but I am on my way to a birthday party.  MINE!

  We had this discussion about a year
ago and I ran some numbers through
John B's MAOFD.

---
To change over to numbers, using your MAOFD
spreadsheed (80mm lens, anear=2metres, afar=inf)

At f11: geometric res=6.4  and diffraction ltd res=0.26
(minutes of arc I assume)
At f16: geo=4.3  diffr=0.38
At f22: geo=3.1  diffr=0.38
At f32: geo=2.1  diffr=0.77
At f45: geo=1.5  diffr=1.08

  So for a medium format camera with a normal
2 metre to infinity scene the geometric resolution
(at anear and afar) is much worse than the diffraction
limited res (at the focal point of 4m) at almost
all apertures. At f45 they are getting close.

  Assuming they add in quadrature then the resulting
res at anear and afar is 1.85 moa. At f32 the
result would be 2.24 which indicates that the
diffraction isn't making anear and afar much blurier
than they were (2.1). Intermediate points that
aren't so blurry will be more affected by the diffraction
induced blur.

---

  Regarding your 50mm lens that you made waterhouse
stops for. Repeating the above (50mm lens, an=2m, af=inf)

At f11: rg=3.9 rd=.42
At f16: rg=2.7 rd=.61
At f22: rg=1.95 rd=.84
At f32: rg=1.34 rd=1.23
At f45: rg=0.95 rd=1.73

  So here f45 is bad news. F32 isn't great
unless the near object and infinity are the
most important in the scene. F22 looks like
the min aperture to use.

---and later---

  I still think you have to weigh the
sharpness of the in-focus areas with
the COC blurred near and far points,
and intermediate points if they are
important to the photo. Thus no
spreadsheet or resolution measurement
is going to tell us what to do in
every photo.

  It is nice to know the limits of
stopping down though.

---and now new blather---

  Basically f32 is fine for medium format
and even f45 can be. With 35mm normally f22
is the limit.

  If you have a main subject you are
focusing on then not stopping down too
much is a good idea (to avoid sharpness
loss due to diffraction). But if 6'
to infinity is your subject the stopping
down will improve the 6' and the infinity
sharpness at the expense of the middle
distances.

Greg E.