Vladamir30 wrote:
John said:
Steve, the best "formula" to use for focusing is to get under the dark
cloth
with a focusing loupe and get the scene sharp. Check the near and far, all
the corners, etc. . . .
With all due respect, I disagree with this advice. It's often difficult to
stop down to the taking aperture and tell whether everything is "sharp" or
not. Many of us photograph early in the morning and late in the evening or
in fog , rain, cloudy conditions, or other times when the light isn't very
bright. Then we're stopping down to at least F22, maybe F32, F45 or
whatever. At those apertures and that kind of light I'm sometimes lucky if I
can even compose an image on the ground glass much less stop down to the
taking aperture and tell whether everything in the scene is sharp or not.
And even in bright sunlight there often are shadow areas where the light is
dim.
So many of us to resort to something other than just looking at the ground
glass to tell whether everything looks sharp or not. I use the method
discussed in Tuan's article on focusing the view camera found at
www.largeformatphotography.info but there are other methods too that IMHO
are more practical than trying to figure it out from the ground glass.
I entirely agree with your comments. Even in bright light, I find it
difficult to see much of anything if I stop down below f/16 or f/22. It
is true that my retina is not that sensitive to dim light after 60 years
of myopia, but I once posted a question about this and found that many
people agreed with me that it is very difficult to evaluate depth of
field by stopping down to the taking aperture.
Steve Simmons has suggested the use of screen brighteners and a loupe.
I have a Maxwell screen which is about as bright as anything you can
find, and I still can't see much of anything when I stop down to the
taking aperture. The use of a loupe is more involved than one might
think. In effect, you are magnifying the picture. If you used a 10 X
loupe to view a 4 x 5 transparency, you would expect less DOF than you
would see with a 4 X loupe. So your choice of loupe involves implicit
assumptions about how much the final image will be enlarged and how it
will be viewed. As a result, it is going to be a individual thing.
One person may find that a certain procedure, developed after years of
experience, may work well for him/her in evaluating DOF, but it doesn't
follow that the same procedure will work for someone else. The
advantage of the focus spread methods, as described by Tuan at
www.largeformatphotography.info, is that they are more objective and
less dependent on the individual.
Having said that, let me add that it doesn't hurt to stop down as far as
your eyes will allow you to check that DOF is in the right ball park and
extends equally from front to rear. Experience will help you estimate
how much more you will get if you stop down further. In my case, I
usually use f/11 to f/16 for that purpose. If you can get to f/32, all
the more power to you.
"John Emmons" wrote in message
...
by the time you figure out the formula, you could have set up, focused and
exposed the film...;^)
Steve, the best "formula" to use for focusing is to get under the dark
cloth
with a focusing loupe and get the scene sharp. Check the near and far, all
the corners, etc.
Keep in mind that you probably won't be able to get the entire scene in
focus with the lens wide open, you'll want to stop the lens down and let
your eyes get accustomed to the light, with a bit of practice you'll be
able
to focus.
The math that Leonard uses is undoubtedly correct, but I think you'll find
that in practice it's much better to actually see the image get sharp on
the
ground glass.
John Emmons