Posted by Les on October 15, 2000 at 22:14:48:
In Reply to: Re: Focus problem on Century Graphic posted by Dennis Lee on October 15, 2000 at 17:26:44:
According to Les Stroebel in "materials &
Practices" The only time there is depth of focus-
-a margin of error for the film plane, is with a
two dimentional subject.
If the subject fills the image area in three
dimensions, then there is no room for error.
This is because when we calculate depth of field,
we a s s ume the film to be in one plane. If the film
were curved, or angled, this effects the depth of
field.
I will refrain from the math but i will a s sume you're
printing a 4x enlgargement (9x13) and you shot it
at f16. Your depth of focus would be 0.04"
As to not putting the lens on the right stops...
If you are getting a sharp image on the ground
gl a s s at anypoint, the the infinity stops are not
the problem. These stops are only critical when
not using the GG.
For instance if you were to set up
to shoot the moon--an infinity shot if there were
one.
Mark on the stationary part of the
bed where the infinity stops were located,when the scale is match
to inifinty and the rails are in their back most position.
and
then
bring the lens out but lock it down 1/2" short of
the stops
Now open the lens and focus on the GG, look at the
mark on the stationary part of the bed where the
infinity stops were. The lens should be aligned
with the marks.
Effctively all you did was move or shift the rails
out 1/2". It's only when you are relying on either
the scale or the rangefinder that you need to know
that the inifinity stops are on infinity.
I don't recall if the Century came with an fresnel
lens or not. If the camera was designed with a
fresnel lens, then it needs to be in front(between
the lens and the GG) with the rings facing the
lens. The GG should have the matte part facing the lens.
If somebody put it in the back, then that
would shift the GG forward and it would cause this
problem. I know this just happened to me and I've
got the soft and sharp negs to prove that a
misplaced fresnel will be a problem.
If the camera came with one and it's not there then
there should be some shims or ??? to keep the GG
tight to the back of the GG mount.