It seams like you aperture is not working well when on the camera.
Perhaps there is lagging when the camera should bring the aperture to f1:1,4
Thats what it should normaly do when attached to the camera housing.
If not, it will be as you describe dark in the veiw finder.

Make sure there is no oil on the aperture blades, commond on old objektivs.

Pepe

Take the picture, shrink it to the relative size of your viewfinder
and judge the difference in focus between the in-DOF and out-of-DOF
features. Could it be the scale of the viewfinder doesn't allow useful
discriminations on wide-open, low-F views?

You're clear but you're wrong and confused.  Please don't snip so much
of the post in the future.

You said:

You wanted to know why what you saw in the view finder ("like as if i'm
at f4 or f5.6") does not look like the finished image (" shallow depth
of field as expected at f1.4  but how come what i see through the
viewfinder is not the same?!").

FIrst I want to ask you how you can judge DOF that precisely.

You have not said what distance the object you are focusing on is, which
also has an effect on DOF.

Oh, and don't go by the view finder. Tell us about the digital image.

But you communicated it all poorly. Maybe try again. Be very specific
with everything, limit the variables.

According to Hussam <hktaha@gmail.com>:

    I think that what you are seeing is that your eye can correct
for minor out-of-focus condition in the viewfinder, especially without
an anchor.  If you turn on the autofocus zone display ("pencil" menu,
item 18 "AF are illm") and the grid in the viewfinder (same menu, entry
08 "Grid Display", you have anchor points for your eye's focus, so you
should compare the apparent focus in the viewfinder while the grid or
the autofocus zone indicator are sharp in your vision.

    But in any case, you don't have the full-screen ground glass
viewfinder area which was used back in the Nikon F days to give a better
indication of the depth of field.  And you are trying to compare a tiny
image in the viewfinder with the much larger image display on your
computer's screen, or a printed copy from a printer.  Depth-Of-Field is
a function of image size, and what is sharp enough in a tiny image may
well no longer be so in a larger image.

    Also -- are you in "Auto" mode on the top dial to the left of
the pentaprism?  If so, it will select whatever portion of your image is
the closest, and autofocus on that.  Switch to "P"rogram mode, and it
will use the autofocus zone which you have selected, while most other
features remain as automatic as you may need.  (Or were you switching
off the autofocus on the camera body, and attempting manual focusing?)

    Enjoy,
        DoN.

The viewfinder on a D70 is very dim, much dimmer than a 35mm camera,
I'd bet that it is dim enough that your eye couldn't resolve the
critical focus. This is due to the small mirror size and the use of
mirrors instead of a prism in the finder.  

Tom

According to John A. Stovall  <johnastovall@earthlink.net>:

    Of course -- they were designed for *manual* focusing, as
autofocus did not exist at the time.  They also had changeable focusing
screens because a microprism and split image which worked well with
wide angle lenses would not work so well with a telephoto and vice
versa -- as well as allowing you to select focusing screens better for a
given set of conditions.

    IIRC, the screens for the Nikon F where this mattered came in
four different focal length ranges, to adapt to your lens focal length
range.  

    For critical focus with really long lenses, or for working
through a microscope, there was a plain ground glass screen (which would
work equally dimly with all focal lengths) with a clear center spot with
a fine '+' in the center.  If you moved your head from side to side
behind the viewfinder (assuming a rigidly mounted camera, of course), if
the center area were truly in focus, you would see no relative motion
between the '+' and the image.  However, the more out of focus it was,
the more relative motions was visible.  This would work when any of the
split image or microprism screens would not.

    Easy to say.  However, the D70 (and presumably the D70s) does
not have interchangeable focusing screens -- at least in part because
the autofocus depends on special microprisms oriented to concentrate on
the autofocus sensors, not on the user's eye.  Also, the focusing screen
has a lot of active electro-optical displays on it, such things as the
autofocus zone indicators and the grid which can be switched on and off.
That means a lot of interconnections, which could make problems with
contact quality every time you changed focusing screens.

    Is this true for the Cannon DSLRs?  If so, does the Cannon DSLR
also have active displays on the focusing screen as the Nikon does?

    Enjoy,
        DoN.

Deeper than your perceived depth of field. <g>