For some camera's and or models you still can buy a focus screen, several
styles in fact. You can also buy eyepiece magnifiers for some cameras.

You can go to manual focus, set infinity, in fact set everything, or you
can go to a canned program, like night shot. sunset/sunrise, and still get
those shots you want. Heh, just experiment, then experiment some more, then
more. Shots are cheap, you may make some great ones along the way and trash
all the bad ones.

According to Tom  <Tom@dontsendmespam.com>:

    In part, you picked the dimmest viewfinder in the Nikon DSLR
line.  (Or, at least the dimmest one which I have seen.) I've looked
through a D50 in the camera store after being accustomed to my D70, and
found it amazingly dark, which makes focusing more difficult.

    The D200, by contrast, is a lot *brighter* than my D70.  That is
one of the reasons why I want it.

    For the moment, I think that your choice is to set the focus
zone (probably center of screen), turn off autofocus, and manually focus
while watching the green dot for confirmation of focus.  Slower than
using a split-image screen, but the best that you have available.  (Of
course, for closer things than your listed subjects, you can use the
autofocus assist light selected from the menus.

    There is someone out there who makes replacement screens with a
focusing aid for the D70 and the D200, so they probably make one for the
D50 as well.  Can someone else remember the URL?

    My eyes are far from young.  I did take time to focus the
eyepiece of the D70 to give a sharp view of the focus zone indicator,
and the viewfinder grid pattern which I keep turned on as well.  Those
have to be cleanly focused first, before you can depend on your eyesight
through the finder and lens.

    Most of the autofocus lenses go beyond infinity -- perhaps to
allow the servomechanism room to search without hitting a firm stop.
Also, many of the zoom lenses shift focus slightly as you zoom, so you
should focus after you zoom -- and your infinity mark might be wrong
under those circumstances.

    A so-called "prime" (that is -- single focal length) lens should
do better with the focusing scale -- and a faster lens than your "kit"
zoom should make focusing a bit easier in dark conditions.  If you are
depending on the focusing scale in the dark, check it out beforehand to
see whether there is a firm stop at infinity, or whether it overshoots
before it hits a stop.  You may want a Mini-Mag-Lite with a red filter
for viewing your focus scale without totally blasting your night vision.
(Or -- you could make something with a small battery, a red LED, and a
switch (perhaps with a shade to keep the LED from shining directly in
your eyes).  You don't want a bright one for this, the dimmer the
better I think -- and that will increase your battery life as well.

    Good Luck,
        DoN.