I'm having trouble shooting with a manual 50mm lens, what can i do?

I have a Nikon D40x. And i have a Nikon AF 50mm lens. This lens however, does not AF on my camera because its a D40. Shooting manually usually wouldn't bother me, but i'm having a problem that is really messing me up when i shoot portraits. When i look through the viewfinder, it looks like it is perfectly focused, but once uploaded, they aren't well focused at all. For example, i shot a man, and the hair around his face was perfectly in focus, but his face wasn't. (i shot it at f/4.5)

I'm almost sure it's the camera, because i had borrowed a friends 50 mm (same kind) and i had the same issue. I've tried adjusting the viewfinder, but nothing seems to work.

Is there something that i'm doing wrong, or something that i could try doing?

Added (1). If it is the viewfinder, is this something i can get repaired?

Are you positive that your lens is compatible with this camera? I believe the Nikon D40X model does not support interchangeable lenses whereas the D40 does.

Sounds like the viewfinder might be messing things up…

I switched to AF several years ago as my visual acuity declined. Can you adjust the diopter on the viewfinder? Here is a DoF table that may help as well:

http://www.dofmaster.com/doftable.html

Also be sure you are putting the focus on the eye.

Whenever you are manually focusing a camera, another factor comes into play that is CRITICAL, and that is your eyesight. You are leaving out some very important information.

Do you wear glasses? If so, are you nearsighted or farsighted? Are the glasses bifocal? Are you of an age to where close focusing on anything with your eyes is becoming a problem?

Modern auto focus cameras are no where near as user friendly for manual focus. Older, true manual focus SLR film cameras had internal focusing screens that made manual focus much easier and more accurate. A modern auto focus camera has nothing to aid with manual focusing which can be a real problem at times, even if your eyesight is not an issue added into the equation.

Look in your camera owners manual. There should be a section in the rear showing any optional viewfinder focus screens available and also any diopter correction viewfinder lenses available.

One thing to check now. Can you SHARPLY see any exposure numbers in the viewfinder? Does adjusting the diopter on the viewfinder make the numbers look more clear or more blurred? If you are having to set the diopter adjustment at anything other than 0, then your eyes are part of the problem. However, if by adjusting the diopter you can get the numbers in the viewfinder tack sharp, then that should suffice.

In the "old days", the best way to set a diopter was to remove the lens completely, and then adjust the diopter until the focusing screen was sharp while holding the camera to a light source.

It could be the lens is faulty or that it has an extreme amount of front or back focus. There are test devices made to check if a lens is truly focusing where it should. Is this a new lens or used?