Focusing using manual lenses

gaetanonline wrote:

I can't change my in-camera focus point. My Pentax K-r focus only in the center using manual lenses. For the picture I want to shoot if camera take focus just in the center eyes would be always out of focus because focus point would placed lower, though focus plane is the same.

can you explain me better your technique?

When you say "focal plane" you need to know for your lens whether it is flat or if there is some curve (common). Remember, as a matter of geometry, the distance from the lens to a range of subjects is not flat but, rather curved.

https://photo.stackexchange.com/questions/73687/what-is-the-shape-of-the-focal-plane

Do some testing with your lens wide open (f/2.8) to see if and to what extent you have such curvature.  For example, shoot at an angle towards a subject with many points of definition such as a lawn, then review to see where the focal pattern falls.

Once you have a better sense of how the lens works, you can adapt your focus technique to achieve the result you wish.  For example, if you find that when you focus on a person's chest the focal plane is in front of the eyes, back off the focus slightly.  You can determine this by using a home-made scale (say an 18" piece of wood with whit paper attached and lines drawn every inch) held by your subject at a 45 degree angle next to the head.  The focus on various parts of the body to determine the best point for getting the eyes in focus.

Hope these thoughts are helpful - good luck!