[tabl10s]

ever for my K5. The 77 Ltd was love at first sight & feel. How do I now fully optimize the lens for accurate focus?

[jaytee]

I use manual focus most of the time, otherwise I have set focus for the rear AF button rather than the half press on the shutter release. Once you get used to using your thumb to focus it feels perfectly natural and you do it without even thinking about it. You never lose a shot or have to put up with the aggravation of the camera refocusing when you are ready to shoot. I'm surprised this is not the default setting for DSLR cameras !
Enjoy the 77 it is said to be an awesome lens!

[jatrax]

I'll second jaytee's recommendation for using the rear AF button, but I think you were asking more about how to set the lens up rather than shooting style.

In most cases, you should not have to do anything, the factory adjustments should be right on.

However, here is what I do with a newly purchased lens, either new or used:
1) Carefully examine all mechanical aspects of the lens, check operation of zoom, focus and aperture rings. Everything should operate smoothly and as expected.
2) Examine the glass itself, using a flashlight and/or white paper to reflect light through the lens. Look for scratches on front and rear elements, look for signs of fungus or internal dust or element separation.
3) Examine the mount and electrical contacts if present, the mount should be clean without undo wear. The contacts should be clean, shiny and in the proper positions.
4) Mount the lens and check for operation again, make sure the camera can control everything properly, check the EXIF to see if the lens is identified properly.
5) Put the camera on a tripod and aim at a well lit, known target. This can be a brick wall, a book case full of books or an actual focusing target. Take a series of shots at different aperture openings. Move the focus ring to one extreme before each shot so the AF mechanism has to work. On MF lens I do the same to see if I get repeatable results with the focusing screen.
6) If the focus results are satisfactory I am good to go. If I am not happy then I break out the Spyder Lenscal for more intensive measurements.

The k-5 is capable of fine focus adjustment for individual lenses if you need to make any corrections. This is under Menu>C4>#26 (AF Fine Adjustment). I would NOT recommend jumping in and making any changes without a lot of testing. Getting accurate and repeatable results from AF testing is not easy and you can quickly decide you have a problem when in reality the lens is fine but your testing is flawed. Never accept the results of a single test, make many repetitions to be sure you are getting the same results before attempting to make changes, especially if this is not something you have done before.

Here is a link to reviews of two of the lens AF testing products with some additional information on adjustments. But unless you are positive you have a problem, it is best not to mess with things.

[tabl10s]

Where is the rear focus button located?

[jatrax]

Where is the rear focus button located?

Directly below the green button on the back. You have to go into the menu Camera>#5 (Button Customization>AF Button>Enable AF And then Shutter Button Half Press to OFF.

This is not for everyone, most are used to half pressing the shutter button to focus and then press the rest of the way to take the photo. With the camera set this way pressing the shutter button takes the photo whether it is in focus or not. So you have to train yourself to focus first with the AF Button then compose then press the shutter button. Try it and if it works great, if you don't like it just things back the way they were.