Originally posted by pero In my experience - not just opinion - focusing at anything but close distances with a wide angle lens with the SAFOX is a hit and miss procedure. And the larger DOF under such shooting conditions is not a substitute for correct focus. After all, large DOF does not mean that everything within it is in focus, only that what's in the DOF *appears* as acceptably sharp. How acceptable depends on viewing conditions etc (for example small screen jpg vs large print). With longer focal lengths I rarely have problems.
So it's not just a question of learning the system and using it correctly (I think I have the hang of it after shooting about 20 000 pics with this focus system). There are limitations with every system and there aren't always ways around them. As for focusing/confirming visually, that is practically useless with a modern ground glass since it shows a too large DOF, being instead designed to give a bright viewfinder with modern slower aperture AF lenses.
Hi Pero,
Your original post suggested that more, smaller focus points and a clearer indication of where the focus sensor areas were would be desirable. All I suggested in my post was that the focus sensor areas could be estimated reaonably accurately and easily and that in my use the larger focus sensor areas don't really pose a severe handicap even though the subjects and circumstances under which I shoot is one that usually would pose problems for an AF system. One aspect of what I called "learning how the AF system works" is mapping out the AF sensor areas that you use so you have some idea where they're actually active. This needs to be done with each individual body because the relative position of the AF sensors to the VF is dependent on the tolerances allowed in the manufacturing process. In my experience, (over 100K clicks with 6 different bodies) none of my bodies have had perfectly aligned AF sensor areas in relation to the etchings on the standard focusing screen (and I never assumed that they would). If you map the sensor areas, then indicators in the VF aren't really unnecessary.
Now you're saying that AF accuracy is hit and miss in your experience with wide angle lenses at distance when it's difficult to see enough detail in the VF to visually confirm critical focus. That is a different matter and I really don't see how my post is contrary as I don't know that smaller AF sensor areas would necessarily make the system more accurate, and smaller sensor areas and a clear delineation of these areas would certainly not effect how well one can confirm critical focus visually.
Your statement that the focusing screen was designed for slower "kit" lenses is unfounded, though with any APS-C VF, this may be of limited actual practical value for many users. Since the K-7, Pentax actually uses a focusing screen that is a bit darker than those on the entry level bodies (I don't know if this includes the K 30 or newer VFs) This was done to make the VF perform better with the faster lenses that they assume would be used with a flagship body. I copied this from a 2009 post on another forum.
This is translated from the K-7 review posted at dc.watch.impress.co.jp on July 14, 2009.
" "Looking through the K-7 finder, it seems slightly darker in comparison to other Pentax's up until now. This reduction in light transmission was done in order to attain ease of manual focus and see boke. Generally when you increase the transmission of a camera's focusing screen diffusion decreases making it harder to grasp the exact point of focus. In other words, brightness of the finder and ease of focus are inversely proportional. A lot of cheap, popular cameras are sold with slow zooms, and ease of manual focus is not seen as important. So there is a strong trend to pursue brightness. In terms of the screen, you could say that the K-7 is aimed at experts. Particularly when using large aperture, fixed focal length lenses, and select the optical preview, you can shoot while confirming subtle changes in the flavor of the bokeh through the finder."
Fumio Nakamura
After working for a camera maker, became an independent photographer in '96. Active in a wide range of the field, mainly writing how-to and technical articles, and also instruction. Posesses a deep knowledge of classic cameras and owns over 300 cameras. Has been a member of the Grand Prix selection committee since '98."
Also, most attention to the K-5II AF system has been on the low light performance, but not much attention has been paid to the fact that in SAFOX X, they use an AF sensor that is optimized for f2.8 lenses for the first time. This might add a degree of AF accuracy since AF lenses are usually used with automatic diaphragm actuation, so the AF system locks with the lens wide open. With a previous SAFOX versions, it might actually be better to manually stop the lens down prior to activating AF for best critical accuracy since the AF sensors are optimized at a slower aperture.
My experience with the K-5 IIs is that the AF is a bit more accurate with my collection of lenses -- not to any astounding degree, but a bit more consistent -- especially with shorter faster lenses (I rarely shoot wider than about "normal", except when space is very limited, so no real distance work with wides). If you've experienced the same frustration with AF consistency with a SAFOX X equipped body, then I'll assume that you are making a relevant point, if otherwise, then it might not be as pertinent to this thread (asking for suggested improvements on the K-5II series bodies) as you might assume.
I was only adding my 2¢ from my personal perspective to the discussion, and I think I was specific enough about the way I usually use my cameras to be very clear where I was coming from. I did agree that more and smaller focus points
could be helpful though. . .
Scott