Focus adjustment on K20D


giofi

Link Posted 24/05/2010 - 22:36
I have read a lot about lenses needing focus adjustment, so I am wondering whether I should adjust focus with my K20D. Is there an easy way to determine whether a lens is front/back focusing? Is there a database of adjustments needed with Pentax lenses or are individual cameras different?
Thanks for any advice you can give me!
Giorgio
Giorgio

Pentax Photo Gallery
Last Edited by giofi on 24/05/2010 - 22:37

chris_jl

Link Posted 25/05/2010 - 00:32
giofi wrote:
I have read a lot about lenses needing focus adjustment, so I am wondering whether I should adjust focus with my K20D. Is there an easy way to determine whether a lens is front/back focusing? Is there a database of adjustments needed with Pentax lenses or are individual cameras different?
Thanks for any advice you can give me!
Giorgio

I can only say from personal experience that each are different. As far as I remember the scale is an adjustment in microns (back and forth) of the focus mechanism. I've found it varies by lens, by body and with focus distance and, for zoom lenses, with zoom. Thankfully the K20D has a memory for several lens adjustments. Also I've found it exceptionally difficult to adjust accurately for lenses with focal length less than about 28mm (any hints gratefully accepted).

There are number of online guides to help you find the focus points and you will inevitably find people who criticize them as inaccurate for various reasons (valid and invalid). I've found http://www.zimbio.com/Digital+Cameras/articles/839/AF+adjustment+test+chart+help... helps.

I'm sorry if that isn't an amazing amount of help, but I hope it gets you started.

C

johnwhit

Link Posted 25/05/2010 - 07:13
chris_jl wrote:
giofi wrote:
I have read a lot about lenses needing focus adjustment, so I am wondering whether I should adjust focus with my K20D. Is there an easy way to determine whether a lens is front/back focusing? Is there a database of adjustments needed with Pentax lenses or are individual cameras different?
Thanks for any advice you can give me!
Giorgio

I can only say from personal experience that each are different. As far as I remember the scale is an adjustment in microns (back and forth) of the focus mechanism. I've found it varies by lens, by body and with focus distance and, for zoom lenses, with zoom. Thankfully the K20D has a memory for several lens adjustments. Also I've found it exceptionally difficult to adjust accurately for lenses with focal length less than about 28mm (any hints gratefully accepted).

There are number of online guides to help you find the focus points and you will inevitably find people who criticize them as inaccurate for various reasons (valid and invalid). I've found http://www.zimbio.com/Digital+Cameras/articles/839/AF+adjustment+test+chart+help... helps.

I'm sorry if that isn't an amazing amount of help, but I hope it gets you started.

C

This one is very good and involves a little less construction, tripod required:

http://focustestchart.com/chart.html

If you're checking a zoom lens, either go for the mid point or the most used focal length.

Hope this helps,

John

Anvh

Link Posted 25/05/2010 - 11:44
chris_jl wrote:
Also I've found it exceptionally difficult to adjust accurately for lenses with focal length less than about 28mm (any hints gratefully accepted).

The only thing I can think of is to place the focus chart as close as you can since the closer it is to the camera the shallower the dof would be.
Stefan


K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
AF-540FGZ

MattMatic

Link Posted 25/05/2010 - 11:59
I would suggest using the test chart on the wall, the camera on a tripod and at 45 degrees to the wall (so the camera is dead upright). That's the way one Samsung/Pentax service manual shows their setup for focus calibration.

(That is, rather than pointing down to a desk as in the link )

It's also a lot easier when working with lenses that have 1 or 2 meter minimum distances

Also - DO IT IN DAYLIGHT

You can get small errors when shooting under tungsten. In fact, with the K20D I found that using the focus chart in daylight and then slightly tuning in tungsten using portraiture (ie the 50mm/1.4 at f/1.4 on a subject's eye) would give the best overall results. (The K7 has colour temperature sensing linked to focus adjustment )

Takes a little fiddling around - but don't get too worked up about it... aim for a compromise that works for your kind of shooting style

Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)

giofi

Link Posted 25/05/2010 - 18:30
Thanks to all of you for your help and suggestions. Now i have some work to do!

Giorgio
Giorgio

Pentax Photo Gallery
Add a Comment
You must be registered or logged-in to comment.