Originally posted by UdoG How can I do such a test? Do you have some test pictures? I will receive the K-5 with the 18-135 lens in the next days and I want to perform such a test too.
Thanks!
Hi, the technique I normally use to check BF/FF is:
1. In a well lit room (daylight, not artificial), or outside if you prefer.
2. Place a table against a wall.
3. Put some small colourfull boxes, or items on the table in a staggered, diagonal, equi-spaced, fashion, from front to back, 4-5 should be enough.
4. Switch off the cameras shake reduction, the shutter speed should be high enough for hand holding.
5. Set the camera to shoot RAW (PEF/DNG) images only, Jpeg's will be no good as sharpening is carried out.
5. Start with the lens set to max apperture and the shortest focal length (F/3.5 18mm).
6. Then from a distance that is just far enough away to fill the viewfinder with all the items on the table, focus on the first box/item and take a shot
7. Focus on the second box/item and take another shot.
8. Continue for all the other boxes/items from front to back.
9. Load the RAW images onto a computer for viewing at full size 100%.
10. It will now be obvious from the images exactly how much of the image (other boxes/items) is in focus both in front and behind the box/item that was the point of focus.
11. The depth of field (zone of sharp focus) will be approximately 1/3rd in front of the focal point and 2/3rd's behind.
12. You will see this as boxes/items in focus and out of focus. There should be more in focus behind, than in front.
13. Taking a shot at each box/item will make it easier for you to judge how far out the focus is, or is not if lucky.
14. If there is too much in focus in front of the focal point and/or the focal point is not in focus, then the lens is Front Focusing and will need some "-" minus adjustment.
15. If there is too much in focus behind the focal point and/or the focal point is not in focus, then the lens is Back Focusing and will need some "+" plus adjustment.
16. If adjustment is required, adjust and repeat.
17. When complete you may want to recheck with a smaler aperture and/or longer focal length (F/5.6 50mm) as things can change slightly with diferent combinations. So best to use the combinations that you most commonly use.
There is another method for checking BF/FF where you shoot at an angled target (45deg). I find this is best avoided as it is only accurate if you can guarentee that the actual focusing sensor matches exactly where the red dot is displayed in the viewfinder. If you can not it will lead to lots of false negatives and make any BF/FF even worse after adjustment.
In the method described above all the targets are perpendicular to the lens so it does not matter if the red dot does not match up exactly with the actual sensor.
I checked my K5 and the center red dot at least does not match exactly where the actual sensor is.
Hope this helps. I can't upload any images for this yet as they are all still RAW files.