Checking front/back focussing

Hi

When checking for front/back focussing issues with a specific lens and K20D do you focus once then change the focussing mode to manual so it doesn't refocus when changing the adjustments from -10 through +10 ?

or do you leave the focus switch to af-s so it focus's before each shot ?

Jason.

I've not got a K20D, but you would have to leave it on AF so that you can see the result from the next test using the adjustment previously made. It's purely an AF exercise, there's probably a separate manual focus error as well, but you can't adjust that.

shim

I'm not saying to manually focus the shot but to auto focus it and leave it at that point and make the adjustments on camera to see which one is the correct one. You would then make the adjustments in camera for each subsequent shot and see which adjustment point was the best.

Confusing myself even more now.

Jason

The adjustment only has an effect when the camera autofocuses. Leave it on AF-S. Take a shot normally. Make an adjustment. Take another shot normally. Compare the two. Simple as that.

You work like this (with the camera in AF-S mode):

1. Put camera on tripod
2. Get a decent test target
3. Set the lens to either maximum or minimum focus point
4. Autofocus and take a test shot
5. Examine at around 11x magnification on the LCD
6. Adjust the AF if needed
7. Go back to step 3 and repeat until satisfied.

HTH!
Matt

and compare with previous shots at the same magnification by turning the front wheel.

Shoot JPEG test shots instead of RAW for the clearest images on the LCD when blown-up (because the "RAW" images displayed are actually highly compressed imbedded JPEGs).

If zoom lens, test different focal lengths. Awkwardly with some lenses, an adjustment that suits the long end doesn't suit the short end. Also test with a subject at a reasonable distance - neither extremely near or far away.