Testing focus

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coldpenguin

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I have always felt that the Canon 28-135 IS I have is a little out of focus.
In the past, I thought it might just be me, but the 75-300 IS and the 18-55 kit lens always seemed a bit sharper (or at least easier to get sharp).
What is a good way of testing the focus?
What should be considered reasonable, and is it worth fixing (how much)?

I set the camera up on a tripod tonight, pointed at a grid (cutting mat), angled at around 45 degrees to the camera, set to a reasonably long exposure, IS off, autofocus, and used the IR remote to take the photo. The picture can be seen here: http://81.156.147.33/focus.jpg

The red square is where the Zoom Browser thinks it got the focus (I thought it was closer to the bit where the two thick lines cross).
The lens is zoomed in, AV mode, 5.6 set for aperture.

To me, the area in focus is set to the left of the point, which is (at least) ~5cm too close.

Is there a better way of testing the focus?
 
There's too many score marks for it to be sure where to focus, I sincerely doubt it actually focused on the red dot, there are much more prominant patches of contract to use
 
Get a sheet of newspaper, iron it, clip it to a piece of card (cornflake packet!). Use that as you target, flat on.

You will soon see if it is focussing short. If it is focussing correctly, it will render the newspring sharp....try at various f-stops and compare, that way you can find the best section of the lens to work with. Some are biased towards the open end of the diaphragm (those aimed at predominantly photojournalists who will mostly shoot wide open) others are biased towards the stopped down end (f22, f32, f45) these are macro/micro lenses which are designed fo rclose up work where to get depth of field they need to be stopped right down - so they are designed to work best at these apertures becauyse that is where, typically, they will be.
 
If you do a search on front and back focusing you will find plenty of evidence that the 45 degree test just isn't the way to test. Was it Pudleduck who suggested a few memory cards stood up and lined up beside ewach other at 90 degrees to the camera set back by their thickness from the adjacent cards. Also make sure you are far from the lens minimum focus distance etc etc.
 
Oh, now I am disappointed. WhenI saw V8burble I thought it meant something sweet, and charismatic....then I saw the little picture with a blasted audi badge in it. And I thought it was going to be a Sunbeam Tiger or Shelby Mustang.

Oh well. never mind. I shall dream of blue bonnet stripes tonight and the sound of an off beat rumble!
 
Lensflare said:
Oh, now I am disappointed. WhenI saw V8burble I thought it meant something sweet, and charismatic....then I saw the little picture with a blasted audi badge in it. And I thought it was going to be a Sunbeam Tiger or Shelby Mustang.

Oh well. never mind. I shall dream of blue bonnet stripes tonight and the sound of an off beat rumble!
Click to expand...

I did have a 1968 Sunbeam... but with 4 cylinders missing (Alpine) ;)

:woot: 'Vorsprung durch Technik' my friend :woot:
 
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