Canon 5d mark ii lens microadjustment

[Dwarak]

I want to know if anyone has tried the microadjustment feature on the canon 5d mark ii. Is there a test to know if the lens is auto focussing properly or not.

[fabian628]

Test is to take some pictures of an object and see if it is in focus. Try to use something that has a surface that is perpendicular to the camera, also try something with contrast. If you are consistantly seeing in focus behind or infront then you may have to adjust. Some lenses are inconsistant, it depends also on the aperture, the camera will have more trouble focusing at very wide apertures are the DoF is very thin and confuses the camera

[markjaffa]

I have a 5D Mk II and I use a LensAlign Mk II to calibrate my gear. Makes it reasonably simple.

[MarkChap]

The chosen aperture of the exposure has no effect on focus, the diaphragm stays wide open until the image is taken,

Test is to take some pictures of an object and see if it is in focus. Try to use something that has a surface that is perpendicular to the camera, also try something with contrast. If you are consistantly seeing in focus behind or infront then you may have to adjust. Some lenses are inconsistant, it depends also on the aperture, the camera will have more trouble focusing at very wide apertures are the DoF is very thin and confuses the camera

[Dwarak]

Thanks for the advice guys had a look at the datacolor spider product and the lens align both seemed good and easy to use will have to test the lens I have first like suggested and I am not in a hurry to buy any new lens so unless my current lens has an issue with the bodies I have there is no point buying the product.

[fabian628]

The chosen aperture of the exposure has no effect on focus, the diaphragm stays wide open until the image is taken,

You are right, chosen aperture has no effect, but maximum aperture does, ie.f/1.2 /f1.4 lenses have more trouble focusing due to very shallow dof playing havok with the Af sensor (or so i am let to believe)

[roburg]

I am not in a hurry to buy any new lens so unless my current lens has an issue with the bodies I have there is no point buying the product.

My 5DII seems to have more trouble getting correct focus with my 100-400L whereas its fine with the 40D body. The 5DII focuses a lot quicker but nat as accurately. Anybody else seen this issue where one lens works fine with one body but not with another?

[Tricky]

I want to know if anyone has tried the microadjustment feature on the canon 5d mark ii. Is there a test to know if the lens is auto focussing properly or not.

Mount camera on tripod. Use 5d2 live view to focus on an object. Then switch off live view and press the autofocus button whilst closely checking in the lens' distance window if there is any movement. If there isn't, then live view = AF and no adjustment is necessary. If it moves, then use micro adjust to front/rear focus the lens, repeating the process until no movement.

Then go capture a few images with and without micro-adjustment, and check at 100% to see if there really has been an improvement - I doubt you'd notice +/-5 but would notice anything over 10.

I've made a few posts previously on this topic, which might help you out if you do a search.

[William W]

In the field, I use a method similar to what is outlined by Tricky.
I use an object which has a definite line or row, which is about 45° to the lens’s axis – usually something is easy to find wherever you are:


My preliminary, with a new lens or change of lens if I believe somethig to be screwy, (in the field): then I use AF a few times on a very contrasty object and then view the image (taken) in the LCD, at magnification – if OK, then Focus is ”OK” (rusty peg centre point AF):


***

In regard to comments about the Lens’s maximum speed and the AF’s functionality: I don’t believe there is any intrinsic reason to suggest that AF will be “worse”, simply because the lens has a fast maximum aperture: in fact I understand the opposite is true, and there are technical reasons to support that - it is how AF works.

A Précis of The Technical Bits:

Most DSLR’s Auto Focus Systems use Secondary Image Registration, (SIR), Through The Lens (TTL) Passive Phase Detection.

This is basically a beam-splitter which takes the light beam light from opposite sides of the aperture and it is looking for the overlap of the images from both sides of the aperture.

If the angle between the paths of those images is too small (i.e. IF THE “f stop” is TOO SMALL), it's hard to tell when the images are in or out of registration.

The diagram below is typical, but not geometrically accurate, but was made as an aid to the explanation above, showing how a smaller max aperture lens, provides less differentiation, for the function of the AF system.



KEY:
1. Lenses of two different max apertures – open
2. Main Mirror position during viewing
3. Main Mirror position during exposure
4. Focusing Screen
5. Pentaprism
6. Viewfinder
7. Digital Sensor
8. Sensor Filter
9. Shutter
10 AF Mirror
11 AUTOFOCUS "SYSTEM"

***

However, Lens design can result in a function referred to as: “Focus Shift” and Focus Shift does interplay with Auto Focus Systems in so far as the AF relies upon the lens being wide open to make Focus, initially.

Because the Auto Focus System is active only when the lens is at its maximum aperture, the AF (assuming accurate) decides ("correctly") where the Plane of Sharp Focus resides for all the conditions and AT THE LENS’S MAXIMUM APERTURE.

But Focus Shift is an “aberration / fault” (colloquial), which has the actual Plane of Sharp Focus slightly different, at different lens apertures.

Or, in other words, the Plane of Sharp Focus moves ever so slightly, as the lens is stopped down.

Logically, Focus Shift occurs (or is more often noticed), when at close shooting distances and using an aperture close to, but not at the maximum aperture of the lens

So it is easy to understand that, with an EF50F/1.2 on a 5DMkII (for example) and when shooting a tight head shot and using F/2.2 why there might be an unexpected result such that the eye lid is just not quite in the same extra sharp focus that the Photographer thought it was, when looking through the viewfinder and AF was acquired correctly on that eye lid.

***

Regarding the 100-400 and the accurate acquisition of focus being different between two different bodies: it is important to (at the least) use the two bodies in an A/B in the field test on the same focus targets upon the test objects and under the same lighting conditions – including AF Functions and Points - thus eliminating as many variables, as possible.

WW

[Arg]

re post #9, if focus shift of a lens is enough to make a sharp max aperture image become unsharp at smaller aperture, then that lens can be considered faulty and replaced or repaired. You have the right to expect that the increase in depth of focus when shutting down the aperture will exceed any change in the actual plane of sharp focus.

[William W]

Whilst answering the OP, the above was added merely to address a couple of other discussions already raised on this thread.
Not sidetracking off the main topic its perhaps relevant to mention Focus Shift can be researched quite easily and in depth.

But, briefly, it is important to note a technical aspect here:

If Focus Shift exists in any lens then there can be no expectation that the increase in Depth of Focus or more likely there was an error and the increase in “Depth of Field” was meant, will exceed the shift in the Plane of Sharp focus - as by definition of the Depth of Focus and the definition of the Depth of Field, the statement does not make sense.

WW

[roastman]

I use a Spyder Lenscal....... It is simple and is easy to use.