Canon 24-70 f/4 Focus Shift Problem

[Dave410]

<p>Hey Gang,</p>

<p>Does anyone know if Canon has fixed the focus shift problem on the 24-70 f/4? The Internet was buzzing about it three or four years ago and people were expecting a firmware fix or a recall or something, but I can't find anything that says the problem is fixed now. Is it still there?</p>

<p>Cheers,<br />Dave</p>

[Marcus Ian]

<p>Not exactly how a FW problem could fix this, as it seems due to an optical limitation in the lens (though obviously mainly affecting macro shooting). Kind of curious why people would think this could be 'solved' simply by a FW fix as well...</p>

<p>I know I've not heard of any fixes, nor do I expect to see any. If you shoot a lot of macro stuff @ 70mm, it's something I'd expect to see if I bought one (I've used it several times, including Macro ring shots at 70mm - I wasn't enamored w/ the quality which is why I don't own one)</p>

<p>...I could be wrong (of course), but maybe they'll fix it in the MkII...</p>

[Dave410]

<p>I don't know either, Marcus, but the guys at Photozone say the lens was somehow "fixed" after they tested it, although they didn't test it again. Sounds kinda fishy.</p>

[Robin Smith]

<p>Sorry, I hadn't heard of the problem and so don't know of any fixes.</p>

[William Michael]

<p>I haven't used the lens but I researched it a little while ago when I was looking to buy a lens in that category, (same time that I used the Tamron Lens that you mentioned in your other two threads).</p>

<p>From what I researched my understandings about the 24 to 70/4 IS are:</p>

<p>> The problem is a <strong>small shift </strong>and is (usually only ever) a relevant consideration when using the "macro mode". (emphasis on "small")</p>

<p>> The problem is not 'fixed'.</p>

<p>> How <strong>practically</strong> relevant the issue will be to you, is be a good question to consider:<br /> 1. how often you'd be using the lens in macro mode and <em>in a critical situation</em>.<br /> 2. for the macro of three dimensional objects you'd generally be using a small aperture which would probably mask most if not all of the small Focus Shift.<br /> 3. if it is macro of a flat object, then the problem could be critical (for example macro of a postage stamp's face). You could use F/4 and by definition there would be no problem. You'd could use Live View if available (or the viewfinder) and stop down to the shooting aperture to achieve focus on the exact plane of the face of the image - (F/5.6 or F/8 would be suitable, I suggest) and that would solve the problem.</p>

<p>The internet can easily hype up problems way beyond their actual and/or potential impact.</p>

<p>*</p>

<p>BTW, if you did not know, the Image Stabilization on that lens is the "hybrid" IS, same as IS on the the EF 100F/2.8L IS (Macro) lens - which, in addition to its uses for "normal photography" it is especially a very good IS for (hand held) macro work.</p>

<p>WW</p>

[PuppyDigs]

<p>I've the 24-70 f/4L IS every week for two years and haven't noticed focus shift. Doesn't mean it isn't there but it doesn't show in typical landscape shooting. I use the macro mode to shoot small products--stopped down and with studio lights--and focus seems spot on but I'm rarely at the extremes of the magnification.</p>

[Dave410]

<p>The whole thing is interesting because some reviewers only talked about the problem when the lens was in macro mode and others talked about it all the time. I also found this video on YouTube showing a focusing problem, although it's a different problem than others have reported. In any case, all this disqualifies the lens for me. Cheers.</p>

<p><a href="

<p>Oops, I took a closer look and I think that's the 24-70<strong> f/2.8</strong> lens, even though this video came up on Google search for the 24-70 <strong>f/4</strong>. Interesting video, however, so I'll leave it up.</p>

[William Michael]

<blockquote>

<p>"I took a closer look and I think that's the 24-70<strong> f/2.8</strong> lens"</p>

</blockquote>

<p>Dave, I just watched that video. The focusing issue with the that lens was a front/back focusing error and not the "<em>focus shift</em>" issue I referenced for the 24 to 70 F/4 IS.</p>

<p>For clarity so we all understand what we are discussing - the '<em>focus shift</em>' issue for the 24 to 70 F/4 IS which I was commenting upon is explained thus:</p>

<p>1. In macro mode, (and normal mode too, but it really doesn't matter for normal shooting), it would be typical that Focus is achieved when the lens is at F/4.</p>

<p>2. Once that focus is achieved <strong>if the shot is made at any aperture other than F/4</strong> the Plane of Sharp Focus shifts (very slightly). </p>

<p>3. This <em>'focus shift'</em> issue can be eliminated by achieving focus whilst the aperture is at the Shooting Aperture.</p>

<p>4. The <em>'focus shift'</em> issue probably would never be noticed during normal workflow, even if the lens were being used in Macro Mode if:<br>

a) the Shooting Aperture were small enough to provide an adequate DoF;<br>

b) and/or the Magnification were not very large;<br>

c) and/or the Object were three dimensional<br>

- any or all of which might cover-up the issue. </p>

<p>WW</p>

<p> </p>

[Marcus Ian]

<blockquote>

<p>3. This <em>'focus shift'</em> issue can be eliminated by achieving focus whilst the aperture is at the Shooting Aperture.</p>

</blockquote>

<p>Unfortunately (in relation to this problem), as we all know, by default AF <em>always</em> achieves focus WO (f/4 for this lens) in the EOS system.</p>

<p>Even manual focus is, by default, executed WO. Only by using the DOF preview button while MFing would you be able to eliminate the fault.</p>

<p>However, that does lend itself to a potential FW solution. All it would have to do is to have the camera activate DOF preview during normal focusing... of course the camera might not be able to achieve focus at all... details!</p>

 

[William Michael]

<blockquote>

<p><em>"Only by using the <strong>DOF preview button while MFing</strong> would you be able to eliminate the fault."</em></p>

</blockquote>

<p>Yes - that's what I was implying - <strong>sorry </strong>I didn't spell it out - <strong>thanks</strong> for highlighting that.</p>

<p>*</p>

<blockquote>

<p>details!</p>

</blockquote>

<p>Yes - before you ask the next question of me . . . I tested it before wrote my <em><strong>first post</strong>, </em>where I mentioned:</p>

<p><em>"3. if it is macro of a flat object, then the problem could be critical (for example macro of a postage stamp's face). You could use F/4 and by definition there would be no problem. You'd could use Live View if available (or the viewfinder) and stop down to the shooting aperture to achieve focus on the exact plane of the face of the image - (F/5.6 or F/8 would be suitable, I suggest) and that would solve the problem."</em></p>

<p>I used as a worse case, with no Live View, using an EOS 20D.</p>

<p>Holding the DoF Preview at F/5.6 and F/8 there is no AF confirmation red light, but there is very reasonable viewfinder clarity to use the <em>wiggle the focus turret back and forward technique</em> to accurately to achieve good focus manually and find an accurate focus plane at those apertures. I was under diffused daylight indoor room light (about EV =10). I used a 50mm prime at a close shooting distance, using the DoF preview depressed and the Manual Focus Ring.</p>

<p>I also tried the <em>move the camera in and out technique</em> and that works fine too.</p>

<p>Thanks for keeping me on my toes!</p>

<p>WW</p>