24-70 f/4 Focus Issues. Is there a Fix?

[jeff51]

Is there a fix for the variable back focus problem?

I just got a new (referb) 24-70mm f/4 direct from the Canon site. They had an excellent deal going for December. Interesting to note that it came packed in a Canon super zoom camera box with no instructions. (Took me a minute to figure out the macro lock thingie).

It suits my needs very well. I live in the 3-7 foot distance at higher f stops in the 40-70mm range. The IS lets me do away with the strobes that I have been using to freeze my shaky old hands. Using it on a 5D-M4.

After playing around with the lens, I started thinking I had soft version or I was missing focus. So I started testing and noticed that as I stopped the lens down, the focus would shift to the rear.

Google informed me that I am not alone.

At about 3’ from the target, at 70mm at f/4 the focus is just behind the focus point. About a -5 correction will fix it. By f/20 the focus has shifted enough that a -20 adjustment just barely get me back to the focus point. This happens at all focal lengths. It’s just more obvious at the longer end.

The lens is in its normal focus setting – not the macro mode.

Putting my old first version 24-70mm f/2.8 through the same tests shows a very slight back focus that stays constant as the f stop changes. This I can live with.

But I really (really) like the size, weight, and the IS of the f/4 version. I was going to sell off the old 2.8 if the f/4 was a winner.

Is there a fix for this?

Or is there to be no joy to the world this X-Mass season, and I’ll have to send it back?

Thanks for your help, All the Best, Jeff

 

[gium]

Focus shift is indeed a known problem for this lens, but some users say it doesn't bother them or they haven't noticed it.
Unfortunately there is no fix for this. If it bothers you (and I would understand that) you should return it while you still can.

The 24-105L is heavier, as sharp in the center, a bit softer in the corners wide open and has more reach. And it doesn't have this focus shift issue, so you might want to go for that one.

Good luck.

 

[jeff51]

glum, Thanks for the reply.

Do all copies of the 24-70 f/4 have the focus shift problem or is is possible to get a version without it?

I really like the lens, but for the stuff I do, the focus shift is a deal killer. Just can't stand seeing my focus not spot on where I want it.

Oh and Merry Christmas, Happy Holidays, or Bah Humbug (as the case may be).

Thanks again, Jeff

 

[arty H]

I don’t have the 24-70, but do have the 24-105F4 and like it very much. I looked at reviews at Optical Limits and Lenstip, and both sites describe problems with spherical aberration- focus shift when stopping down. It seems to be a problem, especially where you would want to use the lens for portraits.

 

[Steve Balcombe]

glum, Thanks for the reply.

Do all copies of the 24-70 f/4 have the focus shift problem or is is possible to get a version without it?

They do. When I got my first, I returned it because I thought it was faulty, and the retailer supplied another. The second copy was exactly the same so I investigated further and soon established that (as you have learned) it is a design fault. For me, a major reason for choosing the 24-70/4L IS was the very close focusing, and I would usually stop down for depth of field. This is of course where the back focus is at its worst, so I returned the second copy for a refund and continued using my old faithful Sigma 18-50 on my crop bodies.

A year or two later I bought my first full frame body, a 5D4, but I still didn't have a full frame standard zoom. In the absence of any other compelling option I decided to buy yet another 24-70/4L IS to cover all those everyday shooting requirements. For people I mostly shoot wide open - it's superb at f/4 - so the back focus doesn't occur. For landscapes and other distant subjects the back focus is not apparent. I'm not sure if it doesn't occur at these distances, or if it is masked by the large depth of field, but either way it doesn't really matter as I'm getting good shots. Now and again I let myself be drawn into taking close ups and every time I regret it. (I know, doing the same thing and expecting a different outcome is the first sign of madness...)

I now have an R5 so at some point I will pick up an RF 24-105/4L IS and that will be the end of the problem.

I really like the lens, but for the stuff I do, the focus shift is a deal killer. Just can't stand seeing my focus not spot on where I want it.

Yep.

--
https://www.flickr.com/photos/stevebalcombe/ or
http://www.flickriver.com/photos/stevebalcombe/popular-interesting/

 

[jeff51]

glum, Thanks for the reply.

Do all copies of the 24-70 f/4 have the focus shift problem or is is possible to get a version without it?

They do. When I got my first, I returned it because I thought it was faulty, and the retailer supplied another...

Now and again I let myself be drawn into taking close ups and every time I regret it. (I know, doing the same thing and expecting a different outcome is the first sign of madness...)

I now have an R5 so at some point I will pick up an RF 24-105/4L IS and that will be the end of the problem.

I really like the lens, but for the stuff I do, the focus shift is a deal killer. Just can't stand seeing my focus not spot on where I want it.

Yep.

Well foo... I tried it outdoors at mid distances and it's just great. Looking at distance shots where there is only a object against the sky, at small f stops, I think it's missing the focus still.

I'd happily give up the "macro" if it would get rid of the focus shift. Nothing else seems to focus as closely in this range, which is what I was looking for. That and the IS.

Got the "other" f/4, the 70-200mm II. Wow, except at 200, this thing is a razor. Even there it's darned good.

Just wish it focused closer.

Thanks for the all the info, All the Best, Jeff

 

[Alexander Rosenwald]

I do own the EF 24-70 4.0 and did some testing about the focus shift issue. That are my results:

1. There is no recognizable focus shift in macro mode.

2. Focus shift between f4 and f11 at 70 mm and minimum focus distance (38 cm) is about 3 - 4 mm. This is significant and will ruin most pictures.

3. From a focus distance of 3 feet and up there is no recognizable focus shift. It stays well within the DOF.

4. At 24 mm focus shift stays within the DOF. Not an issue.

The test was performed with a lens calibration target and the camera both on tripods. My copy is from 2015. Camera used is a EOS R.

Since I like that lens very much I live with its focus shift. Close up I use the macro mode and for portrait work at 70 mm I stay wide open anyway.

The RF 24-105L 4.0 would be a perfect replacement for that lens but I still own a full frame DSLR and a film SLR. Both work with the EF lens but not with the RF.

 

[jeff51]

Alexander,

Thanks for the additional info. I see the same in the copy I have. At 24 mine misses enough at f/20 that without a correction, I miss the focus point by a hair.

Seems odd that Canon let something like this out in the wild without noticing the problem and fixing or redesigning the lens for a II version. Heck it's been how long since this lens was released?

I'm going to fart around with mine some more, maybe try a middle f-stop correction to see if I can stand it. Most likely going to have to send it back.

I'd pay good money for an IS version of the first version of the 24-70mm f/2.8. That one focuses closer than the newer sharper II version.

I really wish the makers would put out some IS primes in shorter focal lengths that focus a bit closer. I don't need the speed, I need the depth of field at arms length. Framing the shot, move just a bit closer to get the perspective just right - And - Crap! - Can't focus that close.

All the Best, Jeff

 

[Alexander Rosenwald]

Alexander,

Thanks for the additional info. I see the same in the copy I have. At 24 mine misses enough at f/20 that without a correction, I miss the focus point by a hair.

I did not test apertures beyond f11 because I very barely use them.

 

[Steve Balcombe]

I really wish the makers would put out some IS primes in shorter focal lengths that focus a bit closer. I don't need the speed, I need the depth of field at arms length. Framing the shot, move just a bit closer to get the perspective just right - And - Crap! - Can't focus that close.

It seems to be happening in the RF lineup, which is great to see. The RF 35/1.8 IS STM and RF 85/2 IS STM are both labelled 'Macro' although some would disagree with the macro label since they are only 1:2. What they really are is small-ish, fast-ish, primes with really good close focusing.

The inexpensive RF 24-105 IS STM kit lens also focuses down to 1:2 but for some reason it doesn't get the 'Macro' label.

I realise this is not much help to you, but my guess is there will be very few new lenses from any manufacturer for the EF mount.

--
https://www.flickr.com/photos/stevebalcombe/ or
http://www.flickriver.com/photos/stevebalcombe/popular-interesting/

 

[Ciriaco Garcia]

glum, Thanks for the reply.

Do all copies of the 24-70 f/4 have the focus shift problem or is is possible to get a version without it?

They do. When I got my first, I returned it because I thought it was faulty, and the retailer supplied another. The second copy was exactly the same so I investigated further and soon established that (as you have learned) it is a design fault. For me, a major reason for choosing the 24-70/4L IS was the very close focusing, and I would usually stop down for depth of field. This is of course where the back focus is at its worst, so I returned the second copy for a refund and continued using my old faithful Sigma 18-50 on my crop bodies.

A year or two later I bought my first full frame body, a 5D4, but I still didn't have a full frame standard zoom. In the absence of any other compelling option I decided to buy yet another 24-70/4L IS to cover all those everyday shooting requirements. For people I mostly shoot wide open - it's superb at f/4 - so the back focus doesn't occur. For landscapes and other distant subjects the back focus is not apparent. I'm not sure if it doesn't occur at these distances, or if it is masked by the large depth of field, but either way it doesn't really matter as I'm getting good shots. Now and again I let myself be drawn into taking close ups and every time I regret it. (I know, doing the same thing and expecting a different outcome is the first sign of madness...)

I now have an R5 so at some point I will pick up an RF 24-105/4L IS and that will be the end of the problem.

I really like the lens, but for the stuff I do, the focus shift is a deal killer. Just can't stand seeing my focus not spot on where I want it.

Yep.

Maybe you could switch into video mode for stopped-down focusing and continuous DOF preview, like Sony behaves with most native lenses. So focus shift won't be a problem. Yes, it has its drawbacks (aspect ratio, maybe range of shutter speed, etc) but the R5 can be configured for a quick switch from/to stills and video modes by just a single press of M-Fn, I think (and its original function could be remapped to another button).

 

[jeff51]

Live view is not the answer with this lens. The problem is that it changes it’s back focus depending on f-stop. Focus on something, and the camera used f/4, then set the lens to f/16. Take a snap and the focus point is several mm behind the original focus.

So you focus at f/4, and all is good. Change nothing and it’s behind at f8, f16 farther out still, f/22 and it moves even farther.

I’ve got the micro adjusts set so I can get mostly good focus points in the f/8-f/16. Also I can cheat and pick a nearer point with focus hold to trick the lens into doing what I want.

Still, one wonders since it would seen that all copies of this lens have this to a greater or lessor degree, why hasn’t there been a version II that fixes the issue?

All the Best, Jeff

 

[Ciriaco Garcia]

I own this lens and know the focus shift behaviour (for my typical use it usually isn't very relevant, though).

What I tried to point is that once you enter in video mode and set the aperture, the lens will be automatically and permanently stopped down to the selected aperture (unlike in the stills mode, where it is always wide open). So, if the lens is focused while in video mode, the photo will be taken perfectly nailing the wanted focus, even if the camera is returned to stills mode for the shot.

Needless to say that all of this using manual focus or if the lens is not refocused (I have a separate AF-On button, my camera doesn't focus when I press the shutter, it only meters and shoots).

The trick could also be used with a 5D/6D camera (entering in video mode; and not merely in live view, which keeps the aperture open even when exposure simulation is enabled).

Ok, that is not a fix for the lens (design) behaviour, but a potential workarround with its limitations, which start for needing separate focusing for each aperture, having less available light...

Another workarround would be to keep pressed the DOF preview buttom while manually focusing.

 

[Kederek]

This is a known flaw with the 24-70 f4 L I have owned one for many years and really like it, however, one learns to never close focus at 70mm or anywhere near it. Indeed, the flaw of the design is one part of the reason Canon enabled the somewhat unusual macro feature of this lens. It allows one to close focus at 70mm mor efficiently and with quite good results too. I use it fairly often. To digress a little, the same lens design was sometimes criticized for poor sharpness at the 50mm FL mark, however, I understand that was cleared quite some time ago. Current production copies do not seem to have the problem.

I should point out that the above noted close focusing flaw IS just for close focusing at or near the 70mm mark. Focusing at “normal” distances at 70mm are just fine. There does not seem to be a definitive point where this flaw occurs as one tries to focus closer at 70mm. A case of “you’ll know it when you see it”. Use the macro mode, it covers the close focus distance of the flawed non-macro function well, so you won’t loose anything.

Overall, an underrated lens that I have come to rely on as my main mid range. I will never go near a 24-105 f4 L again. i used to have one and it was problematic from day 1.

This 24-70 is lighter, and sharper.

D.