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Surprise discovery: Canon lenses have electronic adjustment
#1
Not only Sigma has USB dock to adjust lenses focus Canon also have it, but they never made it public.

Sent my 17-55 to Canon repairs and yes that's exactly what they did... Now the lens has perfect focusing
#2
Yeah, that's quite a smart design. Actually even some adapters have chips inside which allow adjustment of front/back focus that you can tweak so you get beeping AF points right where you need. 

 

Much easier than disassembling the whole lens to move it a fraction of a mm to get the right focus.

#3
Canon have a software plus charts the repairs guy shoots, calculations are done automatically, however dunno why none of it is public

#4
A lot of people expect a lens to be perfect focusing when it comes out of the box - which to some point should be normal. Going public and offering to all owner of 100 million + sold lenses could cause serious troubles on the support side of things. Sigma as well (as Tamron?) offer their dock not only for lens adjustments (which by the way happen to be 4 different distances at 4 differeent zoom positionsm if it's not a prime) and you can try one day for yourself to do those adjustments, toni-a  ^_^

 

Just to realize that at the end of the day the phase AF of a DLSR is a quick and sometimes correct guessing.  Tongue

#5
A friend has been trying for about 1.5 years to get his Sigma ART 50/1.4 focus right on his Canon 6D. He is about to sell the lens out of frustration.

#6
Is it worse than with fast Canon glass? I didn't count more blurred results with one or another brand, most of the times it was also me being in a hurry or haven't fully understood how to autofocus. One difficult candidate was the 18-35/1.8, when going wide there was just too much stuff in the AF frames. But that was on an APS-C DSLR. I think, on Sigma's sd quattro the lens is always tack sharp if the AF has had enough time  :lol:

#7
Although Canon lenses have indeed electronic adjustment - all AF lenses in their lens series have this, from a simple to a very complex implementation -, there are quite a few other factors at play as well. With some lenses it is possible to adjust groups or elements individually, electronically, but to solve decentering etc. a lens generally requires taking apart. Also, electronically adjusting may not be all that easy either, amongst others because of the discrete steps in focusing accuracy present.

 

My perfectly focusing 50L for example took Canon several times to get right, and the last time only because I stayed at the repair centre, explaining exactly to the technician himself how the lens behaved and what I was expecting it to do. It essentially took most of the day to get it right, and I know he did more than just adjust it electronically.

 

It depends on the lens as well,; another notoriously hard lens to fix from an AF POV is the 85L.

 

Of course Sigma has the advantage of being a follower in this respect, which allows for 20 years of experience to be built into their lenses and docking stations, and hence making it possible to greatly simplify the operation for their users. it is a great USP for them, while for Canon it likely is the name and the red ring. Smile

 

Kind regards, Wim

Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#8
Quote:Is it worse than with fast Canon glass? I didn't count more blurred results with one or another brand, most of the times it was also me being in a hurry or haven't fully understood how to autofocus. One difficult candidate was the 18-35/1.8, when going wide there was just too much stuff in the AF frames. But that was on an APS-C DSLR. I think, on Sigma's sd quattro the lens is always tack sharp if the AF has had enough time  :lol:
 

With Sigma AF on 6D are simply too many variables and the whole process is time consuming. You have to remove the lens every single time and put it on the dock to run the software. Also I'm not even so sure that that every AF point on the Canon needs the same amount of microadjustment.

 

What makes things even more complicated and frustrating is that I've seen that Sigma both back AND front focus when I had handled it. It's like the AF motor doesn't disengage when the AF is locked and it moves a bit more. I always had my doubts on this but I saw a few other individuals claim to see the same behavior. 

 

Just too much trouble for what is essentially a 50mm f/1.4 lens. It takes the same photos as my FDn 50/1.4, just sharper and less CA and stuff. Doesn't make you a better photographer in any way, doesn't really let you make THAT shot that you couldn't with any other AF 50/1.4. and is much heavier.
#9
there are 4 different distances to adjust AFMA - with a zoom it's also 4 different FL at 4 different distances, so don't complain-  it's only a prime! The way I did it was using FoCal, getting the AFMA values with Nikon and then use one AFMA and calculate the other 3 distances. So, if I got values like -5, -1, 2, -3 at 0.4, 0.8, 2 meters and ∞, I set the value of the camera to -3 (at ∞) and for the rest I used the -3 and compensated the other values. So, in the dock the same row was -2, +2, +5, 0 because I always calculated then with the final value and subtracted that form the other 3. So, it's doable. I also could have put the whole lens to the values, but my aim was one setting without Sigma values, just Nikon values, so I could use it on another body, check the situation at infinity and the rest should be fine.

 

I admit I didn't check again after setting the lens by the dock, I did that in the beginning to see if Nikon's AFMA value is roughly the same like Sigma's. I found "yes".

 

With a Canon it should be simpler, because FoCal can do the setting of AFMA automatically. With Nikon, you need to change this value manually. It IS at time consuming kind of a non-creative job, it told me things about my lenses I really didn't want to know just to become insecure with focusing afterwards.

 

If it comes to focus reliabilty, I've seen all kinds of graphs from genuine and Sigma lenses - and also, the same lens doing a second test and the graph went ballistic or flat. PDAF the way I learnt it, is a guessing rather than a reliable process. And that was with test conditions. Lighting, tripod, shutter pre-release, waiting time between mirror and shutter and a very high contrast target.

 

If the conditions become worse, you better take a couple of frames and look for the best (if it has to be wide open).

 

You're right with the other focus points - I realized I'm doing AFMA only for the center point. A little field curvature, a little incorrect adjustment of the AF-modue (which I had with the first D810, I got it exchanged by Nikon (and the other went into grey market, hahaha).

 

I wish I could say else, but the reliability curves for the 50 mm Art appear to support your findings. Equally worse was the 85/1.4 G. I think, if I took the time and just run enough tests, every lens could have a bad run.

 

And now, with mirrorless, everything is silky smooth? Not in each situation. BUT: I always can set the manual focus override. Meaning, as soon as I touch/move the focus ring, the EVF enlarges generously and I'll know in advance what's going on with my sharpness. If the object is static, that is.

 

If it's moving, it's also a guess play, just one withe the higher number of keepers  Big Grin

  


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