Why is autofocus off from factory?

heron_AI

heron_AI

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Mattias
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Got my new Sigma 18-35/F1.8 DC today and it didn't take long to notice that the AF was off. Luckily I have the Sigma USB Dock and I have started calibrating it (which is quite tedious), I have a few focal lengths at infinty left to do but the day light is fading. Anyway, AF is atleast, or near, -15 points, which means I have compensate with +15. The adjustment range is from -20 to +20. My question is how it can be so far off, and why is it off at all. I could understand using an FF lens on my crop sensor camera, but this lens is made for Nikon DX. Any ideas?

Thanks.
 
•


Cameras and lens makers all have tolerances in the building
of their equipment. Some makers, and that justifies some dif-
ference in price, have greater tolerances… may that be optic,
mechanic or electronic components tolerances.

I am a chronic Nikon user and this manufacturer has, for the pro
gear, narrower tolerances margins than many others. Nonethe-
less, the -/+ 20 scale IS within the foreseen tolerances.

So, your +15 is nothing to worry about… have a good time!
 
Kodiak Qc said:
•


Cameras and lens makers all have tolerances in the building
of their equipment. Some makers, and that justifies some dif-
ference in price, have greater tolerances… may that be optic,
mechanic or electronic components tolerances.

I am a chronic Nikon user and this manufacturer has, for the pro
gear, narrower tolerances margins than many others. Nonethe-
less, the -/+ 20 scale IS within the foreseen tolerances.

So, your +15 is nothing to worry about… have a good time!
Click to expand...

Ok, thank you.
 
The primary cause is that the AF module is in a different place to the sensor so unless both happen to be in perfect alignment then there will nearly always be a bit of AF error and with a fast lens you are more likely to notice it. Lens calibration also plays a part.

This is one of the advantages of mirrorless cameras, the AF points are actually on the sensor so the chances for error are greatly reduced.
 
Nawty said:
The primary cause is that the AF module is in a different place to the sensor so unless both happen to be in perfect alignment then there will nearly always be a bit of AF error and with a fast lens you are more likely to notice it. Lens calibration also plays a part.

This is one of the advantages of mirrorless cameras, the AF points are actually on the sensor so the chances for error are greatly reduced.
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If the problem was in the camera, then my other lenses would need calibration as well. I have a Sigma 150-600 C and I have scrutinized the AF with that lens thoroughly and it's absolutely dead on from factory. At one point I was considering an earlier version of Sigmas normal/wide zooms, but I was afraid that the AF would be off, and since only the newer series of Sigma lenses can be adjusted through the USB dock I would have needed to send it back. My camera is a D5600 and does not have AF adjustment either.
Like, what is the real reason that this happens?
 
If it's that far off from new I'd send it back for a replacemen tbht. Whilst there are tolerances you have to accept, my experience has been that when a lens needs extreme adjustments (12+) there's always some settings/distances that consistently give results that are softer than others. Obviously YMMV.
 
heron_AI said:
Like, what is the real reason that this happens?
Click to expand...

As has been said, tolerances, and sometimes they work against each other and in those cases the differences become apparent.

You could quite easily put all of your 'good' lenses on another camera and they would all be out, that's just how it is.
 
heron_AI said:
If the problem was in the camera, then my other lenses would need calibration as well.
Click to expand...
The imprecision, tolerance, it from both the lens
and the body… but since one can't do anything
with the lens — I can't and wouldn't dare — the
body is the place to look into.

As the sensor is fixed on a board, the AF sensors
— that are and independent system and built in
separately — may be tweaked and fine tuned.

All my 4 bodies are fine tuned with all my 16 lenses
and the tweaks are saved and recognized automa-
tically every time I change lens.

Yes, you counted well, that adds up to 48 fine tunes!

EDIT That is 64 fine tunes!
 
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GreenNinja67 said:
That's more than the Beatles had!
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I recognize you there, Terry!
:ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO:

Maybe I am a bigger fan than you are
but, I my book, they had a lot more!


I forgot to mention that my bodies
permit up to 20 saved fine tunes.
 
Kodiak Qc said:
The imprecision, tolerance, it from both the lens
and the body… but since one can't do anything
with the lens — I can't and wouldn't dare — the
body is the place to look into.

As the sensor is fixed on a board, the AF sensors
— that are and independent system and built in
separately — may be tweaked and fine tuned.

All my 4 bodies are fine tuned with all my 16 lenses
and the tweaks are saved and recognized automa-
tically every time I change lens.

Yes, you counted well, that adds up to 48 fine tunes!
Click to expand...
Isn't that 64?
 
MatBin said:
Isn't that 64?
Click to expand...



Yes… indeed!
I was telling my older son to put the 12 light stands
in the truck for tomorrow and I hung on that number! :banghead:

Thanks Matt!
 
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snerkler said:
If it's that far off from new I'd send it back for a replacemen tbht. Whilst there are tolerances you have to accept, my experience has been that when a lens needs extreme adjustments (12+) there's always some settings/distances that consistently give results that are softer than others. Obviously YMMV.
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Thank you. I have now e-mailed the seller and Sigma Finland for technical advice. Will update you on what the say.
 
heron_AI said:
Thank you. I have now e-mailed the seller and Sigma Finland for technical advice. Will update you on what the say.
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Be careful with all this as you may end up with lenses that are good on your camera and then disappointing on your next. This is a good and simple explanation on the possible issues...

https://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths/

From that link...

"Addendum I recently saw the greatest real life example of this ever, in an online forum where the poster states ’Canon’s New XX camera sucks’ (I’m eliminating names so the bots don’t pick this up and repeat it.) He goes on to say he had a body for several years, and a hand picked collection of lenses that he knew were perfect because he’d gone through several copies of each to get the sharpest one. Now he bought a new body and all his lenses sucked, and he’d now exchanged bodies twice and they still all sucked. So here is the perfect example of a person starting with a camera at the edge of tolerance, choosing through multiple selection a set of edge-of-tolerance lenses, and now generalizing that all the new bodies suck. The sad part is the new body has microfocus adjustment and he never even tried it. Just sent copy after copy back to the store."
 
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My EOS 1000 35mm film slr had a problem from the factory. I had no idea it what was wrong in the days before the internet. All I could see was soft photos. Sent it to Canon and the difference was night and day. Touch wood all my three other Canons are fine and my Sigma 50 ART works great on my 6D on all AF points. I now include the problems of AF adjustment in future camera purchases as my lens collection has grown.
 
I have done some more testing/calibrating of the four focal lengths in Sigma Optimization software (18, 24, 28 and 35) at ~2 meters. Noticed I couldn't get the parameters right and did some investigation. Turns out that the focus is different for ex. 24mm depending on whether I've been shooting at 18mm or 35mm before. I.e. if I focus and shoot at 35mm and then zoom to 24mm, the lens will back focus, if I focus and shoot at 18mm and then zoom to 24mm, it will front focus, and there's a large difference.
This can't be normal, right?
 
heron_AI said:
I have done some more testing/calibrating of the four focal lengths in Sigma Optimization software (18, 24, 28 and 35) at ~2 meters. Noticed I couldn't get the parameters right and did some investigation. Turns out that the focus is different for ex. 24mm depending on whether I've been shooting at 18mm or 35mm before. I.e. if I focus and shoot at 35mm and then zoom to 24mm, the lens will back focus, if I focus and shoot at 18mm and then zoom to 24mm, it will front focus, and there's a large difference.
This can't be normal, right?
Click to expand...
It can! Back in the day when I used to adjust technical equipment for a living, we always adjusted from a low setting to a high setting. If the equipment was already on a higher setting than we wanted, we would adjust down below the setting we wanted and then up to the required setting. That way, the play in the linkages was always consistent.
 
john.margetts said:
It can! Back in the day when I used to adjust technical equipment for a living, we always adjusted from a low setting to a high setting. If the equipment was already on a higher setting than we wanted, we would adjust down below the setting we wanted and then up to the required setting. That way, the play in the linkages was always consistent.
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You're right. Just got off the phone with a service technician and I could send it in but then I would have to send the camera as well (for lens calibration). He did not think the lens is flawed, if it focus correctly with live view then the lens is ok.
So I'm gonna get the af as good as possible and try to use the technique you described.

Thanks.
 
heron_AI said:
You're right. Just got off the phone with a service technician and I could send it in but then I would have to send the camera as well (for lens calibration). He did not think the lens is flawed, if it focus correctly with live view then the lens is ok.
So I'm gonna get the af as good as possible and try to use the technique you described.

Thanks.
Click to expand...
Hmmm I'm not convinced by what the technician told you tbh. Contrast detect (live view) and phase detect are two very different systems. If a lens didn't focus spot on in live view I'd be very worried.
Can't help but think you've been a bit fobbed off tbh. How old is the lens?
 
snerkler said:
Hmmm I'm not convinced by what the technician told you tbh. Contrast detect (live view) and phase detect are two very different systems. If a lens didn't focus spot on in live view I'd be very worried.
Can't help but think you've been a bit fobbed off tbh. How old is the lens?
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I asked him if he thought the lens was flawed, and he asked me if it focus correctly with live view - which it does - then the lens is ok. I have gone through a couple of iterations setting the tuning parameters and now I'm satisfied. At the longer focal distances the values are in the range of 6-11, with 16 being the highest at 0.28 meters.
I'm a bit curious though, what do people do if they have a lens and a camera that don't support calibration and the AF is off? Since incorrect AF seems to be really common.

The lens is new.
 
heron_AI said:
I asked him if he thought the lens was flawed, and he asked me if it focus correctly with live view - which it does - then the lens is ok. I have gone through a couple of iterations setting the tuning parameters and now I'm satisfied. At the longer focal distances the values are in the range of 6-11, with 16 being the highest at 0.28 meters.
I'm a bit curious though, what do people do if they have a lens and a camera that don't support calibration and the AF is off? Since incorrect AF seems to be really common.

The lens is new.
Click to expand...
Well I wouldn't say it's flawed, but it's certainly not great in terms of 'communication' with the camera using phase detect.

Whilst it's true that a lens can behave well on one camera and not on another, from my experience they've tended to be fairly similar across numerous bodies. Maybe not exactly the same MA needed but if it's needed quite a lot on one it's needed quite a lot on the others. Those that have needed no MA on one have not needed MA on the others either. I'm not sure whether those examples above are in extreme cases, whether my experience is different to most, or whether Nikon and Canon are different in this regard.

If you have your lens set up and you're happy then maybe keep it as you don't know what you'll get if you swap it (although I'd still probably swap it ;)). But all I can say is thank god for the sigma dock ;)
 
heron_AI said:
I asked him if he thought the lens was flawed, and he asked me if it focus correctly with live view - which it does - then the lens is ok. I have gone through a couple of iterations setting the tuning parameters and now I'm satisfied. At the longer focal distances the values are in the range of 6-11, with 16 being the highest at 0.28 meters.
I'm a bit curious though, what do people do if they have a lens and a camera that don't support calibration and the AF is off? Since incorrect AF seems to be really common.

The lens is new.
Click to expand...


Live view uses the contrast detect sites on the sensor. As I said in post #4.
 
Nawty said:
Live view uses the contrast detect sites on the sensor. As I said in post #4.
Click to expand...

Like dedicated contrast detect sites? On Nikon? I thought the camera evaluates the sensor data to determine which focus produces the image with the highest contrast.
Anyway, I don't get the point of your post.
 
heron_AI said:
Like dedicated contrast detect sites? On Nikon? I thought the camera evaluates the sensor data to determine which focus produces the image with the highest contrast.
Anyway, I don't get the point of your post.
Click to expand...
Autofocus using the viewfinder is very different to that from the live view. Live view is contrast detect and therefore like mirror less cameras should always be spot on, regardless of whether the lens is not properly calibrated.

Phase detect autofocus in DSLRs is more complicated and uses a lot of wizardry to get fast accurate focus. However, it's not necessarily as accurate as contrast detect and has tolerances (generally 1/3 depth of focus). However, the lens and camera have to communicate and work in sync to nail focus, and if they are not perfectly in sync you can get front or back focus. You can even find that lenses front focus on close subjects and then back focus on more distant subjects. Getting lenses to nail focus at every aperture, every focal length (if using a zoom), and every subject distance is very tricky. That's why I like lenses that don't need a lot of fine tuning as (from my experience) they tend to be more consistent across the board.
 
snerkler said:
Autofocus using the viewfinder is very different to that from the live view. Live view is contrast detect and therefore like mirror less cameras should always be spot on, regardless of whether the lens is not properly calibrated.
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Might try live view as I've not calibrated my Nikon lens. Would it therefore be beneficial to shoot landscapes in live view only, particularly if different calibration settings are required for different focal lengths? Would a professional change the fine tuning on the fly dependant on the FL they choose to shoot with and shoot through the viewfinder? Or as you say just make sure their lens and body are a good match, calibrate at one commonly used FL and accept any minor back and forward focusing on other FLs?
 
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Gil Bev said:
Might try live view as I've not calibrated my Nikon lens. Would it therefore be beneficial to shoot landscapes in live view only, particularly if different calibration settings are required for different focal lengths? Would a professional change the fine tuning on the fly dependant on the FL they choose to shoot with and shoot through the viewfinder? Or as you say just make sure their lens and body are a good match, calibrate at one commonly used FL and accept any minor back and forward focusing on other FLs?
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Firstly I would say don't get too hung up on it. If you don't notice obvious focussing issues day to day then leave alone and don't start looking for issues that aren't really there.

As for landscapes you can use either or, and some use manual. As you're working with large DOF you're not going to see any front/back focussing errors. That being said I always shoot live view if using a tripod, simply because I like to shoot from lower than my eyeline.

Would pros change the MA constantly? I doubt it, there's no time. But if your lens is calibrated/MA'd well the differences in sharpness between focal lengths, distances etc should be pretty negligible. There may be a hair's difference but nothing to get hung up on. Besides, just to put another spanner in the works you may see a difference using the outer AF points compared to the centre one. But again these differences should be negligible and nothing to get hung up on.

Of course, this is just my opinions, YMMV.
 
snerkler said:
Firstly I would say don't get too hung up on it. If you don't notice obvious focussing issues day to day then leave alone and don't start looking for issues that aren't really there.

As for landscapes you can use either or, and some use manual. As you're working with large DOF you're not going to see any front/back focussing errors. That being said I always shoot live view if using a tripod, simply because I like to shoot from lower than my eyeline.

Would pros change the MA constantly? I doubt it, there's no time. But if your lens is calibrated/MA'd well the differences in sharpness between focal lengths, distances etc should be pretty negligible. There may be a hair's difference but nothing to get hung up on. Besides, just to put another spanner in the works you may see a difference using the outer AF points compared to the centre one. But again these differences should be negligible and nothing to get hung up on.

Of course, this is just my opinions, YMMV.
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is this with Lab coat on or off ?:)
 
heron_AI said:
Got my new Sigma 18-35/F1.8 DC today and it didn't take long to notice that the AF was off. Luckily I have the Sigma USB Dock and I have started calibrating it (which is quite tedious), I have a few focal lengths at infinty left to do but the day light is fading. Anyway, AF is atleast, or near, -15 points, which means I have compensate with +15. The adjustment range is from -20 to +20. My question is how it can be so far off, and why is it off at all. I could understand using an FF lens on my crop sensor camera, but this lens is made for Nikon DX. Any ideas?

Thanks.
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No way should it be that off. I'd be sending that lens back.
 
odd jim said:
No way should it be that off. I'd be sending that lens back.
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Hmm.. well I might just do that. I don't trust the AF and it's more critical with such shallow DOF. I'm gonna talk to the seller on Monday.
 
heron_AI said:
Hmm.. well I might just do that. I don't trust the AF and it's more critical with such shallow DOF. I'm gonna talk to the seller on Monday.
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Where did you buy from?
 
heron_AI said:
From a local store in Finland. They don't seem to have customer service open at Saturdays.
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Not sure how they operate over there. Do they have the same 14 day no quibbles return policy as the UK/EU?
 
I can't make up my mind about this particular lens, should I send it back or not? I've seen people complaining about AF unreliability on the web, I'm afraid I will have to wait just to get another lens with similar issue.
Here are two pictures, one sample image and one showing the settings I have in the lens. What do you think? Thanks.

ISO100 1/100 f/1.8 35mm
https://www.dropbox.com/s/0yv1o0dp7caz3gj/DSC_0011.JPG?dl=0
https://www.dropbox.com/s/tn6tgvdiigi6zeq/sigma 18-35m focus settings.JPG?dl=0
 
heron_AI said:
I can't make up my mind about this particular lens, should I send it back or not? I've seen people complaining about AF unreliability on the web, I'm afraid I will have to wait just to get another lens with similar issue.
Here are two pictures, one sample image and one showing the settings I have in the lens. What do you think? Thanks.

ISO100 1/100 f/1.8 35mm
https://www.dropbox.com/s/0yv1o0dp7caz3gj/DSC_0011.JPG?dl=0
https://www.dropbox.com/s/tn6tgvdiigi6zeq/sigma 18-35m focus settings.JPG?dl=0
Click to expand...
Why not go to the store and try another one before you make your mind up? You should be able to tell if it's off like the one you have or not.
 
snerkler said:
Why not go to the store and try another one before you make your mind up? You should be able to tell if it's off like the one you have or not.
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I ordered it online because it's a long trip (it includes 5-6hrs on a ferry one way), so the only sensible thing to do is to send it via mail. It's so much cheaper than at the local stores. They actually had a discount on selected ART lenses during June so they were a lot cheaper than what can be found on international sites like adorama, amazon, bhphotovideo etc.
 
heron_AI said:
I ordered it online because it's a long trip (it includes 5-6hrs on a ferry one way), so the only sensible thing to do is to send it via mail. It's so much cheaper than at the local stores. They actually had a discount on selected ART lenses during June so they were a lot cheaper than what can be found on international sites like adorama, amazon, bhphotovideo etc.
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Unfirtunately it's a bit of a lottery with lenses, Sigma have been renowned for it in the past and whilst much better now they still have a few issues with QC. No manufacturer is perfect though and Ive had a Nikon prime that went back due to needing +18 MA.
 
Not just lenses, my Nikon D610 ended up going off to be calibrated as with pretty much all lenses it was beyond the capability of the in camera adjustment, once corrected I didn't bother with lens adjustment as they were all close enough.
 
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