Sigma's Dock.. a doodle doo?

[texshooter]

Sigma's Art series lenses come with a "dock" for calibrating the lens. My first thought was: That's cool!   But now  I'm wondering why is such a dock necessary. Canon has no such thing for their lenses. So I'm left with two alternative suspicions: 1) The engineers at Sigma are such precisionists, that they gifted us with this tool to render their lenses better than perfect, or 2) Sigma's lenses fit Canon/Nikon cameras so poorly that they had no choice but to burden us with this thing so to get the lens in working condition. Which is it?

Sincerely,
Confused Shopper

[DeanChriss]

If I'm not mistaken the Sigma dock allows lens AF calibration at four different subject distances and more than two focal length settings for zooms. Canikon don't do that. I don't know whether Sigma needs this due to some design trait while Canikon does not, or whether having more calibration points gives Sigma more accurate focus over a wider range of circumstances than Canikon lenses. I suspect the latter. For instance, Canon first provided microadjustment of zooms only at the telephoto setting and now they provide calibration at both the telephoto and wide setting. Calibrating intermediate focal length settings certainly can not hurt AF accuracy and may help noticeably. More calibration points always make for more accuracy unless the "curve" is so predictable that only one or two points will suffice. The same is true for calibrating at different distances. The only unknown is whether Canikon lenses would benefit as much as Sigma lenses from a similar scheme. In any case I don't think it's a matter of poor fit on Sigma's part.

[chez]

Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances?

[DeanChriss]

Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances?

Canon and Nikon both have lens calibration, AKA micro-focus focus adjustment. Both of them keep the adjustments in the camera, not the lens as Sigma does. Using Canon as an example, you calibrate the focus at one distance, which they specify as 50 times the focal length, though many use 25X instead. You calibrate their zoom lenses at only the telephoto end on older cameras. Newer cameras are calibrated at both the telephoto end and at the wide end. Sigma takes this a step further by calibrating zooms at the telephoto and wide end as Canon does, and also at intermediate focal lengths. And, instead of calibrating at only 50x the focal length, they are calibrated at 4 different focus distances, from near to far. It's better to keep calibrations in the camera since each camera may be different, but Sigma has no control over that so it's stored in the lens.

edit: I should also add that calibrating a lens at one specific distance does *not* necessarily mean any or all other distances will have the same focus accuracy as the calibrated distance. If they did, manufacturers wouldn't specify any particular calibration distance. Only the particular distance (and zoom setting for zooms) can be guaranteed accurate. The rest are within some tolerance of that, and reducing tolerance is what MFA is about. That's all a matter of linearity of the design. If these mechanisms were perfect, you wouldn't need MFA adjustments at both ends of the zoom range, for instance.

[michael]

Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances?

The reason micro-focus adjustments are needed is that autofocus is performed by a separate sensor mechanism from the camera's imaging sensor. Getting these in perfect alignment with all lenses at all distance at all times is simply impossible.

This is not necessary with so-called mirrorless cameras. These have the AF system built into the imaging sensor itself, therefore there is no need for microfocus adjustment. Up until recently Contrast Detection AF was used but now Phase Detection is found right on the sensor. The new Sony A7rII has 399 Phase Detection points covering some 60% of the sensor area.

All other things being equal, this is one of the great attractions of mirrorless cameras.

Michael

[razrblck]

You can also update the lens firmware. If any of the big players decides to change their camera firmware in such a way that makes your Sigma lens stop being recognized by the body, they can push an update to fix that and you can keep using your lens. Up until now you'd have to send it to support and get it rechipped, which would take time and money.

[texshooter]

Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances?

Canon lenses don't need 16 AFMA's per lens. But apparently Sigma does. That's a whole lot'a calibrate'n go'n on.

[Bart_van_der_Wolf]

Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances?

How much are you willing to pay extra for tighter manufacturing tolerances (and handling induced lens decentering, wear from usage, and electronic drift)? As camera resolutions go up, these will drive tolerances down only further.

The reason Sigma offers a solution, is also due to the fact that they make the lenses for different camera systems.

Cheers,
Bart

[michael]

Canon lenses don't need 16 AFMA's per lens. But apparently Sigma does. That's a whole lot'a calibrate'n go'n on.

I think that you're looking at this the wrong way. The more calibration points one has, the better the match between what the sensor is seeing and what the AF module is seeing. Having less calibration points simply means that there is not as good a match as with a system that has more.

More work to calibrate, to be sure, but also higher accuracy.

Michael

[Simon J.A. Simpson]

All other things being equal, this is one of the great attractions of mirrorless cameras.

Michael

Or use a camera with ‘live view’.

[MarkL]

Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances?

Yes. What is more, they leave it to the user to calibrate their bodies/lenses themselves with no guidance rather than just writing a focus profile to the firmware at test stage.

Sigma's solution is a step forward as it is more intelligent than a crude offset but still less than ideal (ie. gear that actually works properly from the factory).

[Otto Phocus]

I am pretty sure that one of these days all the lens manufacturers will offer a dock or dock like functionality. Sigma was just the first.

[texshooter]

The impression I'm getting from users is that the Sigma Art lenses are superb after you calibrate them using their dock system. However, if you don't calibrate with their dock, you are SOOL.

[Rand47]

Canon lenses don't need 16 AFMA's per lens. But apparently Sigma does. That's a whole lot'a calibrate'n go'n on.

If you read up on micro focus adjustments, ESPECIALLY on zoom lenses, I don't think you'd make the statement above.  It just ain't that simple.  Go to the Q&A and forums on the sites that sell the devices that are used for micro focus adjustment.  You'll be surprised.

Rand

[texshooter]

If you read up on micro focus adjustments, ESPECIALLY on zoom lenses, I don't think you'd make the statement above.  It just ain't that simple.  Go to the Q&A and forums on the sites that sell the devices that are used for micro focus adjustment.  You'll be surprised.

Rand

I've used both the Focal system and Lens Align. They both advise to calibrate the lens using the focus distance most often used. So yes, this implies that Canon/Nikon lenses were not (and cannot be) designed to focus light perfectly at every focus distances.  Having said that, I've never heard Canon/Nikon users complain that calibrating their lens at a singular focus distance left them disappointed with their lens performance at every other distance.   Nor has Canon/Nikon ever offered (assuming because it was never demanded) a 4 distance/4 focal length AFMA dock system similar to what Sigma has invented.   Got me thinking either 1) If it's too good to be true then it ain't, or 2) Sigma has just revolutionized lens calibration.

[NancyP]

One of the fears that potential third party lens buyers have is that a new camera may come out, and they won't be able to use the third party lens on the new camera. There's also the mount switching service that Sigma has - all lenses designed such that they can be adapted to any mount. So, if you like your Sigma 120-300 f/2.8 for Canon, but switch to Nikon, you can pay Sigma $150.00 and they will swap mounts on your lens - then you apply the dock to it to recalibrate for your particular new camera.

[Otto Phocus]

The impression I'm getting from users is that the Sigma Art lenses are superb after you calibrate them using their dock system. However, if you don't calibrate with their dock, you are SOOL.

No that is just stuff that is being repeated on the internet.

I have two Sigma Art lenses and using Focal they needed a "2" in adjustment which is practically unnoticeable.  I belong to two photography groups and none of the members has had problems with the focusing of the Art lenses.

I do not believe that anyone is having any more or less problems with Art lenses than with the other lenses being sold. There are always bad copies no matter what the manufacturer is.

[shadowblade]

Yes. What is more, they leave it to the user to calibrate their bodies/lenses themselves with no guidance rather than just writing a focus profile to the firmware at test stage.

Sigma's solution is a step forward as it is more intelligent than a crude offset but still less than ideal (ie. gear that actually works properly from the factory).

That's not necessarily the ideal - just the easy, 'Apple-style', all-in-one-package solution.

Look at professional equipment in most fields - most are not all-in-one packages, but endlessly customisable and adjustable, for different operating conditions. This goes for everything from prostheses used in orthopaedic surgery to precision rifle scopes. You don't just take a pre-packaged hip joint and whack it in a person, or a pre-packaged rifle scope and stick it on a gun. You take the parts, then customise, adjust and calibrate it until you get the perfect piece of equipment for the job you're trying to do. I welcome the same approach in a camera system, and like the fact that Sony's A7 series has also, to some degree, made camera systems modular - that is, you take a body from one place, a lens from another and accessories from a third party, to put together an optimal kit for the task, rather than just taking a pre-packaged, all-in-one solution (with all its upsides and downsides) from a single place.

[GrahamBy]

How much are you willing to pay extra for tighter manufacturing tolerances

As noted by Michael, calibration is needed because the focus is detected by separate sensors to the image sensor. The tolerances in question are therefore about about correcting for differences in the length of the optical path to the two different sensors. Both are in the body.

In other words, the manufacturing tolerances that Sigma is correcting for are actually those of the body manufacturer...

[orc73]

When I bought my Sigma 50mm Art lense, I was planing about buying the dock or at least borrow it from a friend. I then found out, the calibration is for 3 different distances(all quite close) which I never use at all - my models are usualy about 3meters away from me. So I did the calibration for the 3meters distance on my canon.

Additionally, you have to calibrate all 3 distances in a try and error method. You always have to put the lense on the dock to adjust, then back on the camera to test it, until focus is correct.

As my usual distance is not covered and the process is a bit low tech, I decided to safe the money.