Luminous Landscape Forum
Equipment & Techniques => Cameras, Lenses and Shooting gear => Topic started by: texshooter on September 12, 2015, 10:16:59 pm
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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
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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.
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Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances? :o
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Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances? :o
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.
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Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances? :o
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
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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.
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Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances? :o
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.
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Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances? :o
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
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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
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All other things being equal, this is one of the great attractions of mirrorless cameras.
Michael
Or use a camera with ‘live view’.
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Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances? :o
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).
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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...
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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.
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... or 2) Sigma has just revolutionized lens calibration.
I wouldn't go that far, but I do think it means Sigma is aware that a single micro focus adjustment is sub-optimal and has improved the situation considerably. When I was doing research on the options available for lens calibration, I did find multiple complaints from users that indicated that making the focus "perfect" at one distance made it worse at others. This was especially true for those calibrating zoom lenses where both focus distance and focal length compound the difficulties.
Rand
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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.
With dslrs we are talking about mid-range mass produced essentially consumer products. Cameras don’t have complicated interfaces with other systems made by other manufacturers, they don’t have calibrations and settings that drift and depend on environmental variables like moisture or human bodies. These cameras just won’t focus properly with other parts designed to work with it from the same manufacturer.
This is like buying a new Ford with an options package but not being able to drive it properly until you align all the wheels and map the ECU yourself because Ford can’t bothered.
At least this will all be over once the slr dies!
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With dslrs we are talking about mid-range mass produced essentially consumer products. Cameras don’t have complicated interfaces with other systems made by other manufacturers, they don’t have calibrations and settings that drift and depend on environmental variables like moisture or human bodies. These cameras just won’t focus properly with other parts designed to work with it from the same manufacturer.
This is like buying a new Ford with an options package but not being able to drive it properly until you align all the wheels and map the ECU yourself because Ford can’t bothered.
At least this will all be over once the slr dies!
I agree to some extend- i like the dslr for its optical viewfinder- Once that is gone it will never come back. I wish they would make the quality better like the Nikon F3.
I use nikon bodies and focus adjustments are really critical. It takes me half a day to get the focus right for all my lenses. After that i can truly hit focus @F1.4.
The thing i do not like is that in the manuals a chapter is lacking about this focus finetuning problem. As if Nikon is ashamed that they cannot do it right and won't like to admit it.
It took me a year to find out why my autofocus was so off. I thought at the time the AF could not do any better; until i realized it all had to do with finetuning.
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I use nikon bodies and focus adjustments are really critical. It takes me half a day to get the focus right for all my lenses. After that i can truly hit focus @F1.4.
The sigma dock is great but on this point the pain is real. I did a prime and even going in coarse steps of five and then down to one taking off, changing and remounting the lens each time for 4 distances took... a long time. A zoom would be a long affair. In the end worth it (proper focus) but frustrating and irritating it must be done due to cut corners.
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Just finished using the Sigma Dock + Sigma Optimization Pro software to tune a Sigma 24-35mm f/2 HSM Art lens. Yes it makes a big difference over using the in camera Canon AF micro-adjust tool.
External Hardware used (besides the Sigma Dock)
LensAlign Mk II (Gen 4) target in a RRS FAS clamp mounted on a RRS CB-18+CB-10 rail combination. the 28" rail combination was mounted on two tripods ( one fore and one aft), sandbagged to ensure a fixed alignment.
(yes I am being very obsessive about this but since I already had the hardware, why not use it?)
- Lightsource; Monolight with hard reflector (Specifically a paul C. Buff, Inc Einstein E640 with the new 18" Omni Reflector andd its heaviest diffuser sock, even so the Einstein was near minimum power)
Workflow:
1) Started with the LA target at the closest distance recommended in the SOP app, the closest position, the LensAlign target was centered and squared to the sensor in the usual way, and the lens set at its defaults zeroed for each focal length and distance, and with the camera's AF-MA zeroed for both shortest and longest focal lengths.
2) Shot frames at the four recommended focal lengths: 24, 28, 30, and 35mm. Defocused the lens slightly between frames.
3) Examined the frames ((camera-shot JPEGS (fine/large) at 100% and 200% Lightroom CC2015 using the slanted rail of the LensAlign Target as a guide to which direction and by how much to adjust lens for each focal length. Surprisingly the numbers on the scale on the lensAlign ruler tended to be very close to how much adjustment was need ed for each frame.
4) Dialed in the corrections for each focal length as needed and retested.
5) As needed , ran the test a third time.
6) Moved target to the next farthest distance and repeated steps 2-5.
7) Moved target to the third distance and repeated steps 2-5
This portion of the test took about 2 hours what with going back and forth to the camera with SD card and lens and the usual mundane interruptions.
8) For the infinity test I took the camera outside and with the camera on a tripod, used the corner of a neighbors brick house as target,
Conclusion: yes the Sigma Dock and software makes a difference, especially if you shoot wide open (f/2 in this case which even with the lens at 24 doesn't have a lot of depth of field. I had previously spent the entire afternoon yesterday using the camera's AF-MA and the same target and FocasTune software and my results not as good and I could only "optimize" at the longest and shortest focal lengths and with the target at only one distance (25x focal length) for those two focal length settings.
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Surprisingly the numbers on the scale on the lensAlign ruler tended to be very close to how much adjustment was need ed for each frame.
I bet this reduced the time by a lot, I did it is steps of five and then ones for the range that would have the right setting in it. I wish it didn't need a dock and I could just plug in a micro-USB lead; it is the mounting, waiting for the lens to register and then click through the software that makes this process to tedious and time consuming.
Luckily it only needs to be done once!
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"I wish it didn't need a dock and I could just plug in a micro-USB lead; it is the mounting, waiting for the lens to register and then click through the software that makes this process to tedious and time consuming. "
I totally agree. Maybe it has something to do with being connected to the camera at the same time. But you could turn the camera off between changing settings with the Sigma software. I am just speculation here but it might also have something to do with the problem of keeping the port closed and sealed against the elements.
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A Micro usb port could fit in the mount flange perhaps?
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I realize how much film is easier to shoot, sometimes. No real focus problem with sub par 35mm fslr. No need of super-stellar lenses too. I'm amazed how, for example, the Nikon f1.8 line max out films. The digital world is more and more expensive...
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I realize how much film is easier to shoot, sometimes. No real focus problem with sub par 35mm fslr. No need of super-stellar lenses too. I'm amazed how, for example, the Nikon f1.8 line max out films. The digital world is more and more expensive...
Back in the film days, many top pros bought their gear through shops that careered to the professional crowd and try out several iterations of a single lens to find the best one. I learned that trick from Al Satterwhite, and then often had there lenses and cameras calibrated, ground glasses shimmed into the right position, and otherwise adjusted by genius mechanics like Marty Forscher in New York City. Life Magazine and National Geographic had their own techs who calibrated and repaired cameras and lenses as welll as building special cameras and lenses.
That we as individuals now have the power to tune our SLR cameras to the specific individual lenses we use, is in my opinion a boon, but like all powerful craft , is a craft that needs to be respected and learned.
Just be happy (or sad, depending on your OCD level) we can't also collimate our own lenses! :)