[HN Gopher] Canon EF and RF Lenses - All Autofocus Motors
___________________________________________________________________
Canon EF and RF Lenses - All Autofocus Motors
Hi there! I have written an e-book about all autofocus motor types
used in Canon EF & RF lenses from the past 40 years.
Author : ExAr
Score : 357 points
Date : 2025-03-10 13:12 UTC (9 hours ago)
(HTM) web link (exclusivearchitecture.com)
(TXT) w3m dump (exclusivearchitecture.com)
| chaosprint wrote:
| Canon's lenses are great, but they're really expensive. The
| camara body itself has the same issue.
|
| Sony seems to be the first choice for indie filmmakers and
| youtubers right now.
|
| L-mount and M43 also seem to have great potential as Panasonic
| supports Phase Detection Autofocus.
|
| edit:
|
| There is no need to be cynical here. Market figures are cruel. I
| hope they are all good. Competition is the best. I should also
| mention the return of Nikon. The patent threshold of RAW such as
| RED is what we need to oppose.
| BolexNOLA wrote:
| Considering my 70-200 can still hang after 10 years and will
| last another 20 easily with some TLC I was fine with my $1500
| purchase - which I made as an indie filmmaker!
|
| Jokes aside Sony glass really isn't all that much cheaper.
| chaosprint wrote:
| Agreed. EF's short flange focal distance can also be easily
| connected to Sony to utilize dual ISO. Indie uses manual
| focus anyway.
| dylan604 wrote:
| As the old saying goes, buy the glass, rent the body. Camera
| bodies change much more quickly than the lenses, so as an indie
| your money is better spent on the glass. However, shit is so
| cheap now that you can almost upgrade your gear like your
| phone. _IF_ you're a cut ally making money with it, you can pay
| off your gear in one or two gigs. Unless you're the "nephew
| with a 5D asking $500" to shoot that project
| jeffbee wrote:
| Most shops that offered still photo rentals in my city have
| gone out of business, and it's a major city. I used to be
| able to count on renting a big telephoto that I didn't need
| to own, for a few hundred per weekend, but these days I'd
| have to take a long drive to get to the one remaining shop.
| dylan604 wrote:
| Yeah, online rental places have pretty much made the locals
| fade away. The one in my local area requires a "deposit"
| worth the full sales price which makes it out of the reach
| of anyone but those well off.
|
| We used to joke about the B&H rental by taking full
| advantage of the 30-day return policy. Even Amazon's return
| policy qualifies now. You just need to the up front funds
| available and hope that wear&tear is not noticeable to make
| the return acceptable. It's hard for local shops to keep up
| with that.
| genewitch wrote:
| Hard for local shops to keep up with fraud? You don't
| say.
| dylan604 wrote:
| I like how the messenger is getting shot. It's as if my
| reporting of what actually happens is being interpreted
| as that's what I do. Just because I know of how the
| system gets played does not make me a player.
| genewitch wrote:
| I get upset when people defraud my neighbors and friends
| in my community. that's what a local shop is. Just today
| i went to my _local_ pharmacy to look for l-theanine
| based on some commentary on HN yesterday. I could have
| gone on amazon, or to walmart, or to CVS. People
| interfering with that business aren 't cool, regardless
| of the motivation.
|
| let me put it this way - i never even thought of using
| amazon as a rental service. even though amazon loves me,
| and i could get away with it, my brain doesn't spend time
| thinking about unethical things to do.
|
| read this as: "Someone should have gotten upset _before_
| the deposit went up from jerks either breaking or
| stealing the rental equipment " - as my sibling says,
| this is why we can't have nice things.
| igouy wrote:
| aka "This is why we can't have nice things"
| sizzzzlerz wrote:
| I chose early on to invest in Canon's L lenses even though I'm
| an amateur. Yes, they are considerably more expensive than
| consumer lenses but for the price, you get a more rugged,
| weatherproof body, sharper and faster glass, and a greater
| selection of both fixed and zoom lens. The down side is they
| are quite heavy making them more difficult to carry when
| shooting outdoors and they can require a stronger tripod to
| support the weight of the lens and camera. But, the images they
| can produce can be simply stunning at times and that, after
| all, is why we do photography.
| liotier wrote:
| As a Canon user since the mid-80's, I found this fascinating
| reading.
|
| Edit: Wow - there's a whole collection of Canon lens technology
| articles there: https://exclusivearchitecture.com/03-technical-
| articles-CLT-...
| xattt wrote:
| Well, there goes the rest of today...
| ExAr wrote:
| Thank you for your feedback! And great that you've found the
| other chapters - most of them are already complete. Enjoy!
| myself248 wrote:
| Oh neat! I have a Newscale micro motor demo kit from years ago,
| and I wondered if they were ever successful in the market. But
| that hip-gyrating Micro USM action sure looks familiar.
| aziaziazi wrote:
| The graphics are amazing. Congrats for the work!
| actionfromafar wrote:
| Cannot scroll pages in Firefox.
| ExAr wrote:
| Sorry to hear that. I tried on my Firefox and it worked. Not
| sure what might cause that issue.
| SSLy wrote:
| depending on how the UA's anti-tracking is set up, your
| cookie pop-up (non-GDPR compliant btw) might prevent the
| scroll. It's this snippet html.disable--
| interaction.show--consent, html.disable--
| interaction.show--consent body { height: auto
| !important; overflow: hidden !important;
| }
| Retr0id wrote:
| Which aspect of it is non-GDPR compliant?
| SSLy wrote:
| the accept and reject buttons should not have
| differentiated colours. See point 3.4, 3.5 (p. 27
| onwards) in https://noyb.eu/sites/default/files/2024-07/n
| oyb_Cookie_Repo...
| ExAr wrote:
| You are right, I can change that.
| SSLy wrote:
| Hey, nitpicks aside your site is great! Coming from a
| Fuji buyer...
| ExAr wrote:
| Much appreciated :)
| camtarn wrote:
| I had this problem in Chrome. I turned off JavaScript and the
| page worked nicely. (Props for that!) I'm assuming my adblocker
| or auto-accept-cookies plugin did something weird.
| michh wrote:
| I've recently been shooting film with an old EOS camera from the
| 90s I bought used and it was really nice being able to use the
| EOS lenses I bought for my DSLR in the 2000s and 2010s. It's a
| dying standard now but it's really impressive it lasted as long
| as it has, with significant technological innovation on both
| sides of the lens mount while retaining full compatibility. A
| brand new EOS EF lens still works with an 80s camera and a new
| 80D from 2017 can still use the lenses from the 1980s without any
| adapter. 30 years ain't bad for a standard!
| IgorPartola wrote:
| As a Canon owner, Nikon has a much longer back compatibility
| range. Having autofocus motors and IS in body rather than in
| lens seems to be a part of their trick.
| dghlsakjg wrote:
| Nikon lenses will mount on any Nikon body, but that's sort of
| where the compatibility ends.
|
| Their f mount autofocus lenses are a variety of standards
| that are not at all backwards compatible across eras.
| shagie wrote:
| The traditional Nikon mount has a small screw that is turned.
| The camera autofocus speed is limited by the amount of torque
| that can be applied to the screw - which can make focusing
| some of the heavier lenses slower.
|
| https://www.discoverdigitalphotography.com/2012/lens-
| mounts-...
|
| The "AF-D" lenses have contacts back to the camera body that
| communicate distance information (that is in turn used by the
| camera body to calculate flash power).
|
| The G mount lenses remove the manual coupling for the f/stop
| which means that _only_ bodies that can control the aperture
| from the body can use them. My FM3A has no aperture control
| on the body and so with that camera, I unlock the aperture
| ring.
|
| The AF-S camera lenses have the focusing motor in the body.
|
| VR in Nikon is done in lens.
| https://kenrockwell.com/nikon/80400vr.htm It needs to - you
| can't jiggle the film around to keep it in the same place.
|
| ---
|
| The impressive part of Nikon's compatibility isn't only the
| "you can use an AI-S lens on a modern (professional) body,
| but also "you can use any of the F mount lenses on an _old_
| body " (the G lenses don't have the f/stop ring and the E
| lenses have the focus motor in the lens).
|
| While it appears that Nikon has mostly shifted to E and G
| mount, third party lenses are still being manufactured for
| the F mount.
|
| https://www.bhphotovideo.com/c/product/1519140-REG/tokina_at.
| .. - and you can see all the parts of the F mount, manual
| aperture ring control, 5 pins for distance, '-' slotted screw
| for focus.
| mimentum wrote:
| Difference between G and E-type lenses is that 'E' stands
| for Electromagnetic Diaphrapham.
|
| The G type lenses have an aperture tab for diaphrapham
| control as dictated by the camera body, the E-type lenses
| leave this to being controlled by the camera
| electronically.
| dghlsakjg wrote:
| > you can't jiggle the film around to keep it in the same
| place.
|
| Contax had an AF solution (Contax AX) that actually moved
| the entire film plane to focus. I suppose that the same
| thing could be done in other axises, but I also suppose
| that there is a reason that only one manufacturer tried it.
| LgWoodenBadger wrote:
| Nikon his shifted almost exclusively to their Z mount
| lenses. And some of these have in-lens and/or on-camera VR.
| shagie wrote:
| The SLR lenses are still in wide production.
| https://www.nikonusa.com/c/lenses/dslr-lenses/overview
|
| The Z lenses are for the mirrorless bodies and only work
| on the mirrorless bodies.
| https://www.nikonusa.com/c/lenses/mirrorless-
| lenses/overview
|
| As long as SLR bodies are produced, Nikon will continue
| to make SLR lenses (and probably for a while afterwards)
|
| https://en.wikipedia.org/wiki/Nikon_D6 was released in
| 2020.
| hyperbovine wrote:
| I must be old -- I vividly remember the Nikon crowd crowing
| loudly online forums (fredmiranda.com I'm looking at you) about
| how Canon broke backwards compatibility when they moved from FD
| to EF. Whereas you could slap an F-mount lens _from the 1950s_
| on any Nikon DSLR ever made, no problemo. (Remarkably, this
| continues to be true!)
| michh wrote:
| Oh yeah, that's even better, totally agree, but it doesn't
| negate my point. I don't think Canon's 30 or 40 years would
| be matched by a hypothetical present-day camera upstart, let
| alone Nikon's 70 years.
| silverquiet wrote:
| You could always physically mount them but there were
| compatibility issues as Nikon added functionality over the
| years. It was a tradeoff.
| mcbuilder wrote:
| Too bad Nikon practically stopped making DSLRs
| thih9 wrote:
| To be fair, so did everyone else. Except Pentax.
| flipthefrog wrote:
| Except if you mount an old, so called pre AI lens, on certain
| Nikons, you will have to disassemble the camera to get it
| off. Many modern Nikons can't autofocus older AF lenses due
| to not having a motor. And many AF film SLRs couldnt meter
| with manual lenses. So far from perfect compatibility. Nikon
| F mount was introduced in 1959. The oldest mount used today
| is probably Leica M from 1954
| batch12 wrote:
| I have an EOS 35mm lying around that can use the same lenses
| too.
| turnsout wrote:
| This is seriously impressive! Just curious, how do you have the
| time to do all these deep-dives, and how can people give you
| money??
| ExAr wrote:
| turnsout Thank you very much. Trying to understand complex
| things has always fascinated me. Indeed it takes a lot of time
| (rd. 1.600 hours for the complete series of Canon lens
| chapters) but its people like you who drive me forward. I don't
| have a donation page yet, I never thought it would be used :-)
| PaulHoule wrote:
| I was a big fan of USM lenses when I had a Canon, but I had one
| go bad with fungus or something and for a while had only a 35mm
| prime which I even used to take pictures of birds. Then I lost my
| Canon and decided to get a Sony circa 2019 or so because all the
| reviews I saw for Nikon and Canon said the autofocus sucked on
| entry-level full frame cameras.
| MartijnBraam wrote:
| I've always wanted to know how the various autofocus systems
| worked. This page is incredible. I wish there was another one
| with the Nikon autofocus systems since that's what I actually
| have.
|
| I still have several lenses with autofocus that don't have an AF
| motor in it at all, the motor is in the camera body instead
| there's a tiny screw on the lens mount that transfers the motor
| rotation to the autofocus parts in the lense. This was very slow
| and noisy though on my cameras.
| pnathan wrote:
| Tolerably modern Nikon lenses have in-lens AF I believe.
| MartijnBraam wrote:
| Yeah the in-body motor thing is only for the older Nikon
| lenses, I don't think AF for that is still supported if
| you're using Z-mount adapters. Nikon seems to have a few
| similar AF motor technologies like the canon ones in this
| article.
| acomjean wrote:
| Canon being late to the AF party (last century).
|
| They ended up with all electronic contacts when they
| switched lens mounts for the "eos" series cameras though at
| the expense of not having backward compatable lenses. (I
| had a bunch of manual focus lenses at the time...) They had
| one "auto focus" camera for the old lenses the t80.
| (https://global.canon/en/c-museum/product/film115.html) but
| almost no lenses supported autofocus.
|
| I think most of settings the camera sent to the older
| lenses (aperture primarily) was done mechanically.
|
| The way these old cameras autofocused was pretty
| interesting. With some light passing through a semi
| transparent mirror onto different sensors.
|
| Edit: this site has another page about autofocus. Quite
| extensive.
|
| https://exclusivearchitecture.com/03-technical-articles-
| DSLR...
|
| Shorter canon article:
| https://support.usa.canon.com/kb/s/article/ART170280
|
| I have one of those mirrorless slrs now. The focus is
| amazingly good. Lots of software (eye detect etc). The
| focus sensors are integrated into the image sensor I
| believe.
| MartijnBraam wrote:
| All my nikon cameras focus with a semi transparent mirror
| on a specialized autofocus sensor. I even have an nikon
| film camera that has that cicuitry. You can't autofocus
| like mirrorless cameras with PDAF pixels in the main
| sensor with a mirror in the way.
| bydo wrote:
| There's a new third-party F to Z adapter that does have the
| screw drive:
| https://nikonrumors.com/2025/02/28/monsteradapter-la-
| fz1-off...
| hypercube33 wrote:
| Newer Nikon lenses have a few motor types but if I'm not
| mistaken they support old mechanical (body driven) aperture
| and focus drive as well (the D6 and somewhat recently F6 film
| camera were still for sale)
|
| Nikon has a complex ecosystem keeping generally the same
| mount for many decades and general support for it, where
| others developed a specific autofocus mount when they moved
| towards those systems.
| danhau wrote:
| Their mirrorless Z mount and lenses don't have mechanical
| drive. Neither do their official F-to-Z adapters - much to
| the chagrin of people using their older glass.
| nayuki wrote:
| Nikon's lens/body compatibility matrix is horrendously
| complicated. https://www.kenrockwell.com/nikon/compatibility-
| lens.htm
|
| Whereas I think "no metering" is never a problem on Canon.
|
| Over the decades as a DSLR shooter (on Canon), I even saw Nikon
| shoot themselves in the foot not once but twice.
|
| * When Nikon introduced "E" lenses (electronic aperture, like
| Canon and all modern designs), very few bodies were compatible
| with it. They didn't have the foresight to introduce compatible
| bodies before any lenses with E were released. For example,
| this was released in 2008 (
| https://www.kenrockwell.com/nikon/24mm-pc.htm ), and the
| earliest compatible body is from 2007. It doesn't work with
| tons of crop (DX) bodies like the D90, as well as any film
| camera.
|
| * When Nikon introduced "AF-P" (stepper motor) lenses in 2016,
| there were no compatible bodies before 2013. Again, not enough
| future-proofing.
|
| Meanwhile, Canon took a different approach. They pissed off
| users twice - when transition from the FL mount (1964) to FD
| (1971), and FD to EF (1987). They basically got it all right
| with EF - fully electronic, no aperture slider, no focus screw,
| big diameter.
|
| I have even successfully used a year-2017 Canon lens with Ring
| USM AF and IS on an original EOS 650 film body (released in
| 1987), and both AF and IS work perfectly. Mind you, both of
| those features did not even exist at the birth of EOS.
| Presumably the AF electronic protocol is agnostic of what motor
| technology is in the lens, and IS can be a lens-only thing
| without the body knowing.
|
| Nikon's compatibility gotchas don't hold a candle to Canon's
| excellent (albeit imperfect) compatibility. Nikon keeps making
| the same mistakes over and over again, such as not having a
| screw-drive motor in the F to Z mount adapter; the company
| really seems to hate people with old lenses and bodies. Oh and
| this is not new either; Nikon's F to 1 adapter (does anyone
| remember that highly cropped mirrorless camera?) also lacked
| certain features.
| MartijnBraam wrote:
| What annoys me is that the AF-P could probably be supported
| on a lot more cameras, they did add it to the D3300 with a
| firmware update. They just didn't do it for more cameras...
| exar0815 wrote:
| I always wanted to build a controller for Canon Telephoto lenses
| to use them with c-mount cameras and control the focus from a PC.
| Might be helpful for that.
| sizzzzlerz wrote:
| A couple of universities built a telescope called Dragonfly,
| that utilizes 48 Canon 400mm lenses to photograph the skies of
| New Mexico. The kicker is they don't use camera bodies.
| Instead, they designed and built mounts that directly connect
| the lens to a sensor. A PC controls each lens through some
| custom electronics using commands they reverse-engineered from
| the Canon control software. These commands control focus,
| aperture, and triggering a photograph. Images from the 48
| lenses are then combined in the computer into a highly detailed
| final image. This was done back in 2013 so its possible Canon
| has released an API by now but I suspect they still keep it
| proprietary.
|
| https://en.wikipedia.org/wiki/Dragonfly_Telephoto_Array
| contingencies wrote:
| I visited some similar telescope in Australia at
| https://www.sidingspringobservatory.com.au/ run by Macquarie
| University ... the students explained the lens system could
| not be too new and could not be too old. Basically it sounded
| like someone had partly reverse engineered one generation of
| the lens interface only.
|
| I guess the camera and lens manufacturer wants their lenses
| to be used with their cameras and to have better results than
| other manufacturers, whereas random companies want to clone
| the interface and sell cheaper lenses that also work with the
| cameras. Realising how awesome the lenses are, the students
| want an array of them, however they don't have the budget to
| buy a similar array of top end manufacturers' cameras.
|
| In Sydney they have interesting viewing nights at
| https://www.mq.edu.au/faculty-of-science-and-
| engineering/dep...
| cpgxiii wrote:
| A number of machine vision camera vendors have higher-end
| variants that support active EF-mount lenses. They tend to be
| quite expensive models with larger sensor, since you tend to
| lose a lot adapting full-frame lenses to tiny C-mount sensors.
|
| If you want a computer-controlled lens, one of the cheapest
| options is to use Blackmagic cameras that support SDI and/or
| USB control. You can then control either native M4/3 active
| lenses (focus, aperture, zoom) or supported EF-mount lenses if
| you use one of the EF->M4/3 active adapters.
| speed_spread wrote:
| Meanwhile, Pentax screw drives go brrrrr
| amelius wrote:
| These piezoelectric drivers are very cool.
|
| Here's a video showing the mechanism:
|
| https://www.youtube.com/watch?v=7iHL4ZCkCKc
|
| And here's a video showing such a motor at full speed:
|
| https://www.youtube.com/watch?v=JtttNnmCVmU
| ExAr wrote:
| Cool videos, thanks! The driver shown in the first video is
| indeed a piezoelectric actuator, but not the type Canon uses in
| their lenses. The driver shown in the second video is probably
| related to Canon's Nano USM.
| blackeyeblitzar wrote:
| Do companies like Canon manufacture these motors or actuators
| themselves? Or is there some other company that specializes in
| this sort of thing?
| brotchie wrote:
| Thanks so much for putting so much effort into this, loved
| reading it: the diagrams and explanations are top-tier.
| Inspirational.
| notimetorelax wrote:
| Am I spoiled by expecting these images to be dynamic? I remember
| some wonderful posts with graphs you could interact with.
| ExAr wrote:
| On the ring-type USM motor you can click on some images to see
| animations running. But there is no additional interactivity at
| this point.
| bitdivision wrote:
| You're probably thinking of https://ciechanow.ski/mechanical-
| watch/
|
| I can't imagine how long this post took to make, let alone
| trying to do animations.
| ExAr wrote:
| What an absolute masterpiece this website is! Thanks for
| sharing.
| ucarion wrote:
| Such a cool website.
|
| In case anyone else was looking for it, this article from the
| same author covers the more algorithm-y question of how a camera
| body decides to actually use these motors when you press the
| "focus" button: https://exclusivearchitecture.com/03-technical-
| articles-DSLR...
|
| I can't find any articles on how a camera body decides what is
| and isn't a desired subject. I'm guessing there's some amount of
| machine learning-type stuff involved in that, seeing as how they
| can detect human (and bird?) faces?
| Sharlin wrote:
| Nowadays they use pre-trained pattern recognition AI models,
| yes, which has become much more impressive (and CPU-intensive)
| with mirrorless cameras where the entire resolution of the main
| image sensor is available for analyzing the scene. Some higher-
| end traditional DSLRs have a "high"-resolution (around 0.1 MPix
| or so) metering sensor that is used to assist the AF system
| (eg. what Canon calls iSA and iTR [1]).
|
| Traditionally, cameras would just focus using the single focus
| point the photographer has selected, or if they have selected a
| larger area focusing mode, the camera would typically pick the
| closest point of a group of points, assuming that that's
| usually what the photographer is interested in. (Remember that
| traditional (D)SLRs have a discrete AF sensor with at most a
| few dozen focusing points to choose from!)
|
| In tracking AF modes (eg. Canon's Servo AF), depending on
| settings, the camera tries to avoid sudden shifts in focus even
| if a foreground object momentarily occludes the original
| target. Tracking AF also has to predict the subject's motion to
| prevent the focus from lagging behind a fast-moving subject.
| Higher-end cameras allow configuring the AF behavior in terms
| of how reactive vs "sticky" it should be when tracking a
| subject, and how linear the subject's motion is expected to be.
|
| [1]
| https://www.canon.com.hk/cpx/en/technical/pa_Overview_of_65-...
| miahi wrote:
| With mirrorless cameras the focus switched from specialized
| sensors to on-CMOS contiuous exposure sensors, so movement is
| easy to detect. At this point the cameras have specialized AI
| hardware to run the models, and they also accept user input
| (on R5 MkII you can register up to ten people to prioritize
| focus on[1]). The focusing options are now very
| complex[2][3], and combined with lots of customization
| options on the camera's buttons you can have very
| specialized/personalized setups for different types of
| photography.
|
| [1] https://cam.start.canon/en/C017/manual/html/UG-04_AF-
| Drive_0... [2]
| https://cam.start.canon/en/C017/manual/html/UG-04_AF-
| Drive_0... [3]
| https://cam.start.canon/en/C017/manual/html/UG-04_AF-
| Drive_0...
| Sharlin wrote:
| Sure, as I said in the first paragraph, AF is these days
| very impressive thanks to the large amount of data
| available (but of course this would have been _too_ much
| data back in the day, when there wasn 't nearly enough CPU
| power to process it fast enough). I wanted to give more
| historical context for how AF worked before fancy AI.
|
| The AF settings, except those related to face/object
| recognition, haven't actually changed that much since the
| 7D Mk II days. The preset system is more general now and
| allows you to store and recall all AF settings rather than
| just the three tracking-related variables. The high-end
| DSLRs used to have six cases for different types of sports
| that you could modify but not rename.
| divan wrote:
| Sony A9 III even has a configuration setting of whether it
| should focus on the left or right eye of the person :) It
| also can remember faces and prioritize them if there other
| faces. Let's say someone shoots their kid on the football
| field and wants only them to be in focus.
| roblh wrote:
| The left eye/right eye option has been around even on lower
| end cameras for the better part of a decade, which is kinda
| wild. My fuji from 2017 has that, and Fuji are specifically
| known for having worse autofocus performance than Canon or
| Sony or Nikon. Nikon and Sony specifically seem to be top
| of the pile right now.
|
| The Z8 has a whole separate processor dedicated to
| autofocus and the viewfinder which, in practice, means it
| can shoot 20 FPS full quality 45 megapixel RAW files with
| continuous 120fps autofocus without blacking out the
| viewfinder for each shot, which is absolutely insane.
| Clamchop wrote:
| The technical term for the "stickiness" you're referring to,
| where a system is resistant to change or has a memory, is
| hysteresis.
| xattt wrote:
| Similarly, promo materials for the Elan 7 talked about how the
| camera was able to determine exposure based on a database of
| hundreds of photos.
|
| I have no idea how this worked, but would have loved to see the
| photos they used for "training" this system 25 years ago.
| flyinglizard wrote:
| It's an amazing article. And it's only the tip of the iceberg -
| there are many more. This has to be the work of a madman (meant
| in the best possible way).
| DidYaWipe wrote:
| Really interesting work.
|
| I have been aggravated by (and bellyaching about) the ridiculous
| lack of a way to control the focusing motors in these lenses
| directly when shooting video, using a follow-focus wheel.
|
| Video shooters are still strapping janky gear-tooth strips onto
| these lenses, and then bolting bulky mechanical follow-focus
| mechanisms on the OUTSIDE of lenses that have focusing motors
| already built in.
|
| I can only imagine that manufacturers refuse to make direct
| control available in order to protect their "cinema" lens lines,
| where a manual normal lens sells for thousands of dollars. And
| yet they sell some falsely-named "hybrid" lenses that are
| supposedly somehow better for video... despite lacking even
| geared focusing rings that are compatible with follow-focus
| units... let alone a control port that could be used for a
| focusing wheel to use the autofocus motors.
|
| I looked at the Canon camera-control SDK, and sure enough...
| focus control is omitted from their entire line, except for two
| PTZ cameras that aren't suitable for cine use.
| fooker wrote:
| Great write up, thanks.
|
| I have a question I'm hoping you can answer.
|
| I have an EF 400mm f2.8 (2nd gen) lens. This thing focuses
| significantly faster with my old 7Dmk2 than my very new R6Mk2.
| With all other lenses it's the opposite. Why does this happen?
|
| I have been told that this might be due to the old 7D and 1D
| bodies sending more power to the AF motors, but haven't seen this
| corroborated anywhere.
| ExAr wrote:
| Hi fooker, thanks for your feedback.
|
| I haven't heard of this issue before, but a quick research
| showed me that other people have (similar) AF problems with
| longer lenses on an R6 II. See here
| https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Camer...
|
| Sorry for not providing an explanation, perhaps I can find some
| time to look deeper into this - but I can't promise.
| ryandamm wrote:
| A note of possible interest for this crowd: all these motor types
| are open loop, so you can't actually command a specific state
| with any accuracy / repeatability. In other words, if you send a
| signal to the lens to focus at, say, 3m, it won't necessarily be
| in exactly the same state as the next time you focus at 3m.
|
| This is why camera calibration can be tricky, and you often don't
| want to touch the cameras after you've done a calibration pass.
| fusionadvocate wrote:
| The system stops the motors once it reaches focus. Therefore is
| a closed loop system.
| nayuki wrote:
| Correct. The AF sensor continually takes more samples even
| while the motor is moving. You can tell because sometimes the
| motor overshoots and then you can see it come back.
| ryandamm wrote:
| Yup... but it's not necessarily in the same state if you do
| it twice. It's close, but not identical. Even if the image
| metadata claims the focus point is identical, the lens in
| all likelihood is not in the same state and will have some
| deviation in its intrinsics.
| ryandamm wrote:
| It's open loop in that the measurement of it being in focus
| is reliant on the subject matter, and a different
| measurement.
|
| I'm not making this up, camera manufacturers have told me to
| my face that focus is open loop, period. They can't guarantee
| repeatable focus.
|
| Notably the measurement isn't of the state of the
| motor/gearing. Furthermore, being "in focus" means the
| subject matter's out of focus blur is below some threshold;
| there is a range of focus states that qualifies -- but those
| seemingly small differences can affect camera calibration,
| with >pixel-level differences in effective focal lengths.
|
| It's open loop.
| nayuki wrote:
| Amazing website. If I didn't know better, I thought this content
| came from Canon itself. A couple of comments from me:
|
| > The following comparison chart shows all of the autofocus drive
| types that have ever been used in Canon's EF, EF-S, RF, and RF-S
| lenses.
|
| They missed mentioning EF-M, Canon's foray into mirrorless
| interchangeable-lens cameras.
|
| > Although the ultrasonic noise cannot be perceived by the human
| ear, it can be picked up by sensitive microphones which can be
| problematic during video shootings.
|
| I used several Ring USM lenses and can hear the noise when
| focusing. It's a soft swishy kind of white noise, not harmonic.
| The Ring USM definitely generates noise in the audible range, not
| only ultrasonic.
|
| > The latest types of autofocus drives, including the Stepper
| Motor, Nano USM, and Voice Coil Motor, offer focus-by-wire.
|
| Though I have nothing against focus-by-wire on principle, the
| implementations have not been good. Having used several EF-M (all
| STM) and RF (some STM and some Nano USM) lenses that have focus-
| by-wire, I find that the motor actuation significantly lags
| behind the user turning the focus ring (which is a digital
| encoder), and the granularity of the focus steps are visible.
|
| Meanwhile, the old EF Ring USM's full-time manual (FTM) was
| really good by comparison; it didn't take much force, was fully
| responsive with no lag, and was fully analog when turned by hand
| and had no discrete steps. I miss that, as new lenses don't use
| this design.
|
| > Canon EF 15mm F2.8 Fisheye (et cetera)
|
| Please change the syntax to "f/2.8"; this is even in Canon's
| official pages.
| https://global.canon/en/c-museum/product/ef263.html
|
| Why? Because f is actually a lowercase italic variable that
| denotes the focal length (15 mm in this case), and "/" (slash)
| really means division. The size of the aperture is (15 mm / 2.8)
| = 5.4 mm; that is the real diameter of the hole that light passes
| through. The absolute aperture is 5.4 mm and the relative
| aperture is f/2.8. https://en.wikipedia.org/wiki/F-number
| rpearl wrote:
| EF-M is fairly dead at this point isn't it?
| m463 wrote:
| > EF-M, Canon's foray into mirrorless interchangeable-lens
| cameras
|
| Canon's foray into _SMALL_ mirrorless interchangeable-lens
| cameras.
|
| The R series are mirrorless, but not that small. too bad.
| ExAr wrote:
| Thanks nayuki for the detailed comment and positive feedback.
|
| Thanks for pointing out the missing EF-M, I am going to add
| that during the next polishing round. With regards to USM
| noise, the ultrasonic whine can be picked up by very good ears.
| I think the Nano USM is excited in the range of 60+ kHz, so at
| least that type of USM motor is absolutely inaudible.
|
| Syntax-wise with F2.8, you got me. I know it's not 100%
| correct, but it was a deliberate choice that I made.
| Historically, there is either 1:2.8 or f/2.8 which will always
| be correct representments of the aperture (exit pupil)
| diameter. However, pursuing a cleaner look, I avoided the
| division or slash characters because the relation between the
| focal length and the f-number is known by every photographer.
| This is why Canon has also made the transition to the syntax
| "F2.8" in all their RF and RF-S-lenses - at least their product
| names and labels printed on the lens barrels. (The same is true
| with the focal length where Canon doesn't print "mm" on the
| barrel - to achieve a cleaner less mathematical look). So I
| believe what I did here was just go with the trend :-)
| jmorenoamor wrote:
| Amazing size with such attention to detail, congratulations.
| ashishuthama wrote:
| @ExAr - A treasure trove of information, thanks for putting in
| the effort!
|
| Do you blog about how you go about creating these graphics? For
| example, this view finder image:
| https://exclusivearchitecture.com/images/technical-articles/...
| looks very impressive!
|
| How do you simulate the rays+eye?
| ExAr wrote:
| Thanks for your feedback. Until now I have never blogged about
| the creation of these illustrations, but it's a nice idea,
| there is tons of "behind-the-scenes" material. With regards to
| the viewfinder image, the actual path of light was drawn with
| the help of a Japanese optical engineer who was able to provide
| professional raytracing simulations.
| dingaling wrote:
| I used to have to manually focus to take photos of my dog. The
| apparent noise from the early Ring USM AF in the 85mm/1.8 lens
| drove him mad and he would run out of the room.
|
| We did initially wonder if it was some psychological effect of
| pointing a camera at him, but one night I hid behind a curtain
| and used the AF motor and he still shot out of the room.
|
| Subsequent USM AF motors were silent to him and he was then
| content to have his photo taken.
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