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11-01-2009, 11:41 AM   #1
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Factory Adjustment of Lens to Body ?

I own a Pentax lens that has been problematic since it was new. With the outstanding help of a Pentax employee/ forum member I have sent this lens in for factory service under warranty. I was recently asked to send in the body so the lens could be fine tuned to that body. I currently have 3 Pentax DSLR's and 2 film bodys in my household. Here is my question: It would seem that camera / lens tollerances would be tight enough that a per body adjustment would not be needed. If lens is set up for one body then used on another ( especially one that does not allow for per lens focus adjustment)what would results be? It would seem that any Pentax lens would be set up correctly for any Pentax camera right out of the box. Am I missing something here?
What was the fix for all the backfocussing 16-50's?
Understand I'm not trolling here , Love my Pentax bodies and most of my lenes except this one. The Pentax rep that has been helping me has gone above and beyond to make things right and I'm very greatful. It just seems like an unusual request to send in a body so a lens can be adjusted to it. What do you think?

11-01-2009, 05:07 PM   #2
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This used to be a standard service offered by Nikon and Canon as part of their "Professional" service contracts. Each body and each lens has a specific tolerance that, when combined, can produce a magnified front focus (FF) or back focus (BF) issue. It's not that common, but you can see a lens that is simply too far in the same direction as the body and can produce a magnified result but generally lenses and camera bodies are very tight to a neutral tolerance.

The big advantage of allowing the camera and lenses to be calibrated together is that the service center can return everything to as neutral a setting as possible and then fine-tune each lens to perfectly match the body. This is a one-time service that will produce a far better result than the natural standard deviation of lenses and bodies that can be produced by a factory.

So, the short answer would be, no this is not unprecedented for a camera service center to want everything together as a bundle. They are wanting to ensure that your camera is neutral and then adjust the lenses to match it.
11-01-2009, 11:27 PM   #3
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yes - I do think that there is a need for calibration to be done between lens and camera. Without including the tedious details, one example would be my experience with 2 K20Ds and 2 31 Ltds. My first 31 Ltd worked very well with both K20Ds, no problem. I sold the first K20D, and thereafter replaced my 31 Ltd with another copy - that's when I noticed that my 31 Ltds was not performing the way it should, compared to its predecessor.

After putting up the problem here, it seems that the main issue was front focusing. I have managed to get a focusing chart to assess how bad the problem was, and figure how how much in-camera adjustment I should make for the focusing for this lens. As it is, I had to max out the adjustment - applied a +10 maximum value for focusing adjustment for this lens, but the focusing was still not optimized - there is still a bit of front focus. Have also tested other AF lenses, had no prob with the 43 or 77, though my sigma 24 - 70 showed front focusing issues as well, but could be totally corrected with in-camera adjustment.

The only solution to solve the problem entirely was to send the 31 ltd and camera for calibration. But given that I would probably have to send the camera and lens to Japan for servicing, I decided that I could live with the slight off-focus, and use MF for critical shots.
11-01-2009, 11:29 PM   #4
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What does a servicing job like that cost and how long does it take?

11-02-2009, 12:04 AM   #5
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QuoteOriginally posted by legacyb4 Quote
What does a servicing job like that cost and how long does it take?
In the USA there's a good chance Pentax would do it for free, if your having problems with one or more new lenses. Although you'd never get that service if you bought a gray market lens or body.

However, here in Canada Pentax has a habit of looking at your equipment and saying there's nothing wrong with it
So I honestly don't know if they'd even touch your camera.
11-02-2009, 01:11 AM   #6
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AFAIK, unlike Canon, Pentax lens AF cannot be calibrated the way Canon EF lenses do. AF calibration has to be done on the Pentax bodies.
11-07-2009, 05:03 PM   #7
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I returned my Pentax 18-250mm lens to Pentax while still under warranty (soft in lower left corner) and they sent me a completely new lens. The new replacement was backfocusing and when I contacted them, they told me to send both the camera (K10D) and the lens to their service facility in Colorado. When they came back to me, the auto focus was spot on.
11-08-2009, 04:27 PM   #8
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QuoteOriginally posted by wlachan Quote
AFAIK, unlike Canon, Pentax lens AF cannot be calibrated the way Canon EF lenses do. AF calibration has to be done on the Pentax bodies.
Alan,

Your statement is incorrect. All Pentax lenses from the FA series on (newer) are chipped and can be adjusted by the factory for autofocus issues.

11-08-2009, 07:30 PM   #9
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QuoteOriginally posted by Rich_A Quote
Alan,
Your statement is incorrect. All Pentax lenses from the FA series on (newer) are chipped and can be adjusted by the factory for autofocus issues.
Is there any reference, or just hearsay?
11-09-2009, 10:12 PM   #10
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QuoteOriginally posted by wlachan Quote
Is there any reference, or just hearsay?
I love being accused of spreading hearsay simply because it disagrees with your opinion. You might want to read up on it here:

Features and Operation of the Kaf Mount

QuoteQuote:
The KAF mount features the same six electric contacts as the KA, and thus remains fully compatible with the older mounts. However, in addition to those (electric) contacts, it features a seventh — electronic one. Using a yet-unknown serial protocol, the body uses this contact to communicate with a digital chip contained inside the lens housing. The chip provides at least the following information:
  • Focal length of the lens. This allows more efficient flash operation as well as calculating the longest hand-holdable shutter speed. In addition, it is also one of the parameters taken into account when the body is in one of the "smart" picture modes and has to choose a program curve. Prime lenses provide one fixed value, while zooms provide an approximate value that changes as the focal length changes. The focal length information is precise enough to distinguish between 35, 28 and 24 mm lenses, as evidenced by F-flashes that trigger a warning when they cannot cover the field of view of the lens.
  • Lens-to-subject distance. This is used by the more advanced bodies for calculating if the flash is powerful enough to illuminate the subject that is in focus. In addition, this is one of the parameters taken into account when the body is in one of the "smart" picture modes and has to choose a program curve.
  • Exact selected aperture. The KA mount supports displaying the picture-taking aperture when the "A" aperture setting is engaged. The KAF mount supports displaying the aperture even when a numeric f-stop is selected. The displayed value is quantized by half-stops, but is correct even when a variable-aperture zoom lens is used.
  • Lens dimensions. The lens also gives the body enough information for determining if the lens is going to cast a shadow on the subject when the camera's built-in flash is used. This parameter takes into account the size changes due to zooming and focusing too.
The lenses contain a ROM chip that holds the program curve (brightness/shutter speed/aperture) for prime lenses or up to three program curves for zooms at their different focal length settings. The distance information is hardwired on the lens barrel. A number of tiny parallel conducting/non-conducting strips are glued to the rotating part of the lens. The same number of contacts are attached to the fixed part of the lens. As the lens barrel turns during focusing, different combinations of the strips are detected by the contacts. There are four parallel strips in the F 50/1.7, resulting in at most 16 different distance settings. But for that particular lens not all combinations are used.

A similar technique must be used for the focal length.
Or here:

Pentax Lens/Camera Compatibility - Mark Roberts Photography
11-09-2009, 11:40 PM   #11
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Hi Rich! I am not accusing you anything. I am just curious. I am well aware of the KAF design and if I am not reading it incorrectly, each Pentax AF lens consists a single ROM which embedded all data of that lens. But ROM means read-only-memory, which cannot be reprogrammed like Canon EF lenses do in most service centres.Though I am no engineer, the circuit designs of EF lenses are far more complicated than Pentax AF lenses to my untrained eyes. There is never a single source I have come across suggested Pentax AF lenses could be reprogrammed for AF calibration at any service centre (and I don't believe it can be done either). AFAIK, Pentax AF calibraion can be done via the actual AF sensor underneath the mirror box, the camera firmware, or the mirror box itself (no service centre will go this route since it is too labour intensive).
11-10-2009, 01:19 PM   #12
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I wouldn't use the word "accusing" here either, but I too am still curious. There wasn't any question that FA lenses contains chips; the questions is whether those chips allow any form of repgoramming and if so, whether that reprogramming can in some way be used to adjust AF. Nothing in the posted excerpt really supports either claim.
11-10-2009, 02:51 PM   #13
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It looks like I do stand corrected. Why a manufacturer would produce a ROM chip that can't be reflashed is pretty staggering to me. After rereading the information, it does appear that it is read only in the worst sense of the term. This really does beg the question of why the hell Pentax makes AF a one-way street. If a lens with an AF issue can't be adjusted, every camera it is used on would likely produce the same issue. I've seen this first hand with a Sigma 100-300mm f/4. It lacked the DG chip and Sigma basically threw up their hands and said, "sorry, would you like to buy another one?" My answer was pretty obvious.

I understand MTF information, focal length, aperture, etc., can be stored in the ROM chip, which is nice, but why leave it without a brain? It would be different if they were charging less for their lenses but that's not generally the case for most apples to apples comparisons between manufacturers. I freely admit, I've never had a lens adjusted by a manufacturer, but it's nice to know it could be if I got a real lemon. Apparently it's cheaper for them to simply replace it than to fix it.

In body AF adjustment is (theoretically) nice and makes sense considering lenses are pretty much always within tolerance. Seems like a simple chip architecture would provide a lot great latitude than hard-wired ones.

Sorry for claiming the lenses were adjustable. I'm admittedly far more familiar with Canon L lenses than Pentax's line. I'd be interested to know exactly which lines / models are adjustable across the board to get a better understanding of the engineering philosophy of the major manufacturers.
11-10-2009, 06:29 PM   #14
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I don't see why you'd think reprogramming a ROm chip could possibly fix a focus issue. The chip juyst has some numbers on it; it doens't control the focus. The focus is mechanical. any focus adjustments to a lens would involving physically altering it - I can't see any way that programming could possibly have anything to do with it.
11-11-2009, 11:56 PM   #15
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QuoteOriginally posted by Marc Sabatella Quote
I don't see why you'd think reprogramming a ROm chip could possibly fix a focus issue. The chip juyst has some numbers on it; it doens't control the focus. The focus is mechanical. any focus adjustments to a lens would involving physically altering it - I can't see any way that programming could possibly have anything to do with it.
Marc, I tried hard to find a credible link to Canon's Service Center explaining the process I was describing, but no dice. Failing that, here is a link to a blog discussing this topic. Gordon's Tech & Hobby Blog: Canon Auto-Focus Technical Information

The pertinent part is about a third of the way down the page:
QuoteQuote:
When the camera determines how far and in what direction the lens must move to cancel the phase difference, it does so within a tolerance of "within the depth of focus" of lenses slower than f2.8 (down to f5.6) or "within 1/3 of the depth of focus" of lenses f2.8 and faster. The depth of focus is the range at the sensor plane within which the image of a point will be reproduced as a blur smaller than the manufacturer's designated "circle of confusion" (CoC). Canon's designated circle of confusion is 0.035mm for the 24x36mm format and 0.02mm for the APS-C format. The CoC is based on maintaining the appearance of sharpness in a 6x9 inch print at about an 10 inch viewing distance (as revealed by the Euro-Canon web site). There is no guarantee that images enlarged any greater than this will appear sharp.

The depth of focus increases when the aperture of the lens decreases (like depth of field at the subject plane), but it does not change with the focused distance or the focal length of the lens (according to Canon, unlike depth of field). That is why the camera interrogates the lens for that information; it calculates the depth of focus tolerance from the maximum aperture, not the set working aperture.

As a result of this tolerance (within the depth of focus or within 1/3 of the depth of focus), the camera can place the actual plane of focus at random anywhere within the tolerance range, and not necessarily at the same place each time.
It is my understanding, and supported by Chuck Westfall's (Canon's US Technical Adviser) article here a little more than half way down the page) that each lens is calibrated at the factory and an MTF table based on a standard algorithm is flashed onto the ROM chip after it is tested. This is done under controlled conditions but often only at particular focal lengths (such as only 24 and 70mm on the 24-70mm zoom). If the lens is sent in for repair, this table can be recreated through retesting and re-programmed (re-flashed) onto the chip.
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