Why do lenses need to be sent in for calibration?

[emtp563]

I got a Tamron 28-75 f/2.8 last April and sent it back to Tamron for calibration. It was not auto-focusing correctly. It is now almost June and I still do not have the lens back. I've called twice already and each time they say they are extremely busy with calibrations and mine will be done soon.

I asked the Tamron guy this question on the phone and he gave me the run-around saying there is a difference between film cameras and DSLR's. I told him this lense has a "Di" designation and should be "digital ready." Not to mention tyhe fact that this lense is for "Canon mount" cameras, he skirted the issue.

So why do third party lenses need to be calibrated AFTER you buy them? I seldom hear of any one having to send a Canon lens in for calibration.

[steved110]

People are always sending their lenses , and sometimes bodies as well, in to be calibrated, Canon lens or not. If you do a search thru the forum for any of the popular L type lenses, and others, you'll see - people posting pictures anxiously asking if we think they are soft/ blurred/ purple fringed, or just plain no better than the kit lens...

It seems to be one of those things, that not all copies of a lens are as good as they are supposed to be. add to this the more or less instant viewability of digital, with high resolution sensors, and we are probably demanding far more from lens manufacturers than ever before. I imagine in film days very few people were making prints large enough to see the fine detail that our teams of dedicated pixel-peepers take for granted.

This may well be why they are so busy calibrating lenses. But it's a pity they don't take more trouble in the first place, it must cost about the same if they factor in all the warranty work and the problems that returned stock must make.

[kevbailey]

I work in optics, and with ground lenses, but not in the photography side. I would appear, to me, that although the fixed refraction of a lens can be identical and consistant, the actual thickness of the finished lens can vary somewhat. When you consider that these lenses have a series of lenses inside the casing, a few microns difference in thickness would create some variances in the final output in regards to IQ.

In optics, the refraction is based on the variance between the front curvature and the back curature. Whether a lens is 10mm thick, or 15mm thick, if these curves are the same on both lenses, the final refraction would be the same. However, the theory for which these dioptric curves are based, fall on this formula. The speed of light in-air divided by the speed of light passing through a medium. The result is called the Index of refraction. For "crown" glass, this index is 1.5238. Light travels at 186,000 miles per second in air, and approx. 122,000 miles per second through crown glass.

Polishing a chunk of glass to a pre-defined thickness is not difficult when you are talking about millimeters, but it's a whole different world when you are going for exact microns. If you have a lens that is 1 micron thicker then another, your light is not going to reach it's destination at the same time. Add to this several lenses, and several different materials, and you have a lot of room for variance. The image may be perfectly focused, but one lens may be at the edge of tolerance, or all the lenses, and that could result in a slightly soft lens, or more probable, a lens with chromatic abberation towards the edges of the visible light rays, (RED & VIOLET)

Kevin

[SuzyView]

Kevin, thanks for the optics lesson. I wondered when we would get someone here that has actually manufactured something that we love so much and agonize over constantly.

I have a theory about this on the psychological side: a photographer spends $1200 on an L quality lens and it comes looking perfect, he/she puts the lens on the camera that cost as much as that lens and snaps away. The images are not perfect, some are soft, some totally out of focus. After 1000 shots on a tripod, off a tripod, in the dark, in the light, with the flash, without the flash, it's clear that the $1200 is not right. He/She asks their friends here for advice. It's new, it's expensive, send it to be recalibrated. You pay for postage and Canon looks at it again. I did just that. I sent my beautiful new lens for recalibration because I thought something wasn't quite right. I got it back, and amazingly, it was much better. Some people weren't so lucky. When a company manufactures over 30 M lenses now, and if only 1% of their product is not within specifications, that's 300,000 lenses! And I think we talk to each other here so much about wanting to get our gear right, we encourage each other to send gear in for work. And it's a good thing. :)

[MDJAK]

I have a theory too. It's called the placebo effect.

Take a hundred people with a headache. Give 50 a real headache pill and give the other 50 a pill containing nothing.

Result: 25 people with the real pill will feel better; 25 people with the fake pill will feel better.

Maybe I'm not giving proper deference to canon repair facilities, but I highly doubt they will take a lens apart and replace inner elements because someone sends it in claiming it is soft.

But there again, I've got a headache. I'm going to take an aspirin.:oops:

[SuzyView]

That is a valid theory, my friend. But I do admit, in my case, which is not rare, the zoom ring was way tight, and I suggest that may be because of packaging, temperature differences, etc. But the service center replaced the ring and loosened it all up. A big difference and that makes me think they did what they said they'd do and it is better.

[MDJAK]

Suzy, I have no doubt that in your case they are more than capable of doing that and would of course do it.

Heck, when I dropped my camera, they had to take it apart and replace gads of parts and they did an excellent job.

And I'm sure if someone drops their lens and breaks an element, they're capable of fixing that too.

But as you agreed, my point is a different one.

Now, leave me alone. I've got a headache;)

[rabidcow]

I have a theory too. It's called the placebo effect.

Take a hundred people with a headache. Give 50 a real headache pill and give the other 50 a pill containing nothing.

Result: 25 people with the real pill will feel better; 25 people with the fake pill will feel better.

Maybe I'm not giving proper deference to canon repair facilities, but I highly doubt they will take a lens apart and replace inner elements because someone sends it in claiming it is soft.

But there again, I've got a headache. I'm going to take an aspirin.:oops:


hahahahaha,,,I like that. I think that this ailment has a name though...Sympathetic Backfocus Syndrom.

[zacker]

why not take the lens back and give the customer a new one that has been tested? Like in the auto parts Indusrty.... take your car in to get the transmission rebuilt... they take the tranny out and stick in one that has previously been rebuilt... then they give you your car back in a day or two..rebuild your old tranny and stick it on the shelf for the next guy. This accomplished two things, first you get your car back sooner, secondly, you get it back with a n already rebuilt tranny that has been tested so it should (should being the oprative word here) be in good working order.
-zacker-

[YARRO]

Do the manufacturers not test every lens before they ship it?
Is some basic calibration not part of the prduction proces?

[ron chappel]

That's the heart of the question isn't it Yarro.
Of course they do callibrate them when manufactured,and we hear alot about reduced crop DSLR's needing greater AF precision -but these aren't really good enough excuses.
They SHOULD get them right before they ship them.

And i know they can callibrate lenses very accurately ,i've seen the results myself .After my 75-300IS was serviced it was consistantly the most accurate focussing lens i had.
All i can think of is that this exact type of callibrating takes a lot of effort so maybe they don't try so hard on the assembly line?

[kevbailey]

It basically comes down to quality control, and how intensive their final inspections are. Obviously, they have some type of qualifications that these lenses must pass before being packaged, but it would seems that needs to be squeezed a little tighter. I can understand on the lower end lenses having the tolerances a little more relaxed, but on the "L" lenses, these should be perfect! You're not going to be selling these to the general public! The people getting these are paying for perfection(in lens quality), in hopes to acheive perfection(in the raw image) so they can show perfection(the final photograph) to the general public who looks at it and says, "Wow, how did you get that snapshot"? (Photograph arrrrrgggh!)

Kevin

[zacker]

yes Q/C... Its not what it used to be... The evil empire ..the same ones who KNOW youll be back for more prolly do not inspect EVERY lens, just a % of the run.. It would take forever to inspect every single lens and body that ships out! Im positive they arent like me in my job.. (think about that whae you take your meds..lol) I HAVE to be sure the Piece is right when it ships.. then the customer STILL has to get it 3rd party inspected... but in the end, its totally done and done right.
-zacker-

[kevbailey]

I would imagine that they test the lens, then determine if it needs to be calibrated or not. If not, they shelf the job for a few days and send it back. But, more likely than not, they do take it apart and make sure that everything is aligned properly. We are talking about some extremely fine adjustments. Just taking it apart and re=positioning everything could bring it back to it's proper performance level.

Kevin

[NBEast]

That rings true. Only a percentage is QCed. I have to wonder if they didn't make some major change a few years ago (like evil outsourcing to cheaper nations not so quality inclined). The % of peole having real problems out-of-the-box seems higher lately.

If they charge $1200 for a lens that should be costing about $500 in actual mfg. costs, then another $50 should be spent on quality control. Perhaps they should correct the mfg. problem of WHY they have problems. It rings of management direction for quantity rather than quality, not some rogue bad factory workers.

Alas; their solution is a 1 year warranty, supurb service when things are sent in, and knowlege that only a small percentage of people will worry about (or notice) minute problems. Combined with a supurb design (except last year's 24-105 design's flaring problem) and pretty good quaility. Just not top shelf all the time.

Perhaps an "L+" designation could be created that guarentees a scientific inspection on each and every lens. I'd pay it, gladly. Instead, all my stuff is at Canon at present as I await the 7 - 10 day fix-it period. At least I don't have to wait 2 months like the OP.

[zacker]

two reasons... the dramatic up swing in DSRL ownership means more lenses, Alot more lenses being sold... And the time it would take to test each and every lens would be way to long.. "theres gold in them tar hills and we needs to git it first!" I imagine the way the lenses are made with probabblt some really tight tolerances mean, that canon dont need to test the lenses off the production line, and just fix the ones that do come back.
-zacker