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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 01 Mar 2009 (Sunday) 04:25
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front focus/calibration

 
Green_Tea
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Mar 01, 2009 04:25 |  #1

I have had a rebel xt for quite a while. I recently upgraded to a 40D but I kept my xt to use as a backup/ to put a wide angle on at sporting events. My general purpouse/walk around lens is a sigma 18-50 2.8. It focuses correctly on the xt but when i put it on the 40D it front focuses quite badly. I realize that sending it in to sigma can correct this problem. My question is this: when i get it back will it back focus on the xt? This would be a problem because it is the wide angle I use for sports. Is there any way that I will be able to get this lens to serve as both a walkaround on the 40D and still focus correctly on the xt? also... probably more to sadisfy my own curiosity than to actualy solve my problem... why is there such a difference between the two cameras... I mean i realize that they use two different AF systems but really?.... the difference is pretty huge... and why is this the only lens affected? all my other lenses do fine on both bodies. Thank you in advance for any help you may be able to give me.
-Trevor


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Mr-Beama
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Mar 01, 2009 06:05 |  #2

I have exactly the same problem with my 40D and 400D using the 50mm 1.4

https://photography-on-the.net/forum/showthre​ad.php?t=653512

I would also like more info on this issues, cheers :)


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yogestee
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Mar 01, 2009 06:12 as a reply to  @ Mr-Beama's post |  #3

It makes me wonder why lenses focus accurately with most cameras but not the 40D..

I shoot with a 350D and a 20D and would one day like to upgrade..All my lenses focus accurately with my 350D/20D.. I'm getting great image quality out of these cameras so I'll hold off for a while.. I doubt I will update to a 40D because I've read so many focusing problems with the 40D.. Am I being paranoid??


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Mr-Beama
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Mar 01, 2009 06:15 as a reply to  @ yogestee's post |  #4

It does make your head spin yogestee as I have taken super sharp/focused pictures with my 40D with other lenses and also with the 50mm on different cameras. I think in this case it's like the 2 just don't wont to get on :(


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KarlosDaJackal
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Mar 01, 2009 06:22 as a reply to  @ Mr-Beama's post |  #5

blast some air at the focus sensors.

all that junk that comes of the self cleaning sensor has to fall somewhere, and the focus sensors are at the bottom of the camera. Certainly the first thing i'd do as its quick, easy and free (well rocket blowers are almost free)


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Yaamon
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Mar 01, 2009 09:20 as a reply to  @ KarlosDaJackal's post |  #6

I had a xti that focused properly on all my lens including a sigma 24-70mm F2.8 and 18-200mm OS.

I upgraded the body to a 40D and XSI. Guess what the Sigma 24-70mm front focused, 18-200mm OS back focused, and a Canon 28-135mm IS front focused.

My other two lens the 18-55mm IS and the 24-105mm F4 IS focused properly on both bodies.

I sent in the sigma for service and the 24-70mm came back ok and electrical adjustment was made to the 18-200mm OS.

I also decided to send in the bodies to canon for calibration. Both bodies came back with electrical adjustment made for the auto focus. Now all the lens I have focuses properly on both bodies.

Here are a few examples 40d with the sigma 24-70mm. I focused on the flower noticed the bricks nice and sharp.

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO


@F2.8 after body was adjusted.

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO

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Mar 01, 2009 10:06 |  #7

I am curious about this subject as others here. My queston is this: Is the adjustment made in the lens or in the camera?

When the factory adjust (sending your camera & lens), do they adjust camera or lens or both.

When the 50D microadjusts AF, it the adjustment made in the camera or lens?

If it is in the camera, does the camera only make the adjustment when that lens is mounted, and revert back to other AF when others lenses are mounted.

Knowing where the actual adjustment is made would answer that question, I guess. However, if it is in the lens, and I adjust that lens on my 40D, will it also be good on my XTi?


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bohdank
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Mar 01, 2009 10:42 |  #8

If you send a camera and lens in, both are adjusted.

Both are adjusted to certain tolerances.

Both a lens and camera can be in tolerance but the results may not be the best... this happens when..... for example

A camera is adjusted within +5, -5. In this case the camera is at -5.... in spec.

A lens is calibrated to -5, in spec.

Put both together and the results are not acceptable yet both are within spec.

When you send them both in together. Both may be adjusted more precisely.. Camera to -2, for example and lens to +1. Difference is now 3, instead of 10, originally. Much better results. Kepp in mind, both were in spec originally and both are still in spec which means, unless you have other lenses that fall to one or the other extremes (-5, +5), they will work perfecly well on the same body, without having to send the lenses in.

The 50D has Micro Adjustment, which allows you to change the in camera focus compensation for up to 20 lenses (I think it's 20). You can have different settings for different lenses. Works great for primes but not always for zooms where it often happens that you adjust at the short end of the lens which throws off the long end. In those cases you need to send in the lens where they can program the lens differently for different focal lengths etc.


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guntoter
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Mar 01, 2009 10:47 |  #9

bohdank wrote in post #7430745 (external link)
If you send a camera and lens in, both are adjusted.

Both are adjusted to certain tolerances.

Both a lens and camera can be in tolerance but the results may not be the best... this happens when..... for example

A camera is adjusted within +5, -5. In this case the camera is at -5.... in spec.

A lens is calibrated to -5, in spec.

Put both together and the results are not acceptable yet both are within spec.

When you send them both in together. Both may be adjusted more precisely.. Camera to -2, for example and lens to +1. Difference is now 3, instead of 10, originally. Much better results. Kepp in mind, both were in spec originally and both are still in spec which means, unless you have other lenses that fall to one or the other extremes (-5, +5), they will work perfecly well on the same body, without having to send the lenses in.

The 50D has Micro Adjustment, which allows you to change the in camera focus compensation for up to 20 lenses (I think it's 20). You can have different settings for different lenses. Works great for primes but not always for zooms where it often happens that you adjust at the short end of the lens which throws off the long end. In those cases you need to send in the lens where they can program the lens differently for different focal lengths etc.

Interesting.......espe​cially knowing that the micro adjust of the 50D is in the camera and that it keeps different adjustments in memory for that many different lenses.
Thanks for the reply.


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Yaamon
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Mar 01, 2009 13:11 as a reply to  @ guntoter's post |  #10

I think what bohdank explained that the camera and lens need to be within a certain tollerance together. A good tollerance combination will give you proper focus.

This is why you can buy different lens of the same model and on your body, get one lens that focuses more accurately than another.

My thinking is that when you send in a camera or lens they might bring it closer to the 0 scale.


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Green_Tea
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Mar 01, 2009 16:30 |  #11

So... applied to my specific situation.. I feel like my best bet is to start by sending in just the 18-50... and then if necessary send in one or both bodies? right? Also... I have never sent anything in to be calibrated... and this lens is well out of warranty... how much cash am I looking at?
Thanks
-Trevor


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bohdank
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Mar 01, 2009 19:25 |  #12

If you can spare it, I would send everything in together.

Out of warranty cost.... if it's just calibration (no parts) I think it's around $150.... but there have been posters here that ended up getting the calibration done for free when sneding multiple lenses/bodies in at the same time.


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Green_Tea
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Mar 01, 2009 20:37 |  #13

the thing is... it is a sigma lens and a canon body... they wouldn't be sent to the same place.


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goose2
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Mar 01, 2009 20:41 |  #14

This exact question is why I opted for the 50d and not the 40d. I have had 4 different lenses mounted on my 50d and all of them had to be micro adjusted to a different number for a to my liking focusing. If I would have got a 40d I don't know how bad my pictures would have been.




  
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bohdank
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Mar 01, 2009 21:22 |  #15

Green_Tea wrote in post #7434306 (external link)
the thing is... it is a sigma lens and a canon body... they wouldn't be sent to the same place.

oops


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