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Author Topic: Canon lens calibration  (Read 17633 times)
alton
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« on: April 29, 2006, 12:02:57 PM »
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What can be corrected with Canon's lens calibration service and what can not be fixed? Is it a regular service provided by Canon and are people mostly satisfied with the results? What does it cost?
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phox
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« Reply #1 on: April 29, 2006, 04:57:39 PM »
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While this question is on the table, I'm also curious as to what people use as a yardstick for figuring out whether to bother with getting this done or not.
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gochugogi
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« Reply #2 on: April 29, 2006, 07:37:45 PM »
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While this question is on the table, I'm also curious as to what people use as a yardstick for figuring out whether to bother with getting this done or not.
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I merely use the lens normally, noting focus at infinity, marco and midway. If it looks good, that's it.  None of my lenses had a problem with either my 10D or 5D. I had an EF 70-200 4L USM that was sharp on the right but soft on the left (with every camera, even film). Apparently Canon needed to realign the elements. It was out of warranty so it cost about $150. Not the same as calibration to a body but I bet the price is similar.
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David Anderson
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« Reply #3 on: April 29, 2006, 09:02:41 PM »
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I'm not sure what they do at Canon, but I've had the focus and centering done by them.

Lens calibration can make a big difference in the quality of a lens assuming it's out in the first place.
My 135 F2 was focusing in front in a big way when I first got it, but a couple days in service and it's as good as any lens I've ever used.

But not all lenses need it.

You should test them for focus accuracy and sharpness yourself before sending them in.

I have a standard test now with a large wide ruler at a 45 deg. angle for focus testing and a flat wall with with details in all the corners and center for sharpness testing.

Yes pedantic I know, but I would rather see a problem at home then at a job...

As I've also said before, check that your body is focusing accurately before you blame the lens.
If you body is out a bit your photos might look soft when you shoot wide open.

David.
« Last Edit: April 29, 2006, 09:05:14 PM by David Anderson » Logged

thompsonkirk
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« Reply #4 on: April 30, 2006, 09:28:40 PM »
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I've had 2 L zooms with inconsistent sharpness, some focal lengths performing much better than others, as in Michael's review of the 16-35 & 17-40.  

If you send a lens in under warranty with a complaint about sharpness, Canon goes through the whole lens, lubricating it & everything - even though it's brand new.  But the significant step is that they re-set the "best focus point."  

My 17-40 was just like the one Michael reviewed, sharp at short focal lengths & rather a mess at longer ones.  A 24-105 had the opposite problem, soft below 35mm; and another photographer in the same building got a 24-105 that wasn't on target at the longer focal lengths.  

Re-calibration turned all 3 of these dogs into solid performers that compete with non-L primes.  

If I ever need another Canon zoom, I'll anticipate sending it in for re-calibration.  IMO the factory tolerances are way too wide on L zooms, & the glass is good enough to deserve a lot more attention before the lenses leave the factory.
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roli_bark
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« Reply #5 on: May 01, 2006, 08:42:40 AM »
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You should test them for focus accuracy and sharpness yourself before sending them in.

I have a standard test now with a large wide ruler at a 45 deg. angle for focus testing and a flat wall with with details in all the corners and center for sharpness testing.

How can I tell quantitively [at home] whether a lens is sharp or not ?
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jimhuber
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« Reply #6 on: May 01, 2006, 09:29:33 AM »
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I typically shoot a shelf of books and look at the writing on the spines (tripod mounted with self timer and mirror lockup, of course). I'll shoot wide open and then at each conventional full stop (2.8, 4, 5.6, ...).

Sometimes I'll shoot 1/3 stops close to wide open. For example, my 85mm f/1.8 sometimes has moderate "purple fringing" wide open in harsh light, but it decreases some at f/2, better at f/2.2, and gone by f/2.5. It's better to know what to expect before you're in a situation where it's a tight squeeze between aperture, shutter speed, and ISO so you can choose wisely instead of blindly.

Michael Tapes's latest iteration of the WhiBal has a small resolution star on it plus metric and medieval measurement marks. It might work in a pinch.
WhiBal
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spotmeter
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« Reply #7 on: May 13, 2006, 11:07:37 PM »
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"How can I tell quantitively [at home] whether a lens is sharp or not ?"

Print up 5 sheets of the same line of type double spaced from 8 point to 72 point, with the type size included at the end of each line.  This should fill the page. Set up your camera with a 50mm lens 10 feet from the wall. Make sure the camera is level and square to the wall.  Tape one sheet on the wall so that it is in the center of your viewfinder. Tape the other four sheets so that they are in the corners.  Lock up your mirror and use a cable release. Shoot at all apertures. Look at the RAW files at 100%. I consider a lens sharp when you can read the 12 point line in the center and corners--as I can with my Carl Zeiss 50mm 1.7 on my Canon 1DsMkII.  This test will also tell you the best apertures to shoot at.  You will notice that most lenses go soft at f16 and 22.  Some of my lenses are sharpest at 5.6, others 8, some at 11.

Then test each lens in your kit so that the four corner sheets fill your frame. In this way, you can compare the resolution of your primes and zooms at various focal lengths.

You can also check the contrast of your lens. Is the black of the 72 point type really black, or is it blue or brown?  Are the edges of the number sharp, or are they fuzzy? The 72 should be black with sharp edges.

To check focus accuracy, tape a yardstick to a wall, set up your camera at 45 degrees to the wall and focus on a number on the yardstick with the lens wide open.  Look at the RAW file at 100%.   I don't worry if the lens is half an inch off as I don't shoot wide open. If you do, you will want to get it corrected.

Finally, you will want to check focus at infinity. I do this by shooting a commercial sign at a distance of 100 feet or more with the lens wide open, and then examine the RAW files at 100%.

Don't use JPEG on your tests. It really degrades resolution.
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David Anderson
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« Reply #8 on: May 13, 2006, 11:36:32 PM »
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How can I tell quantitively [at home] whether a lens is sharp or not ?
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The posts above answer the sharpness test.

My focus accuracy test is done by shooting a large metal ruler laid flat in the shade of my shed.
I then shoot it at 45 deg. with the camera on a tripod and the center focus square on the 15cm mark.
The shots are done at or near minimum focus.

Alowing the camera to refocus every frame I do half a dozen shots, it's very clear at 100% veiw if the lens is out.

For example if 5 out of the six frames are sharp on 14 cm you have a problem.
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allan67
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« Reply #9 on: May 15, 2006, 01:57:59 AM »
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There's a good article on testing the focusing of camera-lens combo here:
http://www.hkdotnet.com/FrancisPhotographyChannel/AF_Test/

Works well and very accurate.
Allan
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Lukas Bux
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« Reply #10 on: May 27, 2006, 10:21:26 AM »
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Hi...I stepped up to a DSLR because I wanted the option of manual focus. After shooting a couple cards I noticed that my pics seemed front-focused (the ear but not the eyes, the shoulder but not the face, etc). I have performed the focusing tests with two different lenses and my results seem to indicate that in AF mode with the lenses wide open the focus is accurate, but with manual focus the camera (or the lens, or my eye) DOES indeed front focus.

So my question (sorry for the lengthy intro)...in reading other posts on this board a lot of people seem to indicate that they believe "poor technique" to be a main culprit with claims of front focusing. I'm willing to blame myself, but I can't find any more info on why I would be getting front-focusing with manual focus. Can someone help me further diagnose this--most of the focus tests on the web revolve around AF issues and don't really mention what might be wrong if you are having MF issues.

I firmly believe I am seeing things in focus in the viewfinder, so it is not intuitive to me that eyesight would cause you to see something in focus yet focus on something in front. I have made sure the dioptric setting on the viewfinder is neutral. I used 35mm film cameras for years and my pictures seem to indicate that I was focusing accurately.

Any help is greatly appreciated.

LB
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Johnny_Johnson
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« Reply #11 on: May 27, 2006, 07:05:22 PM »
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Can someone help me further diagnose this--most of the focus tests on the web revolve around AF issues and don't really mention what might be wrong if you are having MF issues.

It's not unheard of for the location of the focusing screen to be "off" from the factory.  I had a consistent back focus problem (when manually focusing) with my Canon 5D until I sent it back to the New Jersey service center for correction.

Later,
Johnny
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Roger Krueger
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« Reply #12 on: June 08, 2006, 01:59:49 AM »
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I firmly believe I am seeing things in focus in the viewfinder, so it is not intuitive to me that eyesight would cause you to see something in focus yet focus on something in front. I have made sure the dioptric setting on the viewfinder is neutral.
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Diopter setting won't move the focus point. The light is brought to focus on the focusing screen. The diopter setting merely alters your ability to focus your eye on the screen.

For a good AF/bad MF problem my first guess would be a misaligned focusing screen, my second guess would be a mirror misaligned or not quite making it all the way down. Try using various non-central parts of the screen and see if that changes anything.

To eliminate user error as a possibility try a focus magnifier. The Canon 90 degree finder is pretty expensive, but you can generally find older magnifiers for other brands that fit perfectly on Canon eyepieces. I use an old 70's Minolta magnifier I got used for $15, only drawback is that it's smaller than your eyesocket, so you can jab yourself in the eyeball if you're not careful.
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Gregory
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« Reply #13 on: June 10, 2006, 09:43:49 AM »
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To check focus accuracy, tape a yardstick to a wall, set up your camera at 45 degrees to the wall and focus on a number on the yardstick with the lens wide open.  Look at the RAW file at 100%.   I don't worry if the lens is half an inch off as I don't shoot wide open. If you do, you will want to get it corrected.
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hi.

exactly what might you see if the lens is not focussing accurately? 10" apparently in focus in the view finder but out of focus in the raw image?
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jani
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« Reply #14 on: June 10, 2006, 03:26:03 PM »
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hi.

exactly what might you see if the lens is not focussing accurately? 10" apparently in focus in the view finder but out of focus in the raw image?
Well, if the 10" mark isn't in focus in the raw image, then it isn't in focus.

It's as simple as that.

The mark that is in focus will show you how imprecise the focusing was.
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gochugogi
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« Reply #15 on: June 14, 2006, 11:05:51 PM »
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I firmly believe I am seeing things in focus in the viewfinder, so it is not intuitive to me that eyesight would cause you to see something in focus yet focus on something in front. I have made sure the dioptric setting on the viewfinder is neutral. I used 35mm film cameras for years and my pictures seem to indicate that I was focusing accurately.
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I can manually focus fine with a FM3A or FE. The screen is made for manual focus. However it's not nearly as easy with an AF SLR. The screens are less contrasty, lack a microprism and tend to be lower magnification.

If your DSLR has interchangeable screens, install one meant for MF. It will be more contrasty although darker (you'll need to stick to faster lenses). If a microprism or split is available so much the better. Second, I'll parrot other posters by saying an eyepiece magnifier really helps MF. I'm not sure hat system you use but Canon has a flip-off angle model. Also, the Olympus 1.2x eyepiece magnifier fits both Oly and Canon.
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