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Old Nov 9, 2009, 8:55 AM   #1
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Default any way you can tell if you have a bad lens???

I been reading at a couple of forums online that some folks have returned lenses I was thinking of buying a couple of times before they finally got a good copy.

Is there a way to tell if you have a defective lens?

I was thinking of getting either a Canon EF 24-70mm f/2.8 L USM Lens or Canon EF 24-105mm f/4 L IS USM Lens for standard zoom.

Canon EF 70-200mm f/2.8 L IS USM Lens for long zoom.

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Old Nov 9, 2009, 9:12 AM   #2
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what camera body do you shoot?
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Old Nov 9, 2009, 9:18 AM   #3
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what camera body do you shoot?
Canon 5d mark ii
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Old Nov 9, 2009, 9:27 AM   #4
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I had a slight problem with front focusing with two lenses. However, my camera has the ability to compensate for that issue.

Here's how I determined I had a front focus problem.

1. I placed my camera on a table.
2. I got a thick yardstick and placed it at a 45 degree angle to my camera.
3. I placed the camera and yardstick as close together yet still get the camera's auto focus to work.
4. I used a center focal point , not multiple focus point.
5. I focused on the number 1 at 18 inches. (Actually my focal point was the top of the numeral 1.
6. Then I put that photo on my computer screen and I found that the 1 of the 17 was more in focus than the 1 of the 18. 17 was closer to me than the 18 due to the 45 degree angle of the yardstick.
7. I made an internal adjustment to the camera to compensate for the front focus.
8. Repeated the steps above until I got the results I wanted.

I own 4 lenses. 2 were spot on. One front focused a bit, the other front focused a bit more.

The great thing about my camera is that it remembers when lenses do what and compensates automatically.

Maybe you think you have a bad lens. Maybe it's as simple as front focusing.

BTW, the guy here at Steve's Digicam taught me how to test for front focusing problems. So don't thank me, thank them if this is your problem and you can get it cleared up by compensating.

I shoot a 5D mark II. It has the compensation mechanism built in. Test for front focus immediately. I bet that's your problem!!!!

Faithfully Yours,
FP
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Old Nov 9, 2009, 9:28 AM   #5
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24-105 is a good buy. Earliest version had some issues. The newer date code ones are very good out of the box. For 5D mark II 24-105 is a superb fit.

IS and 105mm works better than the 24-70.

Unless you need f2.8 24-105 is the best buy.

recommendation apart, the lenses are usually(over 90% of the times) perfect. There is a 10% chance that the lens may not conform to requirement.

these lenses are all repairable and replaceable under warranty. So buy it, use it in real life and see if somethings not right.
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Old Nov 9, 2009, 9:29 AM   #6
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the first thing i would do when you get your lens is a focus test. you can download printable "rulers". which you will place at a 45 degree angle. you then will focus on some mid-point on this "ruler" then by seeing which marks are sharpest, you can tell quite easily if its front or back-focusing.

the 2nd test you can run is a resolution test. there are charts and instructions online, you can then compare your results with published tests to see if you measure up.

and finally just do some subjective tests. shoot some scenes in good light with lots of minute details in the center and edges of the frame. and then just take a look, see how it resolves at multiple apertures.
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Old Nov 9, 2009, 9:38 AM   #7
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24-105 is a good buy. Earliest version had some issues. The newer date code ones are very good out of the box. For 5D mark II 24-105 is a superb fit.

IS and 105mm works better than the 24-70.

Unless you need f2.8 24-105 is the best buy.

recommendation apart, the lenses are usually(over 90% of the times) perfect. There is a 10% chance that the lens may not conform to requirement.

these lenses are all repairable and replaceable under warranty. So buy it, use it in real life and see if somethings not right.
Nymphetamine: Sigma's 24-70mm F2.8 IF EX DG HSM is a great lens. I have read several tests and this lens actually has been rated higher than the Canon 24-70 in some of the tests. However, it's about half the price of the Canon. I paid about $825 for mine including shipping.

If you prefer the 24-105 to the 24 70 due to price, then the Sigma may be a better option. Personally, I like the 2.8 f-stop ability of the lens. The 24-105 has IS, where the 24-70 does not. But if I use a tripod or monopod, I like the 2.8 for indoor shooting.

Again, I'm certainly not telling you that you don't prefer the 24-105. I just wanted you and others to be aware of the dollar value in the Sigma lens.

LAST>>>>>>>>>>>> Make sure you buy the right Sigma 24-70 lens. If it does not say HSM, you're looking at an older version of this lens. Make sure it is 24-70mm F2.8 IF EX DG HSM

Best Regards,
FP
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Old Nov 9, 2009, 9:42 AM   #8
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Nymphetamine: Sigma's 24-70mm F2.8 IF EX DG HSM is a great lens. I have read several tests and this lens actually has been rated higher than the Canon 24-70 in some of the tests. However, it's about half the price of the Canon. I paid about $825 for mine including shipping.

If you prefer the 24-105 to the 24 70 due to price, then the Sigma may be a better option. Personally, I like the 2.8 f-stop ability of the lens. The 24-105 has IS, where the 24-70 does not. But if I use a tripod or monopod, I like the 2.8 for indoor shooting.

Again, I'm certainly not telling you that you don't prefer the 24-105. I just wanted you and others to be aware of the dollar value in the Sigma lens.

LAST>>>>>>>>>>>> Make sure you buy the right Sigma 24-70 lens. If it does not say HSM, you're looking at an older version of this lens. Make sure it is 24-70mm F2.8 IF EX DG HSM

Best Regards,
FP
one thing, on a canon body + sigma lens combination. this is one where i would always do a focus test. canon bodies and sigma lenses have a long history of more AF problems than any other combination. however, sigma has great customer service and will gladly replace or fix any lens that is not focusing correctly, so as long as you are willing to do the tests, its not a problem at all.

as for myself, my sigma 80-400 focus's spot on.
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Old Nov 9, 2009, 9:44 AM   #9
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also if you are going to use the micro-adjust. the online test strips already have the 45 degree angle accounted for, so if it is showing 1mm front focus for example, it is truly 1mm apart.
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Old Nov 9, 2009, 11:29 AM   #10
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Thanks I will do a test as soon as I buy a lens. Hopefully I will get a lens with no issues.
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