How to tell if you have a good copy

I'm in the market to purchase a used 24-105L. I've never purchased used before and this would be my first L lens. I currently have a 28-135, but with the arrival of a new 50d this week, I'd like to upgrade to the 24-105L.

I've read on this forum as well as others that there can be good and bad copies of the same lens. The quality in terms of sharpness can vary.

How do I know whether I have a good copy or not once I purchase the lens? Is there specific tests I should do? If I buy a 24-105L w/ date stamp of UV or better, is it reasonable to expect the copy to be excellent and that poor copies (lens creep, sharpness) are few and far between?

Thx.

my response in a similar thread to this, but i'm no expert on the subject.....

https://photography-on-the.net …php?p=8612715#p​ost8612715

Lens creep and sharpness are pretty easy to check for. I'd also look for other mechanical issues - smooth zoom and focus operation, IS works normally with no loud noises, aperture blades operate smoothly (you can use DOF preview to test this), glass is clean inside and out, no signs of major trauma (dents, or paint chips).

Just curious, what evidence did you have that linked a date code with guaranteed improvement over older date codes? Did you come across a source of information that, for example, told you that Canon had fixed manufacturing issues starting in the UV year?

(otherwise, I wouldn't link date code with quality. It's just that, manufacture date. IMHO, newer date code doesn't mean better copies).

To answer your question, I would test for sharpness and back/front focus.

This suggestion may sound way out there, but....I'd go out and use it to take some photos, then download them to my computer and look at them.

The only time I would ever waste my time shooting test charts, batteries, rulers, etc., or micro-adjusting my lenses, would be if I noticed something about my "normal" images that didn't look right. Maybe that's just me, though.

L_F_L wrote in post #8616513
Just curious, what evidence did you have that linked a date code with guaranteed improvement over older date codes? Did you come across a source of information that, for example, told you that Canon had fixed manufacturing issues starting in the UV year?

(otherwise, I wouldn't link date code with quality. It's just that, manufacture date. IMHO, newer date code doesn't mean better copies).

To answer your question, I would test for sharpness and back/front focus.

You shouldn't make such a blanket statement. Early versions of this lens suffered from severe flare, especially at wide angles with a wide-open aperture. This problem affected 24-105L's with a date code beginning with 'UT' and earlier. My lens is a 'UU', is very sharp across the range, and doesn't suffer from the flare issue.

OP: Get a lens with a 'UU' or later date code and you should be just fine.

I didn't make a blanket statement -- I preceded it with a question regarding the issues with this lens' older manufacture dates.

Please revert to the original thread on this topic:

https://photography-on-the.net/forum/...15#po​st8612715

John Swan wrote in post #8617575
Please revert to the original thread on this topic:

https://photography-on-the.net/forum/...15#po​st8612715

What makes yours the "original thread"? This topic has been up dozens of times in the past.

LOL - his thread is more 'original?'

Should I absolutely not expect any lens creep at all from the 24-105L? Sounds like some have issues w/ this and some don't. Variation accross different copies...

Barso23 wrote in post #8618447
Should I absolutely not expect any lens creep at all from the 24-105L? Sounds like some have issues w/ this and some don't. Variation accross different copies...

Hi, as already requested, please refer to the other thread as it was started before this one. If you continue to bump this thread I will be forced to contact a mod to lock or perhaps even delete it. Regards.

rvdw98 wrote in post #8618041
What makes yours the "original thread"? This topic has been up dozens of times in the past.

Its pretty obvious that Mr. Swan is either full of himself (judging by some of his posts), or just simply can't read thread titles. The OP in this particular thread refers to "used" lenses...the thread that Swan is so obviously proud of, and links to, pertains to testing of "new" lenses. He should understand what he's posting about before telling us what threads to ignore...

John Swan wrote in post #8618514
Hi, as already requested, please refer to the other thread as it was started before this one. If you continue to bump this thread I will be forced to contact a mod to lock or perhaps even delete it. Regards.

What's your deal? Maybe I'll report YOU to a mod as being nothing more than a troll. How's that sound?

argyle wrote in post #8618530
Its pretty obvious that Mr. Swan is either full of himself (judging by some of his posts), or just simply can't read thread titles. The OP in this particular thread refers to "used" lenses...the thread that Swan is so obviously proud of, and links to, pertains to testing of "new" lenses. He should understand what he's posting about before telling us what threads to ignore...

My referred to newly purchased. The same thing applies for newly purchased second hand lenses. There is no need for this thread and it needs to be locked asap.