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Author Topic: How to get / test a good copy of a L lens?  (Read 9238 times)

Marsu42

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How to get / test a good copy of a L lens?
« on: February 20, 2012, 02:13:34 PM »
I'm going to buy a 70-300L (but the question is valid for any prime tele lens), and since these are precision optics well below the price of the hubble space telescope, there are big variances and I am wondering how to end up with a sharp / non-ca copy. Two questions:

* Where to buy: Of course I could get the lens at the pro shop 'round the corner and test/return the lens numerous times - but at a premium of at least ~200€. Now you could say I'd get what I pay for, but suppose I didn't win the lottery and have to save $$$. I intend to get the lens from Amazon (I'm in Germany) - any experiences how often and w/o problems you can return the lens if the copy is bad?

* How to test: This is my most important question: If I get the lens, no matter what the source - How do I test that the lens is a good copy? Take pictures of some chart - and then compare them to what? Obviously every L lens takes 'good' pictures, but for me it would be impossible to tell if the lens I have is one that has been returned numerous times before and then ended up with me.

Thanks for your input, just now I really have no idea how to tell a good copy from a bad one...
« Last Edit: February 20, 2012, 03:27:15 PM by Marsu42 »

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How to get / test a good copy of a L lens?
« on: February 20, 2012, 02:13:34 PM »

neuroanatomist

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Re: How to get / test a good copy of a L lens?
« Reply #1 on: February 20, 2012, 08:40:07 PM »
See http://www.canonrumors.com/tech-articles/how-to-test-a-lens/.

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Re: How to get / test a good copy of a L lens?
« Reply #2 on: February 20, 2012, 09:07:42 PM »
I think you're slightly overestimating the importance of hunting for a "good copy" of a lens.  It's not like you have a 50/50 chance of getting a good one, I would just try 2-3 different ones and see if you notice any major differences.  I think you'll notice that most of them perform very well there is just the occasional copy that's perfect and may perform slightly better.
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Mt Spokane Photography

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Re: How to get / test a good copy of a L lens?
« Reply #3 on: February 20, 2012, 10:36:44 PM »
I'm going to buy a 70-300L (but the question is valid for any prime tele lens), and since these are precision optics well below the price of the hubble space telescope, there are big variances and I am wondering how to end up with a sharp / non-ca copy. Two questions:

* Where to buy: Of course I could get the lens at the pro shop 'round the corner and test/return the lens numerous times - but at a premium of at least ~200€. Now you could say I'd get what I pay for, but suppose I didn't win the lottery and have to save $$$. I intend to get the lens from Amazon (I'm in Germany) - any experiences how often and w/o problems you can return the lens if the copy is bad?

* How to test: This is my most important question: If I get the lens, no matter what the source - How do I test that the lens is a good copy? Take pictures of some chart - and then compare them to what? Obviously every L lens takes 'good' pictures, but for me it would be impossible to tell if the lens I have is one that has been returned numerous times before and then ended up with me.

Thanks for your input, just now I really have no idea how to tell a good copy from a bad one...

Maybe you can contribute a few euro to Klaus at photozone and ask him to test it for you?  Most of the lens buyers are in your shoes, they really can spot only the worst errors.  Be warned though, he has high standards for quality, so even a lens he gives average marks to can be pretty good.

dolina

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Re: How to get / test a good copy of a L lens?
« Reply #4 on: February 20, 2012, 11:35:50 PM »
Have you ever bought a bad copy?
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dr croubie

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Re: How to get / test a good copy of a L lens?
« Reply #5 on: February 21, 2012, 12:14:01 AM »
How far West are you in Germany?

Take a trip over the border to fotokonijnenberg.nl, the guys in The Hague shop are good, but there's a shop closer to Germany i've never been to. They'll possibly let you take each outside for a few minutes to test which is best of the copies they have in stock. Make sure you Live-view MF on a tripod and take a picture of a static subject to see if there are any glaringly bad copies, but I don't think you will be able to find the diamond in the rough as easily/quickly.

Oh yeah, and the most important thing, is that they're cheap. I bought my 70-300L there, best price I could find anywhere (including on net-shops) was in their store.
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Marsu42

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Re: How to get / test a good copy of a L lens?
« Reply #6 on: February 21, 2012, 01:13:40 AM »
Maybe you can contribute a few euro to Klaus at photozone and ask him to test it for you?
The photozone site says the testing queue is full: http://www.photozone.de/canon-eos/365-request_canon

I think you're slightly overestimating the importance of hunting for a "good copy" of a lens.
I always like to take advice, but I have to ask: How would you know how many bad or mediocre copies are produced? For example, the lens test at "The Digital Picture" shows significant differences between two "ok" copies.

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=738&Camera=453&Sample=1&FLI=0&API=0&LensComp=738&CameraComp=0&FLIComp=0&APIComp=0

I would just try 2-3 different ones and see if you notice any major differences.
That's the problem: If I get a lens through mail order, I have exactly one lens to test... and I am wondering if it is possible at all to compare this to synthetic data. As I wrote, I'd like to get around the other possibility to go to a pro shop, make the guy order 4 lenses at compare them there because of the price premium .

Have you ever bought a bad copy?
That's the point: I wouldn't know, would I? However, I didn't buy a L lens for 1000€+ yet and thus didn't loose much sleep over it if it "was worth it" (like Ken Rockwell says)

How far West are you in Germany? Take a trip over the border to fotokonijnenberg.nl,
I'm from Berlin, ie too far East :-\

Minimally, shoot blue sky wide open to check for symmetrical vignetting (lack of that means decentering).
I've read the 70-300L doesn't show vignetting at all on crop bodies, so that wouldn't help :-o

See http://www.canonrumors.com/tech-articles/how-to-test-a-lens/.
Thanks for the link! However, it basically says that you cannot check for overall sharpness - only for a broken lens and for for relative sharpness in one quadrant of a lens in comparison to another. Which is better than nothing, though.

I guess one way of solving this problem is to find another person near me with this lens, get there and compare. Or walk into some electronics market with my test chart and at least get some shots from another 70-300...

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Re: How to get / test a good copy of a L lens?
« Reply #6 on: February 21, 2012, 01:13:40 AM »

candyman

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Re: How to get / test a good copy of a L lens?
« Reply #7 on: February 21, 2012, 03:02:16 AM »
........... but there's a shop closer to Germany i've never been to. ...............


What is the name of that shop?
Thanks!

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dr croubie

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Re: How to get / test a good copy of a L lens?
« Reply #8 on: February 21, 2012, 06:45:32 AM »
........... but there's a shop closer to Germany i've never been to. ...............


What is the name of that shop?
Thanks!

Oops, I meant there's another outlet of Fotokonijnenberg. They've got 3 shops, Den Haag, Den Ham (SW of Emmen, NW of Enschede), and Turnhout (is actually in belgium). Currently €1.199 for a 70-300L (they were cheapest when I bought mine about this time last year, don't know if anyone's cheaper than that now though)
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Mt Spokane Photography

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Re: How to get / test a good copy of a L lens?
« Reply #9 on: February 21, 2012, 08:28:35 AM »
You can certainly test the quality of a lens yourself, its just a matter of really wanting to spend the time, money, and self education to do it.

Most people give up when they see how much work it is, and the price.  Look at the Demo, print the charts, and photograph them.  Obvious problems with a lens may show up, but most issues are subtle.

Start here!
http://www.imatest.com/products/software/imatest-studio/

Even the basic consumer software is not cheap, you can print your own test charts, have them printed, or buy expensive ones.

K-amps

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Re: How to get / test a good copy of a L lens?
« Reply #10 on: February 21, 2012, 10:12:45 AM »
I have not heard of people getting bad copies of the 70-300L so far. I have heard it for other lenses.

I got 1 copy and it was great, and I am a bit fussy... I went through 2 copies of the 70-200mkII and 17-40L because they did not seem sharp to me... or as sharp as the 70-300L.

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ejenner

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Re: How to get / test a good copy of a L lens?
« Reply #11 on: February 21, 2012, 11:18:42 AM »
since these are precision optics well below the price of the hubble space telescope

I have to ask if this was a deliberate tongue-in-cheek poke at NASA considering the Hubble optics were softer than a 17-40 at f4 in the corner and possibly the ultimate example of a 'bad copy'?

If so I definitely appreciated the humor.

On the testing question, personally I can only tell if a lens is sharp compared to something else - either the same lens stopped down, or another lens.  For instance my 24-105 seems sharp enough, I suspect it is a decent copy, and people on forums often call it sharp.  But if I compare it at 24mm to my TS-E 17mm with a 1.4x, it looks quite mushy.  Doesn't look all that sharp compared to my sig 85 1.4 either.  I think this is one of the main problems with calling a lens 'sharp' - sharp compared with what?

Anyway, if you have a good idea of roughly how sharp it should be compared to another lens you own (probably a zoom), I would test it against that and unless it is obviously bad, it is very probably a 'good' copy.

If you are one of these people trying to get a super sharp copy for your particular camera then you need some serious testing gear and about 5-10 copies of the lens.  If you want the sharpest copy that will also like be one of the sharpest on a future camera, you're going to need 5-10 camera bodies as well and probably more lenses.  The of course one copy might be slightly sharper at 70mm and another slightly sharper at 300mm.  The point I'm trying to make here is that while there is certainly copy-to-copy variation, the 'bad' copies of any lens are usually obviously bad when compared to other similar lenses.
« Last Edit: February 21, 2012, 11:37:27 AM by ejenner »

Marsu42

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Re: How to get / test a good copy of a L lens?
« Reply #12 on: February 21, 2012, 01:04:01 PM »
since these are precision optics well below the price of the hubble space telescope

I have to ask if this was a deliberate tongue-in-cheek poke at NASA considering the Hubble optics were softer than a 17-40 at f4 in the corner and possibly the ultimate example of a 'bad copy'?

Um - you're right, this joke was on me :-o ... I nearly forgot the hubble telescope was broken and then fixed by software - however trusty Wikipedia says it was a mirror and not a lens...

What I actually wanted to say that I doubt a commercial company can produce something like the 70-300L at 1k€ by dumping all non-optimal copies - it is more probable they'll try to widen their specs and try to sell as many as possible and get them returned if someone notices. On the other hand, this might be a conspiracy theory.

On the testing question, personally I can only tell if a lens is sharp compared to something else - either the same lens stopped down, or another lens.

You're correct, and I think I have at last figured out how to test my new shiny L lens once it arrives w/o having multiple lenses of the same type, this should at least tell me if I have to return it or keep it:

1. determine front/backfocus, have a look for broken bokeh (a German Amazon review states this has occurred with this lens) and then shoot a ISO 12233 chart at different settings

2. compare the lens to itself (i.e. is the top right sharper than the bottom left etc)

3. compare the *differences* of my lens at different apertures to the *differences* of the samples from www.the-digital-picture.com - i.e. does my copy show the expected relative iq improvement/degradation or is for example my lens especially bad at full open?
 
4. compare the *differences* between my 70-300 any my 100/2.8 (I know this is a very good copy) to the *differences* to be expected between these lenses from the samples from www.the-digital-picture.com
« Last Edit: February 21, 2012, 01:08:18 PM by Marsu42 »

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Re: How to get / test a good copy of a L lens?
« Reply #12 on: February 21, 2012, 01:04:01 PM »

neuroanatomist

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Re: How to get / test a good copy of a L lens?
« Reply #13 on: February 21, 2012, 01:42:30 PM »
Minimally, shoot blue sky wide open to check for symmetrical vignetting (lack of that means decentering).
I've read the 70-300L doesn't show vignetting at all on crop bodies, so that wouldn't help :-o

Sorry - didn't notice the 60D in your gear list.  Instead, you'd need to shoot a test chart or flat surface with detailed textures, align the camera so the sensor is parallel to the chart/wall, and compare the corners to each other to see it they're equivalent (not as sharp as the center, but as sharp as each other). 

See http://www.canonrumors.com/tech-articles/how-to-test-a-lens/.
Thanks for the link! However, it basically says that you cannot check for overall sharpness - only for a broken lens and for for relative sharpness in one quadrant of a lens in comparison to another. Which is better than nothing, though.


I don't think it says that at all.  You certainly can test a lens for overall sharpness, and several suggestions have been offered for doing so.  Personally, I use a test chart that costs more than some L-series lenses; there are free versions that can be printed and will work fine.  Likewise, there's the Imatest software which Mt. Spokane linked, but if you'd prefer not to spend the money on that, or like me, are a Mac user whereas Imatest runs only under Windows, Norman Konen provides some download links to macros (free) which run in ImageJ (also free, formerly NIH Image) to perform SFR analysis. 

Copy variation is inherent to the manufacturing process, as made quite evident by Roger Cicala's (lensrentals.com) testing of many copies of various 50mm lenses.  On a smaller scale, Bryan at TDP tested three copies of what is currently Canon's most expensive zoom lens, the 70-200mm f/2.8L IS II.  Two of the three were sharper at 200mm than at 70mm, the third was sharper at 70mm than at 200mm.  Canon's theoretical MTF curves suggest the lens should be sharper at the long end.  Does that mean one of Bryan's lenses was a 'bad copy'?  Not if you'd want to use it more at the short end than at the long end...  But it's an outlier compared to the other two.

I think the point about testing sharpness of a lens that you buy was not that you can't, but that doing so offers no menaingful way to determine if yours is a 'good copy'.  No two testing setups are identical, and to compare results across different testers/setups, they would need to be the same.  Even so...say, for example, that you duplicated Klaus' photozone.de test setup quite accurately, such that you could compare the MTF50 numbers you obtained to his posted data.  What if your new lens was slightly better?  Would you think you have a good copy, and stop there?  All you'd really know is that your copy was better than the copy Klaus tested - maybe that copy was one of the worst, so your copy would only be slightly better than the worst.  Conversely, what if the copy you got didn't perform as well as the photozone copy?  Would you return it and buy another one?  What if Klaus tested one of the best copies - how many lenses would you go through?  What if the next 4 lenses you bought were worse than the first one, but you'd already sent that one back, and of course you would not be able to repurchase that specific copy...

Going back to the original question, "How can I get / test a good copy of a lens?"  Basically, there's only one way to do that - establish a robust and reproducible test setup, then buy 10 copies of the lens you want, test them all, keep the best one and send the other 9 back.  (Then, the return postage with insurance would probably pay for a 17-40L).  Short of that extreme which would be needed for meaningful comparative data, what you can realistically do is not determine if you have a 'good copy' of a lens, but rather, determine that you don't have a defective copy of the lens.  If that's the case, then you have a copy that should meet Canon's manufacturing QC standards, and while there are obvioulsy variations in quality within that range, the a difference of a few 10's of LW/PH that you can detect shooting test charts is not going to make a meaningful difference when shooting things out in the real world.  Still, I've heard of people who send every lens they buy into Canon service, and some report the lenses are adjusted and come back sharper.

Having said all of that, there is a test you absolutely should perform, and one that will make a whole lot more difference than finding the sharpest copy of a lens.  Test the AF performance of your new lens.  Assuming you're not one of those MF-only folks, if your camera AF doesn't play nicely with your new lens, that's going to have a real and meaningful impact on your shots, since shots where focus is off are rarely sharp.  For example, my 70-200mm II IS delivers very sharp results with my test chart (where testing is done with manual focus, by focus bracketing).  On my 7D it requires an AF microadjustment of +2, which means it's off by 1/4 of the depth of focus wide open - in most cases, that's close enough not to notice.  But the same lens on my 5DII needs an AFMA of -6 - that's 3/4 of the depth of focus, and means that without that adjustment, many shots would be noticeably back-focused.  Given that you have a 60D, where you cannot make those adjustments, AF performance will be very important for you to test.  Just keep in mind that if your body is at one end of the range or the other, you might find a lens to match, but if you get a new body later, the lens might be way off.  For me, a backfocusing 100L Macro on my T1i/500D was a big part of my move to the 7D, and I'll never buy a body without the AFMA feature.

AFMA might not be such a big deal for this lens - f/4.-5.6 on APS-C doesn't yield a very shallow DoF, and deeper DoF masks focus errors.  But having said that, I owned a 70-300mm f/4.5-5.6 DO IS lens, and it required a -7 AFMA setting on my 7D to correct the backfocus.  You can see a typical pre-AFMA shot below, focus was not on the eye but rather the plane of critical focus was running through the back legs of the frog - this is a shot at 300mm f/6.3, and the backfocus is evident.
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Marsu42

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Re: How to get / test a good copy of a L lens?
« Reply #14 on: February 21, 2012, 02:19:57 PM »
Thanks for the link! However, it basically says that you cannot check for overall sharpness
I don't think it says that at all.  You certainly can test a lens for overall sharpness, and several suggestions have been offered for doing so.

I didn't make myself clear on this, sorry: The article "How To Test a Lens" says what you just wrote: You can test for overall sharpness, but not for a "good copy" with just one lens to test.

However, on reflection I don't think this is entirely true (see my suggestion: compare the differences between two lenses you own (of which one has to be a good copy for the baseline) to the differences between the same lenses from the digital picture)

Having said all of that, there is a test you absolutely should perform, and one that will make a whole lot more difference than finding the sharpest copy of a lens.  Test the AF performance of your new lens. [...] Still, I've heard of people who send every lens they buy into Canon service, and some report the lenses are adjusted and come back sharper.

That's interesting, because the guy who sold my macro lens said just that - he had it adjusted by CPS, and it indeed is extremely good.

You don't seem to have first-hand experience, but maybe someone else can comment on this - what is Canon service actually able to do?

* AF adjustment (Do I have to turn in my non-afma body with my lens)?
* sharpness / ca-improvments?
* Do they do it for free on warranty / how bad does a problem have to be to make them do it for free?

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Re: How to get / test a good copy of a L lens?
« Reply #14 on: February 21, 2012, 02:19:57 PM »