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04-14-2008, 04:32 AM   #1
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teach me (how to notice) all possible bad copy problems of 16-50???

a seller (in Turkey) who i trust will go to China and i think i will order a 16-50...in turkey it is almost 1500 dolar!!!
i think i should teach him the bad copy problems of 16-50 to prevent him getting me a bad copy...
may you guys tell me all problems you encounter with bad copies???
if you elaborate the problems you encounter, it would be easier to him to notice the problems...
thanks a lot
halil

04-14-2008, 07:12 AM   #2
hll
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hey, i need you guys, come on!!!
04-14-2008, 07:15 AM   #3
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This is the test chart with instructions that will give you all the info you need. make sure you use a tripod with SR off and 2 sec MLU.

http://focustestchart.com/focus21.pdf
04-14-2008, 08:37 AM   #4
hll
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dear peter,
thank you for the chart...
i know it has problems beyond the back and front focus problems...
but i don't know what exactly they are..
i think some people encounter softness issues at 2.8
and "ben" had a 16-50 which has some bad image quality at the corners... (doublig)
any more???

04-14-2008, 08:46 AM   #5
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Hi Halil, tell him to check also inconsistencies in corner resolution (left corner sharper than right corner or viceversa). Some people says that problems develops overtime due to a subestandar piece or ensambling in the focusing mechanism but I dont know exactly what the problem is cos I have never been interested in that particular lens. Hope it helps
04-14-2008, 08:51 AM   #6
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The other thing to do is take a flat piece of well printed newspaper or something similar and tape it to a wall FLAT in a well lit room. Set the camera up on the TRIPOD with SR off and 2 second MLU and get the camera as parallel (horizontal and vertical) to the wall as you possibly can. Ten take some shots of the newspaper wide open.. When you review the shots you're looking for one side of the image to be as sharp as the other side. If one side seems out of focus then the elements could be out of alignment.

But consider that your setup has to be almost perfect to see this. Sometimes we look for things that are not there and the DOF is so shallow in this test, that any setup errors will show a problem that isn't there. If the lens just appears a little soft in the corners then that's not a reason to discard the lens. It's relatively normal for most lenses, even the best ones. to have this.
04-14-2008, 10:20 AM   #7
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hll, I really hate to say that in my opinion your best off to buy any equipment, especially that lens from a store where you can easily return it

Not necessarily a local store, but one that you know will stand up for you if your having a problem with it. And take is back if required

Plus in a case like yours you'll want your friend to ensure that you can easily communicate with whomever he gets the lens from in case of problems.
Theres nothing worst than a language barrier while attempting to resolve issues.

As for testing the lens, any good store should allow him to test it in the store. Which should give you a general idea if it's a good one.
I wouldn't be surprised if some stores let him test it outside with a deposit, or a credit card number.

Lots of luck with your purchase.
04-14-2008, 10:32 AM   #8
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IMO, here is what he needs to bring to the store to test the lens: a piece of newspaper, tapes, a tripod or flash, and a laptop. MLU is not neccessary, but should be used if you use tripod. If you handhold the shot with flash, no need for MLU.

Just tape the newspaper on a flat surface, frame the newspaper so that there are texts in all corners.

Shoot straight (perpendicular) into the newspaper.

Reset the focus point after each shot (hold out your hand in front of the lens for it to focus there).

I did a series of test shots at 16, 29, and 50 with f/2.8, f/4, and f/8 under 15 minutes using this method. After the pictures are taken, fire up the laptop and you can check right there all the issues at 100% mag.

04-14-2008, 12:07 PM   #9
hll
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thank you very much again!!!

thank you guys for your helpful suggestions!!! hey, gruoso it is nice to hear from you
little laker, maybe i should follow your suggestions!!! maybe i should buy from adoroma or something like that...

aegisphan, if it focuses correctly at the center point, does it mean that focus is ok for all 11 points or should we test for every single af point?????

thank you all
halil
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