How to test the lens for good copy?


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gelosbox

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#1
guys can anybody help enlighten me on this one?... i read a lot of people on clubsnap say they got a "good copy" a "sharp copy" or a "bad copy" of lens... how do you determine a good copy from a bad? :dunno:

thanks in advance.. :)
 

Jed

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#2
51 views, no reply prior to mine. I guess that tells you that a lot of people don't know :)
 

night86mare

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51 views, no reply prior to mine. I guess that tells you that a lot of people don't know :)
we have so many gearheads here, jsut that most of them don't bother to post. :bsmilie:

actually, this has been asked many times. you can test, and you can test, and you can test. my version of testing is really rudimentary, i know of people who will use laptop to see the test images on the monitor. i think that's really a bit too far fetched, but whatever floats anyone's bloat.

this will suffice if you aren't a pixel peeper, i like to look at online samples to get a rough idea of what other people are getting, and what a "good copy" should look like, go down to shop, fit lens on, if it is prime, then just shoot one set, if it is zoom, then test at extreme ends and middle.

1) shoot wide open
2) shoot with aperture stopped down 2 stops from wide open
3) shoot at f/8, if that isn't reached by #2, or f/11

check centre sharpness, check corner sharpness for each, see if it is acceptable. we must remember that no lens is going to be as sharp wide open. better if you can find the "sweet spot" for each lens and see if it matches up to YOUR expectations. after all, YOU are the user of the lens.

personally, i think just zooming in on the lcd is good enough.

please note that when you test, you should be ensuring that there is no human error. some people will recommend checking for af problems using a focus chart. all test shots should be done with a TRIPOD that is reasonably stable, and in timer mode to ensure that you don't cause any shake when you trigger the shutter.

this is just for testing sharpness and for focus problems, what i have said so far. if you want to test even more still can, actually.. but really, i think that's what most people are talking about when they say "good" "sharp" "bad" copy.
 

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ijnek

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Feb 4, 2008
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#4
i bring my laptop to test.
viewin it on a large LCD screen tells u immediately whether the pic is in focus or not...
 

giantcanopy

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#5
I suspect many times the labelling of a bad copy / lemon is an overstated hyperbole amongst photog enthusiasts. but thats not to say lemons do not exist in this world

Anyhow for me i usually check for focusing and pixel peep with the camera at the points of focusing and thats about all. So far i haven met any rotten lenses that surprised me post purchase.

ryan
 

Feb 19, 2009
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#6
to addon what night86mare posted,
my personal experience is to identify a really nice sharp shot AND a average sharpness photo (that can been further enhanced thru USM) to be ur gauge of a sharp shot to view thru ur camera lcd zoom in

check optics thru the zoom range, fungus free? dont expect spot-free/ no dust for zoom lense :nono:
shoot wide open to check for lense front/back focus, do take note that ur technique is impt, sometimes it can be due to user error
shoot for wide open sharpness for the zoom range, acceptable sharpness?
shoot 2-3stops down, sharp enough for u?
(centre sharpness for the wide range & centre/corner sharpness for the mid-extreme end)

check the zooming, is it smooth enough for u?
cover the front of the lense with ur hand, half-focus, is the lense motor smooth?

it's a good copy if u come to the last step.
 

aspenx

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#7
Just adding on...

- check exterior
- front element, filter thread, mount
- point at bright area, look through the back at largest aperture
- for fungus/dust/scratches
- check aperture blades
- whether they snap back after each shot at all apertures (except wide open)

bla bla.

Of course you can do more tests, but it's very hard to come up with a truly exhaustive list and actually follow it.
 

gelosbox

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#8
Thanks everyone... I think now I know what to look for; it was much more complicated than what I thought it would be... ;p

What are the chances of getting a bad copy? Say if a shop has 100 units of 50mm 1.8 how many of these would be good? Is there such statistics? :dunno::dunno:

night86mare, I laughed when you wrote "but whatever floats anyone's bloat".. I read some heated argument on Clubsnap regarding this phrase recently... tsk tsk
 

aspenx

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#9
Say if a shop has 100 units of 50mm 1.8 how many of these would be good? Is there such statistics?
It's called sample variance.

There are no officially published statistics of such nature from any makers for any of their lenses as far as I know.

Anyways, if you are buying a brand new lens from a reputable maker (Leica, Nikon, Canon etc.) from a shop, the chances of you getting a lemon should be negligible.
 

Jun 12, 2008
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Jalan Poonpipi
#11
Apart from optical performance, I check the lens physically - zoom ring in and out, AF ring and then, aperture lever. Look at all the screws to see if they are "virgin". Look for scratches and dust and fungus in the glass. [I have encountered one lens with an "elephant" inside the glass that cannot be blown away, so I didn't buy that lens]

I will also shake the lens to hear if there is anything that is loose inside it.

Another aspect that is important to me - focus speed and focus error [like how many sharp pic out of 10shots] and if it hunts in low light.
 

gelosbox

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#12
Apart from optical performance, I check the lens physically - zoom ring in and out, AF ring and then, aperture lever. Look at all the screws to see if they are "virgin". Look for scratches and dust and fungus in the glass. [I have encountered one lens with an "elephant" inside the glass that cannot be blown away, so I didn't buy that lens]

I will also shake the lens to hear if there is anything that is loose inside it.

Another aspect that is important to me - focus speed and focus error [like how many sharp pic out of 10shots] and if it hunts in low light.
thanks bro. ill note this the next time I make a lens purchase.. :thumbsup:

It's called sample variance.

Anyways, if you are buying a brand new lens from a reputable maker (Leica, Nikon, Canon etc.) from a shop, the chances of you getting a lemon should be negligible.
thanks that's good to hear.. ;p
 

Aimevous

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Mar 5, 2009
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#13
For me, I'll just look at the aperture blades (or is it called shutter blades?) as it snaps shut when i shoot and see if it gets jammed and if all close together at the same. Usually this applies more to old lenses (or so i was told) due to oil deposition.

Then the usual looking for dust/scratches. I'll probably shake the lens a little and see if there's any loose parts.

Like what the above have mentioned, bring along your laptop and examine the photos at various apertures and various focal length. Look at sides and centre.

You might want to check for CA too. :)

Sorry if anything above is incorrect. I just started out less than half a year ago :D
 

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