How to tell if I got a good copy of 18-55mm lens?

Started Apr 20, 2013 | Questions
gvdforever
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How to tell if I got a good copy of 18-55mm lens?
Apr 20, 2013

I have two copies of the 18-55lens right now and will be returning one of them.  people mentioned make sure you get a good copy that iS sharp.  How do I test this?  I'm new to this and just want to make sure I keep the better copy.

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calterg
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 20, 2013

Mount your camera on a tripod. Tape it down (the legs), if it moves, you start over.

Focus accurately on a magazine page (full colour magazine) with text at two or three font sizes and a picture. I suggest manual focussing and always on the same spot. Manual exposure.

Controlled lighting, your bedroom at night with curtains drawn and room lights sufficiently warmed up. Perhaps a worklamp across the magazine page if your room lights are not bright.

Take a picture across each aperture range and set focal lengths, maybe at 18mm, 35mm and 55mm.

Swap lens and do the same.

Organise/rename your pictures accurately

Pixel peep.

This will test sharpness only, which most people are concerned with anyway.

All colour and CA faults are easily corrected in post-processing. It is a kit-lens, don't kill yourself over every imperfection.

Would like to know if they really is a variation in sharpness of your two lenses, if you decide to bother after all the above steps.

Shortcut method:

Put on tripod or tape to window sill, take two pictures outside your window, pixel peep and go with your gut instinct. (It's fast and decision of which is better, is largely based on self-deception).

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saintz
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 20, 2013

I had 3 x18-55 lenses and 2 x 16mm lenses. I planned to sell the duplicates. I've heard both of these can be prone to issues. I took quick test shots with all 5. I couldn't tell the difference between any (compared to the others of the same type). I wouldn't sweat it unless one looks clearly bad, like you can't get a decent shot with it.

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OpticsEngineer
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 20, 2013

Here is what I do.  (other people have good ideas too.)

First I make a target board that is lots of text printed out on laser printer, glued to a large foam board.     In the middle, there is a big X and the words "Focus Here".  Aperture full open, making sure line of sight is perpendicular to the target.   Camera on tripod, image stabilization off. Take a photo.  One time I do manual focus.  The next time I do autofocus with the focus set to spot center.  (because I am also looking for any problem with the autofocus.  I do a few cycles of focusing on something else and then going back to the "focus here" on the target board.)

Then look for variations in how sharp the letters look center/left/right/up/down.    The reason for that is lens problems are often are the result of decentered elements.   Those cause patches of fuzziness on one region of the lens.   I do not worry about the image getting fuzzy toward the edges or corners as long as it is similar in the same regions across the lens.

A lot of people recommend then turning the camera upside down and repeating the photo.   A suspected problem should flip sides in the image appropriately, but I have never tried that myself.   This check would make sure problem was not that the target board was not actually perpendicular to the line of sight of the camera.

My E mount 18-55 is fuzzier on the right hand side than the left but I never bothered to return it.  I find it kind of interesting and it did not cost that much since it was a kit lens.      I always have in mind that someday I will get around to testing it a bit more thoroughly but never seem to get around to it.  The thing is I nearly always use my NEX7 with the Tamron 18-200 zoom and it is a really good lens for me (the Sony SEL18200 is a bit sharper though.)

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Jokica
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 20, 2013

Your copy is just perfect!

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Baron LaCat
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to OpticsEngineer, Apr 20, 2013

(the Sony SEL18200 is a bit sharper though.)

The Sony SEL18-200 PZ is even sharper

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evoprox
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 20, 2013

gvdforever wrote:

I have two copies of the 18-55lens right now and will be returning one of them.  people mentioned make sure you get a good copy that iS sharp.  How do I test this?  I'm new to this and just want to make sure I keep the better copy.

Over the years I owned 4 copies of that lens. They all

  • had heavy distortion @18mm
  • soft corners throughout the focal range wide open
  • were critically soft @55mm, no matter how much I stopped them down
  • had different sweet spots/ranges
  • some amount of decentering
  • flared like hell at certain settings
  • want to be stopped down to f5.6/f8 to get the most outa them
  • sucked up dust like nothing else I've owned before
Compared to images shot with a variety of other lenses, mostly legacy glass images from the 1855 have a somewhat 'plasticky' look for lack of a better term. IMO the 1855 is an OK lens for casual shooting but no serious stuff. I kept my best copy for shooting videos. Just my two ...
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miro3
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 20, 2013

gvdforever wrote:

I have two copies of the 18-55lens right now and will be returning one of them.  people mentioned make sure you get a good copy that iS sharp.  How do I test this?  I'm new to this and just want to make sure I keep the better copy.

shoot things with tall vertical lines, using the widest angle,

and look at the distortion that you will get.

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GaryW
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to miro3, Apr 21, 2013

miro3 wrote:

gvdforever wrote:

I have two copies of the 18-55lens right now and will be returning one of them.  people mentioned make sure you get a good copy that iS sharp.  How do I test this?  I'm new to this and just want to make sure I keep the better copy.

I'd set up a tripod or some place to rest the camera and take photos with both lenses, making note of which one was which.  As someone else said, the difference is probably going to be that one of them is "softer" on one edge than the other.  Or maybe not.

shoot things with tall vertical lines, using the widest angle,

and look at the distortion that you will get.

But all 18-55 lenses will have noticeable distortion at 18mm, and it shouldn't differ between lenses.

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FuzzyQball
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 21, 2013

There may be some difference, but if shots from both look fine, I wouldn't worry too much.  That's my two cents.

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Glenn

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cptrios
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to FuzzyQball, Apr 21, 2013

I would do magazine page/board/generic other closeup flat subject tests and outdoor deep/distant scene tests. It's tough to get a good read on a lens from close-range flat field stuff without a very tightly-controlled setup, considering that even the slightest off-kilter angle on either the camera or the subject can make things look decentered thanks to the narrow DoF.

Also...keep in mind that "sample variation" is a semi-myth. Sure, there are QC issues at every photo equipment company, and there certainly is sample variation - but it isn't nearly as big a problem as it seems when you're scouring internet forums. Even with really poor QC, 8 out of 10 lenses will be totally fine. And despite what some people say, there are no magically great copies of the 18-55 that are sharp corner-to-corner at all FLs and f-stops. It's an average-quality kit lens...neither horrible nor excellent.

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gvdforever
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to cptrios, Apr 21, 2013

Thanks everyone for the advices.  So it seems like a good copy and a bad copy can only be determined when you pixel peep?  If Im not a professional and only take pictures of my baby then it doesnt really matter?

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blue_skies
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 21, 2013

gvdforever wrote:

Thanks everyone for the advices.  So it seems like a good copy and a bad copy can only be determined when you pixel peep?  If Im not a professional and only take pictures of my baby then it doesnt really matter?

It is not that straight forward to verify an AF zoom lens and compare two copies.

Decentering check is easy - the 'slanted horizon', followed by the 'upside down - same image', would show if one side is different from the other. (Note - it takes four images - two angles for the horizon). See Jerome Munich pic below.

If the lens is not decentered, you worry about its electronics and its lens alignment. In most lenses, there are tight tolerances, but they should all adhere to a similar quality check.

Comparing the two lenses requires fine precision of the zoom control and of the focus control. Even metering can be tricky. If anyone of the parameters is different, the image will not match at the pixel peaking level, and you'd be hard pressed to decide which one is the better one.

And then you really should use a tripod, otherwise you'll include all of the operator behavior in the lens quality analysis as well.

A lens that has a problem, which is not uncovered by the decentering test, will usually reveal this fairly quickly as you take some images.

The news-papers on wall test is probably the quickest method to verify sharpness across the frame, both wide open and stopped down, at different zoom levels. Doing the test correct takes some diligence, and consistency is very key here.

Plus, you should try different distances to the wall. Lenses have some level of field curvature that may be very pronounced at close distances, but non-existent at far distances, or a mix thereof.

But if you have to pixel peep to find any difference at all, you can assure yourself that the two lenses are nearly identical, or that both met the QA criteria.

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Henry

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GaryR60
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 23, 2013

While a "lemon" may occasionally sneak through in just about any manufactured object, camera lenses are usually made to pretty high standards and the manufacturing process is the same for every lens, thus, any difference between one "copy" and another of any particular model is going to be so minute that it isn't worth worrying about.

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boardsy
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Re: How to tell if I got a good copy of 18-55mm lens?
In reply to gvdforever, Apr 23, 2013

gvdforever wrote:

I have two copies of the 18-55lens right now and will be returning one of them.  people mentioned make sure you get a good copy that iS sharp.  How do I test this?  I'm new to this and just want to make sure I keep the better copy.

Simple version of the test - turn OFF OSS lens stabilisation, sit the camera on a steady table/counter, center focus, center metering, ISO 100/200, 2 second timer on the shutter, focus on a dollar bill or wine bottle  label, and take a shot with each lens at e.g. 24mm f5.6 (this lens' sweet spot) with the camera in exactly the same position for both. View the results at 100% (jpg in Windows picture viewer > Actual Size is fine). If one has more fine detail, that's the one to keep!

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