Can a novice test a lens?

[KirbyKrieger]

Hi.  Is it possible for a novice to do a reliable test of a lens?  Is there a standard "test" that is recommended for new lenses?  If one buys a used lens, how can one assure oneself of its quality?

I recently forayed into the principality of photography with the purchase of a Panasonic G1 with the kit lenses (14-45 and 45-200, all measurements for the MFT system {45 MFT = 90 for 35mm}), and added the highly-regarded 20mm f/1.7 pancake lens.  My 20mm lens doesn't seem to be as sharp as it should be, and isn't (as far as I can tell) sharper than either of the zooms.  My tests are simply still-life shots taken with a tripod and shutter-delay, across the range of apertures, with both auto-focus and manual focus.  I am using LR3beta w. the default settings (I have not zeroed anything).  I have also loaded the camera-made JPEGs into iPhoto.  My conclusion is that all of my shots (with one or two exceptions) are softer than I want, and the 20mm is no sharper than the zooms.  My monitors are a 13" MacBook Pro backlit screen, and a 23" Dell 2301 (a not-very-good monitor).  Both monitors show a gamma-shift with viewing angle -- quite pronounced on the Dell.  I am gauging sharpness from the full size images (4000 x 3000 px.), zoomed no further than 1:1.

Thanks for your insights.  I am prepared to find out that many beginners have the same observation.  Logic leads me to the conclusion that the problem is on the other side of the camera from the subjects being recorded -- in which case a solution should be fairly easy (and please advise) -- but I want to rule out equipment problems.

As always, thank you for indulging me in my novitiate.  

[Slobodan Blagojevic]

It would help if you would post some of those test images, and possibly one example of what you consider sufficiently sharp. It would also help to know what is your expected use of those images (online, printouts, size) in order to judge if those lenses are sufficiently sharp for that purpose.

[KirbyKrieger]

Thanks for the suggestions slobodan56 -- I shot new sets of sample shots to confirm.  Will post after I get a chance to examine them.

[bill t.]

A few things...

The real test of a good lens is how good it is at the edges compared to the center.  Most lenses are OK at the center, but only the great ones are even nearly as good at the edges.  Most zooms will disappoint in this regard.

For pixel-level sharpness, there is no such thing as depth of field, at any aperture.  Even out to pretty far distances you will only get pixel-level sharpness in a very narrow plane.  For any sharpness testing you must be exactly focused on your test object.  The DOF markings on the lens really only mean "kinda OK sharp" over the indicated ranges.  Autofocus systems try to average the focus out over objects at varying distances, which means most things will look acceptably sharp, but very things will be tack sharp.

Most digital lenses perform best at f5.6 through f8.  F11, f16, and on up are usually diffraction-limited, low contrast mush.  In many cases where you need lots of depth of field you are better off shooting at f8 and bringing slightly out of focus areas back with Smart Sharpen, than by trying to carry them in focus at f16.  For that 20mm I wouldn't be surprised if your sharpest aperture was only 1 f-stop from wide open.  When you are testing your lens, also test your various aperture settings, that's a real eye opener for newbies.

If you make prints, your best test is printing some images.  Don't get too target-fixated on the screen, it doesn't do a good job of interpreting what print sharpness is going to look like and may lead you to over-sharpen.

[Plekto]

True.  Most lenses were fine with cheap film and when DSLRs had 6-12MP at most.  But as resolution has improved, it's clear again which lenses are average and which are special.  Expect "good enough" results and not much else for anything you buy these days that's under $500 or so.

[ErikKaffehr]

Hi!

There are a couple of issues at hand.

Is the lens you buy a good design? Reading tests can be helpful. Check out:

http://www.photozone.de
http://www.slrgear.com

Once you have a lens, does it perform according to the design?

My suggestion is to make "bookshelf" or "brickwall" shots. Compare the four corners, they should be similar in sharpness. Assembly errors often show up as asymmetric sharpness.

Don't expect miracles. Very few wide-angles really excel in the corner, for instance. Almost all lenses need some stopping down.

Best regards
Erik

True.  Most lenses were fine with cheap film and when DSLRs had 6-12MP at most.  But as resolution has improved, it's clear again which lenses are average and which are special.  Expect "good enough" results and not much else for anything you buy these days that's under $500 or so.

[markhout]

Hi.  Is it possible for a novice to do a reliable test of a lens?  Is there a standard "test" that is recommended for new lenses?  If one buys a used lens, how can one assure oneself of its quality?

Hi - lenses are important investments that often last much longer (depreciate slower) than a camera. So you need a lens that you are completely comfortable and happy with. I used to shoot with the much-maligned Canon FD 135mm/2.0 and absolute loved its soft rendering and bokeh. Entering the digital age I switched to Nikon and now have a perfect, superbly-tested 14-24mm on the shelf. It is beautiful, very nicely corrected, brilliant but also so sharp (and big) that I never use it. (Before you think I'm a softie - I also sold a 21mm Leica M because it was not sharp enough for my purpose!)

My take is: forget about MTF curves, go out and shoot whatever you normally shoot, process the file as good as you can, print as large as you want and see what you have in your hands. If that exceeds your expectations, keep the lens. If not, eBay is your friend.

Similarly I am now thinking of eBaying my Canon S90 and go back to the G10. The S90 is supposedly higher-tech, but I prefer the G10 lens and rendering.

Don't pay much attention to the image on your display - that image is only relevant for softproofing prints and for internet usage.

Hope this helps a bit.

[Greg Campbell]

Unless you suspect a gross malfunction, I'd suggest you ignore the equipment entirely and concentrate instead on taking pictures!  Pixel peeping and fretting about LP/MM have nothing to do with 'photography,'  and it's far too easy to start down the 'equipment junkie' path.  Worry instead about seeing shapes, texture, light, etc., and composing images that reflect your vision.  

When you can make "Wow, that looks good!" images, THEN you can start to squeeze the equipment for more.  Until then, you are wasting your time chasing wild gooses.

[philber]

Kirby, at the expense of stating the obvious, a picture made with a short focal length will "look" less sharp, all other things being equal, than one made with a longer lens. Being shorter, it will be wider, so the amount of details on the picture will be more, and each one will be proportionately less, if you see what I mean. I have used a 20mm pancake, and can testify to it being as sharp as you want. One thing you might look at is that I found that the Pana camera I used (in auto mode) nearly always selected f:1.7. If that is not the case with the zooms, then you end up comparing a short lens at f:1.7 with a longer one at, say, f:5.6, and the pancake won't look good by comparison. But, many times, sharpness issues have to do with user error. Too slow shutter speed, wrong AF point, all produce soft shots.
Hope this helps.

[Christoph C. Feldhaim]

Unless you suspect a gross malfunction, I'd suggest you ignore the equipment entirely and concentrate instead on taking pictures!  Pixel peeping and fretting about LP/MM have nothing to do with 'photography,'  and it's far too easy to start down the 'equipment junkie' path.  Worry instead about seeing shapes, texture, light, etc., and composing images that reflect your vision.  

When you can make "Wow, that looks good!" images, THEN you can start to squeeze the equipment for more.  Until then, you are wasting your time chasing wild gooses.

+1

I also found the "bosses" statement quite enlightening for myself:

"Most Lenses are Better Than Most Photographers"
Source: http://www.luminous-landscape.com/tutorials/sharp.shtml

[SandroD]

I'm writing the series of posts about this concrete issue... you can follow it here: Image Sharpness 101

There are too many things that can go wrong. Lens can be front-back focusing, camera body can have problems, photographer might lack some skills. I explain all in details.

In short, don't worry about sharpness much, your lens is probably alright - u just need a bit of practice and images will improve.

[KirbyKrieger]

Hi -- Thanks to all for the thoughtful (and useful) replies.  In has, in its way, been something bouyant to grab on to while I have foundered in the beginner's pool.  Since I posted my query I have been learning non-stop.  I will revisit my initial series of test shots (I took two series of each lens at each f-stop at a range of focal distances) when I have some time ... probably in February.  I fully expect the problem will have gone away by then   .  If not, I will post instances of specific problems.  Thanks again!