How To Stress A Camera Lens

By "stress" I mean "to use the lens in such way that its weaknesses are exposed." But first....

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I. How Not to Stress a Lens
Most lenses in history, and especially now, are capable of excellent results—as long as they aren't stressed. Here's how to see the best performance of your lens under optimum conditions:

1. Shoot in strong white light with the camera pointed away from the light source, with no specular reflections or light sources in the picture and no impinging light shining directly on the objective (outermost lens element). Use at least a short lens hood to block light impinging from a radical angle.

2. Use the widest aperture at which aberrations are minimized, which usually involves stopping the lens down several stops from wide open.

3. Use a fine-grained, low-contrast pictorial film, or your digital imaging sensor at its optimum or "base" sensitivity ("ISO"). With many digital cameras, the base ISO is around 200, even if the camera can be set at lower values.

4. Minimize blur caused by subject and camera motion—this might be accomplished with the use of a tripod or other means of mechanically steadying the camera—and  arrange your subject so as to minimize both foreground and background blur.

5. Don't focus too close—lens designs vary, but perhaps stick within a magnitude of 2 or 3 of (50 • ƒ) (where ƒ = the lens focal length). Thus, for a 50mm (2-inch) lens, you would want to place your main subject perhaps 50 to 200 inches (~4–16 ft.) from the camera.

6. Focus carefully. Focus errors are a very common cause of image degradation—much more common than most people realize. (I see focus errors in published work and "great master" photographs regularly.)

7. Don't enlarge the resulting picture in the print or onscreen past a modest limit.

8. (Digital only) to minimize "chromatic aberration" (i.e., purple fringing), don't ask your lens to image complex, fine-lined subjects with high-contrast edges, such as bare tree branches against a white sky, especially near the edge or corners of the frame.

9. (Zoom lens only) use an intermediate setting in the zoom range. Generally, a kit-type zoom will show its strongest performance if you zoom in roughly a third of the way in from its widest setting. (Even though the actual optimum setting will vary from lens to lens, this will usually be close enough.) Doing this will mainly ameliorate geometrical distortion, and falloff (also called "vignetting").

10. Make sure the lens is clean.

With these ten conditions met, you'll probably find that your lens is a very good performer indeed. Even lenses that are very far from state-of-the-art will perform well. This includes many very old lenses and lenses with significant budget compromises, or even the lens permanently attached to an inexpensive consumer camera. Some of the prettiest prints I ever saw were pictures made with a tripod-mounted single-coated Miranda lens from the 1960s. They were just made under conditions pretty close to those described above.

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II. How to Stress a Lens
"Stressing" a camera lens basically involves moving incrementally away from these ideal conditions, such that the lens will be less and less likely to maintain peak performance. Here are a few of the ways this can be done....

READ ON

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Mike

Comments

[Gordon Buck]

It just turns out that almost all devices work best in the middle of their adjustable or operable range. In fact, if a designer inadvertantly developed a product that worked best at, say, the upper end of the range, then I'd venture to say that the next edition of that device would have an "extended" upper range.

[Ivan Glišin]

Good article and well sums up most of what I have learned over the years, and adds some extra points. Here is one thing I especially agree with: the main characteristic I am looking for in a lens is consistency across the frame at various apertures. The lens I have found to satisfy this requirement in addition to being reasonably fast is Pentax FA 35mm f/2 AL (with perhaps even better consistency across he frame than FA 31mm f/1.8 AL Limited). Since any differences between various apertures are for all practical purposes completely irrelevant this is the only lens I have ever used that I simply never had to think about the "sweet spot": to me it is simply an f/2-f/22 lens and the only lens I feel comfortable using in "P" mode.

[Bert]

Once again, I can't leave without thanking you for a wonderful piece, a pure pleasure to read.

[RobG]

Once again I'm delighted by your down-to-earth pragmatism, experience, and uncommon sense. As always, a pleasure to read your articles. Nice to find a blog that makes me think in addition to informing.

[CP]

It should be entitled "The Ten Commandments" in picture-taking (or photography). Hope you don't mind if I post it on my wall (I should have it autographed first...hmmmnn, and send it to everyone I know who holds a camera.

CP

[Adrian]

Still waiting for a ten-point how-to for things to photograph that make lens flaws negligible.

[Mike Johnston]

"Still waiting for a ten-point how-to for things to photograph that make lens flaws negligible."

Why just ten? I could probably think of 100.

I gave you one example in the article re corner falloff. Here are a few more, just off the top of my head:

If you have a lens that's not corrected well for infinity focus distance, don't make pictures that depend on fine detail at infinity focus distances.

If you have a lens with a lot of barrel distortion, don't try to make your pictures of geometrical subjects justified and rectilinear.

Cf. Ctein's latest post in the "New D300 Review and LRViewer Update" thread, if you have a lens/camera with too much focus slop (i.e., "tolerance") in the AF, don't rely on AF to place focus on critical subject details (eyelashes, maybe) when you're dealing with paper-thin d.o.f.

Match your film to the lens--if you've got a lens with low fine-structure resolution (the lowest set of lines in MTF graphs), don't bother using a super-high-resolution film.

If you have one lens that has harsh, jarring bokeh at close-focusing distance, pick another one to photograph flowers with!

Don't pick your sharpest macro lens to do a portrait of aged Aunt Mabel!

That's the sort of thing I mean. I could go on...and on...(and sometimes I do, bah-dum).

Mike J.

[Adrian]

Err, my comment was intended tongue-in-cheek - like in "it's the subject, stupid" ;-)

[Mike Johnston]

Well, I'm not stupid. (At least not very.) Of course it's the subject (hence my third-to-last paragraph, the one that begins "I've found it most amenable..."); but the subject in this case wasn't the subject, the subject was lenses. I trust it isn't yet *completely* disreputable to talk about lenses in a photography blog....

And by the way, is it really the subject? What about pictures that have no subject? What about pictures in which the subject isn't the subject? Is the subject always an object? And other questions along those same lines....

Mike J. (Feeling kind of shocked this morning at the Bear Stearns buyout, hence a bit punchy....)

[Ryan Brenizer]

Great piece. Here's something that shows how great the 24-70 is -- in your hagiography, you actually left something out. It has the best color transmission of any 35mm-format lens I've ever used.

[Mike Johnston]

Ryan,
Damn, I actually had that in there, and then I thought, wait a minute, that's not actually something I *know*. I should at least have pretty good evidence if I'm going to say it. So I cut out the sentence in the final edit.

No kidding!

Mike J.

[Miserere]

This piece should be mandatory reading for all those people in the forums posting questions such as "I'm trying to decide which kit zoom lens is better, X is an f/3.5 while Y is an f/4; I'd like the extra speed of X but my friend with mad skilz says Y rocks. Please help!"

Apart from the fact that 1/3 of a stop is going to make little practical difference, the most important thing here is that neither lens will perform well wide open and you'll have to stop down to f/8 to achieve uniform sharpness throughout the frame anyway. This type of agonising is all too common and would disappear if beginners understood a bit more about lenses. Like Sun Tzu said (maybe I'm misquoting here), "know thy lens".

The advice to have less lenses, but of better quality, is also spot on. Now all I have to do is follow it! :-)

[Stephen S.]

I heartily agree with "(amateurs) tend to overbuy lenses and have too many in their arsenals."

Back when I shot 35mm with Primes, I had:
8mm fisheye, 17mm, 24, 28, 35, fast 50, macro 50, 85, 100 portragon, 135, 200, mirror 500, and a 2x teleconverter.

I really only used on a regular basis the 28, fast 50, and 85.

So, when it came time to go digital, I went with two lenses for the Olympus E-System, 14-54 (28-108mm equiv) and 40-150 (80-300mm equiv) and truth be told, I rarely use the telephoto.

I've never felt I've truly missed a shot due to not having a certain focal length available. More importantly, I have not missed the feeling that I need to dig out my wallet and buy yet another lens to fill a perceived 'gap' in my lens 'coverage.'

Though sometimes, I almost miss juggling two lenses and their respective rear caps in one hand while holding the body in the other.

[XebastYan]

Thanx Mike for this very enlightening article.
Last weeks I often thought about lenses and their right use.
There is one question & I think you are the right one to ask: You have said about the pictured Nikon Zoom that it is well balanced (no s-pot and robust over the whole range of focal width & aperture).
Not everybody has a body on which this lens will fit f.ex.a Pentaxian like me :-) (and G9 User for a week)Can i assume that when a Zoom Lens has the smallest (widest open) aperture over the whole zoom range that it is coming this "Reference" nearer than a Zoom Lens with "changing-aperture" over the zoom range? Or has this aspect nothing to do with this consistency?

[Mike Johnston]

XebastYan,
There's nothing inherent in variable-aperture designs that means they have to be inferior to constant-aperture designs, but having a variable aperture is one way to shave costs, and buyers who need constant-aperture zooms tend to be pros and the more skilled amateurs who will spend more. So for this reason (although you really have to watch generalizations and take each lens on an individual basis), *generally* the variable-aperture zooms are cheaper consumer models and the manufacturers design and make their constant-aperture models to a higher standard. They're also usually more expensive, too, of course. This isn't a strict rule, just the tendency in the real world.

Mike J.

[Grant]

Whew! That was quite a post Mike. I must remember to go to the bathroom BEFORE I read your next one!
Before zooms were the norm, I purchased a lot of prime lenses. Each one had it’s own range of uses and obviously it’s own sweet spot. I used them according to what I felt was needed for a particular shot, and I was seldom disappointed. Today, with an all-in-one zoom, I’m probably out of the sweet spot more often than not. I suspect that the computer darkroom somewhat covers up the flaws of the lens.
In future cameras, will on board processing detect the lens and make corrections for the characteristics of the lens? A scary thought to a serious photographer, but perhaps a way to sell a lot of 16-300mm zooms to the mass market.
One thing I haven’t been able to find. Do photographers who use full frame lenses on reduced format cameras get better results than with digital format lenses?
Thanks for taking my mind off Spitzer and Bear Stearns.

[Mark Sampson]

Curmudgeon alert; you're not talking about stressing your lens, you're talking about stressing you photographs. The last time I can remember stressing a lens, I dropped it, and it went off a 60-foot cliff into the ocean. And that lens cost a week's gross pay (in those days). Wait a minute, perhaps I was stressing myself that day...

[Ben Listwon]

Hiya Mike. Excellent post as usual.

One thing that struck me as I was reading through it is that this is one of the (very) few posts on any blog that begins to define technical photography terms in a human way. For example, one can use wikipedia to read about f-stops, "speeds" of lenses, etc. but there is a distinct lack of actual person-to-person communication of concepts like bokeh.

One of the big reasons I think highly of your articles, as well as those from ctein and other contributors, is that the writing is done at a level that a) assumes some intelligence on the part of the reader and b) takes the time to clarify points that may not be immediately clear across all levels of photographer. It's a tough balancing act to not over-explain everything for the amateur's benefit and to not write completely in the codified language of the pro.

In your copious spare time, perhaps you, ctein and others could whip up a glossary of photographic terms. But, rather than the usual encyclopedic definition of such, you could write out the entries as you do in this article -- with context, examples and a clear understanding of the term as it relates to the bigger picture.

Keep on shooting and writing!