Is there an 'ideal' focal length for zooms?

David Lyga · Mar 11, 2019

Hypothetical question: You are required to take a very sharp photo of a product. You have only two lenses (of the same generic brand) to choose from: a 28 - 80 and an 80 - 200. You MUST use a focal length of 80mm. Which lens would you choose in order to obtain the sharpest result?

Perhaps is does not matter, but maybe it really does. I do not know. Is there an 'ideal' focal length for zooms? - David Lyga

Dennis-B · Mar 11, 2019

All of it depends on the construction of the lens. The rule of thumb, as you probably already know, is that a lens is sharpest @ two stops down from maximum aperture. However, a lot depends on the manufacturer of the lens. For a "product", can we assume macro type photos?

I've gotten very sharp results with a Nikon 24-85 f/2.8-4.0, but still not as sharp as my Nikon 105 f/2.8 macro.

For absolute sharpness, I'd be using a prime at 80mm.

Your question, though hypothetical, is very vague. A bit more detail would be helpful.

RalphLambrecht · Mar 11, 2019

David Lyga said:
Hypothetical question: You are required to take a very sharp photo of a product. You have only two lenses (of the same generic brand) to choose from: a 28 - 80 and an 80 - 200. You MUST use a focal length of 80mm. Which lens would you choose in order to obtain the sharpest result?

Perhaps is does not matter, but maybe it really does. I do not know. Is there an 'ideal' focal length for zooms? - David Lyga

the words 'zoom' and 'sharp' should not be used in one sentence. Your question, however, is a good one but can only be answered with a comparison shot.

narsuitus · Mar 11, 2019

This is an interesting question.

I never selected zooms for shooting sharp product shots; I usually selected prime lenses.

I never selected small format cameras for shooting sharp product shots; I usually selected medium format or large format cameras.

At one time, I used an 80mm f/2.8 Mamiya lens on a Mamiya TLR medium format camera to shoot sharp product shots.

If I were forced to use a zoom to obtain an 80mm focal length, I would use my 28-200mm because I have noticed that my zooms perform better in the middle of their focal length range than they do at the extremes of their focal length range.

If I were forced to use a 28 - 80 or an 80 - 200 zoom at the 80mm focal length for a sharp product shot, I would try them both and select the sharpest image because I am unable to predict which lens would produce the sharpest image when the 80mm focal length is on the extreme of each focal length range.

RalphLambrecht · Mar 11, 2019

narsuitus said:
This is an interesting question.

I never selected zooms for shooting sharp product shots; I usually selected prime lenses.

I never selected small format cameras for shooting sharp product shots; I usually selected medium format or large format cameras.

At one time, I used an 80mm f/2.8 Mamiya lens on a Mamiya TLR medium format camera to shoot sharp product shots.

If I were forced to use a zoom to obtain an 80mm focal length, I would use my 28-200mm because I have noticed that my zooms perform better in the middle of their focal length range than they do at the extremes of their focal length range.

If I were forced to use a 28 - 80 or an 80 - 200 zoom at the 80mm focal length for a sharp product shot, I would try them both and select the sharpest image because I am unable to predict which lens would produce the sharpest image when the 80mm focal length is on the extreme of each focal length range.

+1

David Lyga · Mar 11, 2019

Dennis-B said:
All of it depends on the construction of the lens. The rule of thumb, as you probably already know, is that a lens is sharpest @ two stops down from maximum aperture. However, a lot depends on the manufacturer of the lens. For a "product", can we assume macro type photos?

Your question, though hypothetical, is very vague. A bit more detail would be helpful.

I know that the aperture, to an extent, guides the sharpness. That can be chosen with either lens. I know that a prime would be the lens of choice, but assume that the ONLY lenses available are those I stated.

I simply wish to know if the long or short end of a generic zoom can be considered the favored, optically. That is all. There are no other criteria. The product has to be recorded as sharply as possible. There is NO option to use a prime. Use my limited criteria. - David Lyga

Nodda Duma · Mar 11, 2019

From a design perspective, there are several factors that predict performance of a zoom. These are rules of thumb: there are always exceptions.

The smaller the zoom ratio, the better the correction. Lenses with 3x and under zoom ratios are trivial to accommodate and will see no inherent differences in performance due to the zoom ratio (i.e. don’t nitpick zoom ratios under 3x).

Longer focal length zooms are easier to optimize.

Slower f/# lenses are easier to correct.

Heavier zooms will have better correction (optical performance not as compromised by weight requirements).

Stiffer zoom action / less wobbly mechanics = better optical alignment = better performance.

Rely on trends in lens reviews and higher cost (outside of branding): this indicates tighter manufacturing tolerances and more unit-to-unit consistency of performance. That is, reduced risk of getting a bad apple.

For lenses with similar specifications, if you can’t tell why there’s a significant cost difference outside of markup due to branding, then chances are the cost is due to better manufacturing and optics.

Oh and in this modern day, the myth of zooms not being capable performers is just that: a myth. It hasn’t been the 1970s for 40 years.

Nodda Duma · Mar 11, 2019

All that said, the Nikon 28-80 f/3.5-5.6 is badass.

David Lyga · Mar 11, 2019

Nodda Duma, you have focused on what I have said, given my specifics, and for that I thank you.

Yes, the larger zooms are easier to optimize but I will be the first to state that 'sharpness' and 'zoom' can, indeed, be used in the same sentence, without apology. With zooms, especially the ones that have been used for many years, the wobble and stiffness come into the equation on the negative side, but I assure you that I have taken pictures with (generic) zooms that require no apology for sharpness, even to the microfilm level.

That said, there is another factor that comes into negative play, here. The inner elements are oftentimes prone to hazing over the years and then it is necessary to enter the body in order to fully clean the optics. I have done this an am amazed with the resolution levels thus attained. In fact, I had a Sigma SA SLR body with a Sigma zoom that provided sharpness at the level which, in my half century of photographing, could not be surpassed. - David Lyga

Nodda Duma · Mar 11, 2019

If a lens stays sharp through wobble / stiffness then it's stiff where it counts, down in the barrel. Also David you hit on a good point: What troubles can affect a lens with age. Haziness is due to outgassing of the lubricants and plastics used for the mechanical design, and indicates cost-cutting measures that the design team may or may not have subscribed to. In fact -- and I freely admit I'm going off on a tangent here but someone might find this interesting -- lubricants used for optical assemblies must meet several very stringent requirements and the pitfalls if the designer doesn't select a lubricant that meets them:

Low-outgassing (haze)
Low-creep / don't use silicone (lubricants can "creep" over time, invariably towards glass or shutter blades)
Damping / viscosity properties (slop, too loose or too tight a feel)
Retain lubricating / viscosity characteristics over temperature (stiff at cold, flow at hot)

Problem is, of course, that such lubricants cost more than, say Vaseline, so off-brand optics will typically have compromised these desirable qualities in selecting lower-cost components.

Greases developed for space or vacuum applications typically make good replacement lubricants and today are fairly cheap. Dow Corning Vacuum grease is a good example. Apiezon L is another but it is expensive. Nye Lubricant has a line of low-outgassing, low-creep damping grease which is specifically made for optical assemblies.

Alan Johnson · Mar 11, 2019

I have "Amateur Photographer" test report Book 11 which reports on lenses they tested between 1990 and 1999, the earlier lenses tended to be X-70 and 70-Y
The resolution was a bit better with later lenses (for zooms).They gave on-film results for T-max 100 developed in Acutol.
The later Nikon 80-200mm f2.8 improved from about 70-80 lppm at f 2.8 to a maximum of about 115 lppm at f8 falling to 95 lppm at f16.
The Nikon 28-105 f3.5-5.6 macro best result was about 110 lppm at f11 falling to about 98 lppm at f16.
Appears that so long as the product shot is done at about f11 there would not be much to choose between the two at 80mm.
To get 100 lppm printed out on to paper you would need a top quality enlarging lens or pro grade scanner.
These days I believe it does happen, I have seen bus stop posters that look pretty sharp close up, but it is a pro job.

Eric Rose · Mar 11, 2019

When I was doing newspaper stuff back in the dark ages my two favourite zooms were the Nikkors 43-86 and the 80-200. Now my favourite zoom is the Nikkor 24-120. For your application the Nikkor 28-105 macro is probably your best bet.

macfred · Mar 11, 2019

The old Nikkor 35-105/3,5-4,5 AIS is reported to have great IQ at all zoom ranges.
From German Foto Magazin : "It's unquestionably the best lens in this series, sharpness and brilliance are impeccable at all apertures, a lens that's worth its price."

Mainecoonmaniac · Mar 11, 2019

I'm an Oldster from the 80's. Back then, as a general rule, prime lenses are always sharper then zoom lenses. I don't know if the same applies today 30+ years later. But if you know you need an 80mm, why mess with the baggage of a zoom lens? Zoom lenses are great for most applications. But with zoom lenses, there's extra weight, a slower speeds and a lens that may not be sharp as a prime lens. I've used my Canon FD 1.8 for over 30 years and I love the sharpness and the speed of the lens.

benjiboy · Mar 11, 2019

I find David my most useful walk about zooms are the Canon FD 28-85 mm f4 and 35 -105 mm f3.5 both are a constant aperture and allow one to go out with one camera and one lens, and no need for lens changing.

abruzzi · Mar 11, 2019

I don't know anything from anything, however from my experience reading lens review I have seen more complaints about going soft at the long end then I have seen complaints about going soft at the short end, so with your two option, ceteris paribus, I'd choose the 80-200. On the other hand, I've read even less complaints about softness in the middle range, so I'd take a 28-105 over either of the others.

(of course if these weren't hypothetical "ideal" lenses, I choose based on actual properties of the lenses.)

jim10219 · Mar 11, 2019

It depends on the lens and how it was designed. It's virtually impossible to make a zoom lens equally sharp across all focal lengths. That's why most zoom lenses will be sharpest somewhere in the middle, as that presents the best compromise between the two extremes. However, most zooms tend to be sharper at their shorter focal length than their longer focal lengths, if for no other reason then it's the lower magnification ratio is less demanding, therefore, without knowing specifically which two lenses you're talking about, the 80-200mm would likely be the sharper lens at 80mm.

Still, if sharpness at 80mm is your primary concern, a prime lens would what you want. Primes have the advantage of being corrected for only one focal length, which means compromises don't have to be made to make it work on multiple focal lengths. If a zoom had to be used, something like a 50-135 would probably be a better choice. Unless of course, that lens wasn't as well designed as either the 28-80mm or 80-200mm.

So there's no across the board right answer. And any general "rule of thumb" you wanted to apply might be tragically wrong in a given scenario. But all of that is why I typically avoid zoom lenses and stick to primes as much as possible. Zooms are great for walking around and snapping quick photos. But if a photo is planned out and you have the time to set up a serious shot, I always opt for a prime.

faberryman · Mar 11, 2019

From years of reading test reports, every zoom has one focal length at which it performs best, which varies, but is rarely at the extremes of the range.

MattKing · Mar 11, 2019

Your measurement criteria is "sharpness", so I assume that you favour contrast over resolution.
And distortion doesn't factor into the equation.
With those criteria in mind, I would recommend the zoom with the best coatings and fewest elements, because those are the two criteria that affect contrast the most.

DWThomas · Mar 11, 2019

An interesting thought experiment; I've often thought having two zooms that have no overlap in their range would probably sometimes put me in a situation of madly switching back and forth between lenses for a special shot. Myself, I have the classic Canon FD 35-105, f/3.5 over its whole range, which I expect would be pretty good at 80mm (it even has a sort of "macro" mode). These days there is likely a source in China for an adapter to mount almost any lens on any camera -- perhaps one would have a stray medium format 80 mm and could get a $10 adapter ring! Fortunately my "product shots" are mainly for my own amusement and whatever I get is generally adequate!

trendland · Mar 11, 2019

David Lyga said:
Hypothetical question: You are required to take a very sharp photo of a product. You have only two lenses (of the same generic brand) to choose from: a 28 - 80 and an 80 - 200. You MUST use a focal length of 80mm. Which lens would you choose in order to obtain the sharpest result?

Perhaps is does not matter, but maybe it really does. I do not know. Is there an 'ideal' focal length for zooms? - David Lyga

A manual lens (no autofocus/no zoom) at 5.6 after this (just for comparison) at f.11

But seriously : the 80-200 lens!

Because within tele lense you have some kind of failures (from design)
The same is to wide angeled lenses. But between wird angle AND tele such failures are different!

A 100-300mm tele lens will work with problems from design wich are quite simular.
The same might be with 18 - 35 mm zooms (tele zooms get advantage from "cheaper" design - remember the beginning of zoom construction!

So the theoretically most bad lens (sorry some bought such type zoom and spent lots of money for it) the most bad lens (theoretically) would be a zoom 14mm - 300mm (extreme wide and extreme tele together)

with regards

trendland · Mar 11, 2019

macfred said:
The old Nikkor 35-105/3,5-4,5 AIS is reported to have great IQ at all zoom ranges.
From German Foto Magazin : "It's unquestionably the best lens in this series, sharpness and brilliance are impeccable at all apertures, a lens that's worth its price."

Two issues to your reported lens let me belive (although I am most sceptical to all kind of quality statements concerning zooms)
1) 3,5 - 4,5 (variable speed)
2). 35mm -105mm. (35mm is in the short near to " normal angel" 105mm isn't a great tele)

with regards

PS : First zooms you remember had "variable speed" it was impossible to come to fixed speed
from the design at the begining! Impossible to "normal costs"!
This has changed (fix speed is the normal case today) but it is still more expensive .
So a 1000€ lens 35mm-105mm 3,5 - 4,5 MUST HAVE better optical characteristics in comparison
to a 1000€ lens 35mm-105mm 2.0 ! And a 1000€ 35-105 at fixed 3,5 is more complicate from construction. With the same pricing your chance is that you can get a better lens if lens parameters
are not at high level!

But it is theoretically stated! In realiity a 50mm 1/0,95 lens (high parameters concerning speed)
has better characteristics in concern of a well known 50mm 2.0 lens!
But that is coming from massive expenditure/cost of design! So you can resume a bit from pricing!
~ 1999,- € (the 50mm Voigtländer) ~ 199,-€ the Pentax/Olympus/a.s.o standart lens!

ic-racer · Mar 11, 2019

Use the most expensive Nikkor.

Nodda Duma · Mar 11, 2019

faberryman said:
From years of reading test reports, every zoom has one focal length at which it performs best, which varies, but is rarely at the extremes of the range.

From years of designing lenses, I wouldn’t put much stock in the conclusion of test reports. They are based on a sample set of one example from the production run. That’s a problem for extrapolating expected performance from how the tolerances stack up in the specific assembly reviewed.

John Koehrer · Mar 11, 2019

FWIW, the earlier zooms had fixed maximum apertures. Later ones had variable.

Is there an 'ideal' focal length for zooms?

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