What makes a ‘good’ lens? (part I)

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This might seem like a very obvious question, but the moment you try to define a set of criteria to quantify ‘good’, you soon realize there’s quite a lot more to lens performance than immediately meets the eye. So, for those of you without the ability to try a large number of lenses – let alone samples of the same lens – how do you know if the one you’ve got is ‘good’?

When evaluating a new optic, I look broadly at several categories; this article will explain them a bit further. It’s wroth keeping in mind that most of these evaluations are relative and/or subjective; something that might perform well on a larger, lower-density sensor and balance properly on a large DSLR might not do so well on a very high density crop factor camera without a built in grip. It is therefore important not to consider ultimate resolution alone, but how well the system works together as a whole. A pancake zoom on a GM1 is a match made in heaven; you can mount an Otus on it, and it’ll deliver better resolving power, but it won’t be practical to use simply because of balance and manual focus/ stability/ ergonomic issues. Remember: the job of a lens is to collect and relay information, in the form of wavelength
(color) and spatial position to the recording medium. The less it affects the information along the way, the better.

Resolution
This is perhaps the most important and most easily defined category. Resolution at maximum aperture (and various points in the zoom range, if applicable) is obviously the priority; but one also has to consider whether the lens is symmetric: optical designs may intentionally be compromised (e.g. for long zoom ranges) to deliver high centre performance at the expense of corners or edges; however, they won’t intentionally be sharper on one side than the other. That would be an indication of manufacturing issues. The better the lens, the higher the resolution across the frame it will deliver at faster apertures. It isn’t difficult to make a f5.6 kit zoom with a moderate focal length range that delivers decent performance across the frame, but it’s quite something else if it delivers the same resolution at f1.4 and in the corners.

Correction for aberrations
In order for a lens to deliver high performance in the corners and at fast apertures, it must be well corrected: this is to prevent different wavelengths of light focusing at different points – both laterally and longitudinally. If the focal plane for different wavelengths shifts laterally, then you’ll see spectral separation in the form of lateral chromatic aberration, or blue-red/ green-red fringing. If you see it in front and behind your plane of focus, that’s longitudinal chromatic aberration. Lenses designed to minimize or eliminate this for visible wavelengths are usually given an Apochromatic or APO designation. Note that this doesn’t say anything about spreading/ ‘smearing’ of point light sources – that’s coma, and it’s possible to have an optical design that suffers from coma without having chromatic aberration (and vice versa). Aberrations that cause different wavelengths to focus at different spatial points for a given focus distance setting will land up reducing resolution because they affect the lens’ ability to resolve fine detail structures – i.e. edges – giving the overall impression of being a bit soft.

Microcontrast
This is a property of a lens that has to do with its ability to resolve the very finest detail structures – i.e. of low contrast and high spatial frequency – a lens with ‘good’ microcontrast is able to do this for structures that are close together/ fine and similar in luminance. Although you can increase the apparent gross contrast of a lens by sharpening, it’s almost impossible to ‘fix’ microcontrast because you cannot generate information that simply wasn’t recorded by the sensor to begin with.

Macrocontrast and flare
Overall contrast – recorded luminance between brightest and darkest areas of a scene that take up a significant portion of the overall image width – is quite dependent on the coatings of the individual elements; in order to maintain high contrast, you need to not have any stray light bouncing around inside the lens and landing up on different portions of the image than the area from which they came. A lens that has high flare has high internal reflections and poor coatings; this will affect both global (macro) and micro-contrast. It is especially important if you’re shooting into the light, as this will exacerbate the problem. The very best lenses show very little to no flare and have very good coatings.

Vignetting
I consider this to be the least of the optical maladies, since it’s easily corrected for in post processing – dark corners are not really a big deal so long as they aren’t completely black.

Transmission
If you’re losing light internally, or it’s being reflected out again at each lens-surface interface, then you’re not collecting it at the imaging plane. It is impossible to make a lens surface that has 100% perfect transmission, though it’s possible to minimize losses to the point that the vast majority of light makes it to your recording medium. Lenses with low flare and high contrast typically also have very high T (transmission) stops; the closer the T stop to the f stop (geometric aperture, or focal length divided by effective entrance pupil), the better the lens. Very good prime lenses have T stops that are usually within 0.1 of the F stop – f2/T2.1, for instance – whereas kit zooms that have an f stop of 5.6 may well have a T stop of 8 or lower. Not all f stops are equal – look at the shutter speed to give you clues.

Color
Transmission also affects color rendition: a lens needs to have equal transmission across all wavelengths of the spectrum in order to record an accurate reproduction of the scene; these are neutral. Lenses with color casts are attenuating portions of the spectrum, resulting in an overall shift in colors. Though the sensor or recording medium can affect this, you can generally see the difference between a very neutral lens and one that’s attenuated in a certain color. Neutrality is obviously desirable because it means you’ve got more information to work with later.

Focus shift
We change gears a bit here and look at the behaviour of the plane of focus as the lens is stopped down: if it moves backwards or forwards, then the lens exhibits focus shift. This means that you need to consciously adjust your focused distance in order to get the theoretical depth of field you expect; there can be significant differences between maximum aperture and say f4-5.6. Better lenses will employ floating elements to automatically correct for this as the focusing group is moved to the desired distance; this is computed as part of the lens’ optical formula.

Focus breathing
This is when the apparent magnification of a lens changes as you change focus distance; frequently, lenses will shorten their effective focal length in order to focus closer – this is so they require less helicoid extension and therefore can be made more compact. Although a consumer superzoom may reach its labelled maximum focal length at infinity, you will find that at minimum focus distance, your 18-300 might well be giving you magnification equivalent to 150mm. Let’s just say there’s a reason those 300mm supertelephotos require long barrels, but can only reach around 1.5m minimum focus distance: they do not shorten in focal length. The very best lenses do not exhibit focus breathing at all – cine lenses come to mind; they are designed this way to enable changes in focus plane (‘pulling focus’) to not change the composition of the scene. Few stills lenses are designed to compensate for this, partially due to size, partially because you can always recompose between shots – something that isn’t always possible in a video sequence. In fact, the only stills lens that immediately comes to mind that does not exhibit focus breathing is the Zeiss 1.4/55 Otus Distagon.

Field curvature
Ever have issues with your corners not being sharp, but something towards the front or rear of the frame being in focus instead? This is due to field curvature. If you see a resolution test where the sharpness (resolution) drops off alarmingly towards the edges of the frame, it’s probably because of this; it means that the plane of focus isn’t so much a flat, two-dimensional plane as a section of a much larger sphere. It isn’t always a bad thing because it can create a more three-dimensional effect to the image by making the edges effectively more out of focus than they should be. But it is worth noting for flat-field work – e.g. macro and reproduction.

Distortion
Straight lines should render as straight lines: if there are a lot of elements in the lens to correct for other aberrations across various focal lengths, then chances are they’re going to introduce some nonlinear projection. Some types of distortion – simple spherical pincushion or barrel – are easy to correct for; others like ‘wave’/ ‘moustache’/ or ‘sombrero’ types are trickier, and worse still, tend to vary with focal length. Of course, extreme distortion of any type – simple or not – is not desirable as correction may well result in a change in effective field of view.

Performance at distance
‘Macro’ lenses are designated as such not just because they have shorter minimum focus distances, but also because the optical design has to be optimized for near performance where the object and image distances are relatively similar. This requires (usually) extra glass and nonlinear helicoid movements at closer distances; which of course costs more. There’s a reason why a cheap 50/1.8 with an extension tube does not perform the same as a dedicated macro of the same focal length. By a similar token, not all lenses (including some macros) do well at infinity, either; faster lenses usually start to be compromised at longer subject distances. Very few lenses are good throughout the range, and most will have a ‘sweet spot’. It’s important to take this into consideration if you’re wondering why your fast prime does fine at f1.4 and 3m, but not f1.4 and infinity.

To be continued in part II. MT

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Comments

  1. The link at the end of http://blog.mingthein.com/2014/03/13/what-makes-a-good-lens-part-i/ leads to a 404 page, http://blog.mingthein.com/2014/03/15/what-makes-a-good-lens-part-ii/ being the correct page. The day in the date code appears to be two days behind in the 404 link.
    Feel free to delete this comment, as it isn’t really contributing anything to the discussion.

  2. Focus breathing is a result of what is usually termed ‘internal focus’, whereby instead of moving a lens of specific focal length further away from the sensor/film plane to focus closer, the lens stays in place but is shortened in focal length.

    If you focus your lens by moving the whole lens away from or closer to your sensor/film, you don’t have focus breathing, therefore most older lenses don’t display focus breathing. That is the traditional use of the term. Floating elements that are used not for internal focussing but for close focussing aberration correction is a murky middle ground. Most lenses that use floating elements do not display focus breathing, but some do, especially macro lenses. The latter often employ floating elements and internal focussing together, starting with the Micro-Nikkor 200/4 of about 35 years ago.

    If a lens is designed for cine use, as I believe the Otus is, part of the correction is to maintain angle of view as the lens is focussed. This is done by using the floating elements to shorten the focal length (as well as do other corrections) as the lens is focussed closer just enough to counter the lens extension caused reduction in angle of view. This is a very recent development and is actually ‘focus breathing’ in the traditional sense, but it effectively removes any changes in angle of view and so results in an optimal apparent negation of ‘focus breathing’.

    • A very good explanation, thank you.

      One small correction though – the Otus does not change length (front element does not move) when changing focus distance; I believe there are two sets of floating elements inside – one to control aberrations and counter the focusing group changing effective focal length as focus distance changes.

      • You are right; I didn’t explain it fully. In the Otus the situation is even more complex as two corrections plus the focussing is handled by the moving elements.

        Normally focussing affects the angle of view. In unit cell focussing, the angle of view gets narrower, even though the focal length stays the same because the lens moves away from the focal plane. Usually, in internal focussing lenses, the focal length shortens and the angle of view increases. In the Otus, and other high end cine lenses that have internal focussing, multiple internal groups are used to correct focus caused aberrations, provide focussing via shortening of the focal length and compensation of the shortening to allow the lens to continue to provide the same angle of view.

        Btw, I find your blog very enjoyable. My professional photography took me in different directions.

  3. Reblogged this on This Got My Attention and commented:
    More good advice.

  4. Hi Ming,

    A side question but related to lens. With any lens that one purchase, what’s your though on adding a protector filter? Do you think a UV filter is necessary on a digital camera or a protector filter will do and safe the money from the UV ones? I’ve read many post online but like to hear what you have to say.

    Wondering what what kind of filter do you put on your own collection of lenses.

    Thank you.

  5. Do you think that lenses which can be used on more than one body (i.e. exchangeable lenses) should be compared with lenses which are part of a dedicated lens-sensor combination like the Merrills, Ricoh GR, Fuji X100s, etc? Do you think there is an inherent advantage to a dedicated lens or can this be negated by a very well designed exchangeable lens?

    For instance, your love for the Otus is well known but presumably there will be cameras on which it performs amazingly and others where its power is wasted. On the right camera it can obviously perform better than even a good sensor/lens combo, but on the wrong camera it won’t…or so I would imagine.

    Whereas a dedicated combo of lens and sensor is going to give you consistent results assuming correct use…

    • Dedicated prime lenses are always going to be better than interchangeable lenses simply because because they were designed from the outset to work in concert with that optical system. Fixed zooms are not, because they are always a compromise.

      You could certainly design an interchangeable lens that could come close to what a fixed lens could achieve – there is no fixed lens that’ll outdo the Otus, for instance – but given limits of flange distance etc. and at the same budget, a fixed lens will always be better.

  6. Ahhh, the dreaded Otus lens porn shot to start things off with!
    Still saving up and waiting to pull the trigger and buy that killer lens.

  7. Noirdesir says:

    Marianne Oelund has measured the t-stops of 27 (24 Nikon) lenses. The trends that one can see are that zooms tend to have a lower transmissivity than primes and (fast) tele lenses a lower than normal lenses. Obviously, zooms in general have more glass elements, so this might not be surprising. For the fast tele lenses, absorption of light in the glass might also play a significant role, the more glass (in thickness), the more absorption. http://www.dpreview.com/forums/post/33785471

    • Nope, not surprising at all. It’s not the glass specifically that absorbs the light, it’s the reflections that occur at the various interfaces (air/glass, glass/ glass) that divert light out of the optical path. Coatings can improve this significantly – Zeiss T* or Nikon Nano Crystal for instance – but everything else constant, fewer elements are better.

      • Noirdesir says:

        Glass does absorb light in its bulk as well, just ask people operating glass fibre cables or look it up directly at the glass manufacturers (see http://www.sgpinc.com/materials.htm for the optical transmissivity of some special glasses). And the attenuation of the transmissivity as the light wavelength approaches UV or IR is also not only due to coatings.

        Note that I differentiated between ‘more glass elements’ (ie, larger number of interfaces) and ‘more glass’ (as in thicker glass). That more elements mean more reflection was implicit in the first expression. My only point here (besides simply reporting Marianne’s finding) was that absorption in the bulk probably plays a noticeable role in the transmissivity loss in the larger. Of course, technically, some of that absorption might be due to internal scattering on grain boundaries of crystalline materials or fluctuations in composition.

        I am not really sure that absorption plays a significant role. I have heard both versions, ie, that it is essentially only reflections (like you seem to strongly imply) or that absorption plays a significant role. But I have not come across a source that I would trust 100% on this issue. If you have any evidence or strong arguments, I’d be glad to see or hear them.

        • Across long distances, absorption is definitely an issue. But I’d imagine the few centimetres inside a lens is probably negligible compared to reflective losses?

  8. One more thing Ming, I’ve hear that the Nikkor 70-200mm 2.8G have a ridiculous focus breathing. Some review sites say that the newest f/4 version of this lens doesn’t exhibit this problem.

    • The new version II does have ridiculous focus breathing. At the sub-1.5m MFD 200mm is more like 135mm.

      Haven’t tested the f4 so I can’t say…

      • There’s an amazing scene with tons of focus breathing in The Hunt For Red October when Jack Ryan is being debriefed in the captain’s quarters after he arrives at the aircraft carrier. The camera racks focus from one character to another, and you can see the focus breathing very clearly in the size of the background objects. Interesting that it’s less noticeable with people’s faces …

  9. I have just bought a Nikkor 16-35mm vr and I’m quite disapointed with it performance compared to my sigma 35mm art. I think I’m aproaching this lens with an incorrect pont of view, I should not compare a zoom lens with a great prime, but I cant help feeling kinda sad. The sharpness and contrast of the sigma is just stellar.

    • The 16-35 is actually pretty good if you get a good sample. Unfortunately I have seen significant sample variation. And yes, comparing primes and super wide zooms is not fair at all…

  10. stanis riccadonna zolczynski says:

    Interesting contribution on the subject can be read on Cooke film lenses look. Something about sharp amd mellow achieved by balancing chromatic aberration against each other ( magenta and green if I remember correctly ). Of course horses for courses, while Cooke lenses are much praised for their rendering of humans, filming the Trons and Drons would call for surgical Summicluxes-C or Zeiss Primes.

  11. I’m very curious about the T stops of a lens. When using an incident light meter should we use the Tstop value rather than the f stop value? I could of course test myself……

  12. Lordtrini says:

    Excellent as usual Ming. But imagine a lens that magnetically bends/refracts light with a t stop on zero. A dream.

    • It’s not physically possible to have a T or F stop of zero…I believe 0.5 is the theoretical limit, at which point the lens will be collecting all of the light in front of it.

  13. Tom Liles says:

    Good article Ming. Looking forward to pt.II

    One thing I’ve never really come to grips with, conceptually, about lenses is the “focus past infinity” thing. Did photography just transcend mathematics or am I missing something?

    • No, basically the lenses are out of formation to make an image. Move them back and they do. Except because the optical distance changes with different temperatures, you need a bit of extra throw just in case.

      • Tom Liles says:

        The simplest explanation I’ve found anywhere. Thanks, Ming!

        I was thinking about this article and your conversation with Linden above, on my walk home tonight. Perhaps the very best lens, technically the very best, I have is the Af-S Micro 60 ED; and I use it a lot, but always indoors, and nearly always for pictures of things and not people. But my real answer to the very best thing I have is, honestly, and don’t laugh at me now, the Af-S 35 1.8G DX, mounted on the D3. Yes, mounted on the FX D3. I don’t think about why too much; all I know is I like everything that combo does, and it’s the best, to me. And that does contain both technical and aesthetic considerations.
        I also tried the DX 35 1.8G on the F5 the other week, just to see what would happen, and it was great. And when I thought about it, that lens, a second hander and almost the cheapest one I own, has pleased me on every single camera I’ve tried it on: D60, D7000, D3, F5. Of course I’m not bothered about the corners [though, past f/4 the image circle is pretty much FX; leaving just some mild vignetting to correct, which I don’t correct because I like mild vignetting, at this stage]…

        My biggest disappointment so far: probably a tie between two Ai-s lenses—the 24 2.8 (which was cheap, admittedly), and the 105 1.8. My 24 2.8 gives me moustache distortion (a headache I encountered with the Sigma DP1M) and the 105 1.8 seems to G/M fringe pretty bad at faster than f/4, and that’s even on the D3… I wasn’t expecting that (or should I say, wasn’t hoping for it). To be fair, the angle of view of the 105 is still so foreign to me, and I’ve barely gotten used to or used it enough yet, it’s too early to say really and naturally I’m reserving definite judgement for a good while yet—this is just initial gut reaction. But the 24 I’ve had for over 8 months now, used quite a bit and given a good crack of the whip. And I don’t rate it. I’d sell it if I could, or swap for something else, but the market doesn’t rate them either and it’d just be a waste of money to even try. So I’m sticking with it, too. I made my bed…

        But the moral of the story — I thought to myself, walking home — was: except for the unpredictable and unexpected hits that may please on an aesthetic level, like in my case the DX 35G, buying less but buying quality, is perhaps the best course on lenses. If I could have my time over, I’d have not bought cheaper MF Nikkors in the focal lengths I wanted to explore—but saved up for premium glass in those lengths instead. Like the best I could possibly get [barring ultra-special things like the Otus]. It would have taken way, way longer but there are three benefits to doing it that way: once you get there, you feel like you really earned it, financially, and technically [as a photograper; in all that meantime, you were practicing]; if it turns out that the focal length you wanted to explore just wasn’t you, you don’t take a haircut when it comes time to get out, the used market, here anyway, seems to protect the premium names; and thirdly, the quality will shine through, technically, in the photographs and when it doesn’t, it’s clear who’s to blame—or where the problem finding’s first port of call should be. I went for months, early last year, thinking I had one of those mirror out of alignment issues as correctly focused images from an Ai 50 f/2 I have, shot at 2.8, were soft, dead center; I just hadn’t thought that the lens would or could be so soft at that aperture—I know differently now. But if that had been a ZF.2 50/2… my first thoughts may have been correct. On the other hand, if that had been a ZF.2, I’d be speaking in a very high pitched voice right now thanks to the castration my wife would have given me. So, all in all, it might have been a good thing I bought the 7,000 JPY Ai 50/2 from 1977 :)

        But for all the single, monied, beginner-but-serious photogs out there: the old film-days adage, which I refused to listen to, that pumping money into glass is the way is a good one, I think. Certainly a robust default. It’s just that in the digital age the ceiling on prices just got higher, and the clarity of that priority a little greyer (since sensors, sensor-lens combo, plus PP environment and work flow is a real consideration that will affect things, significantly, too).

        Interesting topic.
        And important!

        • Didn’t someone comment a few weeks ago, if you buy the best, you only cry once?

          Anyway, I noticed the focusing past infinity thing too with my Nikkor 50/1.4 AI (which looks like it’s lived a hard life) on the F3. I chalked it up to a misaligned mirror, but the pictures have been coming back sharp, so it may be the compensation thing Ming mentions.

          Any favorite AI or AI-S lenses for the manual film user? 28/2.8 AIS, 50/1.8 AI, 55/2.8 AIS, 85/2 AIS, 105/2.5 AIS, and 135/2 AIS are all on my list. No idea what a good, compact 35 would be. The Zeiss 35/2 looks great, but it’s heavy and expensive, while people seem pretty divided on the 35/2 AF-D, but maybe because it’s made more for film than digital sensors?

          • Pretty much. But what you don’t get is the education in the process…

            I vote for the Zeiss 2/35 also.

            • I get my education in other ways, like when I took apart my iPhone last night to fix 2 problems, and caused a 3rd problem …

              I rented the Zeiss 28/2 and really liked it, but I have this nagging feeling that 35mm film will be fine with any halfway decent lens you throw at it. Yes, that’s not true, but it’s hard to think otherwise after looking at MF negs.

              • Better lenses will show improvements. But you can’t tell the difference between the Otus and 50/2 MP on a 16-24 MP body, and since film resolves even less than that – I leave you to draw your own conclusions…

        • The best lens for you is clearly an artistic choice: nothing wrong with that. If you can find one that works for you without ‘if only’-type thoughts, all the better. Unfortunately, I have been utterly spoiled by the Otus.

          Surprising that the 105/1.8 was that much of a disappointment. Oh well, the good news is you could trade it for a Voigtlander 90/3.5 APO-Lanthar, which is certainly not disappointing – even on a D800E :)

          • Tom Liles says:

            Mmm, APO Lanthar… I’ve got two CV lenses and both have been good to me; so I might take that under consideration. I’m on a ¥0 policy this year (excepting prints, film, development) so it’d have to be a straight swap.

            Yes, I’d agree my favorite is clearly on aesthetic grounds; but I’d like to speak up a little for the sharpness and relative freedom from abberation in that lens—and how it manages to maintain that performance on higher density sensors (the D7000). It isn’t abberation free but is simple to correct with tools in Lr, and nothing fancier. I’m not sure it’d cope with the D800 sensor; but the 610? I’d imagine it should still do well there. The D7100? Not sure: they are some pretty tiny pixels in there.
            I qualified my veneration of the DX 35 with an “at this stage” type gesture since, honestly, I can admit that “arty” is a kind of wall to hide behind—coming from a beginner. Choosing arty from a position of being able to do the vorsprung durch as well would be a legitimate choice; without any technical stripes on the shoulder it’s just a crutch.
            I can’t control my equipment properly yet… An Otus would be wasted — an outrage, in fact — in my hands; but I’m sure I could learn to work the capabilities of a ZF.2, given the lens and time with it.

            I might find a way to spend some time an APO Lanthar :)
            [This is after spending a suitably diligent amount of time with the Ai-s 105 1.8!]

            • Tom Liles says:

              P/S on the 105, it could just be that I got a sub-optimal example. I need to run it some more to really tell; but it’s all gravy—this is the thing with used lenses: we never really know the provenance. So you pays your money and you takes your chances!

              • Tom Liles says:

                P/P/S APO Lanthars look like they’ll be a bit of a treasure hunt :o :)

              • I remember it being good on the lower density (sub 10MP) bodies – never had a chance to use it on today’s monsters.

                • Tom Liles says:

                  Its reputation is certainly good; so there’s no reason to doubt the lens design, per say. Indoors (flatter light) it’s certainly better; and I’ve yet to run a roll of film behind it on the F2 or the F5—I’m expecting it to do better there (what it’s really for, both in terms of design and what I intend for it).

                  I’m walking around with it on the A7 today; but I’m also walking around with Peter, so of course: much conversation, little photo taking :)

                  • Send him my regards. And I’m curious what he bought…

                    • Tom Liles says:

                      Will do. And it was a good find—not an especially rare lens, but a difficult one to find used. And yet more difficult to find used and in pristine health. He managed both!
                      We’ll be celebrating over sushi tonight: I’ll down some chu-toro for you, MT. Actually Peter and I will down some chu-toro, for you; that volume might be a bit more commensurate with what you’d have been capable of if here with us :)

                    • Indeed. I had to buy a new one…that said, if you find anything used in Japan, they tend to be in pristine health anyway.

                      Save the chu-toro. Have a kampachi or three instead, and perhaps an anago to end… :)

                    • Tom Liles says:

                      Ah yes! I remember now: you prefer a little more “to the tooth” than the very soft stuff like toro; bring on the kampachi!

            • If it works on the D7000, it should also be fine on the centre DX region of D800 – the pixel density is the same.

              You could probably get a straight swap for the 90 APO Lanthar to the 105/1.8, actually.

              • Tom Liles says:

                I think so—it’s just finding a Lanthar! You did quite well I think, getting one. It’s quite surprising, actually, looking at the CV site, how many lenses have ended their production run.

                Peter has just had some good lens news today; I shan’t spoil it by spilling the beans ahead of him.

                I’m going to stick with the 105 for a while though; I think I need to pay a few more dues to it, and my decision, before changing again :)

                • I got lucky. I’ve got Bellamy looking for the 180/4 APO, but he tells me he’s never even seen one for sale…even though they aren’t very expensive.

  14. Reblogged this on CULTURAMUGELLANA DUE and commented:
    Good

  15. Reblogged this on Will Hey Photography.

  16. The best lens is the one that fits your style. Two that you know well are my favorites, Nikon’s 24-120 f4 VR for outdoors and 28 f/1.8 indoors. By the way, I just got those tickets on United.

  17. heykuapp says:

    Great opening paragraph and points on subjectivity. We feel this could be used to describe a variety of topics!

  18. That is one ‘good’ lens in the photo there. :-)

  19. Very nicely summarised, thank you.

    Over the last couple of years you have reviewed a number of lenses, and provided a brief view on still more at Camerapedia. I wonder if you will turn the second part’s attention to some examples of ‘good’ lenses.

    I’m also mindful here of what you wrote about the Zeiss 2/28 ZF.2 – you liked this lens despite (indeed because of) some of is limitations and peculiarities – e.g. the way is distortion characteristics enhanced certain compositions by emphasising the subject.

    And here we get away from the list of technical areas of fault as limitations, and into the realm of discussing the artistic possibilities certain faults, and renderings can give to a final image if used to effect. And that also brings into the debate questions of taste.

    But I’m guessing that you will touch on some of this in part II?…

    Looking forward to reading that.

    Thanks

    • And here we come into the realm of serious subjectivity – we can say a technically flawless lens at f5.6 is good, but it might not be preferable to somebody who just wants bokeh for the instantaneous impact…

      I’ll leave artistic applications of flaws for another time – I don’t have enough examples of that to hand; at the moment it isn’t what I’m after artistically for the most part, so I may also not be the best person to comment either…

      • Interesting. Do you think your thinking has shifted in the last couple of years? I don’t mean that in any loaded sort of a way. I’m just curious.

        Your wrote, of the Zeiss 2/28 ZF.2 (and I’m quoting very selectively here to emphasise this) –
        “I’ve been lucky enough to own and use a lot of lenses in my time. And some of them pretty exceptional [ ]…suffice to say, it would be difficult to pick one as an outright favorite. But I think if there ever was a contender, then it’d be the Zeiss ZF.2 2/28 Distagon T*.

        …Firstly, it’s not a technically perfect lens by any stretch of the imagination. In fact, it tends to score quite lowly on common testing metrics – especially in the corners – because its defining signature is highly pronounced field curvature…. It lends a very unique rendition to subjects shot with it because it has the property of emphasizing the out of focus areas by making them effectively further away from the camera… This property makes for great bokeh and a very cinematic rendering…

        …I don’t say this lightly, but despite its optical imperfections, the ZF.2 2/28 Distagon joins my personal pantheon of great lenses…”

        I think at the time you wrote that you were in search of that cinematic look.

        Given that at the time you wrote this (July 2012) you were looking for that look as it were. But if I understood you correctly then, your argument for this as a ‘great’ lens (different from a ‘good’ lens?) was that it delivered for you a look you were looking for.

        • Definitely. Back then I was shooting a lot more cinematic; the 2/28 is perfect for that, but less so for the Ultraprint objective I have now. Also, I tend to have two cameras – one wide and one tele – and the 28mm hole is filled by the GR, with the Otus or 2/135 APO on the D800E.

          Great/good is relative: there are lenses that test very well on quantitative objective metrics but may not be visually pleasing, and/or suitable for a photographer’s intended artistic objective. There are lenses that test poorly but are good for certain things – as you asked about before – the 2/28 is perhaps the best example of this. Or the Noctilux f1, if you like swirly bokeh.

          • can we see review of 135 soon ? What are your thoughts on that lens???

            • A proper review takes 4-5 days to produce. That’s 4-5 days of downtime and not being able to do any paid work. If I have the time I’ll write one. In short: it’s as close to the Otus as you’re going to get without getting an Otus, and the best short telephoto available.

  20. uditadailymusings says:

    Reblogged this on A Room of One's Own… and commented:
    Compels me to open that black bag, put the DSLR around my neck, and after the work out today, head straight to the head-over bridge to capture some nightlights. Today. #Promises to myself.

Trackbacks

  1. […] Photography News: What makes a ‘good’ lens? (part I) This might seem like a very obvious question, but the moment you try to define a set of criteria to quantify ‘good’, you soon realize there’s quite a lot more to lens performance than immediately meets the eye. So, for those of you without the ability to try a large number of lenses – let alone samples of the same lens – how do you know if the one you’ve got is ‘good’? When evaluating a new optic, I look broadly at several categories; this article will explain them a bit further. It’s wroth keeping in mind that most of these evaluations are relative and/or subjective; something that might perform well on a larger, lower-density sensor and balance properly on a large DSLR might not do so well on a very high density crop factor camera without a built in grip. It is therefore important not to consider ultimate resolution alone, but how well the system works together as a whole. A pancake zoom on a GM1 is a match made in heaven; you can mount an Otus on it, and it’ll deliver better resolving power, but it won’t be practical to use simply because of balance and manual focus/ stability/ ergonomic issues. Remember: the job of a lens is to collect and relay information, in the form of wavelength (color) and spatial position to the recording medium. The less it affects the information along the way, the better. Read full story => MingThein […]

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