Reasons to have multiple lenses in the same focal length/AOV

85mm lenses and equivalents on native or adapted formats – yes, I probably have too many. Upper left row: Nikon 85 PCE Macro, Zeiss 1.4/85 Otus, Nikon 24-120/4 VR, Hasselblad HC 2.2/100; middle row: Zeiss 1.4/85 Milvus, Canon EF-S 18-55 STM (APS-C), Nikon 85/1.8 G, C/Y Zeiss 2.8/85 Leitax converted to Nikon mount; lower right row: Zeiss Hasselblad CF 2.8/80, Zeiss Hasselblad C 2.8/80 T*. I wanted to add the Hasselblad HC 35-90 zoom, but it wouldn’t fit in the picture.  And there also used to be a Zeiss 1.8/85 Batis, Zeiss ZM 4/85, Nikon 80-400 G VR and Voigtlander 90/3.5 APO, but I’m recovering now…

Though this post may seem like a hoarders’ justification more than anything – I can assure you, it isn’t. Whilst you could probably pick one lens in each focal length or angle of view and hack your way into making it work, there are some pretty solid reasons why you might not want to – and this is something I’d like to discuss today. Trust me, there are reasons why I’d prefer not to have to carry two or three seemingly overlapping lenses on assignment – but often there’s simply no choice. Here’s my logic, using the 85mm-equivalent focal length as an example.

Tricky shooting conditions: low light, and mostly monochromatic. Wide open, any poorly corrected lens will display serious aberrations.

Outright performance
This is the reason you’d choose an 85 Otus over the 85mm mark on your zoom, for instance. If you must shoot in very low light and therefore probably wide open, on a high resolution body, you probably the best lens you can get. Or you may be looking to extract that performance under ideal conditions – ideal apertures, fast shutter, 100% controlled lighting. This level of performance of course comes with tradeoffs in size, weight and portability; not to mention criticality of focusing before you start to lose all of that hard-won resolving power. It’s for this reason that when I have the opportunity, I’ll default to manual focus and live view: all AF areas are of a finite size, which means that they will almost always cover a subject that occupies a range of different distances. This variation in distance may be great or small, but the higher the resolution the sensor, the more critical focus becomes – and the plane which the camera chooses to focus on is not always going to be your intended one. For obvious reasons, this is obviously not practical with moving subjects.

A fleeting moment, impossible without AF.

Autofocus
The corollary of the previous statement: when I’m shooting fast-moving documentary work, especially under lower light conditions, AF is a must to have anything like a respectable keeper rate – especially if there is no opportunity to reshoot the image. I use the 85/1.8 G here because it focuses quickly and accurately, and performs well wide open (though obviously not as well as the 85 Otus). For those of you wondering why I don’t use the f1.4 G, it’s to do with performance tradeoffs: the lateral chromatic aberration at maximum aperture is quite visible and distracting, and if I have to use the lens at f2 or smaller anyway to divest myself of it, there’s not a lot of point in paying the significant premium or carrying the extra weight (plus f1.4 is only 2/3 stop faster than f1.8 anyway). There is not much difference in AF speed, either. For similar reasons, if I’m working under bright conditions or mostly stopped down, I’ll use the 24-120 zoom.

Weight
None of us like to carry more than we have to, but there’s always a tradeoff between image quality and overall size/weight. Where that diminishing returns curve kicks in depends on the individual, of course. However: if I’m not going to need wide apertures, or AF, I like the C/Y Zeiss 2.8/85: nice rendering, fast enough, and absolutely tiny. Plus, if you’re using it at f8 or smaller for landscape work – there’s almost no difference between that and an Otus anyway. If you replace all of your 1kg f1.4 primes with 250g f2.8 primes, that’s enough weight saving for a very decent tripod. And I know which will open my shooting envelope wider and make the bigger difference to image quality…

Tilted focal plane to render the entire watch back in focus – single shot, no stacking.

Special purpose needs
I think this category is pretty self-explanatory: you’re not going to produce very good macro images with a lens that cannot focus closer than 1m, even if you use extension tubes. The optics simply aren’t optimised for close range reproduction (the exception perhaps being the 85 Otus, owing to its degree of correction – with extension tubes, it does perform nearly as well as the 85 PCE Macro even close up). Even so, you might get away with this at lower resolutions or output sizes. However, you can’t cheat extended depth of field or perspective control: tilt and shift are tilt and shift. It is for this reason that the 85 PCE is the only real choice for this kind of work unless you want to focus stack, which might not be possible in some situations.

Difficult to demonstrate this one at web sizes; what I’d like you to pay attention to here is the smoothness of out of focus areas.

Specific rendering characteristics
Perhaps the best example of this isn’t an 85mm; it’s the (in)famous f1.0 Leica 50 Noctilux with the swirly bokeh. It’s undeniably distinctive, but this comes with a related problem: it’s too distinctive. Everybody else who owns this lens will also shoot it wide open (who pays a premium for a f1.0 lens to use it stopped down when there are better alternatives?) and land up with images that look the same. This is perhaps an extreme example, of course. Let’s take the two Zeiss 85mm lenses: the Otus 85 delivers ultimate resolution at all apertures but at the expense of smoothness of background out of focus areas under some circumstances because of the aspherical element; the ‘bokeh balls’ are sometimes seen to have texture. The aspherics are part of the optical formula required for that level of apochromatic correction. On the other hand, the Milvus 85 has no aspherics, and a hint of coma and both lateral and longitudinal chromatic aberration wide open, but extremely smooth transitions and out of focus areas. The CA on the Milvus is mostly gone by f2.8, but the bokeh ball texture on the Otus remains. This difference can be quite visible in some kinds of portraiture, for example – which is why I keep the Milvus around.

Not quite 85mm: 75 was required, 75 was available (but not with a prime.)

Flexibility
There are times when you need just a bit more or just a bit less – and you can’t physically move, either through a lack of anywhere to go or a consequent change in perspective and foreground-background relationship. Or, you may simply not want to change lenses given ambient environmental conditions – the only thing for it is a zoom, of course. The highly polarising 24-120/4 is my choice here: it covers just about everything, is fast enough, good enough quality-wise, and pretty much all you need so long as you have enough ambient light. (Of course, your mileage may vary if prefer shallower depth of field; I work stopped down most of the time so it makes no difference to me.) Sometimes, those edges can make or break an image – it’s nice to have the choice. Just don’t get lazy and start making huge compositional and perspective changes with the zoom ring rather than your feet…

100mm on a 44×33 sensor is roughly 79mm – close enough…

Different formats
I think this is perhaps the most contentious of all points here, hence my leaving it for last. The most obvious reason is that we may want more or less DOF for a given angle of view and aperture (and be unable to stop down or open up more for various reasons) – thus necessitating a change in format to achieve the desired presentation. More complex is that though a given angle of view should render foreground-background relationships and projection identically for an ideal lens, the truth is that not all lenses project or render ideally, which is why we have the various kinds of distortion. In practical terms, it is very difficult to make a wide angle that has a flat plane projection; there’s invariably some barrel distortion that changes the relative proportions of the subjects and the way they appear to us. It may be a subtle difference of a couple of percent at most, but it’s still noticeable – even if we don’t consciously pick up on it. It is for this reason that most of the time, a 10 or 14mm lens on a smaller format will not look the same as say a 28mm lens on medium format. Coupled with this, we have depth of field considerations: even though we may have the same angle of view, 10/2.8 won’t render the same as 28/2.8 because of the difference in real depth of field. Now, here comes the contentious bit: due to optical design limitations*, in general, the larger the format, the less distorted the rendering** – even if you have the same overall angle of view.

*Part physics, part system related, part ‘what-can-you-do-at-a-given-price-point’ – people buying a small sensor probably aren’t willing to pay for or carry a perfect 12mm, though it could of course be made.
**By a similar token, if you’re paying for medium format, you’re probably going to be willing to pay for and carry that perfect 28mm.

I hope at the end of this you can see why lens selection at a given angle of view isn’t a straightforward thing, even if you’ve only got one mount or system. There may not be that many native choices for some systems, but adaptors complicate the mix significantly: especially those that allow movements when stepping down from a larger image circle to a smaller one (e.g. medium format to 35mm, or 35mm or APS-C or M4/3). Just beware of planarity issues as always, though the compromise might be worth it for infrequently encountered situations. It might not be worthwhile investing in a tilt shift macro if you don’t shoot off a tripod very often, or require high magnifications, for instance. But at the same time, a zoom might not cut it you do a lot of portraiture.  I really think the only thing you can do is identify the most common kinds of shooting situations you encounter, and work backwards from there in the most commonly used focal lengths (shooting for a while with a zoom and then doing a little EXIF analysis might help here). MT

Some of the lenses mentioned in this post are available from B&H or Amazon:
Nikon AFS 24-120/4 VR** – review B&H Amazon
Nikon AFS 85/1.8 G** – review B&H Amazon
Nikon PCE 85/2.8 Micro** – B&H Amazon
Zeiss ZF.2 1.4/85 Otus APO-Planar** review B&H
Hasselblad HC 2.2/100** – B&H

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