Will My Lens Be still Good in 2016?

Update: Although the article was written with the year 2016 in mind, it's needless to say that the lessons here apply for 2017, 2018, or, heck, 2025 as well. Unless photography changes to a dramatic degree (and by that I don't mean an extra ISO setting), everything you read here is still applicable

Introduction

"Will my Nikkor 18-105 be still good if I upgrade?" "Is the 18-55 OK for the Nikon D5500?" "Is the 18-200 too old for the 24MP sensors?" 

Admit it, you have asked yourself questions such as these. You have also seen them repeated to the point of tedium on forums and articles. Heck, perhaps even I might have said something in the direction of "if you count your pixels, pick this instead of that". The key phrase here is "If you count your pixels", as we will see.

Today's article will try to open up the rather misunderstood issue of a bit older lenses used on modern sensors. The implied problem goes something like this: Lens X was designed at a time when sensors were only Y megapixels, therefore now that sensors are Z megapixels, it is unsuitable.

It was superb for the D70. Is it as good in the D5300?

Well, it's not quite as simple. Let's see things in more detail.

Some Facts

First of all, the issue refers to zoom lenses, not primes. The reason is that primes offer high levels of resolution anyway. For the same reason, high-quality zooms such as the Nikkor 16-85mm f/3.5-f/5.6 or the pro-level Nikkor 17-55 f/2.8 are considered exempt from this situation. The zooms in the spotlight are consumer/kit zooms such as the 18-55mm, the 18-105mm, and the 18-200mm. In fact, these three are the ones most frequently mentioned in connection with this issue, and the reason is that they still offer reasonable solutions to the modern photographer. Conversely, the 18-70mm or the 18-135mm do not, because few would prefer the non-VR 18-70mm over the VR 18-55mm, or the non-VR 18-135mm over the VR 18-140mm. 

What Do We Define by "still Good"?

To answer the question "Will my lens be still good in 2016" we need to define what we mean by "good". More importantly, we need to define "still good", because this is the crux of the matter. You see, most people don't seem to realize something: 

Lenses don't become worse by time! 

Unless there is a physical damage or other deteriorating factor affecting your lens, it doesn't just magically lose resolving power as if it were a leaking barrel. At this point, you might ask: "Hey hang on... But if I mount the lens on a newer sensor, with more resolution, doesn't that mean it will look worse?"

Short answer: NO

Longer answer: No. What happens is that you will not see any improvement considering the fact that you have a sensor with more resolving power. In other words, if before you used your lens on a 12-MP Nikon D90 and then you tried it on a 24-MP D3300, you wouldn't see any significant improvement in resolution (of course you would in other areas, such as dynamic range or other non-lens related aspects of image quality).  At worst, when down-sampling the image back to 12MP you would have a pretty much identical image compared to the one from your D90 (not considering improvements in color rendition or dynamic range).

In fact, even the matter of "improvement" needs to be seen in more detail. You see, a lens design is not a black-and-white thing. What I mean is, even a consumer kit zoom from the time of the Nikon D40 or D200 is not designed in a way that the slightest sensor upgrade will instantly and unequivocally outresolve it. Instead, the issue appears only on the weakest aspects of its design (see: corners and wide-open). In other words, when we consider out hypothetical example above, when you mount your old lens on a 24-MP sensor and then down-sample to 12MP, you would possibly still see some resolution improvements, most probably in the center of the image circle. 

Bottom Line: Will My Lens Be still Good in 2016?

Yes, and in 2017, and in 2018. It will be as good as it was when you first bought it, regardless of the camera you will mount it on. Heck, if we're still around in 2025 and I'm reviewing the Nikon D400 that will have finally been announced (ha ha!) the 18-55mm will look on it as good as it did on the D70, probably better. 

Of course at this point you will say: "Hmm... OK. But I want even better". This is an entirely different topic. If you just got a Nikon D7200 and you want the best DX zoom you can get your hands on, then obviously the topic of this article is not pertinent (although, you should still ask yourself whether a lens such as the Sigma 18-35mm ART is 10x times better than the 18-55mm, because it's ten times more expensive). This is not the point, however. What I'm trying to say here is this:

- If you have a modern sensor and you're looking to get a bit older lens, then everything you read on reviews still applies today. If the 18-105mm was considered a good lens for the D90 or the D300, it still is the same, good lens for the D5500 or the D7200. The only point to consider is that...

- ... if you have an older lens (the 18-105 in our example) and a 12-MP camera, getting a 24-MP sensor will, generally speaking, not offer much if any improvement in resolution compared to what you already have. At the same time, however, it won't be worse either.