"My current 50mm 1.8 works just fine and is very sharp, so what can this new lens offer?"
I get this sort of message fairly often. If you're happy with the performance of your current 50mm, then any improvement from a new optic would probably be useless to you. Be happy that your standards are met with what you have.
And that's today's lesson: establish your own standards.
Too often I see people chasing potential gains because some Internet guru has anointed something as "the new thing to get." The whatchmahoosit on that shiny new thing is .01% better than before, so it must be better and therefore it must be obtained!
There's a turn-of-the-century book—The Tyranny of Numbers—which describes our obsession with numerical analysis and why it's often wrong. You'll find plenty of Internet Web sites that deal with photography that will cater to your desires to provide numbers, many of which use Imatest to generate their stats (disclosure: I use Imatest when I get something new, more on that in a bit).
Just for my amusement, I decided to just take one lens—the Nikkor 24-70mm f/2.8G—and see what numbers are actually being bandied about on the Internet for it. 2856, 3723, 21 P-Mpix. Those first two numbers are the low and high Imatest MTF numbers I found for center of frame at f/2.8, the third is DxOMark's strange, made-up metric. There, are you happy with those numbers?
Of course you aren't. What the heck did you learn from looking so closely at someone else's measurements? Probably not anything that's useful to you in assessing whether or not the product is something you should consider or not.
I know that it's popular today to defer to an expert to make tough decisions. They can't be wrong, right? Thing is, you don't know how consistently they test, you don't know what they're actually testing (what was the test distance where they achieved their MTF results, and what chart did they use?), you don't even know if they didn't have a typo in the data they presented.
What you can know is what you consider good or bad. In fact, I'd argue that you should know that, or you need to do something else before you start flinging your credit card at photo gear.
So let me suggest this: in your arsenal of lenses, do you know which one is the worst, which one is the best? Why is that true? What attribute is it that you see from the best that you don't see from the worst?
I actually know a lot of pro photographers who pretty much think all of their lenses are good. In one respect, they're correct. If you're buying pro-caliber lenses, they're all darned good, and these days the lens makers are managing to eradicate lots of little issues we used to have to just live with. But still, I had one pro say to me recently that he didn't need a particular lens because his current lens is just as good.
He was wrong about that. It isn't. Now, he still may not need the new lens because his standard is at the point where the old lens delivers. This is an important point to understand: he didn't need a particular new lens just because it exceeded his standard, not because it wasn't better than what he had. (Read that last sentence again. Don't proceed until you've understood and embraced it.)
So why is it that I pull out the charts and run Imatest on new gear coming into the byThom office? (Beyond trying to write reviews ;~)
It's because I know I'm pretty consistent in my testing, and through that testing I learn small things that might be useful to me some day. Such testing immediately flags any lens that might have a manufacturing defect, too.
I used the 24-70mm f/2.8G above as an example for a reason, though. The newer 24-70mm f/2.8E tested ever so slightly worse in the center for me, but much better at the edges. That led me to looking at a bunch of photos I took with the 24-70mm (and its predecessors over the years) to see whether that might make a difference to me. In essence, I was about to build a new standard for myself that had to do with a mid-range lens' performance across the whole frame.
As it turned out, a lot of the images I shot with my mid-frame zooms over the years did indeed need more optical clarity towards the edges. Aha! My standard just changed, and not surprisingly newer lenses tend to do much better than the older lenses at meeting my standard.
Aside: since I'm not mount specific, I can comment on 24-70mm's I've tested across a bunch of brands and mounts. So here are my "no, below my standard" lenses: Canon 24-70mm f/4, Panasonic 12-35mm f/2.8, Sony 24-70mm f/4, Tokina 24-70mm f/2.8. My "adequate but I'd like better" lenses: Sigma 24-70mm f/2.8, Tamron 24-70mm f/2.8 G2, Canon 24-70mm f/2.8L (haven't tested the II version), Nikon 24-70mm f/2.8G, Olympus 12-40mm f/2.8. And finally, my "meets my new current standard" lenses: Nikon 24-70mm f/2.8E, Nikon 24-70mm f/4 S, Sony 24-70mm f/2.8. Even these last three have small things I wish were better. But given the task of shooting something with a 24-70mm, I'm going to pick one of those three if I can.
You should note what I've done here. (1) built experience; (2) practiced consistency; (3) did some form of standard test I understand; (4) analyzed the results; (5) re-evaluted past uses and practices; and (6) updated my personal standard.
I happen to have high standards. Both my mom and dad were perfectionists, and that rubbed off on their only child. I always aspire to do better, too. Thus, something that was acceptable to me 20 years ago tends not to be these days. My standards keep moving.
I do now have to provide the rebuttal to my own comment earlier that you should "be happy that your standards are met with what you have", though. And if you've been following along, you might already have a hint as to why.
"If you can't see it, it doesn't count" is Ctein's Axiom. Unfortunately, that axiom is not universally true. It's only true for one moment in time.
What you see today is not necessarily what you'll see tomorrow. If you're seriously practicing photography in any way, I would hope that you aspire to get better over time. As you do, you may find that your standards change. Moreover, we now have the ability to look at images on near wall-sized displays with near perfect pixel representation, where we used to look at images on paper where ink had bled from dot to dot.
Indeed, that "can't see it, it doesn't count" thing is something you should constantly be challenging. Are you seeing everything? Are you sure?
I can name four or five people over the course of my imaging career that taught me how to see better. What I can't see in 2019 is much different than what I couldn't see in 1990. Thus, what I would have accepted in camera and lens performance in 1990 is something I wouldn't tolerate today.
You should be trying to grow. Always. It's one of the unique things about humans: we can get better. We can learn from mistakes, we can learn from experience, we can learn from others, we can learn by just being more attention. But you have to want to learn in order to learn.
So, set your own standards. Make sure you know what they are and why you set them where they are. But don't let them dry into concrete. Challenge them and adjust them as you grow.
