(This post is part of a series of posts reviewing the Fuji 50mm f/1.0 lens.)

If you were designing a lens what would you do?

Ahead of you is a line of trees, planted in a straight row. They form the top of a “T”, you stand at the bottom of the stem, facing them with your camera and your lens. You focus on the center tree. Now what?

Do you want all of the trees in perfect focus? Of course, you might think, they are all the same distance away as the center tree so they should all be in focus. But the other trees are not the same distance away. They are further away and get further yet with each tree as you move away from that center one. An in-focus area all equally distant from the lens would, now it should be obvious, form an arc, form part of a circle, with you at the center.

A flat focus area seems a better choice for those trees, but maybe a curved focus area is better for other things, maybe better for things that are less flat and more 3-D. What to do?

If I photograph an evenly lit, blank wall, guess what I get? An unevenly lit blank wall. The center is bright and dims slowly toward the coroners. On some lenses and at certain settings the change is subtle, hardly noticeable even in pictures of that blank wall. Other times the darkening is dramatic, surprisingly so. Sometimes very expensive lenses have a strong darkening effect like this and that seems puzzling. Is vignetting bad or is it good?

Now we are shooting a picture outdoors and the sun is just outside of the picture’s frame. You can’t see the sun in your viewfinder but its light is indeed striking the front element of your lens. On some lenses you might never know the sun is just offscreen. The image looks clean and sharp. Put another lens on the camera and all hell breaks loose. The entire image washes out a little or maybe a lot. You can see bright spots all in a row in the pictures, sometimes circular or even hexagonal in shape, and sometimes in bright, saturated colors.

If you were designing a lens, what would you do?

There are many decisions like these in making a lens, although on the Internet forums it seems sharpness and the character of the background blur dominate. But there are many factors and they interact in interesting ways.

I write all of this in anticipation of a new lens, just released and arriving on my doorstep in the next few minutes. It’s the Fujinon XF 50mm f/1.0. If you are a photographer the “f/1.0” part caught your eye and you had to read it twice. That number is an indicator of how fast a lens is, how much light it lets in, literally the diameter of the aperture for any given focal length (that’s the “f” part). f/1.0 is fast, very fast. So fast that this lens is the first autofocus lens of this speed ever made. It’s so fast that in daylight, if I want to actually shoot at f/1.0, I will have to bring a filter that dims the amount of light the lens allows in order for my camera to work. It’s just too bright.

The high-speed part isn’t the interesting part for me.

I’m hoping the lens has character. I’m hoping that when the lens designers thought about those trees that didn’t just try to make the area of focus flat, to make the online lens testers happy that their paper test targets look good.

I’m hoping that when the lens designers thought about that blank wall they didn’t spend sleepless nights worrying about how to make it more even, to make the sample blank wall images on test sites look more impressive.

I’m hoping that when they thought about the Sun they found something interesting in the glare and the veiling and all the weirdness that the Sun can do to an image.

I want the lens to be less of a gowned-up clean-room technician and more of a friend. I want the lens to be something special, something different, I want to be amazed and delighted.

The knock on the door, there it is, just now, FedExed overnight from New York, its first day of release. There it is.