What do I look for when I test a new (to me) lens? What are the parameters that are most important?

 

I moved my schedule around today. Instead of heading to swim practice first thing in the morning I decided to go downtown and mess around with the new 50mm lens I wrote about yesterday. I put the Carl Zeiss 50mm f2.0 Planar ZM on a trusty Leica M240 and headed to my usual parking place across from the Treaty Oak. A hug and magnificent tree that's been right there in the middle of Austin for hundreds of years. 

Usually I go out photographing in the afternoons so I thought it would be nice to see what everything looked like when it was lit from the other side. Or backlit by morning sun.

It's always a good idea to test a lens that you've just bought. The one time you use a lens (new or used) right out of the box for client work you might get bit on the butt by the cruel pinchers of fate. Happens. When using a new-to-me used lens I tend to be very circumspect until I've proved to myself that it works as it should.

When testing a lens I want to see how sharp it is wide open, at both close up and distant focus settings. A lot of lenses are good at infinity and fall apart at their closest focusing distances. Many lenses are optimized for best performance at 50X their focal length but lenses with floating lens elements don't fall under that rule of thumb. But good or bad performance at different distances is something you really want to know if you're messing around with rangefinder cameras because while you are out shooting everything looks like it's nicely sharp and in focus through the viewing window. Mostly because the viewing window is very much NOT looking through the actual lens. Funny as it may seem in 2024 it's also possible to accidentally leave the lens cap on and not find out until it's too late. Because....you are viewing through the little window/optical finder and NOT the lens. Embarrassing. All too common. 

When I want to evaluate the sharpness of a lens at the closer distances I look for subjects with a lot of texture. Things like brick walls, peeling paint, rusty manhole covers and the like. For middle distance evaluation one subject that's just great is a tree that's just starting to bud, against a clean blue sky. This is also a good scenario for checking for purple fringing and magenta and green casts as well. 

Good distance subjects are big buildings with lots of balcony railings and other details. I check for sharpness in all these instances at a lens's widest open aperture, then closed down to what I generally consider to be the "optimum" aperture ( usually f4.0 or f5.6) and then again at f11.

It's great if your lens is sharp everywhere but it's even better if it's nice and contrasty at all these settings too. Once a lens convinces me that it's got great sharpness and contrast I also want to start looking at how much it vignettes at various apertures. Most fast primes are going to vignette a bit when used wide open but in most cases the better lenses don't vignette to the extent that software can't fix the issue. My set rule is a lens has grounds for rejection if an f2.0 lens is still vignetting frightfully at f5.6. That's a problem. And one I'm not inclined to mess with.

For me the best way to check for vignetting is to shoot a clean, even blue sky. Generally with the sun directly behind me. Stark, white walls are also good. Shoot in "A" priority and run through all the apertures you'll usually be using and the bring the files into post production and take a good look. You can also use an "eyedropper" tool to actually measure the fall off from the center of the frame to the corners. 

If you are using an after market lens hood and you see too much vignetting you might want to remove the hood and test again. Could be that a generic hood isn't right for your lens even though it's specified for a set focal length. Sometimes that's down to the physical design of the lens. The lens maker's hood is usually the best bet.

One of the most important tests is whether or not the lens in question focuses accurately on your cameras. Back in the DSLR days I had a run of lenses, both Nikon and third party, that backfocused on a Nikon D810 and front focused on a Nikon D800e. You "could" correct for the front or back focus of the lenses using the camera's software but it was a chore and required much trial and error. If you are manually focusing your lenses on a mirrorless camera you'll nail focus every time. Well, if you know how to focus, you use the focusing aids, etc. But even mirrorless cameras can be guilty of having focus issues in AF. 

I've spent quality time calibrating all three of my M cameras and when I get a new lens I focus on a target at infinity and make sure everything is accurate and then focus on a target in the studio at the close focusing distance and evaluate the results on a big screen at 100%. 

For me the focusing accuracy of a lens and the sharpness and contrast are the most important parameters of a lens. Also vignetting under 1.5 stops when used without software corrections. Some people talk about a lens having saturated color but I prefer a lens that's very transparent when it comes to saturation because it's so simple to add saturation to a file after the fact. 

I do all of these tests with raw files even though my preference is to shoot my personal work with Jpegs. The raw files reveal more of the good and the bad in a lens. And if I've shot something at higher ISOs, get more noise than I bargained for, and want to rescue the file I need raw files to take advantage of the A.I. Denoise in Adobe Lightroom. 

I spent the morning downtown with the camera and lens and I have to say that I'm very happy with the performance of both the camera and the lens under test.

I stopped at Taco Deli for a bacon, egg and cheese taco and a cup of their delicious medium roast coffee and then I headed home. A little later I headed to the Rollingwood Pool (AKA: The Western Hills Athletic Club) for the noon masters workout. 68°, brilliant sun, my own lane, and Julie on deck coaching. Heaven. 

My evaluation of the lens leads me to believe that I've got my hands on a small but high performing lens package. Even wide open it's nicely sharp. Works well at f11 and even f16, as well. The lens is slightly less contrasty than the Voigtlander 50mm APO but that's probably good for the environments I usually work in. For the small sum I paid I think I got a real bargain. 

I'm loving the way Leica M cameras handle the color red. 

no lens review seems complete without some mannequin photos. 

Shot near the close focus distance of the lens with the lens set to its widest 

aperture. At least the mannequins are agreeable about standing still and holding

a pose for a while so I can fiddle with the camera settings...

this is not a suit I would consider buying. Or wearing. Or having in my home on

someone else. It's just.....dreadful. Which is why I enjoyed photographing it.

for a popular city with a burgeoning population there sure aren't a lot of people 

out and about in the downtown area before 10 a.m. Hmmmm.

a time honored, middle distance test target that also stays still....

 a decent close-up target for rangefinder cameras. Their minimum focusing distance 

is usually set to (point) .7 meters. Any closer than that and the rangefinder doesn't work

nor do the frame lines move far enough to prevent a lot of parallax. But ---

at 100% I see really great detail on the rusty manhole cover. right?

A lovely medium distance test target. Here we are on the 1st of March and the 

trees are already starting to bud and bloom. If we get enough rain this Spring we 

may just have a green Summer. 

another good test target. lots of textured detail on the pink wall and a sharp line

(where I set the focus) on the metal flashing at the top of the wall.

Any lens testing tips you'd like to pass along?