Is there a way to determine if a lense is doing what it should. I bought a used SUMMILUX and wondering if i'm getting the image that i'm supposed to be.

Thank you, Ilya

-- ILya (shinky@mindspring.com), September 02, 2001

Answers

Ilya, there are test targets that you can photograph, to determine if a lens is performing well. But I prefer to check a lens by taking pictures of real-world subjects. I like to try out a new lens on some architectural subjects, building that have a lot of crisp details, like wrought-iron work, antennas on top, and so on. Sometimes I set the camera on a tripod and photograph a busy downtown scene. Then I look the transparency or the print over with a good magnifier. If the lens is very sharp, and the sunlight is frontal but off to one side,I will be able to see fine details, like being able to read a street sign several blocks away, or see the name of the manufacturer molded into the side of a traffic light.

I try the lens at various apertures, from wide open through at least f/8, and keep notes so I can label the pictures later. A few shots with the sun just outside the frame will show me how much flare the lens has. Focusing on something with the lens at its widest aperture will tell me whether it is focusing precisely at the correct distance.

Some people photograph a newspaper with the lens axis positioned about 45 degrees from the plane of the paper. By focusing on one line at the center of the paper (mark it with a pencil or put a ruler under the line of sharp focus), later you can tell, by whether that line turns out to be sharpest, or another line at some distance from it is sharpest, whether the focus is correct.

Never assume that a lens is bad just because you see something wrong in one picture, or with the first roll. Poor lighting, improper focus, low contrast for any reason, camera shake, curvature of field at close distances; these are all things that could make a good lens look bad. Always try again.

Regards,

-- Bob Fleischman (RFXMAIL@prodigy.net), September 02, 2001.

The fast lenses require extra carful focusing at the wide open settings in order to bring out their best performance. Shoot a lot with the lens uinder different conditions and then you will eventually know whether you like it or not. When I first got my Minolta CLE, I didn't expect that much from the 40 Rokkor. After a few rolls of film, I couldn't mistake the quality of the images at any aperture, and it became a keeper.

-- Andrew Schank (aschank@flash.net), September 02, 2001.

See www.sinepatterns.com

they sell a B&W random pattern which is essentially white noise in terms of spatial frequency content. After processing your negative, you need to digitize it at high resolution and then perform either a two dimensional Fourier transform or a series of one dimensional Fourier transforms on each row and column. You can then extract the MTF at any location in the image field. This is an extremely powerful and accurate technique if executed properly but it is definately not for beginners. Care must be taken in film selection and scanner selection as they will degrade the MTF of the final digitized image. What you really measure is the MTF of the entire system (lens, film, enlarger if you print the image and then scanner). You must take care to make sure that the other components have significantly higher resolution than the lens. Also, the resolution of the scanner limits the final resolution (upper limit of the MTF) which can be measured.

I've had good luck with this technique but have never tried any of my leica lenses - I'm usually testing fiber coupled image intensifiers.

-- mark (mramra@qwest.net), September 02, 2001.

Ilya asks: "I bought a used SUMMILUX and wondering if I'm getting the image that I'm supposed to be."

Please remember not to compare apples and oranges. If you are using the Summilux to do wide aperture available light photography in contrasty light of three dimensional objects (like people), then any "testing" of the lens on flat graphs or charts would not measure the desired results in actual use.

When we use a faster lens, we accept some residual aberrations, some loss of absolute sharpness, to be able to shoot under a lighting condition that a slower and probably sharper lens wouldn't allow due to camera shake. Therefore, when you ask about the image that you are "suppose" to get, ask yourself (and only you can answer this) what image you are trying to get. A 50mm Summicron would no doubt "test" better than a Summilux on a test chart, but at the cutting edge of hand hold-ability, that extra f-stop could make or break the shot. If the image you are suppose to get is a person within an environment in minimal light, and the Summilux allows you to capture that image, then it is doing what it is suppose to do.

The bottom line is that we can get all hung up on theoretical sharpness in a sterile test, or go out and take real photos of the things we bought the camera to shoot in the first place. The f/1.0 Noctilux for example is quite a bit less sharp on paper than a Summicron, but when used for real photography, can produce images that can look more effective. Now if I wanted to hang up a framed photo of a test graph....

-- Al Smith (smith58@msn.com), September 03, 2001.

In my opinion, there is no such thing as a good or bad lens. Each lens is different with it's own characteristics. True, some are sharper than others but, in my opinion, sharpness is not necessarily what makes a lens a "good" lens. My 50mm collapsible Summicron is not my sharpest lens, but it is one of my favorites because it products a softer image than my non-collapsible 50mm Summicron.Colour prints made with the collapsible are more "flattering" when photographing people, especially when doing portraits. The softness of the image is very pleasing and not as biting as the non-collapsible version.Your lens does what it is supposed to do it you are happy with the results. Charts which help to determine lens sharpness are only one aspect of the characteristics of your lens.

-- John Alfred Tropiano (jat18@psu.edu), September 07, 2001.