Testing lenses, and charts.

[waynecrider]

A couple of questions; 1. For barrel and pin cushion distortion, at what focus distance do you set your prime lens, infinity at closest distance?; Does it make a difference if your focused at different distances? And what about zooms. 2. Any cheaper resolution charts then the 1951 Air force test? The 2" glass slide from Edmund is $115. The chromatic aberration chart was only $19 tho.

 

[Claire Senft]

Distortion can change do to magnification even though it does not change due to apertures. A zoom lens will typically change distortion as focal lengths are changed, As far as distance is concerned for testing I can make no recommendation, I would guess if you use it at many different distances than I suppose that a number of different distances are indicated for a complete testing. Mainly distortion is noticeable with lines we expect to be straight. Archetecture is a prime example of such a subject. If you are concerned primarily about architecture then distortion testing at long distances will do,

I can not advise you about the testing chart, It is your money and your needs involved, If you are interested in knowning lpm capabilties then going to the hardware store and buying 3 - 6 inch metal rules that have milimeter markings on them and placing 1 in the center of the field, 1 halfway to the edge on a diagonal and the third in the corner will allow you to determine the lpm if you do as follows: If you are testing a 50mm focal length and you set your camera 21 focal lenghts away..1050mm and take the a photo then if you can see the mm markings on your negative when viewing it with magnification you have 20lpm resolved, change it so that your camera is 2550mm and if the negatives has resolved it you have 50lpm. the formula for computing the distance for a specific reduction in magnification is:focal length x distance + 1 focal length. That is how I got distances of 1050mm and 2550mm for 1/20 and 1/50th reductions. Of course the end result shows the totality of focusing, samera steadiness, film quality etc.

 

[Dan Fromm]

Wayne, Edmunds' $119 USAF 1951 chart on glass, their item R38-257, is for testing relatively low magnification microscope objectives and macro lenses at short distances, not for testing more usual kinds of lenses at normal distances. I didn't know you were a microscopist too.

Yes, for the usual kinds of lenses focused distance is very important. At the recommended distance, (group/element) translates directly to resolution on film. At other distances you have to do calculations, can't just look up in a table. For testing at distance you probably want Edmund's R80-001, priced at $18.95. Or call them, explain what you want to accomplish, and ask for advice on what to buy and how to use it.

Claire, I've used a target with fixed spacing -- a stage micrometer with 100 marks/mm -- for go/no go testing on macro lenses. Your procedure is good for that "at distance," a bit tedious for finding out what a lens can't do at various distances. And if Wayne really wants to test macro lenses, where what a lens can do at a magnification is of interest, there's really no alternative to using a target with many scales, e.g., a USAF 1951.

The USAF 1951 has other advantages over, e.g., my little stage micrometer. It hqs sets of targets at right angles, makes astigmatism very visible. And its targets have three black bars, makes spurious resolution very easy to detect. With my stage micrometer, I had to count very carefully.

Cheers,

Dan

 

[waynecrider]

Claire, (or anyone for that matter) as concerns testing distortions and the results posted in such magazines as Popular Photography, what would you suppose the testing distance was? And on another note, does the test even mean anything regardless of subject matter such as architecture. Would late lenses produced in the last 30 years produce a noticeable line distortion when shot at normal distances? I've certainly not noticed this when shooting and looking at output.

As concerns resolution, what is the possibility of producing a computer generated printed graph that would test this? Thanks for the help btw.

 

[Claire Senft]

I can not answer for Pop Photo. I can not answer for what you might notice or find bothersome. Go out and set your camera in a plumb position on a tripod in front of a building that looks to be straight. Fill your frame so that you have a vertical edge near the edge of one dimension and a horizontal edge near to the frame edge of the other dimension. As much as possible have these edges along the whole of a vertical and horizontal edges. Take your photo. Makes some careful prints. Lay a straight edge along the 2 perpendicular edges. Can you see any distortion without the straight edges? Do you see any distortion with the straight edges ? Do you consider the distortion bothersome?

Buildings I would think are far enough away that being further back from the building is not going to cause a material change in distortion.
Unfortunately when you conduct these tests and you find distortion, you will more readily see it. It is somewhat like noticing a small scratch on a new car. The scratch does not materially change the cars usefullness but you will be very aware of its existence.

 

[phfitz]

Hi there,

waynecrider: 2 are attached, print up all you want. How you measure is up to you.

Have fun with it.

 

[vet173]

I just got a lens resolution chart and was wondering at what distance to shoot it at, with respect to focal length. 10x?

 

[wclavey]

Here is a link to a resolution testing chart that I have found useful. It is marked to be full frame on a 35mm slide, so I simply adjust the camera distance until the image fills the viewfinder. I had some prints of this made by a local printing shop to get the resolution as high as possible on the copy I am shooting. I also use it at various distances for aligning rangefinders, as well.

http://www.graphics.cornell.edu/~westin/misc/ISO_12233-reschart.pdf

 

[Charles Webb]

I am sure all this "testing" of lenses is of some importance to some, but after my first five years involved with photography I developed a bit different view of the value of these tests. For the past 45 years or so, my lens testing has amounted to far less work. I mount the lens on a "plumb" camera, and using my trusty Hasselblad chiminy finder as a focusing aid, focus the image as best I can on the Satinsnow, (really not important what the image is, ) then expose a sheet of film at the aperture you choose, develope it and with a good glass (Hasselblad C.F. again) I anylize the negative, if it appears sharp, I print it. Then carefully study the content of the print. If I like what I see, that lens is a keeper if I don't like what I see in the print the lens is relagated to ah.. er...a.. ebay. ;-) Bench testing and using the charts in my opinion are good for bragging rights, but don't necessarily equate to good photographic images. I have owned many lenses that were/are highly rated on the charts, but coulden't come close to matching one of my 50 year old Wolleys image wise. The final image on the print is what I judge by! Not very scientific, I admit but it works for me! Happy testing, I am off to make some exposures !

Charlie............................

 

[vet173]

I am sure all this "testing" of lenses is of some importance to some, but after my first five years involved with photography I developed a bit different view of the value of these tests. For the past 45 years or so, my lens testing has amounted to far less work. I mount the lens on a "plumb" camera, and using my trusty Hasselblad chiminy finder as a focusing aid, focus the image as best I can on the Satinsnow, (really not important what the image is, ) then expose a sheet of film at the aperture you choose, develope it and with a good glass (Hasselblad C.F. again) I anylize the negative, if it appears sharp, I print it. Then carefully study the content of the print. If I like what I see, that lens is a keeper if I don't like what I see in the print the lens is relagated to ah.. er...a.. ebay. ;-) Bench testing and using the charts in my opinion are good for bragging rights, but don't necessarily equate to good photographic images. I have owned many lenses that were/are highly rated on the charts, but coulden't come close to matching one of my 50 year old Wolleys image wise. The final image on the print is what I judge by! Not very scientific, I admit but it works for me! Happy testing, I am off to make some exposures !

Charlie............................

I've always done about the same as you, as far as how I evaluate a lens. I picked up the chart for a buck and just want to play with it.

 

[Jim Jones]

I agree with Charles Webb -- the best lens test is its performance in practical photography. However, for numerical and comparative tests, charts can be useful. This crude CHART was designed to be printed at 600 DPI and used at 40 focal lengths. An array of these charts for 35mm would be 40x60 inches. If that is too large, the charts can be used at half that distance, and the resolution figures halved. There are certainly better charts available online, often in file formats or sizes that limit usefulness. Lens testing is complex. The subject should be studied before relying on any tests.

 

[craigclu]

If anyone is interested, I've got the Modern Photography Lens Test booklet scanned to a pdf. It's interesting info and at least gets you acclimated to the standards that were set, focus distance for focal lengths, target arrays, etc. It's posted at:

Dead Link Removed

 

[df cardwell]

A couple of questions; 1. For barrel and pin cushion distortion, at what focus distance do you set your prime lens, infinity at closest distance?; Does it make a difference if your focused at different distances? And what about zooms. 2. Any cheaper resolution charts then the 1951 Air force test? The 2" glass slide from Edmund is $115. The chromatic aberration chart was only $19 tho.

Gmorning !

What is the purpose of the lens testing you want to do ?

I mean, what's the context, and the application ?

:confused:

 

[Dan Fromm]

df, the original poster has been silent for nearly a month. Perhaps he figured out what he was after or needed to do to answer his question.

 

[df cardwell]

A month ? HUH !

Oh, yeah.. there's a date on these things !

Guess that's why I do this at night instead of the tablesaw....

.

 

[waynecrider]

df, the original poster has been silent for nearly a month. Perhaps he figured out what he was after or needed to do to answer his question.

Actually I've been looking at this thread every time it comes around into the new post list but have been keeping silent due to the inability to conduct the tests at the time. I'm still very interested in the process. Claire's explanation of determining resolution is based on movement of the camera, quite the labor intensive activity, but this is all in fun for me anyways. My purpose was to try and determine a small range of resolutions for a 35-105 Nikon lens. Now I am more interested in testing fixed focal length lenses on a 4x5 and a couple of 35mm cameras. Jim's procedure above seems more to my thoughts. I wish I could understand reading wclavey's chart and how to use phfitz's referenced chart. If anyone can explain them please do so.

 

[Jim Jones]

The USAF 1951 Resolving Power TestTarget is perhaps the best that is readily available. I haven't found a good download for it yet. Here is a Dead Link Removed that has much more information than I have time to read. A google search for USAF 1951 points to other information. Many years ago the Bureau of Standards published a booklet with several carefully reproduced test targets of a different design, but I can't find anything about it online at the moment.

 

[Jim Jones]

The Bureau of Standards booklet is: Irvine C. Gardner, Charts for Testing Lens Resolution, NBS Miscellaneous Publication M166, National Bureau of Standards, U.S. Government Printing Office, Washington, DC (1940) Two copies are available at bookfinder.com for $40 each. The sellers don't say if the charts are included, but since they were library copies, I rather doubt it. The publication was still in print in 1970 when I bought my long lost copy.

 

[waynecrider]

A different perspective.

I was thinking about this yesterday, and I hope I am asking this in the right way, but I wanted to ask you more enlightened printers as to what film resolution would be needed to print a sharp 35mm 8x10 print, and a sharp MF neg to 11x14 and 16x20 prints sizes for viewing at normal distances. Of course this is open everyones own bias, but I suspect most will be close. If I am asking this in the wrong way, please correct me.