What do these numbers mean? Lens Resolving Power lp/mm

[Dave S.]

I just got my Ricohmatic 225 TLR back from Mark Hansen Classic Camera Repair. He did a terrific CLA / Overhaul and the camera is functioning beautifully. That said, he included a nice detailed report on the camera which included the following:

Lens Resolving Power, in line pairs per millimeter (lp/mm)

Green Filter.......... < 300 lp/mm f:3.5​

Green Filter.......... ≥ 328 lp/mm f8​

NOTE: A green filter is actually two colors of light, Blue and Yellow, with a plain yellow or red, the resolving power should increase, and without filtration it will drop slightly.

I'm not sure if these are good numbers or not?

My questions are:

Are these good numbers?
For example would you consider these numbers poor, acceptable, good, very good, excellent?

Can someone provide a comparison to help me better understand the resolving power of the taking lens on my Ricohmatic 225?

Thank you!

 

[Brian Legge]

I'm curious how he's testing. Those numbers seem really high.

Here are some medium format numbers close to the range I see in most places. The specifics here come down to testing methods, etc.

http://www.hevanet.com/cperez/MF_testing.html

In all likelihood, your 225 is extremely good... but I doubt it beats more modern lenses like that of the Mamiya 7.

 

[ColSebastianMoran]

Measure is resolving power in line pairs (one black line, one white line) per mm.

Those are very good numbers. Maybe something I don't understand; those number seem too high.

There are different ways of measuring this. I watched Jerry Sanford (well known repairer in Boston) do this on a pretty good Nikkor zoom. Starts with a reference slide of test patterns. Projects this through the lens onto a screen 20' away. Looks at image on the screen with a magnifying glass. Looks for the finest pattern where one can still see the lines. My Nikkor measured at 128-161 lp/mm.

Another way is to look at a recorded image on film or from a sensor. Those numbers are smaller because they are reduced by sensor resolving power.

Your numbers seem too high because the theoretical max resolving power of a diffraction limited lens is 1600/f, or 200 lp/mm at f/8. A quick Google shows Zeiss claiming 300 lp/mm on special recording film for a lens at f/5.6.

Norman Koren has tutorials, quite technical, on all this.

 

[ColSebastianMoran]

Here are some medium format numbers close to the range I see in most places. The specifics here come down to testing methods, etc.

http://www.hevanet.com/cperez/MF_testing.html

Those are excellent tests, widely quoted. He's measuring the results on film, so lower numbers than by the process I observed.

 

[Bisakok]

I had a Rolleicord 1a repaired by Mark earlier this year. It came back looking and working like it was brand new. Amazing. Like Dave S, I really like the work notes he provides... very helpful. Anyway, so my 'cord 1a also achieved the >328 lp/mm at f8 with a green filter. I asked Mark about this and he said the results are from his collimator and that actually most pre-war lenses can achieve this maximum resolving power, though they tend to be low in contrast. I can only guess that back then sharpness was more important to lens designers... and lets face it, early color films were pretty contrasty.

 

[Rob-F]

NOTE: A green filter is actually two colors of light, Blue and Yellow, with a plain yellow or red, the resolving power should increase, and without filtration it will drop slightly.[/I][/COLOR]

Green is only one color, namely, green. The three primary colors are Red, Blue, and Green. So green isn't a combination of other colors; it's a primary. Now, if the color in question were, for example yellow, then it would be a combination of red and green. Red + Green makes Yellow. Red plus Blue makes Magenta. Green + Blue makes Cyan (some call it aquamarine). But red is red, blue is blue, and green is green.

 

[Freakscene]

Green is only one color, namely, green. The three primary colors are Red, Blue, and Green. So green isn't a combination of other colors; it's a primary. Now, if the color in question were, for example yellow, then it would be a combination of red and green. Red + Green makes Yellow. Red plus Blue makes Magenta. Green + Blue makes Cyan (some call it aquamarine). But red is red, blue is blue, and green is green.

Primary colors are not a fundamental property of light but are related to the physiological response of eyes or a detection device to light. Green is a combination of yellow and blue in an additive colour model and cyan and yellow in a subtractive colour model. No colour is one colour.

What matters here, and what you can't tell without more information, is the source spectrum (chromatic aberration decreases resolution substantially In these tests even for "apo" lenses) and the contrast threshold of the detector. Back in film days crazy high numbers were commonly published, then if there were details you could see that it was measured on Tech Pan developed to a CI of 0.75 or higher. For a collimator, if it is an extinction type the eyesight of the tester has an influence.

Marty