Resolution for 35 mm lenses?

[RalphLambrecht]

Arent most good films around the 60 lp/mm at 1.6:1 contrast ratio? That is what I call useful resolution, ie: across the texture of an object, the 1000:1 figure is for shooting sharp-edged silhouette backlit tree branches against a white sky ...

Kodak lists Tmax100 at 63 lp/mm and Tmax400 at 50 lp/mm at 1.6:1. That's probably as unrealistic as listing 200 lp/mm at 1,000:1. Nevertheless, it shows that film and paper limit the system performance significantly. I'd like to see the figures for 160:1, which is an average scene contrast of roughly 7 stops. I assume it's around 125 lp/mm.

 

[Athiril]

160:1 contrast resolution would be how sharp one edge is next to edge that is 7 and 1/3 stops difference, not the resolution of a scene that is 7 and 1/3 stops wide. You're extremely unlikely to find any 7 and 1/3 stop edges in any kind of normal exterior scene, the transitions are much lower than that, and most transitions are not hard-edged, you wont get that on the hard edge between direct sun and shadow either, you'd have to set up a controlled situation where there is no ambient bounce back into the shadows.

The texture of bark or someone's skin etc, is not going to be 7 and 1/3 stops of variance over those surfaces as a whole, let along as the texture/transition from each "line" of the surface, surface detail is going to be in the 1.6:1 vicinity.

 

[RalphLambrecht]

160:1 contrast resolution would be how sharp one edge is next to edge that is 7 and 1/3 stops difference, not the resolution of a scene that is 7 and 1/3 stops wide. You're extremely unlikely to find any 7 and 1/3 stop edges in any kind of normal exterior scene, the transitions are much lower than that, and most transitions are not hard-edged, you wont get that on the hard edge between direct sun and shadow either, you'd have to set up a controlled situation where there is no ambient bounce back into the shadows.

The texture of bark or someone's skin etc, is not going to be 7 and 1/3 stops of variance over those surfaces as a whole, let along as the texture/transition from each "line" of the surface, surface detail is going to be in the 1.6:1 vicinity.

Good point. I have some RIT resolution targets with varying contrast (three different setting, I believe). They clearly show the influence of subject contrast on resolution measurements. I also measured my USAF 1951 targets, which I bought from Edmund's Scientific. They have a density range (black printing vs white paper) of over 100:1.

 

[ic-racer]

Here are two examples. An Olympus 50mm 1.4 SLR lens vs a Leica 50mm 1.4 rangefinder lens.

Error bars represent "similar lenses in class."

Y-axis is contrast at a given 50 line pairs per millimeter. So these read a little more like a contemporary MTF chart.

I think this info is interesting to read and also may be of some benefit to the next generation of 35mm film users who need to sort through all the left-over cameras from the last generation.

 

[RalphLambrecht]

Good point. I have some RIT resolution targets with varying contrast (three different setting, I believe). They clearly show the influence of subject contrast on resolution measurements. I also measured my USAF 1951 targets, which I bought from Edmund's Scientific. They have a density range (black printing vs white paper) of over 100:1.

I checked my files. The RIT targets come in three different contrasts:

32:1, 6.3:1, and 1.6:1

 

[Rol_Lei Nut]

Here are two examples. An Olympus 50mm 1.4 SLR lens vs a Leica 50mm 1.4 rangefinder lens.

Those seem to be especially thorough and well-done tests.
I don't have either lens, but the results could seem to fit their reputations (Olympus over-corrected for outer edge?)

Where can I find more?

Best regards

 

[Athiril]

I checked my files. The RIT targets come in three different contrasts:

32:1, 6.3:1, and 1.6:1

It'd be interesting to see lens performance @ 1.6:1, rather than on typical charts, as well as interesting to see how the other low-contrast areas perform that you have there (6.3:1)

 

[Nathan Potter]

Lots of good points here. Need to be careful of terminology though. Any lens is always diffraction limited at its maximum aperture, since the Airy disk size is only a function of the aperture diameter. The best performance may be found at smaller than maximum apertures due to better optical correction by stopping down.

To check the intrinsic resolution of a lens I used to use Kodak High Resolution Glass Plates (HRGP) that used a very fine emulsion capable of 2000 L/mm. For lithography applications we were interested in high resolution at the best contrast we could get since the HRGP plates were very high contrast emulsions. There are no equivalent modern emulsions to HRGP that I know of. For modern photographic purposes it is clearly more important to consider the film/lens performance as a unit as suggested by Ralph.

Nate Potter, Austin TX.

 

[Athiril]

I'm waiting for the day that negative refractive index optical materials start being used by lens manufacturers... lens with resolution limited only by abberration, no diffraction limit, continue to stop down for ever sharper images

They've already been used in the visible spectrum a few years ago.

 

[ic-racer]

Those seem to be especially thorough and well-done tests.
I don't have either lens, but the results could seem to fit their reputations (Olympus over-corrected for outer edge?)

Where can I find more?

Best regards

After a quick search of the net, it indeed looks like the old Modern Photography and Popular Photography magazines do not have PDF archives. So this info is locked in these old magazines.

I got that particular test from a special they ran on "32 Normal Lenses" back in the late 70s. Too bad they did not test the f1.4 Planar 50mm at that time. Later they tested a Contax and ran that cameras Planar 1.4 50mm individually. I can't find that one currently, but as I recall it was between the Zuiko and the Leica Rangefinder lens. I believe the Planar was very similar to the Leica SLR lens. I need to do some more digging.

 

[Rol_Lei Nut]

Too bad they did not test the f1.4 Planar 50mm at that time. Later they tested a Contax and ran that cameras Planar 1.4 50mm individually. I can't find that one currently, but as I recall it was between the Zuiko and the Leica Rangefinder lens. I believe the Planar was very similar to the Leica SLR lens. I need to do some more digging.

I've seen many tests of the f/1.4 Planar (I even have one, collecting dust as I'm not really a 50mm fan...).
It's usually not especially impressive in tests, but is a lovely and much admired lens in practice (low flare, lovely singnature and 3D look).

Another example of real-wold impressions being just as important (or even more so) than tests alone.

 

[Q.G.]

Lots of good points here. Need to be careful of terminology though. Any lens is always diffraction limited at its maximum aperture, since the Airy disk size is only a function of the aperture diameter. The best performance may be found at smaller than maximum apertures due to better optical correction by stopping down.

The Airy disk size may depend on aperture size only, but aberrations do not.
In most cases, you can't reach the resolution limit diffraction alone would set, because the effect of aberrations is far worse when a lens is set to its maximum aperture.

So almost no lens is diffraction limited at its maximum aperture.

Stop a lens down, i.e. reduce the aperture size, and the effect of aberrations may (and usually will) reduce. But so will also the resolution diffraction alone would limit it to.

The trick in stopping down vis-a-vis resolution is to stop down (i.e. reduce the aperture size) far enough to limit the effects of aberrations on resolution to the point where the result is equal to what diffraction will limit resolution to at that aperure size.

Stop down further, reduce the aperture size more, and diffraction will take over as resolution limiting factor.

So "Any lens is always diffraction limited at its minimum aperture".

We must be careful of terminology.

 

[RalphLambrecht]

What Q.G. said.

 

[domaz]

Thank you, that was well stated. The last paragraph hit home because I keep thinking about going into LF.

Steve

Don't forget about the increased ability to crop and get a better composition with LF which often results in better pictures. It's not all about lp/mm.

 

[RalphLambrecht]

Don't forget about the increased ability to crop and get a better composition with LF which often results in better pictures. It's not all about lp/mm.

To compose during image taking or image making is a whole new conversation, but I fully agree with your statement about lp/mm.