New "old Design" from Leica, 50mm F1.4 Summilux

The sample images are a mixed bag for me, some look great, like the kids on the outdoor path, while others have a weirdly featureless and smooshy bokeh. And the colour grading of the first Asian lady makes it look like it was shot with a Sony, kind of drab and slightly ashen.
 
Ororaro said:
Summarit needs a cleaning. All of them have suuuuuper foggy elements 1 and 2. They dont seem fogged until you wipe them. The difference is drastic.

Clean summarit are not low contrast wide open. They are superb lenses throughout.
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Looks clean (like you say) but I will check it out. thanks
 
My 11114 version 2 lens body diameter may have been slightly greater than its mount to filter thread length. The shape of this new one suggests the body is bigger, wider diameter. I’ll pass. The only revival lens I’ve bought is the Summaron M 28. Tiny.
 
Now that I think of it, I'm definitely not part of the market for the Leica Classic series in general. Lots of money for lenses which are being replicated for much less by Chinese companies, or even slightly earlier Voigtlander models like the Nokton 35mm f1.4 MC or SC. I'm sure the build quality is superb, and the lens is guaranteed to be fungus free, but I'm not willing to pay that kind of money for vintage character. This latest lens does look quite promising optically, though.
 
Richard G said:
My 11114 version 2 lens body diameter may have been slightly greater than its mount to filter thread length. The shape of this new one suggests the body is bigger, wider diameter. I’ll pass. The only revival lens I’ve bought is the Summaron M 28. Tiny.
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I traded a late-model Summicron-M 28/2 ASPH for the Summaron-M 28/5.6. No regrets whatever; the Summaron 28 is a wonderful, tiny lens.

G
 
simonOWO said:
What was negative MTF supposed to mean?🤣
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Below from Grok 3:

Can you evaluate this mtf and explain why it goes negative?

You're correct that in the provided MTF charts for the Leica Summilux-M 50mm f/1.4, the solid lines (representing sagittal structures) appear to dip below the zero line on the f/2.8 and f/5.6 charts, particularly toward the edges (around Y' = 18-21 mm). This is an unusual and noteworthy observation, as MTF (Modulation Transfer Function) values are theoretically expected to range from 0% to 100%, with 0% indicating no contrast transfer. Let’s analyze this and explain why this might be happening.

Evaluation of the Charts​

  • Visual Observation: The solid sagittal lines on the f/2.8 and f/5.6 charts drop below the horizontal axis (0% contrast) as they approach the edge of the frame (Y' ≈ 21 mm). This suggests that the measured or plotted MTF values are negative in these regions.
  • Context: The dashed tangential lines (representing tangential structures) remain above zero, though they also drop significantly, indicating that the lens retains some contrast transfer in the tangential direction even at the edges.

Why Does MTF Go Negative?​

Negative MTF values are not standard in typical optical performance metrics because MTF is defined as the magnitude of the Optical Transfer Function (OTF), which should always be non-negative. However, negative MTF can occur in specific scenarios due to phase effects or measurement/presentation artifacts. Here are the likely explanations:
  1. Phase Reversal (Contrast Inversion):
    • The OTF includes both magnitude (MTF) and phase components. A 180-degree phase shift in the OTF can cause the contrast to invert, where bright lines in the subject become dark in the image (or vice versa). This results in a negative MTF value because the contrast transfer is effectively reversed.
    • In the case of the Leica Summilux-M 50mm f/1.4, this phase reversal might be occurring due to optical aberrations, such as severe astigmatism or field curvature, which become more pronounced toward the edges of the frame. The sagittal lines being affected more than the tangential lines suggest an astigmatic difference that worsens as the aperture is stopped down.
  2. Aberration Effects:
    • Astigmatism: The divergence between sagittal and tangential MTF curves indicates astigmatism, where the lens focuses sagittal and tangential structures at different planes. At the edges, the sagittal focus might be so misaligned that it causes a contrast inversion.
    • Field Curvature: This lens may exhibit significant field curvature, causing the focal plane to bend away from the sensor at the edges, leading to defocus and potential phase issues.
    • Coma or Spherical Aberration: Residual higher-order aberrations, even at f/2.8 and f/5.6, could contribute to this effect, though it’s more common at wider apertures like f/1.4.
  3. Measurement or Plotting Artifact:
    • It’s possible that the negative values are a result of how the MTF was measured or plotted. For instance, if the testing equipment or software incorrectly handled phase data or aliasing effects, it might display negative MTF. This could be an error in the chart’s presentation rather than a true optical property.
    • Alternatively, the test might have included frequencies beyond the lens’s resolution limit, where aliasing (due to undersampling) could introduce negative values.
  4. Design Trade-Offs:
    • The Leica Summilux-M 50mm f/1.4 is a high-speed lens designed for maximum light gathering (f/1.4), and such lenses often sacrifice edge performance to achieve their central sharpness and low-light capability. The negative MTF at the edges might reflect a deliberate design choice or a limitation in correcting aberrations across the full frame, especially on the sagittal plane.

Interpretation and Implications​

  • Performance Insight: The negative MTF at the edges (Y' = 18-21 mm) on f/2.8 and f/5.6 suggests that the lens struggles to maintain coherent contrast transfer for sagittal structures in the extreme corners. This is less noticeable at f/1.4, where the drop is severe but stays above zero, possibly because the wider aperture smears the effect.
  • Practical Impact: In real-world photography, this might manifest as a loss of detail or unusual contrast reversal in the corners of the frame, particularly for subjects with fine sagittal details (e.g., radial patterns). However, for most practical uses (e.g., portraits or centered subjects), the central performance (Y' = 0-12 mm) remains excellent, with MTF values above 70-90%.
  • Stopping Down: The fact that this issue becomes more apparent at f/2.8 and f/5.6 (compared to f/1.4) could indicate that the lens’s aberration correction shifts with aperture, potentially overcorrecting or misaligning the sagittal focus as it stops down.

Conclusion​

The negative MTF values in the sagittal curves at f/2.8 and f/5.6 are likely due to a phase reversal caused by astigmatism or field curvature, amplified toward the edges of the frame. This is an unusual but not impossible optical phenomenon, reflecting the challenges of designing a fast prime lens like the Leica Summilux-M 50mm f/1.4. While the central performance is outstanding, the edge performance has limitations that might be noticeable in specific scenarios.
If you’d like, I can search for additional reviews or technical analyses of this lens to see if others have noted this behavior, or I can generate a simplified diagram to illustrate the concept of phase reversal in MTF.
 
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Yes I’m wondering if this is indeed a representation of optical performance or rather simply a measurement or graphing error

That’s a valid question, and distinguishing between a genuine optical performance issue and a measurement or graphing error is crucial for interpreting these MTF charts accurately. Let’s explore this possibility by examining the context, the data, and potential indicators of an error, while also considering what optical performance might look like in this case.

Evidence Supporting a Measurement or Graphing Error​

  1. Unusual Negative MTF:
    • As mentioned earlier, MTF (the magnitude of the Optical Transfer Function) is theoretically non-negative, ranging from 0% to 100%. Negative values suggest a phase reversal, which is rare and typically only occurs under specific conditions (e.g., severe aberrations or aliasing). For a high-quality lens like the Leica Summilux-M 50mm f/1.4, negative MTF at f/2.8 and f/5.6—where aberrations are usually better controlled—raises suspicion of an anomaly.
  2. Inconsistency Across Apertures:
    • At f/1.4, the sagittal MTF drops to near 0% but does not go negative, while at f/2.8 and f/5.6, it dips below zero. This is counterintuitive because stopping down a lens typically reduces aberrations (e.g., spherical aberration, coma), improving edge performance. A sudden introduction of negative MTF as the aperture decreases suggests a potential issue with the measurement or plotting process rather than a progressive optical effect.
  3. Symmetry and Curve Behavior:
    • The charts show the sagittal (solid) and tangential (dashed) curves diverging significantly at the edges, with the sagittal curve dropping below zero. In a well-designed lens, while astigmatism can cause separation, the MTF should not invert unless the optical design has an extreme flaw or the test setup misaligned the sagittal focus plane. The abrupt drop below zero looks more like a graphing artifact (e.g., an offset or scaling error) than a smooth optical transition.
  4. Leica’s Reputation:
    • Leica lenses, especially the Summilux line, are renowned for their optical quality and rigorous testing. A negative MTF at the edges, particularly at f/2.8 and f/5.6, would be an unusual flaw for such a premium lens. This lends credence to the idea that the chart might contain a mistake, as Leica’s quality control and optical design expertise would likely mitigate such extreme behavior.
  5. Possible Testing Artifacts:
    • MTF is measured using test charts (e.g., slanted edges or line pairs) and can be affected by misalignment, improper focus, or aliasing if the sensor resolution or test frequency exceeds the lens’s capability. If the test equipment miscalculated the phase or applied an incorrect baseline, the resulting plot could show negative values erroneously.

Evidence Supporting Genuine Optical Performance​

  1. Phase Reversal Possibility:
    • Negative MTF can occur due to a 180-degree phase shift in the OTF, caused by astigmatism, field curvature, or overcorrected aberrations. For a fast lens like the Summilux-M 50mm f/1.4, designed for f/1.4 performance, the optical design might allow such effects at the edges, especially if the lens prioritizes center sharpness over edge correction. The worsening at f/2.8 and f/5.6 could indicate a shift in the aberration balance as the aperture changes.
  2. Edge Performance Trade-Off:
    • High-speed lenses often exhibit reduced edge performance due to the difficulty of correcting aberrations across the frame. The negative MTF could reflect a real limitation, where the sagittal focus plane inverts contrast at the extremes, a phenomenon seen in some wide-aperture designs under specific conditions.
  3. Consistency with Other Data:
    • If other independent tests of the same lens model show similar negative MTF dips, it would support the idea that this is an optical characteristic rather than an error. However, without additional data, this remains speculative.

Analysis and Conclusion​

  • Likelihood of Error: The most plausible explanation is a measurement or graphing error. The abrupt transition to negative values at f/2.8 and f/5.6, despite improved optical correction at smaller apertures, and the absence of negative values at f/1.4 (where aberrations are typically worse), suggest an inconsistency. This could stem from a miscalibration in the testing equipment, an incorrect baseline in the plotting software, or a data processing mistake (e.g., phase data being misinterpreted as magnitude). Leica’s official MTF charts are usually meticulously prepared, but errors can occur in published materials or third-party tests.
  • Optical Performance Alternative: If this is not an error, it indicates a rare case of phase reversal due to astigmatism or field curvature, particularly affecting sagittal structures at the edges. However, this would be an unusual design flaw for a lens of this caliber, and the effect’s appearance only at stopped-down apertures contradicts typical optical behavior.

Next Steps​

To confirm whether this is an error or a real optical trait:
  • Cross-Check with Other Sources: I can search for additional MTF data or reviews of the Leica Summilux-M 50mm f/1.4 from reputable sources (e.g., lens reviews on X or photography websites) to see if others report similar negative MTF values. This would help determine if the issue is consistent across tests.
  • Request Clarification: If this chart came from an official Leica source, contacting Leica or the publisher for clarification on the negative values might resolve the ambiguity.
  • Visual Inspection: If you have access to images taken with this lens at the edges of the frame (especially at f/2.8 and f/5.6), we could analyze them for signs of contrast inversion (e.g., reversed patterns), which would support the optical performance hypothesis.
Would you like me to search for additional MTF data or reviews to investigate further? Alternatively, if you have more images or details about the source of this chart, I can analyze those to refine the conclusion.
 
Most of Grok3s comments are spot on. But the mtf is not inverting in this lens, you would see that in photos, and, looking more closely, the negative section of the mtf is clearly an artifact of the Fourier transform and the modeling failing to fit the values of the optical transfer function. I am assuming that these are not complex values because the magnitude of the MTF should be symmetrical around the lens centre (unless the sample lens was very decentered!).
 
Freakscene said:
the negative section of the mtf is clearly an artifact of the Fourier transform and the modeling failing to fit the values of the optical transfer function.
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Grok 3:

Yes, your hypothesis that the negative section of the MTF could be an artifact of the Fourier transform and a failure in modeling the Optical Transfer Function (OTF) is a very plausible explanation. This aligns with the technical process of generating MTF charts and could indeed account for the unusual behavior observed in the Leica Summilux-M 50mm f/1.4 charts, where the sagittal curves dip below zero at f/2.8 and f/5.6. Let’s break this down step-by-step to evaluate the possibility.

Background on MTF and Fourier Transform

• MTF Definition: The Modulation Transfer Function is the magnitude of the Optical Transfer Function (OTF), which describes how a lens transfers contrast at different spatial frequencies. The OTF is a complex function with a magnitude (MTF) and a phase component, and it is derived from the lens’s Point Spread Function (PSF) or Line Spread Function (LSF) via a Fourier transform.

• Fourier Transform Process: The OTF is obtained by taking the Fourier transform of the PSF. The real and imaginary parts of this transform yield the phase and magnitude, with the MTF being the absolute value (non-negative in theory). However, inaccuracies in the transform or modeling can introduce artifacts.

How Artifacts in the Fourier Transform Could Cause Negative MTF

1 Improper Sampling or Aliasing:

◦ The Fourier transform assumes adequate sampling of the PSF or LSF. If the sampling frequency is too low (e.g., due to a coarse test chart or sensor resolution mismatch), aliasing can occur. Aliasing can distort the OTF, potentially leading to phase errors or incorrect magnitude calculations, which might manifest as negative MTF values in the plotted data.

◦ At the edges of the frame (Y’ = 18-21 mm), where resolution and contrast are already degraded, aliasing effects could be exacerbated, especially if the test setup didn’t account for the lens’s fall-off in performance.

2 Phase Discontinuities or Wrapping:

◦ The phase component of the OTF can introduce discontinuities or wrapping (e.g., a 180-degree phase shift) if not handled correctly during the transform. If the modeling software fails to unwrap the phase or misinterprets it, the magnitude calculation could erroneously reflect a negative value. This is particularly likely if the sagittal structures experience a focus shift (e.g., due to astigmatism), causing a sudden phase reversal that the model doesn’t accommodate.

3 Modeling Failure:

◦ MTF charts are often generated by fitting a model to measured data (e.g., from a slanted-edge test or line-pair resolution chart). If the model (e.g., a polynomial or spline fit) fails to accurately represent the OTF—due to noise, outliers, or an inadequate fit—it can produce unrealistic results, including negative values. This could happen if the data points at the edges are inconsistent or if the fitting algorithm extrapolates beyond the measured range.

◦ The fact that the negative dip appears more prominently at f/2.8 and f/5.6 (where edge performance should improve) suggests the model might be overcorrecting or misinterpreting the data, possibly due to a mismatch between the expected optical behavior and the actual measurements.

4 Truncation or Windowing Effects:

◦ When performing a Fourier transform, the PSF or LSF is often truncated or multiplied by a window function to isolate the signal. If the windowing is poorly chosen (e.g., abrupt truncation), it can introduce spectral leakage or ringing artifacts in the frequency domain, potentially distorting the OTF and leading to negative MTF values in the output.

Why This Might Apply to the Leica Summilux-M 50mm f/1.4 Charts

• Edge Behavior: The negative MTF is concentrated at the extreme edges (Y’ = 18-21 mm), where the lens’s performance is already compromised by aberrations like astigmatism and field curvature. This is a region where measurement accuracy is harder to maintain, and modeling errors are more likely to emerge.

• Aperture Dependence: The absence of negative MTF at f/1.4 (where aberrations are worse) but its presence at f/2.8 and f/5.6 (where aberrations should be reduced) is inconsistent with optical physics. This strongly suggests a processing artifact, as the modeling might struggle to reconcile the expected improvement with the actual edge data.

• Sagittal vs. Tangential: The sagittal curves (solid lines) are affected more than the tangential (dashed lines), which could indicate that the test setup or model had difficulty aligning the sagittal focus plane, leading to a phase error that the Fourier transform failed to handle correctly.

Comparison to Optical Performance

• If the negative MTF were a true optical effect (e.g., phase reversal due to astigmatism), it would require a significant and unusual aberration profile, which is unlikely for a Leica lens designed with precision. Moreover, the effect should be more pronounced at f/1.4 (wide open), not f/2.8 and f/5.6, unless the lens has an exotic design flaw that defies typical aberration correction trends.

• The abruptness of the drop below zero looks more like a discontinuity or artifact from data processing than a smooth optical transition.

Conclusion

The negative section of the MTF in these charts is most likely an artifact of the Fourier transform and a failure in modeling the OTF, rather than a true representation of the lens’s optical performance. This could stem from aliasing, phase wrapping, inadequate sampling, or a misfit in the data modeling process—particularly at the edges where measurement challenges are greatest. The inconsistency across apertures and the high quality expected from a Leica Summilux lens further support this interpretation.

Next Steps

To confirm this hypothesis:

• Additional Data: I can search for other MTF charts or reviews of the Leica Summilux-M 50mm f/1.4 to see if this negative dip is replicated, which would help distinguish a consistent artifact from a one-off error.

• Technical Analysis: If you have access to the raw data or test methodology behind these charts, we could analyze it for signs of sampling issues or phase errors.

• Expert Input: Consulting optical engineering resources or Leica’s technical documentation might clarify if this is a known artifact in their testing process.

Would you like me to search for more MTF data or reviews to investigate further? Alternatively, if you have more details about how these charts were generated, I can refine the analysis accordingly!
 
Archiver said:
Where would a person go to learn about MTF charts and their meaning
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Well, I would suggest going to Grok!

An MTF (Modulation Transfer Function) chart is a tool used to measure how well a camera lens performs in terms of sharpness and contrast. It’s like a report card for your lens, showing how clearly it can capture details. Don’t worry if it looks like a bunch of squiggly lines at first—I’ll walk you through it step by step.

What You’re Looking At
An MTF chart usually has:
  • A horizontal axis (x-axis): This shows the distance from the center of the image (0) to the edges (like 20 or 30 mm). The center is where lenses are usually sharpest, and the edges are where they might struggle.
  • A vertical axis (y-axis): This goes from 0 to 1 (or 0% to 100%). It represents how much detail and contrast the lens can hold onto. Higher is better—1 (or 100%) means perfect sharpness and contrast, while lower numbers mean blurrier or less defined images.
  • Curved lines: These show the lens’s performance. There are usually multiple lines, and they might be labeled with numbers like 10, 30, or 40 (these are "line pairs per millimeter," but I’ll explain that in a sec).
Key Concepts Made Simple
  1. Sharpness (Detail): Some lines measure how well the lens captures fine details—like tiny blades of grass or the texture of fabric. These are often the lines labeled with higher numbers (e.g., 30 or 40). Think of this as the lens’s ability to "see" small stuff clearly.
  2. Contrast: Other lines measure how well the lens separates light and dark areas—like making a black cat on a white rug stand out. These are usually the lower numbers (e.g., 10). This is about punchiness and clarity in tones.
  3. Line Pairs per Millimeter (lp/mm): This just means how many tiny black-and-white lines the lens can resolve in a small space. Higher numbers (like 40 lp/mm) test finer details, while lower numbers (like 10 lp/mm) test bigger, broader contrast. You don’t need to memorize this—just know it’s a way to measure clarity.
  4. Sagittal and Meridional Lines: You might see solid and dashed lines (or different colors). These test sharpness in different directions—straight lines (like spokes of a wheel) versus curved or diagonal ones. For most photography, you just want them to be close together, meaning the lens performs consistently.
How to Read It
  • High lines are good: If the lines on the chart stay close to 1 (or 100%) across the whole graph, the lens is sharp and contrasty from the center to the edges. That’s a great lens!
  • Dropping lines mean flaws: If the lines dip down as they move right (toward the edges), the lens loses sharpness or contrast away from the center. Most lenses do this a bit—it’s normal—but a steep drop means the edges might look soft or muddy.
  • Compare the lines: If the solid and dashed lines are far apart, the lens might be sharp in one direction but not another (this is called astigmatism). For everyday photos, you’d prefer them to be close together.
A Real-World Example
Imagine you’re photographing a tree. A good lens (high MTF lines) makes the leaves look crisp and the bark textured, even near the edges of the frame. A weaker lens (low or dropping MTF lines) might make the edges blurry or flatten the difference between the leaves and the sky.
Quick Tips
  • Don’t stress the numbers: You don’t need to calculate anything. Just look at the shape of the lines—higher and flatter is better.
  • It’s not the whole story: MTF charts don’t show color, distortion, or how the lens handles light flares. They’re just about sharpness and contrast.
  • Use it to compare: If you’re choosing between lenses, look at their MTF charts side by side. The one with higher, steadier lines will likely give you crisper photos.
So, next time you see an MTF chart, think of it as a lens’s "sharpness map." High lines = clear photos, low or dropping lines = softer results.
 
Can you describe the mtf of an excellent performing lens, compared to an identical focal length lens of average performance?

I can describe a sample MTF chart for you in a way that you could sketch it yourself or visualize it clearly. Since you’ve asked for a comparison between an excellent performing lens and an average performing lens of the same focal length, I’ll walk you through what the chart would look like.

Setup of the Chart
  • Horizontal axis (x-axis): Distance from the center of the image (0 mm) to the edge (say, 20 mm).
  • Vertical axis (y-axis): Performance from 0 to 1 (0% to 100%).
  • Lines: We’ll use two common measurements—10 lp/mm (contrast) and 40 lp/mm (fine detail)—with solid lines for sagittal (straight) and dashed lines for meridional (diagonal).
Excellent Performing Lens
Imagine a lens that’s top-tier—like a high-end prime lens. Here’s how its MTF chart would look:
  • 10 lp/mm (contrast):
    • Starts at 0.95 (95%) at the center (0 mm).
    • Stays nearly flat, only dipping slightly to 0.85 (85%) at the edge (20 mm).
    • Solid and dashed lines (sagittal and meridional) are almost on top of each other, showing consistent performance.
  • 40 lp/mm (fine detail):
    • Starts at 0.85 (85%) at the center.
    • Drops gradually but stays strong, hitting 0.75 (75%) at the edge.
    • Again, solid and dashed lines are very close together.
What this looks like: Two pairs of high, flattish curves that barely dip as they move from center to edge. The lens keeps sharpness and contrast across the whole image—great for landscapes or portraits where edge-to-edge clarity matters.
Average Performing Lens
Now picture a mid-range lens of the same focal length—like a budget kit lens. Here’s its MTF chart:
  • 10 lp/mm (contrast):
    • Starts at 0.9 (90%) at the center—pretty good so far.
    • Drops more noticeably to 0.6 (60%) at the edge (20 mm).
    • Solid and dashed lines might start close but spread apart a bit toward the edge (say, 0.65 vs. 0.55), showing some inconsistency.
  • 40 lp/mm (fine detail):
    • Starts lower, around 0.7 (70%) at the center.
    • Falls off faster, hitting 0.4 (40%) or less at the edge.
    • Solid and dashed lines diverge more, maybe 0.45 vs. 0.35, meaning details get soft and uneven near the edges.
What this looks like: Two pairs of curves that start decently high but slope downward more steeply. The drop is obvious, and the gap between solid and dashed lines widens toward the right, signaling weaker edge performance—fine for casual shots but not for critical detail work.
Side-by-Side Comparison
If you put these on one chart:
  • The excellent lens has higher, flatter lines that stay close to 1 (like 0.75–0.95) and barely separate.
  • The average lens starts lower (0.7–0.9) and dips more (down to 0.4–0.6), with more spread between solid and dashed lines at the edges.
Real-world difference: The excellent lens gives you crisp, vibrant photos even at the corners—think a group shot where everyone looks sharp. The average lens might make the folks on the edges look softer or less defined.
 
One thing Grok3 did not describe is that the quality and type of out-of-focus rendering is shown by the differences between the meridional and sagittal lines in the mtf, specifically which line is higher, how far apart the lines are and how they vary across the field. The best numeric description of out-of-focus rendering is a series of MTF charts at different distances but the same aperture (manufacturers never do this, MTFs are typically made at 50x the focal length, a general approach to optical ‘infinity’).

One thing Grok3 got wrong is that the coarse image structures do not demonstrate contrast. All the lines demonstrate contrast. The contrast is higher the higher the lines are - so a 95% mtf on the 40lp/mm trace has higher contrast in fine structures than a lens with 70% mtf at the same frequency. Resolution and contrast, optically, are largely the same thing.

Film era lenses were sometimes optimised for coarse image contrast (Leica R 35 Summicron is the best example of this that I know, and many of the Zeiss Contax SLR lenses were designed this way too) but modern lenses for digital normally take an all-out approach to get everything as high as possible so you can count eyelashes at 100% from your 60 megapixel sensor. These ‘old design’ lenses are essentially made so that their imaging characteristics look like older lenses, complete with soft edges and aberrations.

Perception of contrast is linked to coarse image MTF for some viewers, but this depends a lot on the viewer, how their visual system is trained and whether they have looked at a lot of photos or not. That is where this interpretation comes from.

Zeiss made an excellent primer: https://lenspire.zeiss.com/photo/app/uploads/2022/02/technical-article-how-to-read-mtf-curves-01.pdf
And for depth of field and bokeh: https://lenspire.zeiss.com/photo/app/uploads/2022/02/technical-article-depth-of-field-and-bokeh.pdf
 
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