Just MTF Charts

Just MTF Charts: Nikon Prime Lenses

We’ll continue our just MTF chart series of posts with the Nikon brand prime lenses. For those of you who have been asking, The Digital Picture is going to add all our MTF graphs to their comparison tool as we release them. That will let you do logical comparisons like ‘is the Sony 135mm f/1.8 GM sharper at the edges than the Sigma 14mm f/1.8‘ to prove your brand is the absolute best in online forum wars.

Three quick answers to questions that I’m sure will be asked:

  • Z lenses testing requires sacrificing a camera and lens for electronics, machining a new mount for the bench, and wiring everything together. It’s a long and expensive process and we won’t have Z-lens test results for at least months. 
  • No, we don’t test stopped down. Lensrentals is willing to pay the cost for 10-copy tests wide open to establish standards for QA testing (which is always done wide open) and we share them. If you really want stop-down results, a 10 lens series costs $5,500. Email me and I’ll tell you where to send your check.  
  • The 24mm f1.8 isn’t missing because I forgot. I didn’t have enough results to post a 10-copy average.

 

A Quick How to on Reading MTF Charts

If you’re new here, you’ll see we have a scientific methodology to our approach, and use MTF charts to measure lens resolution and sharpness. All of our MTF charts test ten of the same lenses, and then we average out the results. MTF (or (or Modulation Transfer Function) Charts measure the optical potential of a lens by plotting the contrast and resolution of the lens from the center to the outer corners of the frame. An MTF chart has two axis, the y-axis (vertical) and the x-axis (horizontal).

The y-axis (vertical) measures how accurately the lens reproduces the object (sharpness), where 1.0 would be the theoretical “perfect lens”. The x-axis (horizontal) measures the distance from the center of a lens to the edges (measured in millimeters where 0mm represents the center, and 20mm represents the corner point). Generally, a lens has the greatest theoretical sharpness in the center, with the sharpness being reduced in the corners.

Tangential & Sagittal Lines

The graph then plots two sets of five different ranges. These sets are broken down into Tangential lines (solid lines on our graphs) and Sagittal (dotted lines on our graphs). Sagittal lines are a pattern where the lines are oriented parallel to a line through the center of the image. Tangential (or Meridonial)  lines are tested where the lines are aligned perpendicular to a line through the center of the image.

From there, the Sagittal and Tangential tests are done in 5 sets, started at 10 lines per millimeter (lp/mm), all the way up to 50 lines per millimeter (lp/mm). To put this in layman’s terms, the higher lp/mm measure how well the lens resolves fine detail. So, higher MTF is better than lower, and less separation of the sagittal and tangential lines are better than a lot of separation. Please keep in mind this is a simple introduction to MTF charts, for a more scientific explanation, feel free to read this article.

 

Nikon MTF Charts

Nikkor 20mm f/1.8G ED

Lensrentals.com, 2019

Nikkor 24mm f1.4 G ED

Lensrentals.com, 2019

Nikkor 28mm f1.8G

Lensrentals.com, 2019

 

Nikkor 28mm f1.4E ED (by special request)

We didn’t put this in originally because I didn’t have 10 copies to test. Here’s the results for 5 copies, it’s all I could get to.

Lensrentals.com, 2019

Nikkor 35mm f1.4G

Lensrentals.com, 2019

Nikkor 35mm f1.8G ED

Lensrentals.com, 2019

Nikkor 50mm f1.4G

Lensrentals.com, 2019

Nikkor 50mm f1.8G

Lensrentals.com, 2019

Nikkor 58mm f1.4G

Lensrentals.com, 2019

Nikkor 85mm f1.4G

Lensrentals.com, 2019

Nikkor 85mm f1.8G

Lensrentals.com, 2019

Nikkor 105mm f1.4E ED

Lensrentals.com, 2019

Nikkor 105mm f2.8G IF-ED VR Micro

Lensrentals.com, 2019

 

 

For a look at all the Just MTF Articles we’ve done so far, be sure to check them out here.

 

Roger Cicala, Aaron Closz, and Brandon Dube

Lensrentals.com

April, 2019

Addendum: The Digital Picture is hosting the MTF charts on their comparison tool, putting them up as we publish them here. It’s a great way to compare two lenses for the one or two of you who like to do that. The Canon and Zeiss primes are already up, the Sigma should be added by tomorrow.

Author: Roger Cicala

I’m Roger and I am the founder of Lensrentals.com. Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.

Posted in Just MTF Charts
  • I could maybe get a 5 copy set done on the Nikon. While I don’t like doing less than 10 copies, I guess it would be better than no data at all.

  • Matti6950 .

    If the Sigma blasts tne nikon 28mm F1.4 in astigmatism and corner sharpness the choice is easy for me. To bad no comparison yet (though i’m already pretty sure i won’t get the nikon, as it seems optimized for close and not infinity.

  • As Brandon said, we do not have the complete set. Also, in those cases we didn’t do 10 copies, we did one copy at different apertures. And got 7,312 fanpeople screaming not fair, that wasn’t a good copy of the lens, they knew it was better than that, we were picking an awful copy to do because we hate their brand, etc. etc.

    So I stopped releasing the single copy stopped down data, although there is some still out there.

  • Brandon Dube

    Please don’t turn a very rough rule of thumb into some kind of statement about the relevance to perceptual image quality. I did not say 20 lp/mm was more or less important than anything else. It is simply the case that unless your lens is dogshit, the MTF is going to be high at very low spatial frequencies (10, 20 lp/mm). Since the range of ‘typical’ values at those frequencies is quite compressed (say, 0.7 – 0.1 instead of 0.1 – 0.8), the sensitivity is a lot higher.

  • Brandon Dube

    I did some (~ Canon and Zeiss primes) in 2015, and we’ve done something like < 10 other lenses since.

  • Samuel Chia

    Roger, I recall Brian from The-Digital-Picture used to have your MTF graphs and for quite a few lenses he had stopped-down measurements as well. Certainly this means you’ve measured lenses stopped down in the past, contrary to what you mentioned. I now can’t find those MTF graphs on the-digital-picture anymore, which is a pity.

  • I don’t want to speak for Brandon, but I’m pretty sure that’s NOT what he meant, it’s a huge oversimplification.

    Put another way, there’s rarely a 10% difference between similar lenses at 20 lp/mm. If we test a dozen or two copies of a prime lens, almost all would be within 2-3% and one that’s 10% lower is almost certainly a ‘bad copy’.

    If we test the same two dozen lenses at 40 lp/mm they’d probably be scattered in a range of at least 10%. If you evaluate images with fine detail critically you would see that some resolve better than others. That’s getting into what we consider sample variation and is inevitable.

    This is why manufacturer’s, who generally test at a 20 lp/mm equivalent, often say a lens is fine while a photographer, who resolves detail at 40 or 50 lp will state ‘it’s obviously softer on one side than the other’.

  • Doug, I may come back to doing it, but the variance data has a bit of an issue that makes me uncomfortable. There are some lenses where every copy has a soft side or corner. The variance formula misses this and says that lens has OK variance because math says ‘normal’ is a soft side or corner; they all have that, so low variance.

    What we probably need is a two-fold ‘variation in center sharpness between copies, variation in edges within a copy’ kind of thing. But I don’t have the math to make that kind of thing.

  • Unfortunately that lens hasn’t been very popular and we don’t have 10 copies.

  • Gerard Roulssen

    A fantastic effort, much appreciated!
    Any chance of 28/1.4E entering the party …?

  • Andreas Werle

    This is realy interesting, thanks for the question and the answer! So, the contrast for 20lp/mm is most relevant for the perception of the image quality. This is an important aspect and may be helpful for the interpretation of the data.

  • Kenneth Tai

    28mm F1.4E please

  • Brandon Dube

    A vertical bar is an increase of 10% (relative to 1.0… it would be +50% to go from .2 to .3) contrast at a particular scale. What is significant is not straightforward to answer. If you take pictures of a clear blue sky, the MTF is irrelevant because the object has no detail. If you take pictures of very fine patterns and textures, you have a great sensitivity to what MTF is measuring.

    0.01 is way below the perceptible threshold. In general, as a very rough rule of thumb two lenses which differ by 0.1 at 40lp/mm are noticeably different. Two that differ that much at 20lp/mm are night and day.

  • Doug McEwen

    Roger, thanks again for being willing to publish this treasure of information for all these lenses. The only thing I wish for is that you would resume publishing the variance data, because for me it was just as important as the MTF data. If I lived in the US I would only buy lenses by renting them first from Lens Rentals, and then keeping the ones that were reasonably close to what reviews and test sites such as yours indicate they should be. But I live in Canada, so I have to purchase them at retail and hope for the best. I would rather buy a lens with a bit worse MTF but good variance, than the other way around which becomes somewhat of a lottery. You indicated in a past post that you stopped publishing the variance data because it was being abused. I was very sorry to hear that – I thought it was good for the whole industry that the variance data be published, because it gave manufacturers incentive to improve that aspect of the lenses, and obviously, customers won too.

  • Carleton Foxx

    Can someone answer the magnitude question?
    What percentage of betterness is represented by each horizontal line in the chart?
    For instance if the 50 lp/mm of Lens A is at 0.4 and Lens B is at 0.5 does that mean Lens B is 10 percent better? Twice as good?
    A related question: How much of a change is significant? Does the lp/mm have to jump a full 0.1 to say that a lens is sincerely better? Or is 0.01 a noticeable improvement?

  • It’s not an absolute, but I’d sure trade a bit of MTF for some off-axis sag-tan separation improvement. Depends on what I’m doing, though. I’m looking for a very different MTF in an architectural lens than a sports lens.

  • Guy, we’ve done up to 400mm f/2.8. But there’s always the question in my mind of ‘are those absolutely accurate’? And let’s just pretend that I did, say, Canon 400 f/2.8 Mk II and III and Sony GM. They’re all going to be excellent and the difference splitting hairs.

    And the fanboys will split those hairs, magnify them like they were looking under an electron microscope, and I’ll spend days and days on forums going “No, that’s not what I said at all. The test results don’t show that.” I’m tired of that.

    As I said the other day, “Fanboys are why we can’t have nice tests”.

    But seriously, let’s say lens A is a tiny bit better than lens B. But B is heavier and longer. Could it be the increased weight, way over the theoretical limit of the bench, is allowing some vibration that makes the results lower? Is it possible the front element is so close to the collimator that it has some effect? I won’t know for sure.

  • Marcello, unlike most kickstarter fund-ups, I’d actually feel like I had to deliver on promises made if I went that route, so it’s a big commitment.

    To give a rough idea, though, to do just f/2.8 and f/4 on 10 copies each for just the prime lenses would take 276 testing days, and the cost (my cost, not retail) would be close to $200,000.

    Last year one of the largest review sites entered into discussions about taking over the MTF project. They’re smart guys and after we talked about everything they basically said there was no way they could afford to do it.

  • Roger Cicala

    Thank you, David. Fixed that.

  • Thank you, David. Fixed that.

  • MassimoTava

    Roger, would you prefer a MTF chart that has perfectly overlapping lines at lower lp/mm vs a lens that has higher lp/mm but Tangential & Sagittal Lines diverge wildly.

  • David Bateman

    Roger that 24mm f0.14 lens looks crazy. Didn’t know Nikon made one. Or you may want to fix that title.

  • David Bateman

    I think Roger could easily collect over 1 million. Thats how the tv show, video game high school collected money to be made. Now that depicted future is a reality with Overwatch leagues.

    The issue is does Roger want to test the full range on thousands of lenses?

  • If i where you, I will test try a kickstarter project to found a stopped down lens test, so we will see how much people really want thoose data! 😀 😀 😀

  • GuyWith

    Based on what I’ve read here before, to you guys the term “supposed to” is less of an impassible limit and more of a challenge to your ingenuity.

  • GuyWith

    Amid the terror and tears of the day Uncle Sam demands his annual pound of flesh, along comes our Uncle Roger with a delightful surprise.
    Thank you for beaming down this ray of sunshine, you have made zTax Day almost bearable.

  • Hi Andy. That’s most likely field curvature; when the tangential field curves more out of focus than the sagittal, you get lower MTF readings. There are also some higher order aberrations that will have that behavior.

  • Yes. At the 200mm f2 is the max size we’re supposed to test.

  • Andreas Werle

    Thanks for sharing the data with us, Roger.

    Another question. In case of the 24mm 1.4 ED there is another “strange” behaviour of the MFT-curve. The contrast measurements for 40/50 lp/mm in tangential orientation follow an “up and down” path, decreasing at 4mm image height, then increasing and 6 mm and decreasing again. At the edge of the image circle the contrast does again increase slightly. Is there any explanation for this?

    Greetings Andy

  • denneboom

    Is there a limiting factor for lenses on the bench (size maybe?) because I dont see tele primes on this list.

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