Just MTF Charts

Just MTF Charts: Zeiss SLR Lenses

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Published March 28, 2019
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Zeiss Lens MTF Charts

Please note: The Zeiss Batis and Loxia Lenses will be presented with the Sony FE mount prime lenses. 

Over the last 5 or 6 years we’ve run more MTF tests than anyone in the world. We do a lot of stuff with those results, but the one thing that’s pertinent is we publish them on our blog posts. I did some checking and as best I can estimate we’ve published mulitple-sample MTFs on over 100 lenses. You got it – I can’t find them all any better than you can.

Not a week goes by that someone doesn’t ask for MTF results for this lens or that because they can’t find them online. Our blog isn’t good at organizing lots of posts, and, well, to be honest, neither am I. While I consider myself to have an organized scientific mind, I’ll admit my blog tends to be a Joycean train-of-thought thing idly wandering through whatever interests me at the moment.

Things are even worse because over the years we’ve improved our techniques. There are still some lenses where if you search carefully you’ll find old results. You can usually tell because the graph colors are different, like this:

Lensrentals.com, 2015

It’s not a huge difference, but techniques and standards changed slightly after this time. Testing is changing a little bit going forward, too, since we’re transitioning to Rapid MTF measurements which are more valuable to us, but different.

OK, I just made a short story long. Let’s try again. I’m going to gather and publish all of our MTF results in a series of posts so that they will be at least easy to find. I’m going to group them by brand and type. No comparisons, no commentary, just the test results for you to use and abuse as you see fit.

Today, we’ll look at the Zeiss SLR prime lenses because only the old-style test results have been published for several of them. Also, starting with Zeiss lenses will give Sony fans an opportunity to comment about how much better their cameras are than other brands, because that’s very important to them.

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.

Zeiss SLR Prime Lenses

Note: Other than the 50mm f/1.4 and 85mm f/1.4, Milvus lenses and ZE/ZF lenses are optically the same. 

Distagon 15mm f/2.8

Lensrentals.com, 2019

Distagon 18mm f3.5

Lensrentals.com, 2019

Milvus 21mm f/2.8

Lensrentals.com, 2019

Distagon 25mm f/2.0

Lensrentals.com, 2019

Milvus 35mm f/1.4

Lensrentals.com, 2019

Distagon 35mm f/2.0

Lensrentals.com, 2019

Milvus 50mm f/1.4

Lensrentals.com, 2019

Makro-Planar 50mm f/2.0

Lensrentals.com, 2019

Milvus 85mm f1.4

Lensrentals.com, 2019

Makro-Planar 100mm f/2.0

Lensrentals.com, 2019

Milvus APO Sonnar 135mm f/2

Lensrentals.com, 2019

 

Zeiss Otus Lenses

Otus APO Distagon 28mm f1.4

Lensrentals.com, 2019

Otus APO Distagon 55mm f1.4

Lensrentals.com, 2019

Otus APO Planar 85mm f1.4

 

So that’s it for the Zeiss SLR lenses. We’ll continue, every week or so, to add other groups so that within a couple of months all of the MTF charts should be fairly easy to find.

 

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

March, 2019

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.

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  • Several ways, especially if you don’t just look at the MTF chart as ‘highest rating’, like an MTF50 number would show. Many of the Zeiss have a spectacular lack of astigmatism-like difference between sagittal and tangential, for example, and astigmatism causes that ‘muddy’ look. They also maintain sharpness well away from center; for example many times a Sigma Art is sharper in the center of the image, but not away from center.

    There’s also stuff these simple MTF graphs don’t show. Older Zeiss often have significant spherical aberration. The 50mm f/1.4 and 35mm f/1.5, for example, look quite soft and almost defocused wide open, but stopped down to f/2.8 they are wickedly sharp.

    I’ll add one other thing: An expensive manual focus lens is not the lens of the masses. I suspect Zeiss lenses tend to mostly be in the hands of people who know how to use them to maximize their image making potential. My own take on all the testing I do is that it should serve to show the owner of a given lens it’s strengths and weaknesses so that he can use his or her technical expertise to maximize the potential of that tool. Sadly, reality is the major purpose these charts are put to is to serve as fodder for internet fan wars.

  • Carleton Foxx

    Interesting, perhaps the engineers optimized them for pictures viewed at art gallery distances rather than a computer screen 8 inches from your face.

    That effect where you see a work that looks good from a distance but fall apart up close stems from your brain’s ability to create a detailed picture for you from coarse or distant details.
    When you get up close and see the real details it’s never as good as what you cooked up for yourself.
    As for magnificent…Maybe majestic is a better word?

  • Roger Cicala

    Nope. Not ever. I’m sure someone, someday will commercialize this stuff a bit, but not until I’m gone.

  • Roger Cicala

    Several ways, especially if you don’t just look at the MTF chart as ‘highest rating’, like an MTF50 number would show. Many of the Zeiss have a spectacular lack of astigmatism-like difference between sagittal and tangential, for example, and astigmatism causes that ‘muddy’ look. They also maintain sharpness well away from center; for example many times a Sigma Art is sharper in the center of the image, but not away from center.

    There’s also stuff these simple MTF graphs don’t show. Older Zeiss often have significant spherical aberration. The 50mm f/1.4 and 35mm f/1.5, for example, look quite soft and almost defocused wide open, but stopped down to f/2.8 they are wickedly sharp.

    I’ll add one other thing: An expensive manual focus lens is not the lens of the masses. I suspect Zeiss lenses tend to mostly be in the hands of people who know how to use them to maximize their image making potential. My own take on all the testing I do is that it should serve to show the owner of a given lens it’s strengths and weaknesses so that he can use his or her technical expertise to maximize the potential of that tool. Sadly, reality is the major purpose these charts are put to is to serve as fodder for internet fan wars.

  • Frank Kolwicz

    I guess that first we have to explain “magnificent”, then we might have a discussion.

    Related, in a kind of obverse way: I’ve seen images that at first tingled my interest from a distance, only to be disappointed when I couldn’t enjoy them up-close and in detail. Of course, that’s me as a pixel-peeper of my own work.

  • Carleton Foxx

    No revenue? Put a big fat spot for ads on these pages. Endorse Ford Pintos and asbestos cat toys. Take your sexy self to Japan and star in ads for Suntory whisky.
    We know your heart is pure, we won’t mind.

  • Carleton Foxx

    The charts for the older Zeiss lenses don’t particularly spectacular yet the lenses produce magnificent photographs. How do we explain this?

  • Brandon Dube

    The lines go down at higher frequencies away from the center because of changes in focus caused by focus shift.

    In the center it would be because of the particulars of the bench focus algorithm or diffraction.

  • Bryan is redoing his database as we publish these, so that link now contains the new graphs for Canon and Zeiss, and will add the others as we publish them. The comparison tool they have is really useful.

  • The graphs are dated. Basically everything dated 2017 and later is up to date.

  • Brandon Dube

    When you see wild swings like that, 9/10 times it is astigmatism. So, it will show up in the pictures as a weird defect in the bokeh at that image height, and a belly of (relative) unsharpness in landscape images.

    This has more to do with the particulars of a certain design than a family of designs (double gauss, sonnar, etc).

  • Craig

    Just a suggestion: Please come up with a label for each type of MTF testing. I suggest a simple version #. This should help when finding MTF charts and wondering if the results for for new, or old style of testing. Should be pretty simple to do. Better than trying to figure out what chart is what based on the line colors.

  • Thanks again Roger! This was an unexpected but welcome surprise. And the lens looks great in the center.

    Despite my own copy’s tilt, I really like what it does especially stopped down, so I’m not complaining about it (OK, maybe a little about the tilt), but do you know why the highest lp/mm curve would go down at smaller apertures? Are we seeing the error bars of the instrument here instead of the actual performance?

  • It looks like The Digital Picture will be setting up a comparison tool so you can look at MTFs side-by-side.

  • xWidget

    I doubt I have the capabilities/time at the moment to make a webapp myself for it right now, but would you guys consider releasing the raw data at some point? Perhaps behind an API if you wanted some level of access control (I think you could probably set this up using Amazon’s AWS web UI without any programming.)

  • Andreas Werle

    Thanks for that Roger, realy beautiful Charts!

    I sometimes wonder about the strange separation of tangential and sagittal curves at the margins of the image circle. In some lenses this seems not to appear at all as in the 100mm Macro and in other cases these curves are very strange for instance the “jump” of the 50 lp/mm sagittal curve in case of the milvus 85/1.4 at 18mm image height to nearly 60% contrast, whereas the tangential curve is constantly decreasing.

    Does this show up in the picture in some way? And – more important for those who like to read the MTF charts – does this curious behaviour predict certain lens aberrations?

    I also tried to predict the existence of such jumps in certain lenses and thought it might be characteristic for some special designs (fast, old, wide-angel etc.), but it seems not to be the case. The old and fast Canon 50/1.4 doesnt show such a prominent separation and/or a “jump” of the sagittal curves. This is weird, isnt it?

  • Andre, I did confirm what we were seeing, and did a stop down on one copy which demonstrates the sudden sharpness improvement stopped down. The 35mm f1.4 Milvus and the 50mm f1.4 both do this. It’s almost like two lenses – soft and dreamy wide open, sharp as a razor stopped down just a bit. (This is just one copy, not a series of 10, but it serves the purpose, I think.)

    https://uploads.disquscdn.com/images/bbfaf246309352f731f2ed5cc1ce13ce96c002312e3210e61643ed3e6dfb3bf9.png

  • Brian Smith

    That 100mm Macro chart is a thing of beauty.

  • Hi Mikko,
    It takes a 3-5 days of optical bench time (that’s a $250k machine) to run a complete set of tests. We need the wide open data to set standards for routine testing and optical repair, but not stop-down data, so the cost is out of reach.

  • Andrej Belic

    WOW!!!!!!!!!!!

  • mikko

    More interesting data, much appreciated indeed!

    I have no knowledge about how the testing works and how time consuming it can be, so without wanting to come across the wrong way, I wanted to ask if there´s any chance to see future tests of lenses stopped down, for more comprehensive overall comparisons?
    Another aspect I think would be interesting is the individual charts of lenses, in order to get an idea of copy-to-copy variance, and pehaps get an impression of quality control of different manufacturers.

    Cheers!

  • That would be Lensrentals call, they own the data now. (I don’t make those calls – it’s a big company with executives and stuff now.)

  • Actually that’s the new one the MTF is up for, I put up a bad label because I remember the old one. Changing it, and thank you.

  • David Braddon-Mitchell

    The 18mm f2.8 Milvus is a new design as well. Probably won’t cause confusion as the one you have tested is f3.5 which must be the old one.

  • Olaf is going back to being a division of Lensrentals. We still do outside testing and you can contact us through the Olaf website for now, or me at Roger at Olafoptical.com

    The blog posts generate some traffic but not any revenue. Given the choice between buying some new lab equipment and paying someone to develop a website, well, you guys know what I’m going to do. But we are allowing a third party to do so, and that should be starting in a few weeks.

  • Thanks Roger: I appreciate it! I’ll still enjoy my lenses no matter what, and checking up on the official Zeiss MTF charts, your results and theirs aren’t too far off: the shapes match, and it’s mostly the higher frequency stuff that’s a little lower in yours.

    A mutual friend also pointed out that if the dominant aberration in the 35/1.4 is spherical, as perhaps it may be since the lens is advertised for its bokeh, then its performance will improve dramatically as it’s stopped down, as we’ve seen in the field.

  • Neal G

    That wouldn’t be very hard to develop into a web app. The question would be if Lens Rental allowed others to download and re-use these images on other websites.

  • Lee

    Definitely very useful to have these combined here, but I still think y’all ought to hire someone to put together a comparator app to pull whatever lenses one wanted to see side-by-side. Even putting them together in one blog post the format isn’t ideal. I bet people would even pay a few bucks for access. This is a valuable data collection for sure.

    Also, off-topic, is Olaf Inc still active doing paid testing for people? Who should I contact about that?

  • Andre, I thought the same thing when I replotted the results. The bottom line is the 35 f/1.4 is a bit like the 50mm f1.4; stopped down just a bit its much sharper. The average also suffers a bit from variance in the samples tested. All that being said, I found it surprisingly low and I’ve sent for some more copies to just retest. The results are on tests performed a year ago; I looked over them, they look like they should, but I want to redo some just to double check. I didn’t expect a really sharp lens, that’s not what this one has been about, but I thought it was better than this shows.

  • Thanks for publishing all of these MTF charts! A minor correction: the Milvus 35/1.4 is also a new optical design, though judging it only by its wide-open performance, you may not guess so!

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