Just MTF Charts

Just MTF Charts: Perspective Control Lenses

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Published April 29, 2019
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I had a little hesitation about whether we should post these. Most people considering a tilt-shift aren’t thinking ‘I want the absolute best sharpness.” Plus what we show is the MTF without the lens tilted or shifted, both of which will affect the resolution to some degree, but you’re probably using them tilted and shifted. And finally, because tilt-shifts aren’t mainstream we don’t have 10-copy data for most. Generally, we have 5 or 7 copies tested, although we do have 10 copies for most of the Canon brand.

On the other hand, there really is no resolution data out there for Tilt-shift lenses, and no MTF charts. So I’m going to go ahead and post what we have.

Again, this is MTF with the lens in ‘straight-up’ position, neither tilted nor shifted. Some playing around we did with a few lenses shows the MTF drops pretty significantly with significant tilting or shifting. Also remember, with these lenses we’re comparing some designed 30 years ago with some designed in the last few years. The difference is pretty apparent.

 

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.

 

Canon Tilt-Shift Lenses

Canon TS-E 17mm f4L

Lensrentals.com, 2019

Canon TS-E 24mm f3.5L II

Lensrentals.com, 2019

Canon TS-E 45mm f2.8

Lensrentals.com, 2019

Canon TS-E 50mm f2.8L Macro

Lensrentals.com, 2019

Canon TS-E 90mm f2.8

Lensrentals.com, 2019

Canon TS-E 90mm f2.8L Macro

Lensrentals.com, 2019

Canon TS-E 135mm f4L

Lensrentals.com, 2019

Nikon PC-E Lenses

PC-E Nikkor 19mm f4E ED

Lensrentals.com, 2019

PC-E Nikkor 24mm f3.5 ED

Lensrentals.com, 2019

Nikon PC-E 45mm f2.8 ED

Lensrentals.com, 2019

PC-E Micro-Nikkor 85mm f2.8D

Lensrentals.com, 2019

Schneider Super-Angulon and Makro-Symmar

Schneider 28mm f2.8 Super Angulon

Lensrentals.com, 2019

Schneider 50mm f2.8 TS Super Angulon

Lensrentals.com, 2019

Schneider 90mm f4.5 Makro-Symmar

Lensrentals.com, 2019

Rokinon

Rokinon-Samyang 24mm f3.5 TS

Lensrentals.com, 2019

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.

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  • Samuel Chia

    I think you’ve just perfectly demonstrated that regular photographers (like myself) are not likely to have the means to make such measurements. The method we used cost us next to nothing in additional equipment and we didn’t need to figure out algorithms to derive the amount of shimming required. We’ve never had this problem with Canon DSLRs in the past. I’ve also not seen any actual proof that the IBIS system in Nikon’s Z7 is causing problems with maintaining the straightness of their sensor mounting, and we now know that it’s mounted by spring-tensioned screws.

    Also, this should not be a problem that regular photographers need to solve on their own.

    I read that precision ceramic bearings can be as low as grade 5, or 0.127 microns. That’s way less than the error you’re suggesting. Theoretically, I follow how you on how this prevents perfect straightness in the sensor mounting, but are you actually seeing this occur in practice?

    Our intention is only to make the mounts straight relative to the opposite side, not machined to a precise thickness. There is only so much we can do to ensure the precision of our measuring equipment without spending hundreds to thousands more.

  • Brandon Dube

    The roundness spec on a typical “precision” ball bearing is 1 mil (25 microns). If you assume independent, normally distributed errors then you would expect (25^2 * 3)^0.5 = 43 um of runout from 3 of them. Compound this with the flatness of the Vs, which will be worse.

    The IBIS systems that use 3 ball bearings place 3 balls in 3 Vs, two of which are in a line. This is not kinematic; the system is not fully constrained.

    Interferometry isn’t fancy – it’s a 70 year old technology and you can build a twyman-green interferometer for ~$2k in parts. To measure tilt of the mount and the sensor that way, all you would do is simultaneously capture fringes on both of them, evaluate the tilt over each in angular units, and take the vector difference of them. That will be the orthogonal components of the tilt between them. The bayonette is a high reflector and the sensor is a relatively low reflector, so your phase unwrapping algorithm needs to be reasonably robust to contrast mismatches. You could do the measurements separately if you had a pellicle and a very stable cavity, eliminating the reflectance mismatch for the metal part.

    Repeatability is also not the same thing as accuracy.

  • Samuel Chia

    Hi Andy,

    Actually it would be more difficult to make precise adjustments when the sensor sizes and mount diameters get smaller, not easier.

  • Samuel Chia

    Hi Brandon,

    It seems to me that you don’t understand how IBIS systems work in these cameras, and Andreas too. No, you cannot adjust the sensor tilt or swing electronically. This is a common misunderstanding when manufacturers claim “2/4/5 axis correction”. The sensor moves parallel to the image plane at all times on three ball bearings. You may argue that ball bearings are not perfectly spherical, but I have yet to see proof that the parallelism error introduced by the bearings are in the order of 30 microns or more at the sensor edge. Post custom shimming work, the presence of IBIS has not yet shown observable detrimental effect as far as I can tell.

    It seems that Sony uses shims in increments of 50 microns to adjust the straightness of their sensors in these alpha 7 series cameras. Roger’s teardown was one piece of vital evidence for this. Given where the shimming points are, if that’s true, then that means that adjustments are possible each way across the sensor in increments of just under half that, (the shimming points are twice the width and the height of the sensor respectively) so 22 to 23 micron steps or so, then, theoretically, the actual error could be limited to half of that at best. However, the errors we are seeing are typically 3x-6x that or even more, so the assumption is that Sony isn’t shimming cameras individually, but rather as an entire batch. Some Canon and Nikon sensors are mounted using spring-tensioned screws, meaning infinitely variable precise adjustments possible, and the entire thing during assembly is mounted on a device where they are able to adjust the positioning and verify straightness in real time. We haven’t studied enough Canon cameras (and no Nikon cameras yet) to make conclusive statements, but we’ve also not yet found one that isn’t straight.

    This is a serious problem plaguing Sony cameras today, and they need to know that it is affecting people who are needing their excellent quality sensors to do high end work.

    Interesting points about re-engineering the bayonet mount with new designs and materials. However, my equipment is treated with great care unlike rental gear typically, and the amount of material wear over the useful life of the camera+lens is not likely to introduce errors of 4 mils at the mount. I’ve not seen any observable shifting yet since the shimming was done to my camera. One is just as likely to argue that thermal expansion can also be large enough to introduce focus shift. So I don’t think this path is worth pursuing.

    A micrometer is useful when measuring the flatness of a mount or a lens adapter. I have been able to achieve a measurement repeatability of under 2 microns. However, it is useless for measuring the amount of tilt and swing in a lens (or of the sensor). You’ll only be measuring the relative parallelism of the mount to the front of the lens barrel, and that has no direct bearing on the optical performance. For a lens, a giant ruler sort of target is best. Tiles of equal size and spacing over a gigantic area, or lines painted at equal distance in a field/road/running track. You want to focus at about 100+ feet. Observe the plane of focus and how it is curving on either side so you don’t confuse field curvature for swing/tilt. Use the formula to convert errors in focus distance to errors in tilt/swing in microns at the sensor edge, then figure out what that is at the shimming points on the mount.

    Measuring the sensor tilt/swing was considerably more difficult. One might be able to do it with fancy laser interferometry, though I don’t know enough about that to make any useful comments, and it’s not likely that regular photographers would have the means to do so. My friend figured out a brilliant genius method which was shared with Roger. I can forward the email to you if you are interested.

  • Andreas Werle

    Thanks for the link, i missed that.

  • Andreas Werle

    Hi Franz,
    this is also true for the Canon 135/2 and the 200/2,8. In these lenses the MTF-Diagrams are indeed a little bit boring, perhaps due to a solid and unspectacular design. I own a Canon EF 200 2,8L II, it is a very nice lens and shines with my Canon 6D. A beautiful and pretty inexpensive combination.

    Greetings Andy

  • Andreas Werle

    Hi Brandon,

    with the new generation of lenses and cameras with huge megapixel-counts, the correct orientation of bayonet, mount and sensor will be more important, simply because you can see the deficits. This raises some questions.

    One would expect, that with a small sensor and a short flange-distance – for example in case a mirrorless micro 4/3 like the Lumix GH5 – there will be less problems and easier manufacturing of a correct bayonet-mount-sensor-orientation. With a mirror and a larger sensor, the problems should increase and my guess is, that mediumformat cameras – especially those with interchangeable data-backs – need individual adjustments to eliminate errors from a misalignement of image and sensor plane.

    In case of consumer-cameras with IBIS it should be possible to adjust the sensor electronically. The sensor moves anyway, so it should be possible to correct the plane. As always thanks for your work and your kind responses!

    Greetings Andy

  • Brandon Dube

    Our bench only does +/- 20 mm. It is not possible to do a measurement that is at all automated if we used the lens’ shift feature. Non-automated at $300/hr would value a shifted dataset at 4 to low 5 figures per sample.

  • Brandon Dube

    The flatness of the mount is important – only the pose of the lens’ boresight to that of the sensor. In a completely different unit, our mounts have a “runout” of under 10 microns from +20 to -20 mm across the image plane. This works out to parallelism of a bit better than an arcminute.
    A runout of 4 mil over the mount of a sigma lens is certainly too much. How are you measuring? At this sort of tolerance, you really need either a nice micrometer with a constant force thimble or a CMM – calipers won’t do. A good mic, good set of calibration gauge blocks, and good user will get you to about +/- 5 microns.

    If you want this to be a relatively constant thing, you will wish to replace the bayonet on your camera with a very hard metal (ex, Ti or a stainless alloy) and your lens bayonets with a softer one (ex. Brass) and re-engineer the bayonets to guarantee constancy of force so they wear evenly, or preload them such that the actual bayonet — the part normal to the sensor — takes all of the wear. Otherwise time will rob you of your precision.

    4/5-axis (and probably even 2-axis) IBIS systems will also be useless to you since they cannot maintain this sort of tolerance.

  • Samuel Chia

    Thank you for the insight Roger. Wanted to be sure if there were any subtle issues to bear in mind owing to different mount types and your confidence in the data out towards 20mm away from the optical axis, or sensor cover glass issues etc.

    Btw I was just then wondering about the precision your mounts are machined to in terms of flatness in microns. In shopping for lenses that would perform well for astrophotography, I have observed that a great number of lenses are tilted and/or swung in their focus plane, and not merely decentered. Recently a friend acquired 3 Sigma 40mm Art lenses and they were all tilted and swung to different degrees. We estimate the tilt to be some 50-100 microns at the mount for those lenses. This is severe enough that the depth of field at f/2.8 isn’t enough to image sharp stars at infinity. We want the flatness to be within 20 microns, ideally 10 (custom shimming work gets us there for now). We have also found that Sony a7R II sensors to be mildly to grossly tilted or swung, and little has been discussed about the appalling mounting design of the sensor assembly. (Joe has emailed you about this before). Despite our experience, we were misled to believe the lenses were all defective until we realised the cameras were instead, and we have yet to find a straight a7R II, and the III are not of a different design.

    Reviewers who photograph test charts instead have tended to show for the better lenses, peak center resolution is reached at ~f/2.8 rather than f/4. In your experience, have you observed this?

  • At same aperture you can compare our MTF difference between brands; that’s the benefit of using an optical bench instead of on-camera measurements. The aperture, though, does make a difference, and that makes the measurements different. The Sony should be markedly better a stop down.

    Like everyone else I’d love to have a straight ‘at f/4’ comparison for all lenses. I just simply can’t afford to do it and while people are very kind about helping to support it the reality is it’s not reasonable. We’d probably need to raise, at minimum, half a million dollars to run every lens at f/4. And I’m not certain that would be enough.

  • Samuel Chia

    I am aware that the Canon was measured at f/2.8 and the Sony was f/1.8 which would account for quite a fair amount of the difference. Would of course be interesting to see both at f/2.8, though I know you don’t measure stopped down these days (apart from the 100lp 2.8 test).

  • Samuel Chia

    Hi Roger, in a previous post for the Sony GM 135mm, you mentioned “We would consider an MTF of 0.5 at 50 lp/mm to be very acceptable. This is hugely better, nearly 0.8 in the center. We’ve never seen that kind of resolution before.” Now looking at the (truly insane) MTF of the Canon TS-E 90 Macro, not to mention it wasn’t measured at macro distances, I’m wondering what you think. Is it totally unfair to compare MTF graphs across different brand lenses? P.S. I own multiple camera systems so I have no interest in making up if one brand is better than another. Would love to hear your thoughts. Thanks!

  • A bit surprised/disappointed the lenses weren’t tested with larger image circles. I agree that it’s tough to really wrap one’s hands around tilt measurements, but shifts are straightforward and meaningful if you don’t have a larger sensor that can otherwise capture the larger image circle.

  • hendrik

    Thanks Roger for this amazing database. Yes, for the T/S Lenses there are only real world tests, and chart pic’s (from TDP).

  • lwestfall

    But it does look like the Canon TS-E 90mm f2.8L Macro (at f/2.8 in the center) is sharper yet.

  • Kers

    May thanks for this – indeed – missing TS test.
    Clearly the new Nikon ( 19mm) and Canons are making a jump in quality.
    They are all very impressive…

    What is lacking in this test is that no owner of aTS lens uses the lens wide open- usually at f8-f11.
    Having used all Nikon PCE lenses the test confirms that the 24mm PCE is the weakest link in the line-up.
    ( a curved filed of sharpness is its main problem) The 45 and 85 PCE are still good enough on 46 MP.

    The 19mPCE is a very strong contender, also because it can handle the 12mm shift very well.

  • That’s the one. The Schneiders were rare birds for me; I only saw most of them the day I tested them.

  • Max Manzan

    If it’s the older one, it’s not “PC-TS” but only “PC Super Angulon”, as it was only shift, not tilt-shift.

  • Franz Graphstill

    The Canon TS/E 135mm f/4L shows impressively flat MTF curves.

    However the Sony 135mm f/1.8 is still sharper at f/1.8 than the Canon 135mm f/4 is at f/4, in the centre. 🙂

  • It’s the older f/2.8 Alan, I corrected the label.

  • Sorry Lee, the data is for the older f2.8 28mm. Same problem as below, the computer database was guessing on proper graph labels. I corrected the label.

  • We can test at Macro distances, although it’s a PIA and we usually don’t.

  • Thank you, the computer defaulted to what it thought was best and I missed that. Corrected it now.

  • Daniel Eggerstorfer

    Roger already published the MTF Data of the Canon 100mm 2.8 Macro (both), Nikon 105 2.8 Micro and Sony 90 2.8 Macro.
    Hopefully there will be a nice “Macro Round up” . Most of them are very pretty Portrait-Lenses

  • Alan

    Thanks for doing this!

    I’m also wondering which Schneider 28 this is. Info on the newer one is non-existent out there.

  • Lee

    The text says the Schneider 28 tested is the old 2.8 PC, but the graphic says it’s the 4.5 PC-TS? I’ve heard the latter isn’t on par with the 90 PC-TS, but it’d sure be sad if it was *this* bad.

  • lwestfall

    Hopefully this means the next batch of MTFs will be for macro lenses? 🙂

  • Andreas Werle

    Thanks for the TS-Series, Roger.

    Now you have done, what you denied to do, measuring Macro-Lenses. 🙂 If i remember well, Macro lenses are optimized for a distance of about 1 meter, not for infinity. Am i correct, that OLAF cannot speak MTF at short distances? Guess the new 90mm TS-E will do even better in a close up view.

    Greetings Andy

  • l_d_allan

    Thanks … for the whole MTF series.

    Seems like the chart for the
    Rokinon-Samyang 24mm f3.5 TS
    has an incorrect label for Canon 24mm.

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