Geek Articles

Finally, Some More m4/3 MTF Testing: Are the 40s Fabulous?

It took me a bit longer to get back to m4/3 testing than I expected, but we have an interesting set of primes to look at today, the ‘about 45mm’ group, which includes several 42.5mm and a couple of 45mm lenses. Please don’t get all worked up about that small difference in focal lengths; it’s really not significant. One of the 45mm lenses is a 43.5mm, one of the 42.5mm is a 43mm lens. Plus if you (or your camera) does any distortion correction that may change a bit.  Anyway, I really can’t imagine anyone going ‘wait, I need to change my 42.5mm to a 45mm for this shot’, so it seems a reasonable grouping.

For those of you who haven’t read our previous m4/3 tests, I want to emphasize a couple of things. First, we’re testing the lenses with no camera involved; all we’re evaluating is the optics. My interest is in the lenses, and the lenses only. Making lenses for a smaller imaging circle has some distinct theoretical advantages. Whether the lensmakers use those advantages for good and make better lenses, or for evil to cut corners and raise profit margins, well, that interests me quite a bit.

When you take a picture, you’re using the system (the camera and lens each add their limitations). Despite what many self-described experts say, it is very, very rare that just the lens or just the camera limits the output of the system. In practical terms, unless you have a really horrid lens or a 4-megapixel camera, both camera and lens contribute to the final output. (If you have both a horrid lens and a 4-megapixel camera then you don’t need to be reading this.)

One other point: with m4/3 lenses you can’t make broad generalizations about the name on the outside, because that doesn’t necessarily reflect who made the components on the inside. So if a given Olympus or Panasonic lens is superb (many are), don’t take that to mean all that brands lenses are pretty awesome (many aren’t). The name on the outside means “We paid the people who designed the lens, made the different components, and assembled it. Some of them actually get paychecks with our name on them, some don’t, and the ones who did this lens didn’t necessarily do that other lens.”

Let’s Meet Today’s Players

We have several lenses that meet the criteria of being around 45mm primes and being testable on our machine.

Because some of theses aren’t common renters, I wasn’t able to get a complete set of 10 tested for every model, as noted above.

I think the big question I have today is do they make the name longer because of some inferiority complex? If my theory is correct (it seems to hold for SLR lenses), then a graph of image quality should look like this:

Roger Cicala, 2018

If that holds true, then pretty soon we won’t have to do these tests. We’ll just go ‘that things got five words and six initials in the name, it’s gotta be horrid’.

Olympus M. Zuiko Digital 45mm f/1.8

At $400 this isn’t a cheap lens by any means, but it’s certainly a lot cheaper than some of those we’re looking at. At f/1.8 it’s not the fastest, either, and its seven aperture blades aren’t the most. But it is nice and small; 2.2 inches long and 116 grams in weight, and it does come in your choice of silver or black, so it’s got that going for it.

Olympus M. Zuiko Digital 45mm f/1.2 ED PRO

It’s priced equivalently to three Olympus 45mm f/1.8 lenses ($1200) but you get over three times the weight (410 grams) for your money, so that seems fair. Seriously, this lens is reported to be excellent, with a lot of design care for smooth bokeh, nine aperture blades, and reportedly excellent image quality.

Panasonic Leica DG Macro Elmarit 45mm f/2.8

This lens is probably not fairly compared to the others since it’s a 1:1 macro lens and not a wide-aperture prime, but well, it had to get tested somewhere. It’s a bit pricey at $800, and moderate in size compared to the others. It’s also an older design, and I didn’t expect it to be awesome.

Panasonic Leica DG Noctitron 42.5mm f/1.2 ASPH Power OIS

Of course, this is mainly about the Battle of the f/1.2 lenses, and Panasonic’s f/1.2 entry is the most expensive ($1,400), the heaviest by a hair (425 grams), and a clumsy hood design. But it has the Leica name on it, which means, well, nothing. But it does have the nice 9-blade aperture and the Power OIS system. So while we’ll compare it optically to the Olympus, your choice is probably going to come down to which body you shoot. And because I like to put my preconceived notions out there since they do affect my judgment, I want to not like this lens because it has both the longest name and the pretentious, yet meaningless, Leica badge on the outside; a Marketing Perfecta.

Panasonic Lumix 42.5mm f/1.7 ASPH Power OIS

Of course, if what you’re most interested in is having Power OIS, this gives you that, along with the lowest price of the group ($350) in a nice small package. I always root for the underdog, because, well, I’m cheap. So I’m going into this test hoping this lens will kick serious butt; or at least run with the big dogs.

Voigtlander 42.5mm f/0.95 Aspherical

OK, I stated on the last set of tests that I despise Voigtlander lenses. That’s because they simply can’t be repaired reasonably and parts are not available, so they are basically disposable lenses. But, I have to say, I was markedly impressed by the 25mm Voigtlander’s performance. And this lens provides by far the widest aperture at a middle-of-the-road $800 price tag. You pay a weight penalty because of the metal housing (and if you think a metal housing makes lenses more reliable, come spend a day in our repair shop). But you get a 10-bladed aperture with that. And yes, I’m aware a lot of you won’t consider a manually focusing lens. But some of you will.


For this section, please remember that the wide-open MTF is the average of 10 copies unless otherwise noted, taken at the widest aperture. As we’ll show later, MTF will be higher with smaller apertures, so the f/1.2 and f/0.95 lenses are at a disadvantage wide open, while the f/2.8 Macro-Elmarit has a big advantage.

So let’s change the order a bit and start from the smallest aperture to the largest; that should make scrolling up and down easier.

Panasonic Leica DG Macro Elmarit 45mm f/2.8 (8 copies only)

Well, just to get it out of the way, this isn’t a very good performance. MTF is fairly even with only a moderate amount of sagittal – tangential separation, but it’s low. It’s extraordinarily low given this is a f/2.8 lens, and particularly low at the higher frequencies which are where the fine detail lives. That being said, some macro lenses do perform better close up than at distant focus, which is where this test is done. But if you aren’t looking for a macro lens, there’s not much on the MTF chart to recommend this one.

Olaf Optical Testing, 2018

Olympus M. Zuiko Digital 45mm f/1.8

This is a pretty impressive performance at a f/1.8 aperture; in fact, it’s far better at f/1.8 than the Macro was at f/2.8. There’s a bit of sag-tan separation and performance does drop off away from the center, but this is pretty good.

Olaf Optical Testing, 2018


Panasonic Lumix 42.5mm f1.7 ASPH OIS (6 copies)

The smaller Panasonic also does very well. It has a little bit more separation of sagittal and tangential out at the edges of the image but otherwise is nearly identical to the f/1.8 Olympus as far as sharpness goes. I won’t hair-split the slightly wider aperture because m4/3 manufacturers run a bit fast and loose with f/# and I honestly can’t say for sure this is really wider than the f/1.8.

Olaf Optical Testing, 2018

Olympus M. Zuiko Digital 45mm f/1.2 PRO

Remember you’re at much wider aperture now, so we expect a fall-off in MTF compared to the lenses above. The Digital Pro looks quite good for an ultra-wide aperture. It has a good resolution that it maintains across the field and a mild-to-moderate amount of sagittal-tangential separation.

Olaf Optical Testing, 2018

Panasonic Leica DG Noctitron 42.5mm f1.2 ASPH Power OIS

The Panasonic f/1.2 is very similar to the Olympus. The MTF is a tiny bit higher in the center but lower at the edges, but probably not enough of either that you’d notice a difference in an image.

Olaf Optical Testing, 2018

Voigtlander 42.5mm f/0.95 Aspherical

As expected, when we get to mega ultra-wide apertures, resolution falls off. This is a pretty decent performance for a f/0.95 lens, though.

Olaf Optical Testing, 2018

Stop-Down Tests

These are not 10-copy tests; we picked one average copy of the lenses to do stop-downs on.

Voigtlander at f/1.4

This was the first easily measurable stop-down for the Voigt, just to get an idea if it would be similar to the f/1.2 lenses once it was stopped down a bit. The answer is yes, it is. In the middle 1/2 of the image, it’s actually sharper now than any of the others, although it fades quite a bit in the outer 1/3 of the image. Still, it’s nice to know you can get very high resolution in the center if the aperture is stopped down just a bit.

Olaf Optical Testing, 2018


All Lenses at f/2.8

We’ll make side-by-side comparisons of each lens at wide open and f/2.8. Again, these are single copies so that the wide open MTF will be a little different than the averages above.

Olympus M. Zuiko Digital 45mm f/1.8

If your question is ‘how did it get sharper in the center, but softer in the edges when stopped down,’ well, the answer is it didn’t. This can happen when a lens has a lot of field curvature. We’re focused in the center for the MTF test, the field curvature (we’ll show that in a minute) is significant enough that the edges remain out of focus despite being stopped down. I explain in more detail in an addendum, if you’re interested.

Olaf Optical Testing, 2018

Panasonic Lumix 42.5mm f1.7 ASPH OIS

Primarily a similar improvement in the center, but since this lens doesn’t have field curvature, a more predictable result away from the axis.

Olaf Optical Testing, 2018

Olympus M. Zuiko Digital 45mm f/1.2 PRO

Really impressive f/2.8 performance here, and better at f/2.8 than either of the less expensive lenses.

Olaf Optical Testing, 2018

Panasonic Leica DG Noctitron 42.5mm f1.2 ASPH Power OIS

Another impressive improvement, although not quite as sharp in the center as the Olympus. On the other hand, it holds sharpness better in the middle of the field before fading at the edges.

Olaf Optical Testing, 2018

Voigtlander 42.5mm f/0.95 Aspherical

With its ultra-wide aperture, I’m impressed that the Voigtlander can sharpen up comparably to the two f/1.2 lenses. In the outer half of the image, it’s not quite as good, but I think within ‘sample variation’ of the other two.

Olaf Optical Testing, 2018

Field Curvature (MTF vs. Field vs. Focus)

For those of you who don’t read our technical articles very often, the field curvature may be the most useful thing we give you. This is NOT distortion; rather it’s how the plane of best focus curves. The tangential and sagittal fields often curve differently; when they do you know, there will be astigmatism in those areas.

There’s other information you can get from field curvatures and if you’re interested here are some background articles: Fun with Fields of Focus 1Fun with Fields of Focus IIField Curvature and Stopping Down. I should mention these are done at f/5.6 because that gives a nice, clear picture of the field. Stopping down (or opening up) doesn’t change the curvature significantly. Keep in mind that when you’re shooting at a wider aperture, though, the field is much narrower.

Also, the fields shown are a single copy, so you’ll see some field tilt. That’s relatively common in these lenses.

Panasonic Leica DG Macro Elmarit 45mm f/2.8 (8 copies)

You’ll notice this field is both tilted and the tangential curve decentered. This is pretty typical for the copies of this lens we tested. It’s theoretically quite flat, which a macro lens should be, but in reality, is generally going to be a bit tilted.

Olaf Optical Testing, 2018

Olympus M. Zuiko Digital 45mm f/1.8

The little Olympus has quite significant U-shaped curvature, and in a photo, you should quickly notice that it’s not going to get everything from side to side in focus, even stopped down. This explains the MTF fall-off at the edges we saw above, even stopped down. Note also that the tangential field curves more than the sagittal, so you’ll always have astigmatism (red area in the difference graph) out at the edges, again, even stopped down.

Olaf Optical Testing, 2018

Panasonic Lumix 42.5mm f1.7 ASPH OIS (6 copies)

Now, how about this one for a nice, flat field with little astigmatism? I’ll take it. But you can notice there is a little curve in the sagittal field. Wide open with a narrower depth of field, this does give a little astigmatism, which you can see in the wide-open MTF graphs above. Still, very nice.

Olaf Optical Testing, 2018

Olympus M. Zuiko Digital 45mm f/1.2 PRO (8 copies)

The Olympus Pro is also fairly flat. You can see a bit of inverted “U” in the tangential curvature, and some mild resultant edge astigmatism.

Olaf Optical Testing, 2018

Panasonic Leica DG Noctitron 42.5mm f1.2 ASPH Power OIS

Another slightly tilted and decentered tangential field, but again the field is fairly flat. Notice how in this copy the field tilt results in increased astigmatism on one side of the lens. You might notice this one if you pixel peeped a bit.

Olaf Optical Testing, 2018

Voigtlander 42.5mm f/0.95 Aspherical

The Voigtlander again surprises me. I didn’t expect so flat of a field in such a wider aperture lens.

Olaf Optical Testing, 2018

Copy-to-Copy Variation

Micro 4/3 lenses, in general, have a lot of sample variation. Why this is I can’t say. What I can say is it’s not the fabled “they need to up their QA check” that people imagine happens. Micro 4/3 lenses, as a rule, don’t have any compensating adjustable elements, so what you get at the end of the assembly line is what you get unless something is broken inside.

Because we didn’t have 10 copies of each lens, I was hesitant to use our usual variance numbers and graphs; that system depends on having 10 copies. What it did show,  in general terms, was that the Panasonic 45mm f/2.8 Macro has what we consider unacceptable amounts of variance, the other two Panasonics were fairly high. The two Olympus lenses and the Voigtlander were all in the ‘usual’ range for primes.

But I’ll let you judge for yourselves. For each lens below I’ve put thumbnails of our Full Frame MTF map for the first eight copies tested. Remember, with m4/3 you can’t make manufacturer generalizations. One brand looks better at these focal lengths. It is NOT any predictor of how any of the brands will look with lenses of different focal lengths.

Panasonic Leica DG Macro Elmarit 45mm f/2.8 (8 copies)

As I said above, this amount of variance is not OK, but a good copy is pretty good.

Olaf Optical Testing, 2018

Olympus M. Zuiko Digital 45mm f/1.8

There’s obvious variance here, but if you are shooting centered subjects, these would all be good. It’s a good example of a lot of lab variation that probably doesn’t affect pictures very much.

Olaf Optical Testing, 2018

Panasonic Lumix 42.5mm f1.7 ASPH OIS (6 copies)

Yes, you can tell the difference between the better two and the others.

Olaf Optical Testing, 2018

Olympus M. Zuiko Digital 45mm f/1.2 PRO (8 copies)

This one is pretty danged impressive for a f/1.2. The center of sharpness is in the center of the lens pretty much in every copy. A couple aren’t quite as sharp as the others, but that’s the nature of the beast.

Olaf Optical Testing, 2018

Panasonic Leica DG Noctitron 42.5mm f1.2 ASPH Power OIS

Here’s a great example of why we have internet arguments. Two of these eight lenses are better than any of the Olympus Pros; three are worse. Reviewers or photographers who compared one copy of each are probably going to draw different conclusions.

Olaf Optical Testing, 2018

Voigtlander 42.5mm f/0.95 Aspherical

Lower resolution wide open because this is f/0.95. But for this ultra-wide aperture, I have to say this is very reasonable.

Olaf Optical Testing, 2018

So What Did We Learn Today?

Well, I learned that no matter how much I dislike Voigtlander, the company, I sure do admire Voigtlander lenses. The performance of the 42.5mm f/0.95 is spectacular. Of course, you also have to be OK with manually focusing, but still, that’s a lens worth considering.

If you want a f/1.2 lens in this focal length, well, let’s face it, it will probably come down to whether you want Power OIS or not. If you don’t, the Olympus 42.5mm f/1.2 PRO is slightly less expensive and has less variation. But a good copy of the Panasonic 42.5 Noctitron is excellent.

Both of the less expensive lenses in this range deliver a lot of bang for the buck. They have very good image quality, and if you don’t need the widest aperture, they give you a lot for 1/3 the price of the wide-aperture duo. If I were most interested in this focal length for portraits, I’d probably want the Zuiko Digital f/1.8; that field curvature will help throw everything other than the subject out of focus. For landscapes or architectural shooting, the flat field of the Panasonic f/1.7 would be an advantage.


Roger Cicala and Aaron Closz

March 2018

Addendum: Field Curvature and MTF

When we looked at the stop-down curves for the Olympus 45mm f1.8, I mentioned that off-axis the MTF didn’t raise because the field curvature was so significant. This is a discussion of why that is so, even stopped down.

First, let’s look at the field curvature of the lens at 20 lp/mm frequency (the orange lines in the MTF graphs above). Below is the sagittal and then tangential field curvatures. For each, I’ve put a black line across the graph at the center focus position.

Olaf Optical Testing, 2018

Olaf Optical Testing, 2018

If you wanted to mentally read the MTF as you follow the line from center to edge, you’d get curves very similar to the MTF measure above for f/2.8. You should notice that the sagittal field isn’t as curved as the tangential, and therefore the sagittal MTF is higher. But I’ll do that for you below (this is only going to 8mm away from the center, but that’s plenty to make the point).

Olaf Optical Testing, 2018

You might ask the very pertinent question, “The MTF is higher away from the center at a different focus position than best center focus. What if I focus out on the edges”? Well, you’ll get a much sharper image. The lens is very sharp away from the center; it’s just that the sharp area is in a different focus plane. But we can graph the best MTF for each point and get something very different; a graph that shows how sharp the lens could be if you focus off-axis. We call this the BIF graph, for Best Individual Focus.

Olaf Optical Testing, 2018

The BIF isn’t real, though, it’s theoretical. If you focused at that point 5mm away from the center, your image at that point would be very sharp, but then the center of the image would be very soft. So with a lens like this, you can get a sharp portrait, for example, anywhere in the field of view. But you can’t make the image sharp from one side to the other, even stopped down.

Author: Roger Cicala

I’m Roger and I am the founder of 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 Geek Articles
  • Ivar, it certainly is in industry in general. Many lens manufacturers do things nearly all or all in house (Canon, Sigma, Zeiss and Leica; probably Nikon). Some sublet all of their glass one place, electronics somewhere else, assembly somewhere else. And all phases in between.

    Premium means whatever you want it to, I think, depending on how you define it. But don’t overestimate how much brands check and know about there stuff. I make most of my modest living doing rechecks for industry; I still find it shocking how often I say, “So the supplier promised you a certain spec, you couldn’t check it, so you just believed them?”

  • Ketan, it is definitely possible. Look back at the graphs above and you’ll see some mildly tilted fields. Some are more tilted, some the field is decentered.

  • Ketan Gajria

    Is it possible for different copies of the same lens to have different curvatures of field? I bought the best of 4 copies tested for the Olympus 25mm f/1.2 but the outer image regions don’t really improve from f/1.2 to ~f/4 while the center does and it boggles my mind. My Sony Zeiss 55mm f/1.8 FE is similar.

  • cb5107

    Thanks for a great article. This helps me understand why I chose the P42.5/1.7 over the O45/1.8 based on my testing using architectural (i.e. stone or brick walls) type shots.
    In general, it looks like you cannot lose with any of these lenses.
    Hope you find time to look at the 17mm lenses too :).

  • Samuel H

    I have a doubt about your statement that “for portraits, I’d probably want the Zuiko Digital f/1.8; that field curvature will help throw everything other than the subject out of focus”.

    I hope this means that the curve in these graphs means the sides are focused closer than the center is. If it means that the center is focusing closer than the sides, then your background is going to be “more in focus” and the field curvature will be fighting against you.

  • Ilya Zakharevich

    Roger, Brandon:

    I think what you wanted to say is, basically: the central part of the lens has very different field curvature than the outer part of the lens.

    Above, “central” means “near optical axis”.

    This is very familiar to me from my attempts to design a symmetric triplet in “exact optics”. This effect (it may even have a name: spheri-field-curvature? 😉 is what everybody misses when they claim that curved sensors are better than sliced bread!

    Anyway, without 2D maps of MTF (as colormaps above) taken separately: wide open and closed down, it may be hard to qualify.

  • Ilya Zakharevich

    > In principle we can derive the aberrations from MTF data, with more time
    for software and a very powerful computer we may begin doing that in
    the soonish future.

    Do not you need to know the complex (meaning ??) transfer function, not only its absolute value, to do this? I think one may be reconstructed from the other, but do not remember how numerically stable the result would be. (This might be similar to the question “deconvolve when all you know is MTF”.) And since you know |?-MTF| only in 10 frequencies (5 tangential and 5 saggital), this may be quite a trick to achieve!

  • Ivar Brekke

    Regarding who designs, produces and brands lenses, with many actors in the process, is this not how most industries work today? like an iPhone with one designer in California, one producer of chipset, one of glass, one of camera module, and one who sets it all together, etc. Still it is clearly an iPhone. I think the premium brands is just a sign that these are designed and produced at a higher standard and with a consistent design, it beeing cosmetical or optical.

  • Ivar Brekke

    Interesting article as always. There is a lot more characteristics of any lens than sharpness though, that most online testers do not consider, but is clearly seen when comparing lenses of similar focal length side by side. I would even argue that these other characteristics (example colour, dynamic range and bokeh) are more important and what often separates the premium lenses. I have been using m43 for years and after a while, you certainly see that some lenses shoot nicer pictures than others lenses with similar field of view in similar circumstances.

  • Impulse_Vigil

    Was that a funny at the end of the comment? Keep the long blog posts coming IMO, there’s knowledge here that’s not easily gained anywhere else.

  • Impulse_Vigil

    It’s a good practice in general if you have the time or aren’t averse to using the touchscreen to set the focus point (which I find faster on any camera w/a joystick for it)…

  • Impulse_Vigil

    Very interesting tests and info! I hope there’s more M4/3 testing on the way, or at least a similar grouping of wides (even tho the focal length selection for the system is all over the place there)… Pretty please?

    I’ve read a few reviews of the 45/1.8 & 42.5/1.7, and seen a few comparisons in the boards, and not once did I ever see anyone suggest there might be a field curvature issue or difference (depending on how you look at it); even tho it’s something that’s come up for other lenses (Olys in particular, like the 17/1.8 & 7-14).

    That actually helps explain some of the differences and conclusions I’ve read regarding comparisons between those two. I *think* I’ve read the linked article regarding the subject, but I’ve might’ve missed this nonetheless, is there an easy-ish way to figure out if there’s some significant field curvature for a lens at home?

    Worth pointing that the Pana 42.5/1.7 has OIS too *and* it focuses much closer. FWIW I owned both and kept the latter mostly because of this rather than any of the IQ/bokeh differences that get over analysed on the boards/reviews (w/o access to multiple samples etc).

  • tom

    Hello… Great work again and actually the best technical evaluation of optics around the Web…

    In his publication i wonder whether the curves of the Olympus 45 1.2 and Pana 42.5 1.2 are differing in the charts at the beginning and when stopped down… my personal experience when using both: the latter seem to be more realistic because the olympus really is sharper already in the center and especially in the corners

  • David Bateman

    Thank you Roger for an other M43rds review. I am glad to see your done playing with minivans.
    I find it interesting that you recommend the Olympus f1.8 for portrait and the Panasonic for others. I would have thought the field curvature would hurt, as part of the background could come into focus, depending on subject to background distance. I think for close up flower shots the curvature would be benificial with the Olympus. But now that we know it helps for the final image plan.
    I do wonder about the large variation in M43rds lenses. If this is due to not having adjustable elements to correct line errors and how the camera software handles this. If DFD and internal camera lens corrections can take this into account. Or if internal corrections act to average out the variations.

  • J L Williams

    I always enjoy these articles, but this time I even got a practical takeaway. I use the Olympus 45/1.8, and out of longtime habit (I learned on rangefinder cameras) I almost always focus at the center and then recompose; with most lenses it makes little difference. I can see now, though, that when using the 45 I’ll be better off composing first and then moving the camera’s AF point to where the main subject is, so it will adjust for the field curvature at that position. Right?

  • David B

    I’ve owned many of these lenses over the years and I agree with conclusion. Ultimately I settled on 45/1.8 I am happy with rendering and size, size makes it so easy to take when traveling

  • cpt kent

    Thanks. It’s probably my imagination, but I’ve always shied away from OIS due to uncertainty about long term durability. Seems to me, the less moving parts, the more durable something should generally be…

  • They weren’t all out of the box, but all were pretty new, less than a year old. Plus we test them (not to this degree, of course) before and after each rental.

  • Brandon Dube

    Field curvature + focus shift. The focus is shifted away from the paraxial plane wide open on-axis. This focus shift is maybe 80 microns in magnitude (but obviously highly variable between different lens models, spectral content of light, etc…) while the field curvature may be, say, 300 microns. With the example of the 45/1.8, the field curvature of both S and T shifts in the positive direction, i.e. focus beyond infinity. If the focus shift is in the same direction, then as you close the aperture the on-axis focus position moves in the negative direction, opposite to the field curvature, and the image quality for a flat object will become very bad at the edges. This is what happens with that lens in particular.

    The focus shift, in the monochromatic case, is related to the relative balance of the various orders of spherical aberration. As you stop down, the third order spherical reduces by aperture^3, the fifth order aperture^5, and so on. Obviously this means the higher order terms rapidly vanish, and their balance, i.e. the ratio of the coefficient of any two orders to each other, changes as the aperture is closed.

    Since the focus shift from paraxial is associated with the balance of them, and that balance changes as a function f aperture, the focus shift from paraxial varies with aperture, and this is what we understand colloquially as focus shift.

    In principle we can derive the aberrations from MTF data, with more time for software and a very powerful computer we may begin doing that in the soonish future.

  • Deanaaargh,

    I don’t recall ever seeing an adjustable element in an m4/3 lens, and the manufacturer’s repair centers in the US don’t seem able to do optical adjustments. BUT we don’t open up nearly as many m4/3 lenses as we do others so my ‘I’ve never seen’ doesn’t mean as much as with some lens types.

    I suspect some of the physically larger lenses (200 f/2.8, 300 f/4 IS, or some of the big zooms) might have some. We argued amongst ourselves if one of the medium telezooms had a centering front element, on the basis that we screwed a couple up cleaning out dust and had to spend some time getting them back right; but we decided it was more about us not marking position properly then it actually being a centering element.

  • Ilya,

    You are correct, of course, but I was trying to not go there (and failed obviously). I explained why the MTF curve doesn’t improve, but not why it would deteriorate in places.

    The ‘deteriorate’ part probably has more to do with a bit of focus shift, either classic as we talk about on the camera, or bench focus shift (focus is done by detecting highest point spread function at center). With a flat field, it’s no matter, but with a wicked-steep curve it can shifts the MTF readings, particularly at higher frequencies where the field narrows, to an area where the reading is actually lower off center. I think that’s the more accurate explanation.

    It gets even more perplexing with the “W” field lenses, where we sometimes see the center and edges sharpen, and the ‘halfway’ area not improving.

    What I think would be better is showing the MTF v F v Focus at different apertures, one could then see the sharpening happening even though it’s not reflected in the MTF curve. But I fear my blog posts are rapidly becoming far too long.

    I probably

  • cpt kent

    I may have missed it in the article (or another) but are all the lenses that you test ‘straight out of the box’, or ones that have been rented? I just wonder if some lenses go out of tolerance quicker than others? (I’m specifically thinking that the Nocticron has been around for a while, and that it has OIS). Thoughts?

  • Deanaaargh

    This made for excellent reading, as usual. I was caught however by your phrase ‘as a rule’ m43 lenses do not feature adjustable elements. I doubt that this is something that is covered by the m43 coalition specification. I wonder whether it is because Panasonic/Olympus have relatively small repair operations and are not staffed up to provide re-centering services etc.
    However, I am curious if you would feel comfortable estimating the proportion of new lenses produced today that do not allow for post assembly adjustment. I have some sense based upon the teardowns you have posted on this (excellent) blog but I would appreciate your considered opinion.

  • Dariano Bisotnik

    Roger, with compelling data like this you are the party-pooper for forumtographers.
    One can simply link your article in reply to their arguments of “this lens is best… blah blah” and suddenly there could be just “crickets” 🙂
    Thank you for the great work you do.

  • Ilya Zakharevich

    Roger, thanks for this interesting writeup?—?as usual!

    However, I do not think that your addendum (which is very good standalone) would actually address the question you claim it addresses: why widely-open can be better than closed-down.

    Essentially, you want to explain why MTF is 0.3 widely open vs. 0.05 closed to ƒ/2.8 (at the edge of the frame). Your explanation, essentially, goes like this: “In fact, this part of the image is out-of-focus w.r.t. to the curved surface of best focus”. Right?

    However, closing down IMPROV?S out-of-focus areas?—?so if your explanation did hit the main contributor into softness, the effect would be exactly OPPOSITE to what is observed.

    CONCLUSION: it is something else (in ADDITION to field curvature) which makes MTF worse when closed down…

  • It may be worth pointing readers to this article on macros, just so that we all see data on the difference between distance focus and close focusing MTF:

    Anyway, thanks as always. The best individual focus for the Olympus is exactly as I have experienced…and also the curvature…which can hurt the out of focus blur since it curves away from the sensor toward the distance in the outer frame.

  • They stopped making it, didn’t they? I blame the name length 🙂

    Actually, I loved that lens and kept waiting for it to explode in popularity. Which is why Lensrentals stopped letting me decide what to purchase.

  • I do and I fixed that. Thank you!!

  • YS

    Thanks for the write-up. Good to know most of the ~45mm lenses are all good. Also ” For landscapes or architectural shooting, the flat field of the Olympus f/1.7 would be an advantage.” Surely you mean the Panasonic?

  • Lee

    I dunno man, my Schneider PC-TS 90mm f/4.5 Makro-Symmar HM is pretty good for such a long name 😀

Follow on Feedly