Focus Shift and LoCA in the Coastal 60/4 macro

This is a continuation of testing of  the following macro lenses :

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

The test starts here:

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

I have done longitudinal chromatic aberration (LoCA) studies on each of the lenses in this test. I’ve started doing some rendering studies.  I got to wondering how rendering is affected by LoCA. Is the Leica 90/2 Apo-Summicron-M ASPH in the previous medium telephoto test such a good image renderer because it has a lot of LoCA, in spite of the fact that it has a lot of LoCA? Same with teh Leica 100mm macro in this test. It’s probably impossible to tell for sure, but while I was thinking about it, it occurred to me that I had a lens with very little LoCA.

Or maybe not.

I thought that the Coastal 60mm f/4 UV-VIS-IR macro lens should have very little LoCA in the visible region, since it is supposedly corrected for infrared and ultraviolet, too. But I’d never tested it for LoCA.

Today, I fixed that.

For those of you coming in late, here’s a review of the test procedure:

Towards a macro MTF test protocol

Here are the results at f/4:

coastal loca 4

 

The vertical axis is MTF50, measured in cycles per picture height (cy/ph). The horizontal axis is camera position shift in mm. The points on the left side of the graph are with the camera farther away from the subject than the points on the right. I used a 50 um (0.05 mm) step size. The three raw channels are plotted. They all peak at essentially the same place. That means no LoCA.

At f/5.6:

coastal loca 56

None there, either.

At f/8:

coastal loca 8

 

Now there is a tiny bit, with the blue channel peaking with the subject a little farther away than the red channel, The difference is about bout 100 um, or 0.1 mm, or the average diameter of a strand of human hair.

At f/11:

coastal loca 11

Any LoCA will be swallowed up by the depth of field.

OK, so this is a great lens if you care about LoCA. How about focus shift?

coastal focus shift

Not so much.

You can focus wide open and stop down to f/5.6 and still get sharp images, but at f/8 and f/11 you had better focus at the taking aperture.

 

 

 

 

 

Four macros on the a7RII — overall closeup rendering details

This is a continuation of testing of  the following macro lenses :

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

The test starts here:

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

In yesterday’s post, I showed full frame images of this scene with the four lenses in this test:

Leica f/4

 

Today I’m going to show you 100% crops of the reflection of the light source in the lower right corner.

Zeiss f/2

Zeiss f/2

The light source is a Westcott LED panel set to 5000K, so with enough depth of field, you’d see a grid of yellowish and bluish dots arranged in a checkerboard pattern. I find this an, ahem, illuminating area to inspect to determine the OOF characteristics of a lens. Since the Sony is much shorter than the other lenses in this test when focused to this distance, I’ve modified the location of the crop in the Sony images.

Nikon f/2.8

Nikon f/2.8

Sony f/2.8

Sony f/2.8

Leica f/2.8

Leica f/2.8

Zeiss f/2.8

Zeiss f/2.8

In all cases, the granular nature of the light source is apparent. The effect is greatest in the case of the Sony, but that may be because it has the shortest focal length and the greatest depth of field. It is interesting that the Leica and the Zeiss renderings are so similar.

Nikon f/4

Nikon f/4

Sony f/4

Sony f/4

Leica f/4

Leica f/4

Zeiss f/4

Zeiss f/4

Stopping down another stop:

Nikon f/5.6

Nikon f/5.6

Sony f/5.6

Sony f/5.6

Leica f/5.6

Leica f/5.6

Zeiss f/5.6

Zeiss f/5.6

Now f/8:

Nikon f/8

Nikon f/8

Sony f/8

Sony f/8

Leica f/8

Leica f/8

Zeiss f/8

Zeiss f/8

And finally f/11:

Nikon f/11

Nikon f/11

Sony f/11

Sony f/11

Leica f/11

Leica f/11

Zeiss f/11

Zeiss f/11

Again, I’ll let you draw your own conclusions. Let me know what you think.

Four macros on the a7RII — overall closeup rendering

This is a continuation of testing of  the following macro lenses :

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

The test starts here:

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

I will do some sharpness testing at longer distances eventually. But it’s really labor intensive. Boring. Monotonous. Soporific.

So I’d like to put it off for a while.

Today I’ll show you some examples of how the lenses render a closeup — but not  really macro — scene with a lot of out of focus stuff in the image.

Here’s the scene with the Zeiss 100 wide open:

 

Zeiss f/2

Zeiss f/2

I focused on the nose. All the other pictures are with the camera mounted the same distance from the subject, so the perspective ought to be pretty much the same. The framing is quite different, however, because the lenses have different focal lengths. Not only do they have different focal lengths written on the barrel, two of them, the Sony and the Nikon,  have different focal lengths depending on where they’re focused.

They are all color balanced the same way, so any color differences that you see are due to the lenses themselves.

Here are all four at f/2.8:

Nikon f/2.8

Nikon f/2.8

Sony f/2.8

Sony f/2.8

Leica f/2.8

Leica f/2.8

Zeiss f/2.8

Zeiss f/2.8

You can see that all but the Sony appear to have about the same focal length at this distance. The Sony is much shorter. At infinity, it is the shortest lens in the test, but the difference is more than the 10% from the Leica and the Zeiss that would come from that. The Nikon has gotten about 5% shorter than its infinity focal length. The Sony has gotten shorter than that.

At f/4:

Nikon f/4

Nikon f/4

Sony f/4

Sony f/4

Leica f/4

Leica f/4

Zeiss f/4

Zeiss f/4

At f/5.6:

Nikon f/5.6

Nikon f/5.6

Sony f/5.6

Sony f/5.6

Leica f/5.6

Leica f/5.6

Zeiss f/5.6

Zeiss f/5.6

At f/8:

Nikon f/8

Nikon f/8

Sony f/8

Sony f/8

Leica f/8

Leica f/8

Zeiss f/8

Zeiss f/8

At f/11:

Nikon f/11

Nikon f/11

Sony f/11

Sony f/11

Leica f/11

Leica f/11

Zeiss f/11

Zeiss f/11

I think I’ll let you draw your own conclusions about the rendering.

 

Macro depth of field and focusing considerations

This post is related to a test of  the following macro lenses :

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

The test starts here:

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

Recall the focus shift curves from earlier in this test. Here’s the one for the green raw channel of the Sony 90/2.8:

sony green focus shift

I’m going to ignore the focus shift information in this graph, which is embodied in the difference in horizontal location of the peaks, and concentrate on the vertical differences in the peaks, and how rapidly the curves fall off with distance.

Considering just the green channel, f/4 is the sharpest f-stop, with f/2.8 a very close second, and f/5.6 third. I only ran the tests at whole f-stops, so it’s possible that there is an intermediate stop that is sharper than the ones that I tested.

Others have reported that the sharpest stop for this lens is narrower than f/4, and the idea that it’s at nearly its sharpest wide open is not conventional wisdom. Why is that?

One possibility is that sharpest stop using a the luminance of demosaiced image as the image to be analyzed is indeed narrower than f/4. Another cause might be that other people have done their testing at different magnification than 1:2. I know that I’ve not seen another report on 1:2 on-axis sharpness. A third possibility, which I consider likely, is that other reviewers have missed the critical focus point at the widest apertures.

No shame there, if that’s the case. I know that my former methods, before I started doing what is in this context automatic focus bracketing with a motorized focusing rail, I never could have consistently hit the best focus distances with this lens, or any other fast, high performance lens that I’ve tested. I could get close enough to compare different lenses, but not close enough to precisely, repeatably, hit the peaks bang on.

To give you an idea of how fine the distance differences are at those peaks, consider this table from the Sony 90/2.8 test with the lens at f/2.8:

Sony 90 28 peak detail

Let me orient you. The left column is distance in cm. The other columns are, moving from left to right, red channel MTF50, green channel MTF50, blue channel MTF50, and luminance MTF50. All the MTF50 numbers are in cycles per picture height (cy/ph).

I shaded the peak values for each column in green. Then I identified the points in each column where the MTF50 values dropped to more than 200 cy/ph from their peaks. This is about the difference between a really good lens and a great one. I shaded the cells in between in tan.

The first thing to notice is that the red channel spread is broader than the other two raw channels. We are at a point in the aperture range where diffraction should not be playing much of a role (the Sparrow distance at 550nm covers more than four pixels), so I don’t think we can explain this as red light suffering from more diffraction. Rather I think it’s a phenomenon I’ve see often since I started doing this testing, but don’t have an explanation for: the lower the peak, the broader it tends to be. This would of course be the situation if we were limited by DOF, but I also see it across lenses. If it is a near-universal occurrence, then truly outstanding lenses need to be focused more accurately than run-of-the-mill ones.

Now, let’s look at the range of distances for which less the MTF50 is within 200 cy/ph of the peak. In the luminance column, that range spans 300 micrometers (um), or 0.3 millimeters (mm). In the green and blue channels, the range is even less: 250 um. In the red channel, we see a relatively relaxed 400 um. That shows how little margin for focusing error there is at f/2.8 and 1:2 magnification.

I never could have found and characterized those f/2.8 peaks without the motorized rail. The focusing ring is marginal, and moving the camera by hand on a rail in 50 um increments is an exercise in futility.

In my mind, that’s the most likely reason that others have reported this lens sharpest apertures are narrower then f/4. This criticism also applies to the slanted-edge  lens testing that I’ve done before I started using the motorized rail.

There’s also an implication for photographers trying to get the most out of fast, high-performance lenses. You really have to nail the focus, and that isn’t easy, even with live view (I believe that it’s essentially impossible without it, unless you use autofocus in a way and for a subject that makes it reliable).

 

 

 

Macro on-axis sharpness, focus shift, and LoCA — summary

This is a continuation of testing of  the following macro lenses :

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

The test starts here:

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

I’m going to attempt to summarize the LoCA and sharpness measurements of the last few days. I won’t be summarizing the focus shift issues except in the most general way. I’ll deal with that last, so be patient.

If you haven’t read the results of the studies that I’m summarizing, I encourage you to follow the link above and do so. Otherwise, you may draw the wrong conclusions from this post.

I calculated the worst spread of the individual  raw channel MTF50 peaks for the four cameras, and here’s what I came up with:

loca vs fstop

Keep in mind that the spread become less important as the lens is stopped down, since the LoCA is obscured by the depth of field.

It’s clear that the Leica Apo Macro is the worst. It’s interesting that that’s the only lens in this test with the magical word “Apo” in its name, and yet it does the worst on the acid test of what we might term apoism.

It’s not easy to pick a winner among the rest, but let me give you a guided tour. First, let’s ignore the f/8 and f/11 entries, since the DoF will probably make them unimportant.  The Nikon is the best at f/2.8, and the worst at f/5.6. The Sony is the most consistent performer, and is the winner at f/4 and f/5.6.  I’m gonna give it to the Sony, but I don’t think that LoCA is a reason to decide among those three lenses.

Now let’s look at the peak MTF50 in each raw channel:

red ntf vs fstop

htrrn mtf vs fstop

blue mtf vs f stop

At f/8 and f/11, you could throw a blanket over all the lenses; diffraction has made them all essentially equals.

The Sony is the clear winner at the other f-stops, with the Zeiss in second. The Nikon is right on its heels except wide open in the blue channel.

The Leica is last. Keep in mind that I know from experience — but not, I admit, at 1:2 — that the Leica is an excellent lens. Do we have another instance of Leica lenses performing well and measuring badly, like with the 90mm Apo Summicron (another Leica lens with those magic three letters in its name)? Time will tell; there is more testing to come.

Here are the broad strokes on focus shift:

  • The Leica has a lot of it, and you should make sure you focus at taking aperture.
  • The Nikon is quite good. You can get away with focusing wide open in all but the most critical of situations.
  • The Zeiss is a little behind the Nikon, but can still be focused wide open most of the time.
  • The Sony is amazing. Feel free to focus wide open.

For details on focus shift, be sure to look at the curves associated with the post on each of the lenses.

Keep in mind that this was all done at 1:2 magnification. We saw a month ago that the Sony had greater focus shift at 3 meter subject distance.

Focus Shift and LoCA in the Nikon 105/2.8 macro

This is a continuation of testing of  the following macro lenses :

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

The test starts here:

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

The first series of tests is aimed at determining focus shift and longitudinal chromatic aberration (LoCA) at 1:2 (half size on the sensor), See this page for the test protocol:

Towards a macro MTF test protocol

The current version of the Nikon 105mm f/2.8 macro lens it the latest in a long line of 105 macros (Micro-Nikkors in Nikonese). Over the years they’ve gotten faster, learned how to focus to 1:1, acquired autofocus, and now, vibration reduction. Through all that time they have enjoyed an enviable reputation for superlative performance. The lens has grown in size over the years. With the adapter for E-mount attached, it’s the largest lens in this test, although not by much. The focusing helicoid is numb and very fast. It doesn’t take much over 180 degrees to get the focus point from infinity to life size. As you might expect, the lens is essentially impossible to focus accurately with the ring. However at distance you can use the autofocus and close up you can leave the ring alone and move the camera, so that is not a crippling flaw.

LoCA at f/2.8:

nikon loca 28

The vertical axis is MTF50, measured in cycles per picture height (cy/ph). The horizontal axis is camera position shift in mm. The points on the left side of the graph are with the camera farther away from the subject than the points on the right. I used a 50 um (0.05 mm) step size. The three raw channels are plotted.

The spread among the peaks of the three raw channels is about half a millimeter, which is excellent.

The peak MTF50 of the blue channel is disappointing.

At f/4:

nikon loca 40

The lens as a whole is getting sharper, and the blue channel, though still last, has improved dramatically. The LoCA remains low.

At f/5.6:

nikon loca 56

Now we are seeing good solid sharpness, and the LoCA remains low.

At f/8:

nikon loca 80

We’ve lost some sharpness, and the depth of field has increased to the point where the LoCA will not be a problem.

At f/11:

Nikon loca 11

The LoCA is inconsequential.

Now we’ll regraph the same data in order to show focus shift.

In the red channel:

nikon focus shift red

Focus shift is non-monotonic. That’s a good thing. focusing wide open should not be a problem.

The green channel:

nikon focus shift green

F/4 and f/5.6 are the best apertures.

The blue channel:

nikon focus shift blie

For the blue channel, f/5.6 and f.8 are the best apertures. F/5.6 sounds like the plan.

 

FOCUS SHIFT AND LOCA IN THE Sony 90/2.8 FE Macro

This is a continuation of testing of  the following macro lenses :

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

The test starts here:

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

The first series of tests is aimed at determining focus shift and longitudinal chromatic aberration (LoCA) at 1:2 (half size on the sensor), See this page for the test protocol:

Towards a macro MTF test protocol

The Sony 90mm  f/2.8 FE macro debuted last year to rave reviews. It uses internal focusing, and had a focusing ring that is slid back and forth to invoke autofocus or manual focusing. It has a 270-degree focusing ring throw, which is marginal for accurate manual focusing. It has optical stabilization, and a handy focus lock button on the front of the barrel.

Let’s look at LoCA first. At f/2.8:

sony loca 28

The vertical axis is MTF50, measured in cycles per picture height (cy/ph). The horizontal axis is camera position shift in mm. The points on the left side of the graph are with the camera farther away from the subject than the points on the right. I used a 50 um (0.05 mm) step size. The three raw channels are plotted. Three things are apparent:

The blue and green channel peaks occur at identical distances.

The red channel peak occurs farther away from the subject — the very definition of LoCA —  but the difference is well under 1 mm.

The sharpness obtainable, as measured by the height of the peaks, in outstanding.

At f/4:

sony loca 40

The lens get sharper, but little else changes.

At f/5.6:

sony loca 56

Not quite as sharp. The LoCA remains low.

At f/8:

sony loca 8

The depth of field is starting to swamp out the LoCA.

At f/11:

sony loca 11

The LoCA is inconsequential.

Now we’ll regraph the same data in order to show focus shift.

In the red channel:

sony red focus shift

This is astounding. Focus shift is essentially nonexistent.

In the green channel:

sony green focus shift

Same idea.

In the blue channel:

sony vlue focus shift

Now we can see a tiny bit more focus shift.

I am very impressed.

FOCUS SHIFT AND LOCA IN THE Zeiss 100/2 Makro-Planar

This is a continuation of testing of  the following macro lenses :

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

The test starts here:

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

The first series of tests is aimed at determining focus shift and longitudinal chromatic aberration (LoCA) at 1:2 (half size on the sensor), See this page for the test protocol:

Towards a macro MTF test protocol

 

The Zeiss 100mm f/2 Makro-Planar has an excellent — and, as we will see,  well deserved — reputation. It is reasonably small for such a fast lens. It has a 360-degree focusing helicoid, which is adequate, but not as luxurious as the Leica’s 720-degree one. It has backwards compatibility in spades; my version, the ZF one (not the ZF/2), even has the little clot to engage the pin that the mid-sixties Nikon FTn used to determine what f-stop the lens was set to.

Let’s look at LoCA first. At f/2:

zeiss loca f20

The vertical axis is MTF50, measured in cycles per picture height (cy/ph). The horizontal axis is camera position shift in mm. The points on the left side of the graph are with the camera farther away from the subject than the points on the right. I used a 50 um (0.05 mm) step size. The three raw channels are plotted. Several things are apparent:

  • The green channel is the sharpest, followed by the green and red ones in a tie for last.
  • The point of best focus is about the same for the green and blue channels,
  • The red channel has a different point of best focus; that means the lens suffers from LoCA.
  • The spread among the peaks is a bit under 1 mm, which is about the same as the Leica at f/2.8.

At f/2.8:

zeiss loca f28

The lens is getting sharper. The LoCA spread is about the same.

At f/4:

zeiss loca f40

If anything, the LoCA spread is getting better. The lens continues to get sharper.

At f/5.6:

zeiss loca f56

The LoCA is not getting worse, and is reaching the point where the depth of field will cover it up. At this point the Leica lens had about 1.5 mm of LoCA spread, too much for depth of field to make up for.

At f/8:

zeiss loca f80

The LoCA spread has decreased to about half a mm, roughly a third of what we saw with the Leica at this aperture.

At f/11:

zeiss loca f110

You’ll never see this amount of LoCA in a real photograph.

Now we’ll regraph the same data in order to show focus shift.

In the red channel:

zeiss red focus shift

There is very little focus shift, and it has the nice property that it moves first closer, then reverses course and moves farther away as you stop down.

In the green channel:

zeiss green focus shift

Pretty similar.

In the blue channel:

zeiss blue focus shift

That’s worse, but still not bad. In all cases, f/4 and f/5.6 are the best apertures. In the green channel, f/2.8 is impressive.

Focus shift and LoCA in the Leica-R 100/2.8 Apo Macro

I’m going to be testing the following macro lenses over the next couple of weeks:

  • Sony 90mm f/2.8 FE Macro
  • Leica 100mm f/2.8 Apo Macro-Elmarit-R
  • Zeiss 100mm f/2 Makro-Planar ZF
  • Nikon 105mm f/2.8 Micro-Nikkor G VR

There will not be a loser in this test. These are all excellent lenses. But in what areas does each succeed? We shall see.

I will be using the Sony a7RII for all the testing. Not only does this camera offer high resolution, it has good focusing aids, which we’ll need in some of the tests.

My first series of tests will be aimed at determining focus shift and longitudinal chromatic aberration (LoCA) at close focusing distances. I will use 1:2 (half size on the sensor), since all four lenses are capable of that magnification — two of them, the Sony and the Nikon, can go all the way to 1:1 (life size on the sensor).

The Sony and the Nikon lenses use internal focusing. The Zeiss and the Leica lenses do not. That means that the Sony and Nikon focal length when focused at 1:2 will be shorter than the advertised focal length. There are ways to measure this, and some are more accurate than others. I may get into this, but for now, let’s just be aware that the effect exists.

My first test will employ a recently -developed regime for determining three things: on-axis sharpness, focus shift with aperture, and LoCA. That protocol is described here:

Towards a macro MTF test protocol

The Leica 100mm f/2.8 Apo Macro-Elmarit-R has achieved cult status. In its day, it sold new for about as much as an Otus 55 does now. It is a heavy lens, with construction that exudes quality. The focusing helical makes two complete turns, allowing easy focusing at all distances, which is often a problem with macros. One potential problem with a focusing arrangement like that is where to put the markings for the second turn of the focusing ring. Leica dealt with that by engraving distances and magnifications on the part of the lens barrel that is covered during the first 360 degrees of the ring rotation, showing that information just when it’s needed, Like many Leica lenses, it has a built-in sliding lens hood (way to go, Leica). The front element of the lens does not rotate during focusing, and it takes 60mm filters.

First, let’s look at LoCA. Here are the results at f/2.8:

Leica 100 LoCA 28

Let me orient you. The vertical axis is MTF50, measured in cycles per picture height (cy/ph). The horizontal axis is camera position shift in mm. The points on the left side of the graph are with the camera farther away from the subject than the points on the right. I used a 50 um (0.05 mm) step size. The three raw channels are plotted. Several things are apparent:

  • The blue channel is the sharpest, followed by the green one, with the red bringing up the rear.
  • The point of best focus is different for each of the raw channels; that means the lens suffers from LoCA.
  • The spread among the peaks is a bit under 1mm.

Stopping down to f/4:

Leica 100 LoCA 40

The peaks are a bit broader, indicating that there is more depth of field at f/4 than f/2.8; no surprise there. There is slightly more LoCA than at f/2.8, as measured by the spread. This is in contrast to the conventional wisdom that LoCA decreases upon stopping down, but is consistent with what I have measured in the past, albeit at greater camera/subject distances.

At f/5.6:

Leica 100 LoCA 56

More of same. The peaks are broader, and the total spread is now about 1.5mm.

At f/8:

Leica 100 LoCA 80

The curves have stopped spreading,

At f/11:

Leica 100 LoCA 110

Now they’re coming closer together. But more importantly for real-world photography, the depth of field has gotten large enough that it will take care of  much of the LoCA.

We can take the same data and crunch the numbers another way to get a handle on focus shift. We’ll make the horizontal and vertical axes these same, but now we’ll plot all the f-stops on each graph, but only one of the raw channels.

The red channel:

leica 100 red focus shift

You can see that there’s about 2 mm worth of focus shift from f/2.8 to f/11. It is monotonic, with the focus point moving farther away as the lens is stopped down. If you focus wide open, you will have pretty nearly optimum sharpness at f/4, but you’ll be way off at the other f-stops. Conventional wisdom is that DOF will save you by f/11, but that’s not the case here.

The green channel:

leica 100 green focus shift

Rougly the same idea, but, because of LoCA, the peaks occur at different places.

The blue channel:

leica 100 blue focus shift

There is less focus shift in the blue channel, and it is not monotonic, moving slightly closer as you go from f/2.8 to f/4 before turning around and going the other way.

Note also that the optimum aperture for on-axis sharpness is different depending on which channel you’re looking at.  If you look at red, f/8 and f/5.6 are tied. F/8 wins if you look at green, but f/5,6 wins if you are looking at blue. These are not important differences, but it does show that there’s a lot going on here.

That this is a lens designed for an SLR camera, where it will probably be focused wide open. Obviously, if you have a choice and you’ve seen these curves, you won’t do that.

This is a lens with Apo in its name, indicating that LoCA has been corrected. That is not the case for the wavelengths separated by the a7RII color filter array, although — beng generous here —  I suppose it’s possible that there are three wavelengths which are all brought to a focus at the same point. This is not a surprising turns of events. We saw the same thing a month or so ago with the Leica-M 90/2 Summicron ASPH.

Photography meets digital computer technology. Photography wins — most of the time.

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