Photomacrographic lenses, part 3: Shootout at the Zeiss corral:
Zeiss Luminar 63 mm f/4.5
Zeiss Luminar 40 mm f/4
Zeiss Luminar 25 mm f/3.5
Zeiss S-Planar 74 mm f/4
On other pages of this site (1, 2, 3, 4), I tested lenses designed for
use in photomacrography, as well as lenses not designed for this application,
but usable when a specialized lens is not available or affordable.
In all these tests, the Zeiss Luminar lenses performed best. By now, I have
assembled quite a few pieces of Zeiss photomacrographic equipment, either by
design or by taking advantage of unexpected opportunities. Thus, the next
logical stage is to pit these Zeiss lenses against each other, and see which one is left standing at the end of the day.
An additional purpose of these tests is to check whether any of the Luminar
lenses provides a clear advantage over Luminars of other focal lengths. In other words, since
Luminars are not exactly available in every neighbourhood shop, if you
can only have one, which focal length should you choose? It is true that each
Luminar focal length is optimized for a specific range of enlargements, but
these ranges overlap considerably, and at any given magnification likely there are two or three
From a theoretical point of view,
resolution is ultimately limited by diffraction, and the effect of diffraction is the same at a given
magnification and effective aperture, regardless of the focal length of the
lens. Therefore, there are no theoretical reasons to prefer a given focal length
(as far as resolution is concerned). In practice, however, the higher
working distance provided by lenses of longer focal lengths and/or of special
designs does make a difference, especially in comfort of use and in the freedom
of placement of light sources. Contrast also affects picture quality. Other less quantifiable and more
subjective factors, like bokeh, may also play a role. In
the end, given the fact that all the Zeiss lenses tested here are excellent,
these factors may end up playing a major role in the present evaluation - or
none at all, if results should turn out to be visually identical.
The three Luminar lenses tested here (leftmost
three in the above picture) are from different
versions (or "generations") of these lenses. Luminar versions are discussed here. A complete test would require me to purchase a series of Luminars of all focal lengths for each version, and to
compare all these lenses. Since this would be a problematic, as well as rather
extravagant, purchase (as the Chief Financial Advisor of this home also reminds me), my small present collection
of Luminars and related lenses, assembled for the purpose of using them in
practical macro photography and photomacrography, will have to do (quite some time after writing this page, I did have a chance to test the version 1 and version 3 of the 63 mm). In addition,
I decided to conduct this test in realistic conditions that I am likely to
encounter in practical photomacrography. Although I could assemble a long stack
of bellows and extension tubes to test the whole magnification range of these
lenses, I decided not to do so, because I would avoid it also in routine
photography (instead of using an extreme lens extension, I would rather use a
lens of shorter focal length mounted on Nikon PB-6 bellows alone, and live with
the shorter working distance).
The diaphragm of Luminar lenses has "a lot" of blades (often more than normal
lenses promising a "good bokeh" because they use 7 or 9 blades to achieve a
rounded diaphragm shape). My Luminar 63 mm has at least 12 blades. All my
Luminars show very round apertures. On the other hand, the S-Planar 74 mm and
the Tessovar have only 6 blades, and an unashamedly polygonal shape. I have seen
comparable polygonal apertures also in
the Schneider Betavaron (probably the most sophisticated enlarger lens ever made, and very expensive in
its time, but with only 5 blades), and even in the Canon 35 mm f/2.8 for photomacrography. We will see in the present test if aperture shape makes any difference.
Zeiss Luminar 63 mm f/4.5
This lens (left in the above picture) is optimized
for a magnification range between 2x and 10x (as declared by Zeiss). However,
based on my calculations of diffraction effects, this lens detectably
loses some resolution already at 5x and beyond, even when fully open. This is not to say
that this lens should be used only below 5x, but that resolution will be
unavoidably lower beyond this limit. In practice, the Luminar 63 mm is rarely
used above 4x-5x because of the relatively high focal length, which requires
long bellows. I used this lens as a term of comparison in a few other tests (1, 2, 3), in
which it always outperformed other lenses. This 63 mm is a Version 1 probably from the 60's.
Zeiss Luminar 40 mm f/4
This (second from the left in the above picture) is declared by Zeiss as optimized for magnifications between 4x and 16x. My calculations indicate 8x as the magnification at which diffraction
causes a loss of resolution even when fully open. This 40 mm is a Version 2 from the 70's or early 80's.
It uses the completely re-designed optical scheme (with maximum aperture f/4)
that superseded the f/4.5 Version 1.
Zeiss Luminar 25 mm f/3.5
This lens (second from the right in the above picture) is declared by Zeiss as
optimized for magnifications between 6.3x and 25x, or up to 10x according to my
calculations. Earlier on, I tested this lens here. The tested lens is a Version 4, probably from the
early 90's. It has the dedicated 10 mm extension ring that always
accompanied this lens in Versions 2 to 4.
There is also a Luminar 16 mm f/2.5, optimized for 10x-40x.
I have none, and it is low on my list of priorities. This lens is notoriously
difficult to use. In practice, already at 10x you cannot close its aperture by
even one stop without loosing resolution to diffraction, and at magnifications above 20x it is visibly unsharp (if you
look at picture crops) even when fully open. A few photographers have reported
better resolution and working distance with specialized microscope objectives
(e.g., see here) than with this Luminar.
This result is supported also by theoretical considerations. In addition, specialist
lenses like the Zeiss Tessovar (discussed below) are easier to use, and have
much higher working distances at high magnifications.
Zeiss S-Planar 74 mm f/4
This (above picture, rightmost) is an unusual lens.
It lacks a focusing helicoid, and its attachment thread (an odd 32 mm x0.5) is
located high up the barrel, so the rear of the lens projects about 17 mm behind the mounting flange. This lens is unusually long for its focal length and speed (40
mm between front and rear elements, or roughly twice the Luminar 63 mm
f/4.5). It is unlikely you can make it focus at infinity on a DSLR, but the placement of the
attachment thread does allow a low magnification factor when attached to a
focusing mount or bellows. It is shown above mounted in a home-made
adapter with Nikon F bayonet.
This lens is optimized for a 1:1 reproduction ratio,
and it says so not just once but three times on its barrel,
lest you forget it. It is meant primarily as a copy lens with very high resolution and very low
distortion, to be used for 35 mm film duplication. The data sheet does not mention any other enlargement factor, so it
is left to my guesses to anticipate that it should work optimally in a range between
0.5x and 2x (and quite possibly 0.25x to 4x), therefore complementing the Luminar series at its low end. The
optical design is completely symmetrical, so there is no reason to reverse this
lens. The optical formula is simple by today's standards, with just 6 elements in 4
groups, and not unlike the design of most EL-Nikkor enlarger lenses (the EL-Nikkor 63 mm f/2.8 came in second when used as a photomacrographic lens, after the Luminar 63 mm). Luminars are even simpler (typically, 3 or 4 elements),
and yet are top performers. This makes me wonder whether the complex
designs of current macro lenses (e.g., 10 to 16
elements in Sigma lenses, and up to14 in Micro Nikkors, with floating groups and a couple of aspheric elements and another couple of exotic
glass elements thrown in) really are necessary.
Perhaps I am too suspicious, but I have a feeling that such a large number of
elements is more a way to compensate for mass-production with relatively poor manufacturing
tolerances (besides making a selling point) than to provide top optical
performance. After all, the sharpest eyes in the animal kingdom only use a
single optical element (albeit a very optimized one, accompanied by additional
matched optimizations in the rest of the eye).
The aperture of the S-Planar 74 mm as indicated on the barrel is not the nominal
aperture (given by F/D, where F is the focal length and D the diameter of the front element). Instead, it is the effective aperture at a
magnification factor of 1x, i.e., 2 stops closed-down with respect to the nominal aperture.
The diameter of its front and rear elements (approximately
24 mm) would be enough for a maximum aperture around f/3, and the "waste" of
lens surface with respect to the f/4 nominal aperture suggests design parameters
that place the emphasis on top performance even
when fully open, rather than price. At 1x, it generates
an image circle of 60 mm (if a very slight darkening at the edges is tolerated), or
40 mm with less than 5% fall-out in the corners (i.e., less than 1/8 of a
stop, which you will never be able to detect visually). Distortion is practically
absent on a 24 by 16 mm sensor (<0.05%), and resolution - from a theoretical point of view - remains highest between fully open and nominal f/11 (or f/22 as indicated on the barrel). The two additional stops available beyond f/11 come in handy when resolution can
be sacrificed to extra depth-of-field.
Although the S-Planar 74 mm is advertised at prices
exceeding 600 € in second-hand shops, it can be had for less than half of this amount
on auction sites, thanks to being more obscure than its Luminar cousins. The only
problem is finding one, because they are also much less frequent than Luminars.
I have failed to find any historical data, but based on its appearance it may
have been manufactured in the 80's and/or 90's, and is in fact a more
modern design than the Luminars.
A possible concern is the fact that it does not have a lens shade, nor a filter thread, nor
sufficiently recessed front elements, and therefore it could
be vulnerable to flare in certain conditions (although this did not emerge
during my test). However, a lens shade or lens cap can easily be made out of a
plastic 35 mm film canister, which has the right internal diameter (30 mm).
I described and illustrated the
Zeiss Tessovar in detail here, and also provide a
copy of its original documentation. This is a parfocal zoom
photomacrographic lens with numerous accessories, and provides a magnification
range between 0.4x and 12.8x (when used with a rotating nosepiece containing
special add-on lenses). This lens is characterised by a very narrow maximum aperture (nominal f/22), and therefore is difficult to focus at low
magnifications. In addition, practical resolution is reduced by diffraction at
most apertures and magnifications. The working distance changes with each add-on
lens used, but remains constant throughout the zoom range of the lens (as long
as the camera is mounted on an extension tube of appropriate length). The
working distance is 36 mm in the range 3.2-12.8x, and increases roughly twofold
for each lower magnification range, reaching a hard-to-beat 320 mm at 0.4-1.6x.
The above lenses (except for the Tessovar, see the setup here) were tested mounted on Nikon PB-6 bellows
attached to the table-top focusing stand of the Tessovar and a D200 DSLR.
Illumination was provided by an incandescent lamp for focusing, and a Nikon
SB-800 flash in iTTL mode for the exposure (with manual exposure compensation if
In earlier occasions, I carried out tests of these lenses in similar
conditions. However, this time all lenses are of very good quality, and
therefore, examining the results turned out to be much more difficult. Two main
problems became apparent. The first is that the incandescent lamp used for
framing and focusing did contribute to the exposure. Since the tests were
carried out at different lens apertures, this lamp contributed more when the
diaphragm was open, and therefore did affect the colour balance. The solution
was simple - just turn off the lamp before exposing.
The second problem is that evaluating the resolution of high-resolution
lenses in photomacrography requires the subject to be perfectly focused. This
turned out to be especially difficult at the borderline between macro
photography and photomacrography (i.e., in practice, between 1x and 2x). At
lower magnifications, DOF is high enough to be slightly forgiving. At higher
magnifications, DOF is so small that it is easy to see what is in focus, and
what is not. In this critical range, however, a small detail appears focused in
the viewfinder (even with a 2x viewfinder magnifier) for a rather large interval
of movement of the focusing rack, but not when the picture is examined at 1:1
pixel ratio on a large and sharp monitor (while old-fashioned CRTs were a little
fuzzy, with pixels slightly overlapping each other, today's LCD screens are as
sharp as anything can get). This is a much harder problem to solve. A factor in
this problem is that the lenses tested here do not have especially large
apertures (f/4 and f/5.6, respectively). Modern macro lenses typically have
f/2.8 apertures, and are easier to focus when fully open.
My solution was to take pictures of a subject with a slightly convex surface,
so that, no matter where the focal plane was located, I could always find an
area that was completely in focus. The drawback of this solution is that I am
unable to show crops of exactly the same spot for comparison among different
lenses. However, the subject (a sea shell with a lot of small-scale surface
detail, see Fig. 1) is sufficiently uniform to provide similar detail in
different areas. Also, DOF is so low that even in a 400 by 400 pixels crop some
spots may be out of focus. Thus, in evaluating the results, concentrated on the
sharpest areas and disregarded unfocused ones. Also, reddish colours are
predominant in the chosen subject. Since red light has a longer wavelength than
other colours, diffraction shows its effects (i.e., loss of resolution) in this
colour more than in others. A green or blue subject would have a higher
sharpness (in an objective sense, regardless of our perception or the
sensitivity of the camera sensor), and would allow closing the diaphragm between
half and one more stop. Nonetheless, this test object is quite representative of
real-world photomacrographic subjects.
The present tests differ from earlier ones also in testing all lenses at the
narrowest aperture that still provides a resolution visibly unaffected by
diffraction. This aperture can be computed as a function of magnification,
sensor resolution and circle of confusion (see here), and is independent of
focal length and lens design. Of course, it is entirely possible that, in a real
lens, aberrations and other design faults will cause a loss of resolution at
this and/or more open apertures. The computed value is a theoretical limit that
no lens can exceed, i.e., beyond this limit, visible diffraction does arise no
matter what the lens designers may choose. Thus, the aperture computed in this
way is a theoretical "sweet spot" in photomacrography, because it provides the
maximum possible DOF and resolution at the same time. It should always be used,
unless DOF becomes more important than fine resolution. A truly excellent lens
will be designed to perform at its best when used at this aperture. As the main
target for the current test, this criterion ensures that excellent lenses can be
separated from poorer ones.
The above criterion, of course, is very severe. It is based on a circle of
confusion as small as 3 pixels (20 μm) on a D200
sensor, i.e., the smallest distance that theoretically can render two points as
separate in an image. It results in a recommended range of apertures and
magnifications narrower than those specified by Zeiss for the same lenses. However, this is intentionally a severe test. If you allow
a larger circle of confusion, you will end up with maximum magnification ranges
similar to those specified by Zeiss.
The following figures are either full-frames reduced to 600 by 400 pixels, or
crops of areas of pictures with an original size of 400 by 400 pixels, displayed
at 1:1 resolution on the screen. Both
types of pictures are compressed for web publication, and therefore may display
compression artifacts and are of lower quality than the originals. The main data
relevant to each picture is indicated in the caption below a picture.
The above pictures show that the S-Planar 74 mm is extremely sharp throughout
the range of magnifications allowed by the PB-6 bellows. The reduced full-frame
in Fig. 1 shows excellent contrast and colour saturation. The detail in Fig. 2,
at 0.62x, shows a slightly lower resolution than at higher magnifications (Fig.
3-4). Resolution improves by opening the aperture one stop. Fig. 2-4 are taken
at the narrowest aperture settings that are still unaffected visibly by
diffraction (as calculated on a theoretical basis). These apertures provide the
best DOF and resolution at the same time. Fig. 5 shows a very slight loss of
resolution (the smallest white dots are more diffuse) by closing one stop
further than in Fig. 4. Fig. 6 shows the result of closing the diaphragm all the
way (5 stops from the optimal), which produces unacceptably fuzzy pictures even
when substantially reduced. In other words, diffraction is not to be trifled
with. In Fig. 6, closing the diaphragm also produces a large DOF on the side of
the film/sensor plane, which causes microscopic dust particles sitting on the
antialiasing filter of the camera to become visible (the darker round "doughnut"
at center-right, surrounded by diffraction haloes).
The Luminar 63 mm is also extremely sharp, but loses a little of its
legendary performance at 0.9x and aperture 15 (opening to 8 improves the
results). Since this magnification is quite outside its design range, it can
hardly be regarded as a fault. It attains maximum sharpness at 2x, and is still
at top performance at 3.5x. Also in this case, the pictures shown above are
taken at the optimal aperture and DOF. The S-Planar 74 mm has a slight edge on
the Luminar 63 mm below 2x, but the two lenses are essentially equal between 2x
and almost 3x.
At 1.75x and the theoretically optimal aperture 8,
the resolution of the Luminar 40 mm is slightly degraded, but improves
if the aperture is opened to the 4 setting. This is the most consistent
deviation from theoretically expected behaviour I encountered in this
test. It is not very important, because this lens is optimized
for a magnification range starting with 4x. At 2x, performance at the
"sweet spot" aperture is already improved. At 3x and above, performance
is virtually undistinguishable from the Luminar 63mm.
The high magnification provided by the Luminar 25 mm forced me to choose a
different subject (the juvenile portion of the same shell, which is green rather
than reddish), as the original one was running out of useful detail at this
scale. The Luminar 25 mm performs well also at
magnifications lower than its optimal range according to Zeiss
specifications (6.3x-25x), and is fully usable at least from 4x (which is the lowest
magnification I tested; Fig. 16). For optimal resolution, the aperture can be
closed only one stop (or none at all above 7x), which makes this lens difficult
to use on non-flat subjects (Fig. 17-19). Albeit, this is true of any lens in
this magnification range. At 11x, diffraction slightly reduces resolution even
with the aperture fully open (Fig. 20), and becomes more visible after closing
it one stop (Fig. 21), although DOF slightly improves as a consequence, making
the effective resolution more difficult to detect. Therefore, I do not recommend
using this lens above 10x.
The Tessovar was tested only with turret rotated at positions III and IIII, and at the minimum and maximum magnifications
obtained by zooming at these positions (Fig. 21-26). Zeiss recommends letting
the aperture be regulated by the interlocking mechanism with the zoom knob. This
varies the aperture from 4 (fully closed) at the lowest magnification of all
ranges, to 1 at the highest magnification. However, it is possible to manually
override these values, and I tested all magnifications at 1 and 4.
It is evident that diffraction is affecting resolution at all tested
magnifications, even with the aperture fully open. However, roughly in the first
half of the zoom range, resolution is acceptable when fully open, if you don't
need very fine detail. In fact, resolution is qualitatively better than I
expected from the horrifically small effective aperture. Beyond this
magnification, diffraction becomes quite visible even when you reduce the whole
picture to fit onto the screen (about 40% of the original picture resolution on
my monitor). The other side of the coin is a higher DOF than in preceding tests
(Fig. 24). Working distance is also quite high.
It is a pity that the Tessovar is so difficult to focus at low magnification
by using the camera's viewfinder. At magnifications below 1.6x, the effect of
diffraction is lesser, and resolution higher. It approaches that of the Luminars
Summary of settings
The following table lists several measurements useful if you need to choose
or use one of these lenses. All measurements are based on lenses mounted on
bellows with the front standard moved to the front of the rail, and the rear
standard at the specified distance, as read from the scale on the rail of the
bellows at the back of the rear standard (since there are two scales, it felt
natural to use the one that increases with increasing magnification).
Magnification factors may be slightly approximate. Apertures are as indicated on
the barrel. Luminars and the Tessovar indicate apertures as exposure factors
relative to fully open, while the S-Planar 74 mm indicates the effective
aperture at 1:1. Non-optimal apertures (framed in red) are those at which
resolution is visibly degraded by diffraction (but still may be used if a higher
DOF is worth a lower resolution). A few empirical tests show that the values
framed in red correspond very precisely, at least for the lenses tested on this
page, with the apertures at which diffraction effects become visible in test
images. I am using this table as a practical companion when shooting with these
S-Planar 74 mm
Luminar 63 mm
Luminar 40 mm
Luminar 25 mm
(1): values in red are experimentally verified, and
slightly different from theoretically computed values.
(2): Topmost range is according to my tests and calculations, second range (in
parentheses) is specified by Zeiss.
(3): Position of the Tessovar rotating turret.
(4): I recommend this range because it is difficult to focus at lower
magnifications, but resolution is high also at magnifications below this range.
From the above tests, the following results may be summarized. They deal with
all lenses tested on this page, except for the Tessovar. Since the latter is a
very different system, it needs to be discussed separately.
- All tested lenses are exceptionally sharp, and free from
aberrations. They all out-resolve the camera, when used at an appropriate
aperture. There is no absolute winner, although each lens clearly has
an optimum magnification range. In all cases, within the optimal magnification
range, diffraction is the only factor that lowers resolution to any detectable
amount (i.e., to a point where the lenses do not out-resolve the camera sensor).
Since there is no workaround that eliminates the effects of diffraction (short
of using frame stacking or similar multi-image methods), we can safely conclude
that all the lenses tested on this page are "perfect" (i.e.,
essentially, they cannot be improved to provide visibly better results). They
differ very slightly in color rendition and contrast, probably as a result of
different lens coatings, which is to be expected of lenses manufactured over a
time-span of about 30 years.
- For the tested Luminar and S-Planar lenses, the optimum range
of magnifications starts at or below the lowest magnification specified by Zeiss (see above table). At the opposite (highest) end of the magnification range, the maximum specified
by Zeiss causes visible diffraction even with the lens fully open. I
provide more conservative values of maximum magnification for each lens
in the above table. Of course, the limits at both ends of the range can be
exceeded, as long as you are aware of the consequences. At low magnifications,
these lenses may need to be opened one stop, with respect to the computed
- The S-Planar 74 mm is specified only at 1:1, but performs exceptionally well throughout the tested range (0.62-2.9x). At
magnifications lower than 1x, it should be opened one stop
with respect to the computed optimal aperture.
- Working distance, ease of use and the optimal range of
magnifications are the only factors to consider when choosing one lens
among those tested here. Aside from this, you cannot go wrong with any of these
lenses. Within their optimal magnification and aperture ranges, they all
out-perform your camera in terms of resolution. Just as a reminder, DOF does not depend on focal length, but only on
aperture and magnification, so DOF cannot be a factor in your choice (unless
you are considering a special-purpose lens with a fixed and/or very small
- Any of these lenses will need numerous accessories,
a precise focusing rack.
The one built into the base of the Nikon PB-6 bellows is not adequate to shoot
with the bellows in a vertical position. For this test, I used the focusing
stand of the Tessovar.
- The Tessovar suffers from diffraction to a larger extent than the other lenses, because its small maximum aperture causes diffraction to
be visible also when used fully open (and as a consequence, also provides a
higher DOF than the other lenses). Aside from this, it is every bit as good as
the other lenses, in spite of being a 4:1 zoom with a total 32:1 range of
magnifications. The Tessovar is a specialized system. If you want maximum resolution
in absolute terms, as well as maximum freedom and versatility, do not
choose a Tessovar. However, the Tessovar is generally faster and more comfortable to
use for long periods of time, and also far sturdier and more durable than bellows, especially if
you take photomacrographs for hours on end and/or on a daily basis.
- Focusing at and below 1x is more difficult with all these lenses,
than with a modern macro lens. Focusing becomes easier at higher
magnifications, as long as you have sufficient light. In general, I would prefer
to use a good macro lens, rather than one of the specialist lenses discussed here, up to 1x. I
may choose to use the S-Planar 74 mm at 1x, if top performance is an issue.
Above 1x and up to about 10x, the unquestionably best choice (as far as picture
quality is concerned) is to use the
S-Planar 74 mm or one of the Luminars, depending on the required magnification.
The only case in which I could see myself using a normal macro lens above 1x is
in emergency situations and/or in the field. I would use the Tessovar if a high
DOF is needed at the expense of resolution, and/or if I had to take hundreds or
thousands of pictures in a relatively short time.
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