Review: Sony Carl Zeiss Planar T* 85mm f/1.4 ZA New

 

1. Introduction

On a full-frame camera, the 85mm focal length offers the perfect blend of imaging characteristics for the human face. Being a short tele lens it offers only mild levels of image compression, which tends to flatten faces and rob them of dimension. Still it is indeed a tele lens and thus provides enough compression so that in a full face portrait, the nose will not seem objectionably larger than the eyes or ears, as happens with wide angle lenses.

The 85mm lenses usually have a very low linear distortion and therefore create an accurate reproduction of the human face, even at the edges.

The fast maximum aperture combined with the focal length gives clear subject separation from the background and produces smooth out of focus areas. It is also great for candid pictures being able to shoot without a tripod or flash in relative low light. Prime lenses are also usually smaller and lighter than zooms making them easier to carry although you have to give up the flexibility of different focal lengths.

The Sony Carl Zeiss Planar T* 85mm f/1.4 ZA was announced in June 2006 and released to market in September the same year. It was, together with the Sonnar T* 135mm f/1.8 ZA, the first Alpha lenses produced as a cooperation between Carl Zeiss and Sony.

Exactly who designs and produces the lenses are still not officially revealed and often debated on different web forums. But for photographic purposes what matters is the performance of the lenses and not who manufactures them. So let's see what the Planar T* 85mm f/1.4 ZA has to offer.

Remember, this is a test of one lens only and based on my subjective opinions so you have every right to disagree.

2. Lens data















  Dhidhoofinolhu, South Ari Atoll, Maldives
  A850, 85mm f/1.4 ZA f/1.4, 1/640s, ISO 200
  (Photo © Marcus Karlsen)

  • Focal Length: 85mm (APS-C: 127.5mm)
  • Filter diameter: 72mm
  • Hood Mount: Round bayonet type hood
  • Dimensions: 81mm x 75mm (diameter x length)
  • Weight: 640g
  • Aperture:
    • Largest: f/1.4
    • Smallest: f/22
    • Diaphragm Blades: 9 blade circular aperture.
  • Focusing:
    • Method: In camera focus motor, barrel extends when focusing,
      auto clutch - non-rotating front element.
    • Minimum distance: 0.85m
    • Maximum magnification: 0.13X
    • One focus hold button
    • AF/MF switch on lens barrel
  • Optics:
    • Construction: 8 elements
                             7 groups
    • Angle of view: 29° (APS-C: 19°)
  • Standard accessories:
    • Front cap (ALC-F72Z)
    • Rear cap (ALC-R55)
    • Soft lens carrying case (LCL-90AM)
    • Round shape lens hood (ALC-SH0002)
  • Optional accessories:
    • Circular polarizing filter (VF-72CPAM)
    • Multi-coated protector filter (VF-72MPAM)
    • Neutral density filter (VF-72NDAM)

3. Appearance and Handling

The Planar T* 85mm f/1.4 ZA gives a solid impression. The lens is compact but heavy, weighing 640g, with a satin black finish. It has a focus lock button on the left side of the barrel. As long as the button is pressed the autofocus is locked. The build quality of the lens is excellent. It is not weather sealed like the newer Sony Carl Zeiss lenses, but so far this has not caused me any problems.

The autofocus is driven by the in camera motor and is noisy and slow. Focus tracking is very difficult as the lens is too slow to follow moving subjects. However this is really a specialized portrait lens, so focus tracking might not have been highest on the list of priorities when designing it. In manual focus the lens is smooth and it takes about 120 degrees to focus the lens from 0.85m to infinity. When used wide open, at close focus, the plane of focus is razor thin and one must be very accurate in placing the focus plane. Here the Focus magnifier function on the A99 is almost essential. The close focusing is limited to 0.85m which makes this lens less suitable for capturing details and small objects.

When focusing the length of the lens changes by a small amount. The front element does not turn, so it causes no problems when using a circular polarizing filter. However I find it a little annoying and would have preferred an internal focusing design. This would also make it possible to add weather sealing to the lens.

The lens uses 72mm filters, the same as the Distagon T* 24mm f/2.0 ZA SSM and the Planar T* 50mm f/1.4 ZA SSM. The lens hood is circular and uses interior flocking to reduce flare. It uses a bayonet mount to attach to the lens.















           Sony Carl Zeiss Planar T* 85mm f/1.4 ZA

4. Optical Performance

The 85mm focal length, f/1.4 maximum aperture and Carl Zeiss T* coated Planar optics, should all add up to superlative performance and handling for portraiture or medium-telephoto landscapes, shouldn't it? Let's see.

The MTF graph

The graphs below are Sony's own MTF graphs for this lens.
Figure 1. The graph shows MTF in percentage for the three line frequencies of 10 lp/mm, 20 lp/mm and 40 lp/mm, from the centre of the image (shown at left) all the way to the corner (shown at right). The bold lines represent sagittal MTF (lp/mm aligned like the spokes in a wheel). The thin lines represent tangential MTF (lp/mm arranged like the rim of a wheel, at right angles to sagittal lines). On the scale at the bottom 0 represents the centre of the image (on axis), 4 represents 4 mm from the centre, and 21 represents 21 mm from the centre, or the very corner of a 35 mm-film image. Separate lines show results at f8 and full aperture. This is Sony's own MTF graph for this lens.


4.1 Sharpness

The test shots show that the sharpest apertures for the Planar T* 85mm f/1.4 ZA is f/2.8 to f/8. Centre sharpness is still good at f/2 and even at f/1.4. This looks pretty consistent with measurements done by Zeiss (se figure 2 below), although here the smaller apertures holds up better than in my test images.

From "How to read MTF curves, part 2" by H.H.Nasse, Zeiss.com
Figur 2. MTF of the Planar 1.4/85 ZA lens at 10, 20, 40, and 80 Lp/mm as a function of the aperture stop. The optimal aperture stop is f/8 as the lens is diffraction-limited at smaller apertures. The limits from diffraction theory are indicated by the red lines for 40 and 80 Lp/mm. From "How to read MTF curves, part 2" by H.H.Nasse, Zeiss.com
When fully open, the contrast is clearly lower at low frequencies up to 40 Lp/mm but it increases when the aperture stop is set to f/2.8, see Figure 2. On stopping down further to f/5.6 we note a clear increase at all frequencies and aperture stop 8 is optimal again (yellow curve). The curve of aperture stop 16 is positioned somewhat lower than the curve for aperture stop 5.6. The curve for aperture stop 22 drops steeply, especially at high spatial frequencies - evidencing the effect of diffraction.
Figure 3. System MTF of the Planar 1.4/85 ZA on a 24 MP camera, JPG, medium sharpening, six different aperture stops: 1.4 .. 2.8 .. 5.6 .. 8 .. 16 .. 22. From "How to read MTF curves, part 2" by H.H.Nasse, Zeiss.com.


4.2 Chromatic aberration / Colour fringing


Different wavelengths of light come into focus at different planes. The lens inability to correct this and bring all colours to focus at the same point is known as chromatic aberration. Chromatic aberrations can cause a coloured halo around points of light and reduced sharpness. Chromatic aberrations can be divided into two types, longitudinal or axial chromatic aberrations and lateral or transverse chromatic aberrations.

Longitudinal or axial chromatic aberration is the inability of a lens to focus different colours in the same focal plane. Axial colour fringing is identified by a single colour all the way around an in focus object and can occur anywhere in the image. Axial colour fringing is particularly seen in areas that are just out of focus. You will see purple colour in front of the plane of focus and green colour behind it. Axial colour fringing will go away as you stop down the aperture.

Lateral or transverse colour fringing is caused by a sideways displacement of the focus point (instead of along the axis, longitudinal). Look for colours like red, green, purple or blue that occurs along the image edges in areas of harsh contrast. Lateral colour fringing only affects tangential details and will give two differently coloured fringes at either side of it. It will not go away by stopping down the aperture.

See toothwalker's site for more information about chromatic aberrations.

The lens suffers from longitudinal chromatic aberrations. This show as green 'halo' around out of focus areas behind the plane of focus and purple 'halos' around out of focus areas in front of the plane of focus. These will gradually decrease until they are gone at about f/4. As an example, look at the image of the LUX sign, if you look closely you can see a narrow green line around the white sign. The image is shoot at f/2.8. If you look at the bokeh-test image below, shot at f/1.4 it is even more visible.















  LUX Resort, Dhidhoofinolhu, South Ari Atoll, Maldives
  A850, 85mm f/1.4 ZA f/2.8, 1/2000s, ISO 200
  (Photo © Marcus Karlsen)

The lens also have some lateral colour fringing along the edges that does not go away as you stop down, but I do not find this distracting.

From "How to read MTF curves" by H.H.Nasse, Zeiss.com
Comparing MTF in white and in coloured light helps to understand the reasons of colour fringes in images of high contrast edges and highlights. The following curves illustrate the longitudinal chromatic aberration of the Planar T* 85mm f/1.4 ZA high speed short telephoto lens by measuring MTF as a function of focus:
Figur 4. Focus MTF of the wide open Planar 1.4/85 ZA in white light (black curve) and in blue, green and red light. The cross symbols connect position on the image side (horizontal scale) to the subject distance (vertical scale on the right), the lens has been focused in white light to a distance of 5m. From "How to read MTF curves" by H.H.Nasse, Zeiss.com.
MTF values in coloured light are higher than in white light, but at the same time the maximum is at different positions, they don't have a coincident focus. In the best focus for white light (position 0) the red light MTF is the lowest of all. From that follows, that the red line spread has the largest diameter; the image then shows a slight reddish fringe. This is getting even stronger, when the subject is at slightly shorter distance, where the green MTF is at its maximum. Thus this kind of fast lenses produces fringes at highlight details which are red or purple, if the detail is in front of the focal plane, and which is green, if the detail is behind the focal plane. The saturation of these colours, called secondary spectrum, depends on the distance of the MTF peak positions and on the slope of the focus MTF curves. If lenses exhibit more monochromatic aberrations (like old lenses), the curves are more flat and the colours look pale. Just modern, highly corrected fast lenses tend to show more saturated colours. Since the distances between the peak positions can't be made infinitely small, the only chance to make the fringes disappear is stopping down, since then the depth of focus is large compared to the longitudinal colour aberration, and coloured MTF differences are getting small, see Figur 5.
Figur 5. Focus MTF of the Planar 1.4/85 ZA at f/ 5.6. From "How to read MTF curves" by H.H.Nasse, Zeiss.com.


4.3 Spherical aberration / Coma


Spherical aberration is caused by the spherical shape of the lens elements. Light that hits the lens elements close to the optical axis is focused at one position, while light that hits the outer areas of the lens elements are focused at a position closer or further away from the lens. That means that the focus position depends on where the light is traversing the lens element. When the marginal focus is closer to the lens than the axial focus it is called under corrected spherical aberration and when it is located beyond the axial focus the lens is said to suffer from overcorrected spherical aberration (see toothwalkers site for a more detailed explanation).

Figur 6. Spherical aberration is an image imperfection due to light hitting the lens close to the optical axis being focused at a different position than light hitting the outer areas of the lens.

Coma is an artefact of spherical aberration, and shows itself as oblong shapes in the corners of images. It is especially evident at wide apertures in wide angle lenses.

In the paper "How to read MTF curves, part 2" written by H.H.Nasse from Carl Zeiss, it is said that the 85mm f/1.4 ZA is designed with spherical under-correction (see figure 7 below from Zeiss) which means that the light from the edges of the lens elements are focused just a bit closer to the lens than the central ones. This gives a more pleasant and creamy background bokeh, although the forground bokeh becomes more edgy and not so pleasant, see Jakub Travnik's site for more detail.

The test shot above and the graphs on the right side shows this to be true. However the lens is pretty well corrected, with just a little bit of under-correction. This gives a very pleasant background bokeh and the front bokeh is not that bad either.

The picture above is a shot of a row of white points taken whith the camera angled and focused on the centre point so that the left side of the screen is farther away (background bokeh) than the point of focus, and the right side is closer (front bokeh).












             Front bokeh                                                                              Background bokeh

             The graphs show the light intensity through the out of focus highlights in the image above. The Front bokeh has more
             defined edges than the background bokeh, this makes the highlights more distracting to the eye.


Coma is not a problem with this lens.

From "How to read MTF curves, part 2" by H.H.Nasse, Zeiss.com
All lenses with incompletely corrected spherical aberration have a different type of blur before and behind the focal plane, in particular in its close vicinity, and this includes all camera lenses with a large aperture.
Lenses with spherical under-correction, which is felt to be more pleasant, have a flat MTF curve in the background and a steeper MTF curve in the foreground. This is evident from the following focus MTF curve of the Planar 1.4/85 ZA:
Figur 7. Slanted focus MTF curve of a spherically under-corrected lens. The values for positive defocusing describe the imaging of objects behind the focal plane. The values for negative defocusing apply to the foreground. From "How to read MTF curves, part 2" by H.H.Nasse, Zeiss.com


4.4 Illumination / light fall-off / Vignetting


Vignetting is the unintended darkening of the image corners in a photographic image. The effect is strongest when the lens is used wide open and will disappear as the lens is stopped down.

Vignetting on the 85mm is visble at f/1.4, but I do not find it distracting and it is easily correctable in post-processing if you don't like it. It is almost gone at f/2 and not visible at f/2.8.

4.5 Geometric distortion


Geometric distortion is probably the most easily recognisable aberration as it deforms the whole image. Distortion causes straight lines to be projected as curved lines by the lens. Distortion is usually rendered in two different ways, barrel and pincushion distortion depending on how the line is distorted, bulging or bent inward. Distortion is independent of the aperture used.

For this lens geometric distortion is nearly non-existent.

4.6. Bokeh: When the image is out of focus


The word Bokeh is of Japanese origin and relates to the fashion in which the out-of-focus areas of the image are rendered. A sharply focused subject set against a pleasingly silky smooth background characterizes a good bokeh. The transition from in-focus to out-of-focus should occur gradually. A large number of aperture blades give a more circular opening when the lens is stopped down, but this in itself is not sufficient to give a good bokeh. Another feature of the lens that affects bokeh is the degree of spherical aberration correction. Spherical aberration is when the rays of light from the middle and from the outside edges of a lens do not focus to exactly the same point.

Longitudinal chromatic aberration often operates in tandem with spherical aberration to shape the bokeh of a large-aperture lens. The combined effect of longitudinal chromatic aberration and spherical aberration is also known as spherochromatism.

Overall I find the bokeh of this lens very nice. But watch out for the purple and green halos around out of focus areas caused by the longitudinal chromatic aberration, as they sometimes can be distractive.

4.7. Flare and ghosting

This lens handles flare and ghosting very well.


5. Summary and Conclusions

The Planar T* 85mm f/1.4 ZA is an excellent lens offering sharp images at very wide apertures. It is perfect for portraits, low light photography and as a midrange telephoto lens for landscape and street photography were fast autofocus is not required. It can give you these sharp images with smooth, visually pleasing out-of-focus backgrounds that add an extra dimension to your photographs.

Pros
  • Sharp
  • Great portrait lens
Cons
  • Slow and noisy autofocus, would benefit from an SSM upgrade.
  • Close focus distance of 0.85m, I would prefer to focus closer for product/detail type photography.
  • Lens extends when focusing, I would prefer an internal focus design














  A99, 85mm f/1.4 ZA f/2.0, 1/800s, ISO 1000
  (Photo © Marcus Karlsen)

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