View Full Version : Legacy Lenses Sigma 400mm f5.6

First Light
07-22-2006, 03:29 PM

This is a super-telephoto catadioptric lens that is no longer in production. You can find used ones via eBay. These kinds of lenses are also called "reflex" or "mirror" lenses because they use mirrors to fold the focal length into a shorter lens body. This Sigma 400mm lens has two silver evaporation coated reflective mirrors. The lens body is all metal and seems very rugged. The photos below show the lens without its hood. You can see the large rear mirror in the right photo. The black disk in the middle of the lens covers the smaller front mirror.


Another unique characteristic of catadioptric lenses is their fixed aperture. This lens has an aperture of f5.6 and it cannot be changed. This means that there are only two ways to control the exposure: (1) by adjusting the shutter speed, and (2) by adding one or more neutral density (ND) filters. However, the latter would seldom be needed since an f5.6 aperture is a modest size, giving the lens a moderate sensitivity to light. An exception would be solar photography when the included rear ND4 solar filter would be used to protect both the photographer and camera from concentrated sunlight---remember that the lens acts as a magnifier---including both visible and infrared wavelengths.

Unfortunately, this lens was not available with a 4/3rds mount. Instead, I used a model that had an older Olympus OM mount. This required the use of an OM-to-4/3rds adapter (like the Olympus MF-1).

This is a popular "moon lens" because you can take great shots of the moon with it. With its f5.6 aperture it may also serve as a wildlife lens. There is no equivalent with a 4/3rds mount---the 4/3rds lens with the longest focal length is the Zuiko Digital (ZD) 300mm f2.8 ED lens. Since this Sigma is not a 4/3rds lens, you must operate your camera in either Manual or Aperture Priority mode and focus manually. This, along with its modest aperture, make it a poor choice for action shots that require fast shutter speeds and rapid changes in focus (although an E-1 equipped with a third-party split-prism focusing screen can help quite a bit with focus). Even still, I wouldn't recommend this lens if you plan to snap quick shots of moving critters owing to its manual focus.

One of the big advantages of a catadioptric lens is its small size and light weight. This makes this lens very comfortable to shoot by hand. However, with such a long focal length and a 2x focal length factor on a 4/3rds camera, you would need to shoot at about 1/800th second or faster in order to avoid motion blur. That will be very difficult with its fixed f5.6 aperture unless you are outdoors in bright sunlight. Therefore, a tripod or monopod will be helpful most of the time with this lens.

The big question is, how well does it work on a 4/3rds camera? Remember that this Sigma 400mm lens is designed for film cameras so its image circle is sized for a 35mm film frame. With a 4/3rds camera, only half that diameter is used and, as a result, you can expect the image to be slightly less bright compared to a lens that focuses all of its light onto a 4/3rds image sensor at the same f-stop.

- Focal length: 400mm
- Angle of view (AOV): 6 degrees (3 degrees on a 4/3rds camera)
- Aperture range: f5.6 (fixed)
- Lens construction: 7 elements
- Coating: multiple-layer coating
- Minimum focus: 6.6 ft (1.7 m) from the focus plane
- Filter size: 86mm (front), 30.5mm (rear)
- Length without hood: 4.41 inches (112mm)
- Length with hood: 6.81 inches (173mm)
- Weight: 19.4 oz (0.55 kg)

The following photo shows the lens, hood, front lens cap, rear filters and case. Five rear filters were provided including a "normal" filter mounted in the lens, a neutral density ND4, red R60, yellow Y52 and orange O56.


The photo below shows how the rear filter fits into a convenient sliding mount that makes it very easy to swap filters. All tests were conducted with the "normal" filter installed.


My measurements are based on the Imatest (http://www.imatest.com/) system (version 1.6.3). The camera was mounted on a tripod and located an appropriate distance away from each of several precision test targets. All tests were performed with my Olympus E-1 with an MF-1 OM adapter and an RM-CB1 remote shutter release cable. My E-1 is outfitted with a Katz Eye Optics split-prism focusing screen and an HLD-2 battery grip. The mirror was locked up (anti-shock mode) for each shot.

During the sharpness tests the lens had to be located a sizeable distance from the test target. With a focal length of 560mm with the EC-14 teleconverter it was necessary to perform these tests outdoors. Fortunately, the sky was overcast, transforming the sun into a diffuse light source.

Sharpness - The easiest way to measure the sharpness or resolution of a lens is with a camera. However, this makes the camera a part of the measurement. That means we are measuring the lens and camera together---the camera cannot be removed from the measurement. For this reason it would be best to use a camera whose image sensor has the highest available resolution. That's why PhotoZone uses an E-300 for its 4/3rds lens measurements. I don't have an E-300 or E-500 (both 8 megapixel cameras) so I used my trusty E-1 (a 5 megapixel camera). Therefore the values I measured will not be the highest possible.

Fortunately, this should not present a problem because we are not making absolute measurements of the lens' optical resolution. What we are doing is making relative measurements where we compare one lens to another on the same camera. I chose to use my award-winning ZD 150mm f2.0 ED lens for these comparisons because: (1) it is recognized as a very high quality, high resolution lens and (2) it is the best telephoto lens that I own.

There are several measures of image sharpness and before we can compare results, we have to make sure that we use the same measure. I chose to measure MTF50 in lw/ph. The MTF50 is the "modulation transfer function" or spatial frequency where the contrast drops to half (50%) of its low-frequency value. I know that sounds technical and you don't need to understand it because as long as you read my tests, I'll always measure the same thing so we can compare "apples to apples". But readers of my review should not compare my results to those of another reviewer unless they first make certain that they measured MTF50 also. As for "lw/ph", it is the units and it means line widths per picture height. Lw/ph is calculated as follows: lw/ph = 2 x lp/mm x picture height. Where lp/mm is the number of line pairs per millimeter and the picture height is also in millimeters. I won't bore you with any more technobabble. Suffice it to say that if you want to compare someone else's sharpness measurements to mine, they need to measure MTF50 in lw/ph using an E-1 camera. For more information about measurements, see Imatest (http://www.imatest.com/).

Since this lens has a fixed f5.6 aperture, I measured its sharpness at just the one f-stop. The following results show the sharpness of the lens with and without a teleconverter:


Notice that I made two measurements for each test. First, I measured the sharpness in the center of the field of view (FOV). Second, I measured the sharpness in one of the corners of the FOV (I used the lower left corner). That way you can see whether a lens is sharper in the center or at a corner.

This lens has relatively poor sharpness and I was disappointed with it.

Some readers may ask what the MTF50 numbers mean in practical terms. An MTF50 less than 1000 lw/ph should be considered "bad" or "poor" because it will produce a very soft picture with low contrast. You need at least 1150 lw/ph before the picture begins to look "good" and I'd rather see 1450 lw/ph or more. This lens measured a lowly 722 lw/ph in the center of the FOV.

The graph also shows the sharpness with an Olympus Digital EC-14 1.4x teleconverter. The sharpness was further reduced with the teleconverter and I recommend avoiding teleconverters with this lens. Note that the teleconverter changes both the focal length and the f-stop of the lens. The 1.4x teleconverter changes the lens to a 560mm f8.0 lens.

Now, the moment we've all been waiting for... How does the Sigma 400mm f5.6 compare to the ZD 150mm f2.0? The next graph shows:


Notice the amazingly strong sharpness of the ZD 150mm all the way down to f2.0. That is phenomenal. See my second ZD 150mm review (http://www.fourthirdsphoto.com/vbb/showthread.php?t=146) for all of my test results. The Sigma lens has only half the sharpness. But is the Sigma lens bad? Yes, I think so. Using a scale of poor-mediocre-okay-good-very good-excellent, I rate the sharpness of this lens "poor". It might produce better results on an OM film camera but it is not a good choice for a 4/3rds digital camera.

Chromatic Aberration (CA) - This test measures color fringing and it wasn't really necessary because a characteristic of catadioptric lenses is no CA. It measured so low as to be totally "insignificant".

Distortion - This test measures whether or not parts of the image are bent, stretched or squished. An extreme example would be the barrel distortion that is common to some wide-angle lenses like a "fisheye" lens. To measure it, a grid pattern of equally spaced horizontal and vertical lines are photographed and measured. This Sigma 400mm lens is basically free of distorion by itself. The highest deviation I measured was 0.144% which is very small. The distortion was noticeably higher when the lens was used with the Olympus EC-14 teleconverter. However, the highest deviation was -0.93% which is still modest.

Vignetting - This test measures the light drop-off near the corners of the picture. I used worse-case conditions with the lens focused to infinity. The lens exhibited modest vignetting---no more than -0.783 f-stops (or EV). The vignetting may have been worse had it not been for the fact that only the center half of the lens image circle was being used on a 4/3rds camera.

Pros - This is a well-made super-telephoto lens with a strong metal body, no CA, low distortion and modest vignetting. It accepts both front and rear filters. It included five rear filters which were easy to change.

Cons - It has poor sharpness and will produce soft pictures. Since it is not a 4/3rds lens, it must be manually focused and you cannot use the Program or Shutter Priority modes of your camera. The lens is not weatherproof.

On balance, I think this lens deserves a "bad" rating. That's a shame because I was hoping for and expecting better performance.

Copyright 2006 by Harris Technologies, Inc. All rights reserved.

04-11-2010, 09:25 AM
Thank you for this review. I am considering buying this lens second-hand (obviously). Unfortunately the attachments in the review are no longer available. It would be nice to link the correct images.


04-12-2010, 01:18 PM
If you can get past the bokeh of these lenses consider the Zuiko 500 f8. Much superior all around.