Saturday, 29 June 2013

Yasuhara Madoka 180 7.3mm f/4 circular fisheye

The Yasuhara Madoka 180 7.3mm f/4 is an unusual lens. It is one of the very few circular fisheye lenses, and the only one, that I know of at this time, for a mirrorless camera. A circular fisheye lens is one that projects a circular image on the centre of the imaging sensor, usually with 180° coverage. This is in contrast to full frame fisheye lenses, which fills the whole imaging sensor, and generally feature 180° coverage across the diagonal only, see the illustration below:

The specifications are given by the name of the lens: The lens projects an image circle of 180° field of view, and has a maximum aperture of f/4. The focal length is 7.3mm. This is pretty much all you need to know about a fisheye lens. I'll get back to the significance of the focal length later.

To understand just how wide this lens is, I compare it with the 16-50mm f/3.5-5.6 kit zoom lens at 16mm, which is already quite wide. The images are taken on a tripod at exactly the same spot, using the Sony NEX-3N:

Sony E 16-50mm f3.5-5.6 OSS @ 16mm f/8Yasuhara Madoka 180 @ f/8

Physical appearance

The lens appears fairly solidly made, with a metal construction in a matte black finish. The supplied lens cover is plastic, and fits over the lens by means of friction, which works just fine:

Looking at the rear end of the lens, we see that the exit pupil is unusually small. As the digital imaging sensors are generally quite sensitive to the angle of light hitting it, small exit pupils are usually a bad thing. It means that light hitting the corners of the sensor will come at a steep angle, causing vignetting. However, keep in mind that with this lens, there is no light hitting the corners, or even the edges, of the sensor. So the small exit pupil might not be any problem with this lens.

The lens mount is made out of metal, however, the mount appear to be somewhat crudely finished, with unevenly extruded areas. Since this lens is completely manual, and has no electronic contacts, you must set the "Release Without lens" option to use it on the Sony NEX camera.

The focus ring only rotates about 30°. In practice, the narrow angle of rotation is not a problem. It is quite easy to set the focus as you want it.

What's more, it is not dampened. This means that the focus ring rotates very easily. This is unusual for manual focus lenses, since it means that it can easily be knocked out of place accidentally. So you must make a habit out of continuously checking that the focus is set where you want it. I found that the focus ring markings were quite accurate.

When focusing, the whole lens array moves back and forth, but not by a lot. After all, this is a lens with a very short focal length, so only very little lens movement is needed for focus. The tip of the lens wobbles a little bit, but nothing unusual for a manual focus lens. The front of the lens does not rotate when focusing.

The aperture ring has stops at full apertures (f/4, f/5.6, f/8, f/11 and f/16). You can set the aperture in the middle between these as well, with a bit of dexterity, but setting it to any positions is a difficult. But you hardly need more aperture choices with this lens.

When mounting and un-mounting the lens, it is annoying that there is nothing to hold on to. The only surfaces available are the aperture ring and the focus ring. And they both rotate, obviously. So I always end up moving the aperture all the way to f/22 when mounting it, and to f/4 when un-mounting.

Here you see the lens used on the Sony NEX-3N camera:

In use

Don't be put off by the manual focus. For most uses of this lens, it is very easy to focus. Mostly, you set the focus quite close to infinity. For indoor use, I generally set f/4, the largest aperture. This makes the focus somewhat critical, especially for near objects. But mostly, I find that my images are well in focus, even at f/4. Using the focus peaking function is a good assistance when focusing manually, and it is also possible to bring up the magnifies focus assist function.

Outdoor, I generally set the aperture to f/8. That gives a good depth of focus, and focusing is not very critical any more. Most of the time, setting it around infinity will be fine.

Focusing is only critical when taking pictures of near objects. At distances of around 0.5m and closer, you may need to bring up the magnified focus assist mode. And at 0.1m distance, the closest possible with this lens, it may take a bit of experimenting to set a good focus distance.

Since this lens only fills out a circle in the centre of the image frame, you don't need to worry about the orientation of the camera. You can use an image editing program later to rotate the image, with no loss of resolution.

Here is an example image, taken at the Saint Paul’s Chapel next to the World Trade Center in New York City. It was taken at f/8, with the Sony NEX-3N, using the built in flash for a fill-in effect. As you see, the sun is in the image frame, and for that reason, there is a bit of flare. But not much. The lens appears to handle flare very well, which is a good sign for a wide lens:

On the Sony NEX-3N's 16 megapixel sensor, the image circle measures 3157 pixels in diameter. This makes up a total of 7.8 megapixels, calculated as π×(3.157/2)2. That is to say, only about 50% of the image sensor surface is used when mounting this lens.

It is not possible to mount a filter to this lens, neither on the front, nor on the rear of the lens. Some fisheye lenses accept a filter outside the exit pupil, inside the lens mount, but not this lens.

Video use

When recording videos with a Sony NEX camera, it crops the top and bottom of the image circle. This is a bit unfortunate, but I guess there is a balance: Should the image circle be as large as possible within the APS-C sensor format, or smaller to fit the 16:9 video crop. Yasuhara have chosen the first of these, and hence, videos are not going to give you a full, round image circle.

Here are some video clips recorded using the lens on a Sony NEX-3N camera. Generally, I used f/4 on the indoor clips, and f/8 outdoors. It is generally quite easy to focus when using video, since the resolution is smaller anyway.


To evaluate the lens sharpness, I set the camera on a tripod, and photographed the same scene at f/4, f/5.6 and f/8. I used the Sony NEX-3N, and set the ISO to 200, the base value. The focus was set to infinity. Here are the full images:




To better evaluate the sharpness, I present some 100% crops from the outer part of the image circle:

We see that the sharpness is very good, even in the edge of the image circle, and at f/4. There appears to be negligible vignetting at f/4, which is very well done.

When there is a high contrast, the lens tends to give a bit of Chromatic Aberration (CA) artefacts outside of the centre. But not a lot. Here is a 100% crop from the image above from Saint Paul’s Chapel:

There appears to be around 1-2 pixels of purple fringing around high contrast areas in the very edge of the image circle, which is not bad at all.


For a circular fisheye lens on APS-C format, the Yasuhara Madoka 180 has a quite long focal length. For example, Sigma also makes a circular fisheye lens for APS-C, and it has a focal length of 4.5mm. As promised, I get back to what that means in practice.

It turns out that fisheye lenses don't all have the same projection. They all feature heavy barrel distortion, obviously, but the amount of distortion differs.

I previously compared the Lumix G 8mm and Samyang 7.5mm fisheye lenses on Micro Four Thirds, and found that the Samyang lens has the least distortion. This makes it easier to use. By using an adapter, I can mount the Samyang 7.5mm f/3.5 fisheye lens on the Sony NEX-3N, and take the same image. Even if they don't cover the same image circles, their images can be scaled so that both cover the same area with 180° diagonal field of view. Here are the two images superimposed:

And to more easily see which lens makes which image, I have done edge detection, and coloured the Yasuhara image red, and the Samyang image blue.

This shows us that the Samyang lens packs the image more evenly across the field, while the Yasuhara compresses the image more in the edges, relative to the centre. This makes the images come out more distorted, and de-fishing is going to be more difficult. I believe this is due to the relatively long focal length of the lens, for an APS-C circular fisheye. Ideally, I believe it should have had a focal length around that of the Sigma lens, i.e., around 4.5mm. That would have given more pleasing looking circular fisheye images.

On the other hand, getting a shorter focal length involves using a larger retrofocal lens design, which is larger, heavier, and more expensive. So perhaps Yasuhara have struck a good balance here, making a small and affordable circular fisheye lens.

LensSigma 4.5mm f/2.8Yasuhara Madoka 180
Focal length4.5mm7.3mm
Maximum/minimum aperturef/2.8/f/22f/4/f/22
Field of view180°180°
Image circle diameter12.7mm15.1mm
Lens elements/groups13/97/6
Number of diaphragm blades66

Example images

By pointing the lens upwards, you can capture the buildings around you in all directions (Times Square):

Combining near and far objects is easy with this lens:

The Apple Store in NYC:

Photographing round objects can be more fun:

The Flatiron building, with the sun inside the image frame:

Can you capture both the New York Stock Exchange and the Trinity Church in one picture? With this lens, you can:

The lens has a very short minimum focus distance. Here is an example image taken at the shortest focus distance, and f/11:


The Yasuhara Madoka 180 is a fun circular fisheye lens, with good image quality, and easy operation. The images are sharp, and it handles flare well, an important factor for a fisheye lens, since you are likely to capture the sun or an other bright object in the field.

On the negative side, it produces more distorted images than better, and more expensive, fisheye lenses do. But it still has its place due to the combination of a small lens and a relatively low price. It is also quite exclusive. My copy has a sub-200 serial number. How often do you see that?

The focus ring is not dampened, and rotates a bit too freely. This is not a big problem in real life use, but you must make a habit of checking the focus ring position now and then, to see that it has not been knocked out of place accidentally.

The image circle is a tad bit too large for video use, which is a bit sad.

1 comment:

  1. Great review and convinced me to buy the lens (got lucky and found one on ebay for $150.00).

    Check out my fisheye work: