Saturday, 1 June 2013

Wanderlust Pinwide review

From Wanderlust Cameras comes the "Pinwide" for Micro Four Thirds:



The tin case it comes in The pinhole "lens" itself

Background


Pinholes are nothing new. Far from it. The first cameras were pinhole based. The principle is easy. If you mask the windows of a room, and make a very small hole in the curtain, you can see an upside down picture of the outside on the opposite wall. So why do we need glass lenses, anyway? The answer is that to achieve sharpness, the pinhole must be very small, only letting through a very small amount of light, far too little to make a decent exposure. Also, glass lenses can be made to have better vignetting properties.

DIY fans have made pinholes for their cameras for years. The principle is simple: Drill a hole in a spare body cap, put some tin foil over the hole, and carefully make a tiny, round hole with a needle in it. And there you are!

The downside with this method on traditional SLR cameras, is the long register distance: This means that the pinhole has a focal length of around 50mm, corresponding to a normal lens. With Micro Four Thirds, this is a bit better. The register distance is 20mm, meaning that the pinhole becomes a short normal lens, but still not very wide.

The Wanderlust Pinwide fixes this by recessing the hole into the camera lens mount. This gives it a focal length of about 11mm, i.e., an ultra wide angle lens. Much more fun to use! This corresponds to 22mm on a traditional film camera, and gives you a massive 80° field of view.

Physical


The pinhole comes in a nice, retro looking tin case. The pinhole itself is made out of what appears to be good quality plastic. However, don't let that fool you into thinking that this is just a molded plastic piece. The hole itself is in fact made in a piece of metal glued to the centre of the plastic item. Also, the hole is recessed from both sides, meaning that the hole itself is well protected. Here is the hole as seen from the rear side, photographed with the Leica 45mm 1:1 macro lens at maximum enlargement:



Looking at a 100% crop, it does look like the hole has a nice circular shape to it:



The picture was taken with a Panasonic GH3, which has 4608 pixels horizontally. The hole itself is 30 pixels wide, hence, we can conclude that the hole is about 0.11mm in diameter (17.3mm * 30 / 4608). This corresponds to an aperture of around f/96. (Focal length divided by the hole diameter.)

f/96 is a bit abstract for most people, since it is so far from what we are used to. It is nine stops slower than f/4, which is what you would normally find on a similarly wide lens, e.g., the Lumix G 7-14mm f/4.

You should take care not to touch the hole with anything, e.g., a needle or other sharp objects. That will ruin the roundness of the hole, and make the images look bad.

Compatibility


The Pinwide can be used on any Micro Four Thirds camera, except if the camera has some built in ND filters, like the Panasonic AF-AG100. The ND filter mechanism sits between the sensor and the lens mount. Since the Pinwide has a deeply recessed end pointing into the camera, it can interfere with the ND filter, potentially damaging the mechanism. So don't use the Pinwide on that camera!

In use


Since the Pinwide does not have any electrical contacts, you must select "shoot without lens" in the camera menu:



Other than that, it is just a matter of mounting it to the camera and go!

There is no optics, and, hence, no focus adjustment. Everything is in focus. On the other hand, the sharpness is rather limited, so I might be tempted to rephrase that to everything is in "focus".

At ISO 200 (the base ISO for most newer Micro Four Thirds cameras), you can use a shutter speed of about 1/2 second on a bright, sunny day. If you set the ISO to 3200, you can use a shutter speed of about 1/30s, which should be possible to handhold.

This is also useful for video: Set the shutter speed to 1/30s and the ISO to 3200, and use 25fps (PAL version) or 30fps (NTSC version). If the light is dimmer, set a higher ISO.

Here is how to mount and use the pinhole, as well as an example video. The video at the end was done in sunlight, with ISO 3200 and 1/25s on a Panasonic GH3:



Example images


Here is the same image taken with the pinhole and with the Olympus 9-18mm f/4-5.6 @ 9mm:



Pinwide, ISO 200, 1.6s Olympus 9-18mm f/4-5.6 @ 9mm, ISO 200, 1/100s

Note that the perspective is a bit different in the two images, even if the camera is at exactly the same position during both photos. This is because the Olympus 9-18mm f/4-5.6 extends around 10cm further from the camera than the pinhole does. This creates a different perspective, especially for near objects.

Here is another example image:



In this example image, I use the fact that the even near objects are in "focus":



Vignetting


As you see in the images above, there is a significant amount of vignetting. This is very easy to explain. The light simply travels further from the hole to reach the corner of the sensor, compared with the centre of the sensor. And the further the light travels, the larger area it spreads out to, i.e., losing intensity. The formula is simple: The light intensity is inversely proportional to the squared distance. Hence, the light intensity is significantly smaller in the corner. See this illustration:



Based on this insight, we see that the centre of the vertical borders should have 0.7 stop less light than the centre, and the corners should have 1 stop less. But the pictures clearly show that there is much more vignetting.

What's going on here, is that the angle of the light hitting the corner is too steep. Generally, digital imaging sensors require that the light hits them fairly straight on, ideally at a 90°. That is why the original Four Thirds lenses were designed to be tele-centric, with the light from the rear lens pupil coming straight to the sensor.

Since the Four Thirds system was conceived, sensors have evolved to handle a greater angle, and hence, Micro Four Thirds lenses are no longer entirely tele-centric.

But the pinhole still gives far too steep angles for the sensor to handle, and that is the main reason for the severe vignetting.

Also, we can see that the colour is wrong in outside the centre of the frame. The colour becomes magenta in the corners, indicating that the green is missing. Hence, it is reasonable to think that the sensor green photosites handle steep angles the worst.

A pinhole with a more narrow field of view does not have this problem to the same degree. If the focal length is longer, there is a more similar distance travelled for the light hitting the centre and the corners of the sensor, and what's more, the angle also becomes more similar. But a pinhole tele lens is not as interesting, in my opinion. So I like the choice done by Wanderlust here, to make the pinhole as wide as possible.

By the way, this is the same challenge that Leica have had when designing their full frame digital camera. Most Leica lenses are far from tele-centric, especially wide angle lenses. This works well for film, which handles light coming from steep angles well. Digital sensors, on the other hand, do not. Hence, it was not until quite late that they did launch a full frame digital camera, the Leica M9. And the sensor was made especially to handle the Leica lenses, with microlenses on top of each photosite offset outside the centre of sensor, to better handle the steep angles.

Conclusion


The Wanderlust Pinwide is an interesting pinhole. With the recessed design, it achieves an impressive wide angle effect. On the other hand, the wide angle effect is the reason for one of the disadvantages: The very strong vignetting. There is simply a much larger distance from the pinhole to the sensor corner than the sensor centre, giving this very pronounced vignetting effect.

It is fairly inexpensive, small and light. The tin case takes about the same space as the Lumix G 20mm f/1.7 lens:



But keep in mind that if you bring the pinhole, it is likely that you also want to bring an extra rear lens cap. This is to put on the lens that you remove from the camera when mounting the pinhole. You cannot mount a rear lens cap to the pinhole, due to the recessed design.

So why buy this pinhole? If you spend a bit more money, you can get the Olympus 15mm f/8mm compact lens. It is a proper lens, with some focus mechanism. It gives you significantly better images, and is just as compact. On the other hand, it doesn't have the same wide angle effect. And: The focal length is most likely already covered by the kit zoom lens that most people have. So why get the 15mm lens? Perhaps for the novelty effect.

And the novelty effect is probably the main reason for getting a pinhole lens, as well.



3 comments:

  1. I hadn't heard of this pinhole lens, but I got a 15mm f8 with my OM D as a promotion. It immediately felt right as a prime lens and easy to work with making the camera truly pocketable. Then the penny dropped - the Lumix 14mm f2.5 - is not much bigger and is a 'real lens' with a decent maximum aperture. Picked up new one for a reasonable price and wow. A walk around 28mm that is reasonably fast in my ideal focal length. I started out in the 60s with a Nikon and always wanted a 28, but went for the 20mm instead. I've put the 15mm onto my semi retired EPL 1 and use it as a point and shoot.

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    Replies
    1. Yes, I think one should not mistake the Olympus 15mm f/8 lens cap with a real lens. It is just a novelty combining a compact lens with "interesting" lens distortions. It is a toy lens.

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  2. I haven't used the 15mm on anything that would show up distortions - have to give that a try. I drove right from the camera store where I picked it up to the bush to see how it would go on the Australian landscape and was immediately impressed with the reasonable sharpness and the capacity for keeping near and far objects in focus @f8. Then I reread your review of the 14mm Panasonic pancake and it was straight to ebay. Your own fondness for the 14mm is not hard to understand! Thanks again for a really helpful blog.

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