Monday, 27 February 2012

Samyang 7.5mm f/3.5 fisheye lens review

The Samyang 7.5mm f/3.5 fisheye lens, also marketed as Rokinon and Bower, is special in that it is one of the first third party lens designs made specially for Micro Four Thirds. Some other manual focus lenses for Micro Four Thirds are older designs with a new mount.

The Samyang fisheye lens is an alternative to the native Panasonic Lumix G 8mm f/3.5 fisheye lens, so it makes sense to compare them. Here they are, with lens caps:


They have different type caps. The Samyang, on the left, has a cap held in place with clips, operated by pressing the side tabs. The Lumix's cap is held in place with friction only. I prefer the latter, since the Samyang cap must be inserted correctly rotated, which is somewhat more awkward.

Sunday, 26 February 2012

Reverser ring for macro

There are many ways to achieve macro possibilities. The simplest is of course to buy a dedicated macro lens, like the Leica-Lumix 45mm f/2.8 1:1 macro. This lens does macro very good, and is easy and fun to use. The only negative side is that it is rather expensive, probably in part because of the premium Leica branding.

Another way is to get a cheap legacy lens, and some macro extension rings. If the lens has a mechanical aperture ring and focus ring, then it is quite easy to use with macro. Of course, you must control the focus and aperture manually on the ring, and there is no EXIF information to the camera. For even better control, you could buy some macro bellows, for stepless extension distance.

A third method would be to buy a macro lens to put into the filter threads of the lens. There are a number of third party macro filters to buy, and Panasonic has even launched their own, which can be used with the Lumix G 14mm f/2.5 pancake, and the Lumix G X PZ 14-42mm powerzoom pancake kit lens. I have not tried any of these.

A fourth method is to buy a macro reverser ring. A reverser ring is quite simply an attachment which allows mounting a lens reversed on the camera. I have tried one such ring, easily available on various auction sites for around US$10. It is a simple thing. On one side, it has a Micro Four Thirds lens mount. The red dot makes mounting easy:


On the other side, it has a 52mm lens thread:


The 52mm threads is a good choice, since it fits a number of lenses.



Here is the adapter mounted to the Panasonic GH2. It will of course fit any Micro Four Thirds camera.


Mounting a Nikkor 24mm f/2 AIS lens

I have got an old, rather banged up Nikkor 24mm f/2 AIS lens. It has got a 52mm front lens thread, and hence fits well onto the adapter. Here is a video showing how to mount it:



After mounting the lens, you can still control the aperture with the mechanical aperture ring, which is a good thing. When used like this, the lens has a very short focus distance, good for macro, but it also has a very thin depth of focus. Hence, you will normally want to stop down the aperture to at least f/5.6 to get more in focus. Normally, you will focus at f/2 (for the best focus accuracy), and stop down to f/5.6 (or more) before taking the picture.

I took this test picture of a ruler (in millimeter) to test the magnification:


The test picture shows that the magnification is 17.3:13 (with 17.3mm being the horizontal width of the Four Thirds sensor, and 13mm being the width of the object depicted). This corresponds to 1:0.75 magnification, also written as 1.33x. This is slightly more magnification than what is possible with the Leica-Lumix 45mm f/2.8 1:1 macro. On the other hand, no focus is possible at all with this solution. You can only take pictures at 1.33x magnification.

Mounting a Lumix G 14-42mm f/3.5-5.6 kit zoom lens

The Lumix G 14-42mm kit zoom lens also has a 52mm front thread. Hence, you can mount it to this adapter. Here is a video showing how to mount it:



Using this is quite different from the manual Nikkor 24mm f/2. First of all, the negative sides: The Lumix G 14-42mm lens does not have an aperture ring. Hence, you cannot easily adjust the aperture. This makes macro use difficult, since you will normally need to stop down the aperture for more depth of focus (DOF).

The positive side is that you can use the zoom ring for changing the magnification rate. The focus distance is also changed at the same time, but at this enlargement, it makes more sense to use the word "magnification" than "focus". At 14mm, you get the maximum magnification, and the minimum at 42mm. Let's take a look at this.

@14mm

Again, I photograph the ruler to find the magnification:


The ruler shows 7mm, hence the magnification is 1:0.4, or 2.5x:


The working distance is 2cm, which is quite short. I try to photograph a LEGO figure here, and as you can see, the subject is almost touching the rear end of the lens:


Here is the result, at 14mm f/3.5. I focused on the eye, but due to the very thin DOF, only one eye is in focus:


@42mm

Here is the photo of the ruler, showing a 1:0.87 or 1.15x magnification ratio:


At 42mm, the working distance is 4cm:


And here is the result, at 42mm f/5.6:


Example image

This is a picture a tooth brush, and was taken at 14mm, f/14. I could probably have stopped down the lens even more for more depth of focus.


Also note the dots throughout the image. They are probably dust particles on the sensor, and come into focus when using extremely small apertures, like in this case. Otherwise, they don't cause any negative effects.

Mounting a Lumix G 45-200mm f/4-5.6 tele zoom lens

The Lumix G 45-200mm tele zoom lens has a 52mm front lens filter thread, and hence mounts directly to the adapter.

However, when mounted reversed, it focuses near infinity at 45mm, and nowhere at longer focal lengths. Hence, it is useless for reverse macro use.

Mounting other lenses

Both these lenses have a front thread of 52mm, making them easy to mount. But let's say you have the Lumix G 20mm f/1.7, with a front thread of 46mm. What to do?

You can get a step up ring. Mount a 46mm-52mm step up ring to the front of the lens, and then mount the front of the step up ring to the adapter. A step up ring is very cheap to get on various auction sites.

Take care that mounting a wide attachment to the Lumix G 20mm f/1.7 lens can cause the focus mechanism to jam. So don't power the lens with the step up ring attached.

Conclusion

Using the reverser ring adapter, the Lumix G 14-42mm lens can be mounted reversed, and the zoom ring can be used for focusing. The magnification rate is 1.15x-2.5x, which is not a very large range. For comparison, Canon has a specialized macro lens called Canon 65mm MP-E, with a macro focus range of 1x-5x.

Changing the aperture is not very easy with this lens, but it is needed. You cannot photograph macro images using the lens wide open, since the DOF is too thin. To stop down the lens, you can mount it to a camera, and start a long exposure at f/8, 4s, for example. As the camera is exposing, remove the lens. That way, the lens is stopped down to f/8 when you remove it. Do this at your own risk.

This is a cheap way to achieve macro possibilities with the kit lens, a lens that quite many users probably have already. But is is not very easy to use. First of all, the working distance is very short, so you cannot photograph live insects. They will be scared off.

Second, changing the aperture is awkward. And third, the macro range is limited, at 1.15x to 2.5x.

But if you want to experiment with macro images of static objects, than this is a very inexpensive way to do so.


Thursday, 23 February 2012

Fisheye lenses, different projections?

The Samyang 7.5mm f/3.5 fisheye lens is an interesting addition to the Micro Four Thirds lineup. While most third party Micro Four Thirds lenses so far have been existing manual lens designs given a new mount, this lens is designed for the Micro Four Thirds format from ground up.

How can I tell? A full frame fisheye lens has 180° diagonal field of view. Hence, the lens must match the sensor size exactly. If the lens was designed for APS-C, a larger format, then the corners would not correspond to 180° angle of view. A fisheye lens which does not project to 180° in the corners is pretty much useless. Then it is just a wide angle lens with a lot of geometric distortion.


Compared with the existing Lumix G 8mm f/3.5 fisheye lens, the Samyang lens is a much more traditional design, with a manual focus ring and aperture ring.




Some say the Samyang lens features a different projection type, the Stereographic projection. This is supposed to be less distorted than the Spherical projection traditionally associated with fisheye lenses. Let's look into how their projections differ. Here is a picture taken with both lenses, and also using the Olympus Zuiko Digital 9-18mm Four Thirds wide angle zoom at 9mm:



Samyang 7.5mm
Lumix G 8mm
Olympus 9-18mm @ 9mm
By superimposing both the fisheye images in one image, and doing edge detection, we can see how their projections compare:
And let's look at another example:



Samyang 7.5mm
Lumix G 8mm
Olympus 9-18mm @ 9mm
Superimposing the two gives:

(Click for larger images.)

Conclusion

So, what is the conclusion of all this? First of all, from the second example, we observe that both lenses have pretty much the same diagonal field of view. This experiment does not verify that the diagonal field of view is exactly 180°, as it should be, but at least both lenses have around the same maximum diagonal angle. To be more precise, the Samyang lens appears to render a slightly wider diagonal field of view. This might be due to the shorter focal length, 7.5mm versus 8mm.

Regarding the distortion, we can see that the Samyang lens renders objects which are inside the border of the image a little bit smaller. This means that it distorts the images somewhat less. So the rumor is true: The Samyang lens does give less "fisheye distortion".

But surely, the differences are pretty marginal. You're not likely to notice much difference, unless comparing head to head, as I do in this article. So if you're looking at the Samyang 7.5mm lens to avoid the fisheye distortion, you are going to be disappointed.

One thing to note is that if you plan to convert to rectilinear images in post processing, the Samyang lens has the potential for giving you the widest possible rectilinear images of the two fisheye lenses. This process is called defishing, and you can read about the topic here. It is probably not true that the Samyang lens features stereographic projection. It still has fisheye projection, but with slightly less distortion than the Lumix G 8mm f/3.5 fisheye lens.

Saturday, 11 February 2012

What can we expect from the GH3?

The Panasonic GH series has comprised the premium camera models for Micro Four Thirds. The Panasonic GH1 and GH2 have had the best video quality among mirrorless cameras at the same time, and they are also considered to have the best sensor for photos. They are not intended to be volume models, but rather to sell at a premium price for those who want the best camera.


Panasonic GH1 (left) and GH2 (right)

The Panasonic GH2 was announced in September 2010. I bought it the very first day it was available in my market, which was in December 2010. Hence, this camera is starting to get old. In this article, I would like to speculate a bit about what we can expect from the GH3.

Wednesday, 8 February 2012

Canon G1X, sensor size the same as GH1

The Canon PowerShot G1 X was announced recently, and took a lot of people by surprise. While Nikon have launched their mirrorless, large sensor cameras in the Nikon 1 series, not many rumors existed about Canons mirrorless competitor. It turns out that their answer was a large sensor compact camera, without interchangeable lenses.

The sensor size was also a bit surprising: Larger than Four Thirds, but smaller than APS-C. This sounds like an odd sensor format. But is the sensor format really that odd? Let's try to have a closer look at it.

We know that the Canon G1X sensor is reported to be 18.7mm x 14mm. The Four Thirds sensor size, on the other hand, is somewhat smaller at 17.3mm x 13mm.

But the Panasonic GH1 and GH2 have employed oversized Four Thirds sensors. This design choice was implemented to get the same diagonal field of view in the 16:9 and 4:3 modes, utilizing the full image circle also for video. The Panasonic GH1 has 4000x3000 pixels in 4:3 mode, and is 4352 pixels wide in 16:9 mode. This means that the width of the sensor must be 17.3mm x 4352 / 4000 = 18.8mm. Which is rather close to the reported width of the Canon G1X sensor.  The differences in reported size might be due to rounding off differently.

What about the vertical size? The GH1 sensor is reported to have 14 megapixels in total, which corresponds to a vertical resolution of 3217 pixels. Hence, the vertical size must be 13mm x 3217 / 3000 = 13.9mm. Again this is very close to the reported height of the Canon G1X sensor.

And the total resolution of the Canon sensor? 4352x3264. Again, this is very close to the GH1 horizontal resolution times the estimated vertical resolution based on the total 14 megapixel resolution. This can be illustrated like this:


Both sensors are of the CMOS type, and both have a base ISO of 100.

My conclusion is that the specifications of the Canon PowerShot G1 X sensor are remarkably similar to the Panasonic GH1 sensor. This doesn't mean that they are identical, though. But given that there are not that many sensor manufacturers out there, and certainly not for the Four Thirds sensor size, I would say this is a good indication that Panasonic do in fact produce the sensors for the Canons G1X. As you understand, this is of course purely speculation.

A fundamental difference between the two cameras is that the Panasonic GH1 only gives you a maximum resolution of 12 megapixels for one single exposure, with the option of changing the aspect ratio with the same image circle. 

The Canon G1X, on the other hand, gives the full sensor resolution output for a single exposure.  However, when using video (16:9 aspect ratio), only a smaller image circle is used, meaning that the effective focal length changes.