Thursday, 19 April 2012

The megapixel race is back

There is no doubt that Canon and Nikon have been competing fiercely in the SLR and DSLR camera segments for many decades. Looking at the most recent decade, Canon made a head start by introducing the affordable models 300D and 350D back in the early 2000's. Then, Nikon launched the D40, which combined a small form factor, low megapixel count and a good high ISO capability. This made Nikon once again the number one in some markets.

Later, Canon replied with the feature laden and moderately priced 450D, 500D, 550D, which all topped the Japanese sales charts during the years 2008-2010.

With the most recent D3x00 series of cameras, Nikon is again a good seller, especially in Japan. Their most recent announcement, the D3200, packs a massive 24 megapixel resolution. It is worth noting that this is more than Canon have ever had in any DSLR camera.

This development can be illustrated graphically like this:


With the blue line being the Canon entry level models (300D, 350D, 400D, 450D, 500D and 550D), and the red line being the Nikon models D50, D40, D40X, D60, D3000, D3100 and D3200.

It seems that while Nikon has traditionally believed in a moderate megapixel count, they have decided to trump Canon at the megapixel race, believing that the market now wants a high number of megapixels. And perhaps they are right. After all, the recently announced Nikon D800 has generated a lot of interest, with the staggering 36MP sensor.

On the other hand, Nikon has continued their moderate philosophy with the mirrorless Nikon 1 line, with both introduction models only having 10MP. This could be to protect their DSLR line from cannibalization.

The 24MP D3200 model might be a reaction to Sony's mirrorless NEX-7 model, also sporting 24MP. In fact, their sensors might very well be related.

So, what does this mean for the Micro Four Thirds cameras? I'd say it makes it even more probable that future models will sport more megapixels. When the GH2 was launched, it upped the megapixel count of the GH1 from 12MP to 16MP. In an interview, some Panasonic professionals said that this was done largely for market reasons, not because it benefitted the images significantly.

With the competition now re-entering the megapixel race, I think it is more probable that the GH3 will come with a higher megapixel count than the GH2.

It seems that to get a camera with a moderate amount of megapixels, you must look to Nikon's professional D4 model, sporting only 16MP on a full frame sensor.

Sunday, 15 April 2012

Defished fisheye compared with ultra-wide

I have previously looked at how to defish the images from the Samyang 7.5mm f/3.5 fisheye lens. Even with a generic fisheye lens profile, it is easy to defish the output images so that they appear rectilinear. But my example image does not show how wide the output image really is. To illustrate that, I will present the same image taken with an ultra-wide lens.

But first, let's compare the specs:


Lens

Focal length

Diagonal field of view
Samyang 7.5mm f/3.5 fisheye lens7.5mm180°
Lumix G 7-14mm f/47mm114°
Olympus 9-18mm f/4-5.69mm100°

As is apparent from this table, the fisheye lens has a vastly wider diagonal field of view. However, we also know that the fisheye lens has a more compresses field of view the further we get from the centre. Hence, not all of the 180° diagonal field of view can be used when defishing the image.

This can be illustrated by looking at the defishing process. Here are the same images taken with the Samyang 7.5mm fisheye lens, defished, and taken with the Olympus 9-18mm lens at 9mm:



Original fisheye image
Defished, not cropped


Defished and cropped
Olympus 9-18mm @ 9mm

The defishing process was done with Hugin, and is described in this article. In this example, I used the "orthographic" lens type, rather than the "fisheye" lens type.

We clearly see that a lot of the fisheye corner image is lost in the transformation process.

Letting the Hugin program calculate the optimal resolution yields a defished and cropped image of 11385 times 4750 pixels.  This reflects the true resolution only in the centre of the image, while the resolution is less the further from the centre one gets.

Hence, to compare the wideness of the lenses, it is better to look at the horizontal and vertical field of view:


Lens
Focal length
Horizontal field of view
Vertical field of viewDiagonal field of viewAspect ratio
Samyang 7.5mm f/3.5 fisheye lens7.5mm132°86°180°4/3=1.33
Samyang 7.5mm f/3.5 fisheye lens defished7.5mm132°86°135°2.40
Lumix G 7-14mm f/47mm102°85°114°4/3=1.33
Olympus 9-18mm f/4-5.69mm87°71°100°4/3=1.33

When given the diagonal field of view, the horizontal field of view can be calculated as:

2*DEGREES(ATAN(TAN(RADIANS(114/2))*COS(ATAN(3/4))))

with the diagonal field of view being 114° in the example formula above.

From the table, we can see that the fisheye lens loses a lot of diagonal field of view when defishing. This is not surprising, since the image must be stretched into the corners. The image also loses resolution in the corners due to this.

The Panasonic Lumix G 7-14mm f/4 is a very wide lens, and it is also very expensive. But using a fisheye lens, we get a resulting defished image which is still far wider in terms of horizontal field of view, and only marginally wider horizontally. This can be further illustrated by showing what crops I would have gotten if I used the two ultra wide zooms to take the same picture:


However, the flip side of the coin is of course that due to stretching out the image into the corners, the resolution suffers. Here is a 100% crop from both the original and defished images from the corner:


If I had used the Lumix G 7-14mm lens at 7mm, this would have been in the extreme corner of the image frame. Now, I don't have this lens, but I think it would have achieved somewhat better sharpness than the defished example above.

Conclusion

When defishing images from the Samyang 7.5mm f/3.5 fisheye lens, the resulting image becomes much wider than that from the widest rectilinear lens for the Micro Four Thirds system, the Lumix G 7-14mm f/4. However, you also lose some resolution in the corners.

Note: After having published this article, I have take actual comparison images using the Lumix G 7-14mm f/4 ultra wide lens and the Samyang 7.5mm f/3.5 fisheye lens.