Digital Camera and Photography: Tips, Information and News | Neocamera Blog

To quote Yogi Berra, it ain’t over till it’s over. We are talking about the megapixels race here. Not too long ago, Sony announced the 12 megapixels Cybershot DSC-W200. It has not arrived in stored yet, but based on its small form-factor and headline-catching megapixel count, the Sony W200 will probably be quite popular among people who do not read digital camera reviews.

Not to be left out of the race, Casio just announced the Exilim EX-Z1200 which also features a 12 megapixels sensor combined with a standard 3X optical zoom lens and built-in stabilization. Nearly simultaneously with that announcement, Panasonic announced the Lumix DMC-FX100.

With the FX100, Panasonic is really racing forward. Not only does it boast an incredible 12 megapixels of resolution but also high-ISO modes up to 6400! That is at 3 megapixels. Based on physics, that should basically look like an ISO 1600 image from the 12 megapixels sensor. Not to be pessimistic, but ISO 1600 shots from lower-resolution ultra-compact digital cameras are generally quite noisy – with exception granted to the Fuji Finepix F30 and F31fd. One place where the FX100 did increase resolution in a useful way is with its movie-mode which can capture video at 1280×720 @ 15 FPS. That equivalent to HD television in terms of resolution but slower in terms of frame-rate.

It seems like manufacturers are just racing because it is an easy way to advertise a camera as better and improved. After all, it is simple to see that 12 is more than 10. But how many people who use point-and-shoot digital cameras make the large prints that benefit for so many megapixels? Probably not that many. Most sharing of images is done lately through websites that automatically resize user’s images to less than 1 megapixel! Most prints are still 4″x6″ which also require much less than 12 megapixels.

What would be truly useful is to have a camera that increases sensitivity to light at the expense of resolution. A 3 megapixel camera with a modern sensor design can probably produce high-quality ISO 1600 images and still have enough megapixels for the occasional 8″x10″ print. At this pixel-pitch it would be possible to have a full-color image rather than a bayer-interpolated one using a conventional CCD or CMOS sensor. Such a digital camera would produce higher quality output for the web and common print sizes. A smaller megapixel count has other advantages too like smaller files which means faster writing speeds and a faster continuous drive with greater depth. That would be more useful to most snap-shooters than a noisy 12 megapixels camera. The trouble is that they do not know it yet!

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Perhaps because ultra-wide lenses are harder to manufacture, or simply by lack of popularity compared to longer lenses, there are very few options for ultra-wide angle lenses. Still, even with a handful of choices, someone has to choose.

This time, I wanted an ultra-wide rectilinear (non-fisheye) zoom for the recently-reviewed Pentax K10D. The options readily available are:

• Pentax DA 12-24 F4 – Digital Only – 77mm filter
• Sigma 10-20mm F4-5.6 EX DC – Digital Only – 77mm filter
• Sigma 12-24mm F4.5-5.6 EX DG – Full-Frame – Rear type gelatin filter

These three choices represent possible compromises fro ultra-wide zooms. Depending on your needs, you may consider other options like the Pentax 10-17mm f3.5-4.5 ED (IF) fisheye or a prime lens like the Pentax DA14 F2.8. On all Pentax DSLR cameras, which use a 1.5X focal-length multiplier, the Sigma 10-20 has the widest field-of-view. Although the difference is only 2mm at the wide-end, it represents an angle-of-view that is 20% wider. Compared to the Sigma 10-20 F4-5.6, the Pentax 12-24 F4 is narrower in terms of angle-of-view, but it is one full stop brighter at the telephoto end. Representing, the other end of the spectrum of compromises, the Sigma 12-24 F4.5-5.6 is possibly one of the most ambitious lenses to date. At 12mm, it represents the widest full-frame rectilinear field-of-view currently available. With respect to specifications, the side-effect is that this Sigma lens cannot support front-mounted filters and has a more narrow maximum aperture at the wide-end. Since Pentax has no full-frame DSLR cameras, the Sigma 12-24 is therefore the most limiting choice among these lenses: it neither has the largest field-of-view nor the largest maximum aperture.

Since specifications are not enough to obtain satisfactory results, research was required to choose between those lenses. Here Sigma lenses have an advantage because their availability for multiple lens-mounts means that they have a greater potential user-base and therefore more people write about them. First up, the formal testing at SLR gear is excellent and covers sharpness, vignetting, distortion and chromatic aberrations. They tested the Sigma 10-20. Although they apparently never test any Pentax lenses, they have a test for the Tokina 12-24 F4. Apparently, the optical elements of the Tokina 12-24 were co-designed with Pentax and should perform similarly. Although that is not certain, most user feedback on the Pentax 12-24 is quite similar to the Tokina 12-24.

Based on research, it seems that neither of these three lenses are poor performers. In terms of sharpness, the Pentax 12-24 F4 appears to be the sharpest, specially at the wide end. Second the the Pentax, the Sigma 10-20 is also quite sharp. Samples images posted on the internet from these two lenses show that both of them are acceptably sharp for more uses. A critical inspection of sharpness gives the Pentax 12-24 a clear advantage near the edges at wide apertures. The Sigma 12-24 is relatively sharp but it is less consistent across the frame than the wider Sigma 10-20. That can be seen in the MTF charts posted on Sigma’s website.

There are a number of optical characteristics which are not represented in MTF charts. Distortion, which is normally the biggest problem of wide-angle and ultra-wide-angle lenses, is controlled rather well again by the two digital-only lenses. Based on sharpness and distortion, the Sigma 12-24 somewhat falls behind the two other options. Plus, it does not bring anything in terms of specifications for Pentax DSLR cameras.

The major differences between the other two lenses fall under vignetting and chromatic aberrations. Choosing between them may be a matter of taste. Personally, I despise vignetting much more. It affects all images and gives an artificial tunnel-like look. The same effect is used in movies to show that the viewer is looking through a telescope or a pair of binoculars – a very artificial effect. Chromatic aberrations do not appear natural either but tend to only occur near areas of over-exposure. Obviously, those areas are very local and can be minimized by proper metering.

That being said, the lens which exhibits the most serious vignetting is the Sigma 10-20. According to SLR gear, it can vignette as much as 0.75 EV at its widest aperture. Closing the aperture, this Sigma lens only reaches 0.25 EV at F16. While at 0.25 EV vignetting is not very noticeable, F16 is rather dark and approaches the diffraction limit of the K10D. The Tokina 12-24, on the other hand, drops to 0.25 EV just at F5.6. This is consistent with samples from the Pentax 12-24 too. To the Sigma 10-20’s favor, it does suffer less from chromatic aberrations and flaring. However, those are intermittent problems based on lighting conditions which can be easily minimized, vignetting cannot be avoided.

The bottom line is that I chose the Pentax 12-24 F4 based on its excellent sharpness, low distortion and low vignetting. The consequence is that I use the supplied lens hood often to minimize vignetting. As for chromatic aberrations, the K10D’s metering system does a very good job at minimizing over-exposure which reduces the risk of chromatic aberrations.

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