Are pentax and sigma cameras worth getting?

Or would it be a better decision to go with Nikon or Canon?

Thanks for answering

Added (1). Thanks both of ya!

Sigma is a very small camera system, so the number of lenses and accessories are limited

Pentax is an excellent camera system, but again, it is not the system used by pros

Nikon and Canon produce not only over 65% of the dSLR cameras made, but have over 70 current lenses and have more accessories. They are also supported by Adobe and one of the best third party lens makers, Tokina

Here is a link where you can compare the sensor performance of those cameras

http://www.dxomark.com/...or-Ratings

Which you pick will have more to do with your future goals as a photographer

You will notice that the Sigma cameras have not been tested. They are just not mainstream cameras

Deciding on a camera system to invest in depends on what your goals are. If all you plan to do is enjoy photography as a hobby then my suggestion would be the Pentax K-30. The K-30 is the lowest-priced weather-sealed DSLR currently available. This makes it safe to use in the rain or very dusty conditions. However, if video is important to you then look at the Sony SLT a58 which should be available around May 1, 2013 and replaces the a37 and a57 models.

Although the Pentax K-30 has been well received, the future of the company is somewhat shakey due to several mergers/acquisitions over the last few years.

Pentax introduced the first Japanese manufactured 35mm SLR camera in 1952. Canon and Nikon didn't release a 35mm SLR until 1959. Nikon's real claim to fame is that they still use the "F" lens mount introduced in 1959. Pentax didn't introduce a bayonet-style lens mount - the "K" mount - until 1975 but its current DSLR cameras still use this lens mount. Canon introduced their "FD" lens mount in 1971 but abandoned it for the "EF" lens mount when they introduced their first AF 35mm SLR cameras in 1987. Current Canon DSLR cameras still use the "EF" mount. Minolta introduced their first bayonet-style lens mount - the "SR" - in 1959 and used it on their 35mm SLR cameras until the introduction of their Maxxum AF 7000 (the Minolta Maxxum launched the auto focus revolution) when they abandoned the "SR" mount for the "A" mount. When Sony acquired the DSLR technology and manufacturing rights from Konica-Minolta in 2006 they wisely kept the "A" lens mount.

Both Sony and Pentax have a focusing motor in all their DSLR models and they also have their respective versions of Image Stabilization (IS) in their camera bodies. Nikon deletes the in-camera focusing motor in all their DSLR models below the D90/D7000 models. In their D3xxx and D5xxx models only the Nikon AF-S lenses will auto focus. Canon has always had the focusing motor in their lenses. Both Nikon and Canon have their respective versions of IS in some but not all of their lenses. With Sony and Pentax any AF lens ever made in their respective mounts will auto focus and be, in effect, an IS lens.

To further confuse matters, Canon, in order to offer a competitive line of consumer-grade lenses, added the EF-S lenses which are designed solely for their entry-level DSLR models - any model below the 6D. The EF-S lenses can't be used on their full-frame models such as the 6D, 5D and 1D. Only Canon "EF" lenses can be used on their full-frame DSLR models.

Although Nikon offers a line of lenses designated as "DX" for their entry-level DSLR cameras, these lenses can be used on their full-frame (FX) DSLR models - D600, D800, D3X, D4 - since the camera automatically "crops" the full-frame sensor to the same dimensions as the smaller "DX" sensors.

Nikon, Pentax and Sony have the overall best backwards lens compatibility.

If you're a bit of a gambler the Pentax K-30 offers a lot for the cost. If you'd like to differentiate yourself and not be part of the Nikon/Canon herd then the Sony SLT a58 would be a good choice. In my opinion the future for Sony is considerably brighter than it is for Pentax.

A good resource for camera reviews is http://www.imaging-resource.com

Always remember this: "It isn't the camera its the photographer." Give an experienced photographer a Canon T5i, a Sony a58, a Nikon D7000 and a Pentax K-30 all fitted with a 50mm f1.4 prime lens, have them shoot the same scene with all 4 cameras and it will be all but impossible to tell which camera was used for which picture.

I have been using Pentax SLR and DSLR cameras since 1975.

Of the current models I particularly like the weather sealing of the camera body and many of the Pentax lenses. The K5 has excellent dynamic range and very low digital noise, making it good for difficult lighting situations.

http://aviewfinderdarkly.com.au/2013/01/02/pentax-k5-ii-features-new-autofocus-system/