Sony Alphas do not use pentaprism or a pentamirror; instead they use an electronic olev view finder and the battery life is almost 40% less than that of the Nikon or Canon.

Sony’s range of lenses is not great either, not as much as Nikon or Canon.

The differences you may find with the Sony is that it is catered towards the firmware and menu set up of the Sony NEX range by implementing a sort of point and shoot system with a very intuitive menu navigation to allow any one with no camera experience or the foundations of photography to sift through with ease.

Rather than Nikon or Canon which require you to take a course or at least learn before trying to take any shots.

For my choices at the time, I was going to buy a Canon EOS 7D with an L series 24-70mm F/2.8 lens; but I didn’t because I knew many people had one of these and the camera it self was getting on a bit in terms of its release onto the market. And since at the time, I wanted something different and I also didn’t want to follow NIkon or Canon as another reason. Which is why I went with Sony’s SLT-A77.

You’ll find that when you look at these cameras on any computer website, it’ll give you specifications and its various bells and whistles; but you need to go to a camera store and instead of just looking; you need to put it into your hand and based on your own experiences will determine whether the camera is right for you. So how it reacts in your hands, whether it is comfortable and so forth.

The Nikon D3100 and the D5100 are newer models that replaces the D3000 and the D5000 series; but I have found them to be smaller than usual, especially the D3100; it looks more like a toy in my hands being so small. The price is fairly well balanced amongst the others.

With my opinion for the Sony range, I think you should avoid it unless you’re going to buying something higher than a SLT-A35. For me, I’ve had to go and buy an extra 2x batteries plus a Sony Grip and a flash unit.

The SLT-A77 has a 12 fps shooting rate; if you are intending on shooting nature, you will need something that has at least higher than 6 fps and a reasonable lens. At present I only have a Tamron 18-270mm lens and I have been looking at a Sigma 150 to 500mm lens as I am also into similar shooting as yours with landscape and portraits though not so much with nature and wildlife.
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Good luck, and if you have any questions, I recommend digital-photography-school.com.
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Photographer shooting with Nikon D5100

As far as the camera itself goes…The "BEST" camera is the one that feels natural in your hands with controls/menu system that you can operate instinctively. If the camera feels "unnatural" to you and you have a hard time finding/operating the controls, you will miss shots because you are fumbling around with it.

Both Canon and Nikon make nice cameras. The best thing to do is visit an actual camera shop (not bestbuy/walmart) and try the different models within your budget to see which feels the best to you. I bought a Canon for its ergonomics/feel/menu and control layout and a fellow photog chose Nikon for the same reason….it is about personal preference.

The one thing to remember is to budget in extra money to cover an extra battery, memory cards, camera case, a USB memory card reader, and taxes (these can add another $200-$250 to the entry level camera price).

Also, most camera shops offer free beginner camera/photography classes (and free prints) when you buy a camera there.
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Here is how their sensors compare

http://www.dxomark.com/index.php/Cameras/Compare-Camera-Sensors/Compare-cameras-side-by-side/(appareil1)/698%7C0/(brand)/Nikon/(appareil2)/692%7C0/(brand2)/Canon
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proFotog

http://www.steves-digicams.com/2008_reviews/panasonic_fz28_pg5.html

It’s an all-in-one 10.1 megapixel digital camera which includes (i) built-in image stabilization; (ii) HD720 quality video [Quicktime] which permits zooming while videoing skateboarding, action sports; (iii) a 18x zoom [27 - 486 mm (35mm equiv.)] "Leica" lense for nature and concert photography; (iv) up to 0.39 inch macro option; (v) up to 6400 ASA; (vi) takes up to 380 pictures per 120 min. battery charge; (vii) has a "burst speed" of 13 fps; and sells new for $464 at amazon.com. in the U.S.

Here’s an actual handheld picture of the moon:

http://g-ecx.images-amazon.com/images/G/01/ciu/bf/1b/a83ac060ada0881604bad110.L.jpg

Good luck!
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http://www.bestbuy.com/site/olspage.jsp?skuId=8721733&st=nikon+d60&lp=5&type=product&cp=1&id=1200703005185
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