SLR camera lens help?

I'm getting a lens filter kit for my boyfriend and all I know is he has a Nikon D5100 camera with a 55mm lens.

Now, can I get any 55 mm lens? Like could a sony one fit on this as long as it's 55mm? Or do I have to get a Nikon brand one?
>>> SLR camera lens help?

Camera settings on Nikon D90?

I want to know what the settings should be on my Nikon D90 to capture my kids wrapped around Christmas lights, or my kids in front of the Christmas tree.
>>> Camera settings on Nikon D90?

How are Nikon cameras distributed?

I have a project on my camera and i need to know how they are distributed from the factories, in a very detailed way.i have a nikon d3100
>>> How are Nikon cameras distributed?

Best valued Nikon lens for sports photography?

Im currently in high school and Im going to begin doing sports photography with a Nikon D7000.Im going to be shooting both indoor sports and outdoor sports.Id like to get something with a large zoom capacity, but could also go wide angle. I dont care if its Tamron or Sigma or some other brand as long as its a good lens.My budget is under $900. Thanks!
>>> Best valued Nikon lens for sports photography?

Im 14 years of age and I dont know what I want for christmas.help!

I already have on my list, eye shadow holder, an nikon camera, and money ( for clothes, makeup, ect.)
>>> Im 14 years of age and I dont know what I want for christmas.help!

Buying a camera now or straight after christmas?

OK i have decided to ask for a NIKON D3200 for christmas which retails for £401 from amazon. Should i get her to buy this now or wait till directly after christmas when there could possibly be sales on. This is currently £424 from PCWorld. Would it go down on boxing day? If so by how much? So should i order from amazon or buy it from pcworld after xmas?
>>> Buying a camera now or straight after christmas?

Tamron 28-75 2.8 vs sigma 24-70 2.8?

The 28-70 is a bit cheaper, but whats the difference, I have heard great things about both
The Nikon 24-70 is out of my range.
Thanks
>>> Tamron 28-75 2.8 vs sigma 24-70 2.8?

Will any tripod fit my Nikon D3100 DSLR?

I have a Nikon D3100 and i'm looking for a sturdy but fluid tripod that can also support the camera's weight, do you recommend any?
>>> Will any tripod fit my Nikon D3100 DSLR?

Small slr nikon camera?

Does/has nikon made a camera body that is an slr but doesn't use film (saves photos onto a memory card)? i am looking into buying a smaller, more portable slr but i take a lot of junk pictures and it would be so wasteful if i had to use film.

thank you!
Added (1). Hmm, i have a d3100 right now, but i was wondering if they made anything smaller? maybe around the size of an MILC but with lesser functions (aka less expensive, i am an amateur so i would prefer convenience over function).do you know if there are any older models like that?
thanks!
>>> Small slr nikon camera?

MacBook Air for photography?

I'm desperate for a new laptop that will keep up with my photo's.
The camera I use is a Nikon D3100.
I'm looking at the MacBook Air, 13inch, 128GB.

I will not be editing videos, just photographs, on Apperture, and maybe photoshop elements.

Would this be suitable? If not, what laptop would you suggest?
>>> MacBook Air for photography?