I bought a used Sigma 28mm 1.8?

So yesterday i bought a used Sigma 28mm 1.8, I got it for $150, it has a little tiny scratch in the glass, but its not noticeable in the pictures (i already took a lot of pictures with it and i didn't see anything) The only problem that when i'm on manual focus (i can only use manual focus since i have nikon d3100) its a little hard to focus, its smooth but it kind of gets stuck, but JUST A LITTLE and it makes a scratchy noise when i'm focusing, i noticed that when i bought but i didn't care for it since i felt like i was getting a good deal and i thought i could just get used it to, and i will, but could that scratchy noise be a sign of a bigger problem? Could i fix it? And when i switch it to AF (which i can't use) it doesn't make the scratchy noise.

How to pick a proper UV lens for my DSLR?

I bought my refurbished Nikon D3000 a couple months ago, and I'm looking into UV filters. I have a kit lens (18-55mm) and a lens I bought a few weeks ago (55-300mm), and I hadn't even considered UV filters until now. I finally have money again, haha, so I can afford to get one for my lenses.
Anyway, how do I select a proper filter? Do I even really need one? What company would you recommend? How much should I expect to pay?

Sorry for all the questions, but I need to get this right.

First Photo Job! Senior Pictures

I have been asked by a friend to to her Senior pictures. We're planning on doing it on a beach near Lake Michigan (which has a lot of sand dunes and forests as well) and are planning on taking some even underwater (I have an underwater pocket camera). My main camera is a Nikon D90. (lens are 28-300, 18-105, and if i can borrow it 50mm 1.8) She is planning on bringing at least three changes of outfits. So my question(s) are (being my first time and all)

I have taken college classes (which I'm studying to be a Media Minor) about photography, so I know the basics of ISO, Aperture, Shutter Speed, and Filters, angles and know how to use Photoshop CS5 fairly well, so feel free to give me more advanced advice!

1. What poses should I do (on the beach, forest, sand dunes, underwater)?
2. What (and how) do I get her to do unposed pictures (so it looks less fake, or posed) or should I not do it at all?
3. How should I charge her for them? (per pic, per hour?) Should I send the pictures she wants via email, and how to embed a watermark?
4. What lens should I bring(lens I have are in the description above)?
5. Should I bring my SB-800 flash?
6. What should she do to prepare? (makeup, hair, (she wants some with hair up and hair done) eye shadow, etc)?
7. What are some good Senior photography blogs/websites (not just ordinary one, good ones) that I should look at to get some ideas?
8. Should I do more than just photos, should I do a video as well, and if yes, how should I go about doing the video (or should the video just be for my portfolio)?
9.Is there anything else that I should know, that I might not have asked above?
10. This is my first time with pictures, I'm nervous. Haha

Thanks a ton for all your help. I hope to be able to use this to get me into the world of more professional photography!

Alternatives to the build in microphone on the Nikon D3100 DSLR?

Before you ask, there isn't a jack for an external mic. I've been reading about using something else to record the audio, like a zoom h4n (I think?) but that's way out of my price range.

Any suggestions on cheaper alternatives/any other ways I can use a shotgun microphone for filming would be really appreciated as I audio is really the only thing bringing my quality of films down.

What is the use of the white balance setting for dslr camera?

I'm confuse what is the use of the color to be set in dslr when choosing the white balance. For example i'm selecting the cloudy then i press the o then it will let you choose different colors. Can you explain to me the use og that color? Please help me. I'm just and beginner in this hobby. I'm using an nikon d60 dslr.

New Photography lenses?

I have a Nikon D3000.
I was wondering what lens would be great for taking photos of models? (a crisp, sharp, and clear image)
and macro shots. And would you recommend getting a nikon shutter remote?

Tamron 17-50mm NON VC or vs 17-50mm VC?

I have a Nikon D90 and want to buy a tamron 17-50mm lens. So i'm confused which one should i go for Tamron 17-50mm NON VC or vs 17-50mm VC

Nikon D40 6.1 Mp - Best lenses to have?

Hi, I'm trying to get into photography and just bought a Nikon D40 6.1 mp camera on ebay, but it is body only. I do a lot of macro and landscape shooting. I also like to take a lot of pictures of people and friends at parties and such.

What are the must-have lenses for these type things? I'm trying to find them on the cheaper side though, I'm not trying to buy a $1000 lens or anything. Any help or advice you could give me, would be great, thanks for your help!

I want to sell the body of my Nikon D40. Any suggestions how much it would sell for?

I'm only selling the body and not any of the lenses i have because i want to put the money i get from my nikon towards a better nikon for college. I have had this camera for 3 year this december, so pretty much 2 and a half years now. It is in perfect condition not a scratch or dent or anything on it. Does anybody know how much this would sell for if i tried to sell it? Also, any suggestions of a better Nikon DSLR camera would be perfect.

Is my Nikon D3000 SLR camera compatible with a Nikon Nikkor Q. C 200mm f/4 Lens Non Ai?

I don't understand completely all the details of the shapes of the lens, so before I purchase this lens I want to be sure it is compatible.