Best lens for depth of field shots near macro

Hi! I am a new D3100 owner and am very happy. Got one of the red ones. Reminds me of a sports car. (grin)

I have been exploring my camera for a few weeks and really enjoying the learning curve. I have not had a SLR since an old Pentax I had in the 80's.

I am primarily a model railroader and want to take better pictures of my models. Aside from macro abilities since the models are small, I also need a lot of depth of field. Since I really know very little about cameras, I assume I need a lens that can gather a lot of light, allowing me to use a very small aperture or throw a ton of light at the subject and use very long exposures. Since lighting is not always optimal on the layout, I would prefer a lens that can gather a lot of light.... Any suggestions here?

Also, if I am off base on my understanding, please correct me so I can understand better.

Thanks!

-SeanM

Focus stacking?

you dont say what lens you have but a smaller focal length gives more depth of field as does a smaller aperture so 18mm and F22 might be what you need with extra light ( led lights? ) or correctly positoned flash ie above the lens. Google depth of field calculator and try some figures for the train shots you want to take .

If you have an IPhone there is an app called SinpleDOF that is a pretty good guide to DOF for any lens/camera/aperture combination. Great to play with sitting in your recliner at home BEFORE you go pout into the field.

Google... Hyperfocal distance points !
using this could prove to be very useful to you
its something I use a lot !

Thanks for all the tips! I will look into each of them. I am sure I will eventually find a way to improve my results.