Photographing macro is technically very different to shooting wider angles. Here is a post explaining how I think when shooting macro. The article is about shooting macro under water, but in theory it will be much the same on land.
First of all the area you shoot is very small and you have control over most of the elements in the scene. One exception is if you shoot creatures, they have their own plan. In some cases they can be predictable and in other totally strange things can happen but that is half the fun. Having control over the rest means you can prepare a lot for the shoot before knowing what you will find. It is like setting up a small portable studio.
Selecting a lens
There is a lot of lenses to choose from but some are more common and for a reason. I guess the 60mm and the 100/105mm are the most popular shooting underwater. I made an easy graph to help you understand the difference between them. You see clearly that with the 60 lens you are closer to the object than the 100 with the same size focus area. The difference is inches but there is a some factors to consider. With the 60 you are closer and therefore have less water between the camera and the object. This gives you fewer particles and somewhat more sharp and clear pictures especially shooting at dive sites with less visibility. When you dive sites that are low visibility this is probably the only chance you have to come out of the water with decent shots. But, you sometimes want to shoot small elusive creatures that are very hard to get close to. You approach with giant camera, flashes, lights, divegear and noisy bubbles and that whole package is quite scary if you are a 2 gram shrimp. Often you do not even get the chance to focus before it is gone.
In a lot of cases the extra distance you get with a 100mm lens is your chance to get real close and the time you need to shoot before it disappear. So for me, the 100 lens is the preferred choice when shooting high visibility dive sites.
Flashes and lights
Then you have to set up your lights. Yes!, you have to bring lights and flashes. Our sun only provide light directly from above and even in the clearest water you start loosing colors in just a few feet of water. So if you photograph under water you bring lights.
The usual setup is to bring two flashes connected with cable and optional one third flash running on slave mode. In addition you need to bring a quite wide lead light that gives enough light to have the camera focusing and to see what you are doing. The modern UV Flashes usually have this built in.
The third you typically want to use for fill in background to add more depth or to do silouetts. If you go for three lights you need help from your buddy. Just plan this before the dive. Show him/her what you want to achive and agree on some easy hand signals about directing the light source. There is one more trick I often use and that is to bring some sort of reflector. You get wonderful small mirrors made of plastic that are white on the other side i find the perfect size is about the same as a birthday card. This mirror you mount on a flexible arm and use to fill up the shadow areas just as you would in a studio.
Now the fun starts. How you place your lights and adjust them is off course up to you but there are some basic tricks. When the light source is far away from the object the shadows get sharp, and soft if you move them close.
Think of your lights as a hierarchy ranging from 1-3, if you bring three. One should be dominant and the second less dominant both in placement and intensity. The third light even less. Place your main light really close to your lens and pointing towards the object. This light you can alter to your liking. You can soften it by just taping a transparent plastic bag in front. Experiment with different types of transparency bags. You find lots of different bags in grocery stores. If you want diffusers you can contact a plastic supplier they sell you sheets of plastic in all different levels of transparency. Experiment also with masking the front end of your flash. Use opaque plastic material. Cut shapes and mount them in front of the flashes. This makes the light hit the object in stripes or other diffuse patterns. In some cases this makes a very nice dramatic effect. Think of your little portable system as a small studio. And you are so lucky now living in this age. You don’t have to develop film! You get the result right away and can experiment live. Change the backlight, fill or front. Try tilting, masking, bouncing, etc. Have fun.
Then you set up your camera. I know it is different strategies on this but here is how I do it and why. I put my camera in “manual” mode, because I want to set all the parameters and have no need for any automatic or preset functions. Then i set the shutter speed to quite fast, usually 1/250. I want the movement both my own and the creature I shoot to be sharp and need the speed. Then I set the film speed to the lowest possible. I usually set it to ISO 100 but also have the opportunity to set 50. This setting will give you the least amount of graining in your image. Then the last thing you set is the aperture. I set this usually to 32 that is the max. This is to get the maximum depth of field in your image. Sometimes I compromise a little and go down to 22 or even 16 to make more use of the light. At 32 you get very hard contrast images if you do not have enough light sources you can play with the aperture.
Hope this gave you an understanding of how I set up my gear. When I dive with this setup I feel I can do just about what ever I want within a small area. I usually play a lot with placing lights and adjusting the intensity etc. to compose the image. Every scene you create have some varieties you want to take advantage of.
Then the last thing you need to know when photographing macro is this: When you set this up and jump into the water. Check that nothing leaks and sinks down to the reef. Then the giant whale shark shows up with its baby along the side. It passes you very slow and close and you have no chance of getting a shot. That is just life.