Here is a simple lens torch I made to illuminate subjects on my 60mm macro lens, as I found I often blocked out the light when closing in on the subject.
You require a small soldering iron and to be able to solder.
To make it you require enough 3.0 volt LEDs to cover the edge,mine has about 60, buying them in a bulk pack they are very cheep, I used ultra bright white LEDs , you have a little white balance to adjust in the shots but they are normally very good.
Stiff plastic, card could be used but plastic is more durable.
I recommend you experiment to get the correct fit and length of tube, make it as long as you can, when looking through the viewfinder it should not be in view
Copper wire, I used a single strand of mains twin and earth 1.5mm
A battery holder.
Method
1: cut a strip of the plastic about 2 inches wide, depending on your lens it may require to be wider but you can check later. Wrap the plastic around the end of your lens like a lens hood. Cut it length so that its just a nice fit without falling of, you can use a bit of tape to hold it in a tube shape while you get it right.
2: put batteries in your holder and find out which way round the LEDs work, the only work connected one way. Note down the connection.
3: Using a bit of single strand copper wire make one ring that fits inside the plastic tube, and one that fits round the outside of the plastic tube, solder the ends of the rings, they can be a slightly loose fit but assembly will be easier if they are good.
4: Fit the battery box, mine had 2 wires under it, make small hole for them to go through, bend one wire up towards the front the other towards the back. Fit your copper rings to the inside and outside connecting one to each end of the batteries, install the batteries for a few minutes to test an LED, slip it over the end so that one wire goes each side of the plastic and it should illuminate, now all LEDs must be mounted in the same manner, either long wire inside or outside depending on how the first one worked.
5:remove the batteries, start fitting the LEDs side by side, soldering each one as you go, trying to keep them all pointing straight forward, clipping the excess wire off as you procede.
Your done, simply install the batteries and they will all light up, the batteries will last a long time, slip it on the front of your lens and off you go.
I hope the images help illustrate the idea and demonstrate the light pattern, its nice full flood that gets into all the wee spaces reusing shadow.
Have fun, Bob