First the simple answer
I would not recommend the Olympus flash set. Besides this flash being over priced the flashes need to be as close to the front element of the lens as possible. If you are photographing a posterior tooth the cheeks retractors and anterior teeth will block the light with this unit. Canon have a similar unit and for an extra charge you can get a bracket that mounts the flash closer to the lens, but it’s not worth it in my opinion.
Do not consider a LED flash as I have not seen one that has a high enough light out put for dental photography. With the traditional flash units you can use f32 which gives you the depth of field that you will require.
As Matt has mentioned I have had many years of teaching and doing dental photography. When I started the best set up for photographs was the single flash mounted on a ring at the front of the lens. It gave depth and modelling of the teeth. The problem was that at some point you would forget to move the flash to the correct side of the mouth. It was also fiddle to be moving it around all the time so I started to recommend a ring light. If I really wanted to show texture on a tooth surface I would just reduce the output of one side of the ring flash.
The problem today is what flash to buy. The market for ring flashes has shrunk to all most nothing. If I was looking for a flash I would ask around at study clubs and conferences to see who has a dental ring light stuck in a counter not being used. Something like a Sigma EM-140 or similar. Apparently they are still available for around $375 Canadian, but I would look around for a used flash. Many of these units have been sold to dentists that are no longer using them. You just have to make sure you have the right adapter for the lens or can order a step down ring. There are also other flash units that sell for about $145 but I don’t have any experience with them(Yongnuo and Godox).
Here are some of things to consider.
- It needs to be a true flash not an LED.
- The flash needs to be as close to the front element of the lens as possible.
- The flash should be set to manual. The reason for this is that TTL metering is not set up for dental photography, it is set for people, groups or average type pictures. The TTL is fooled by dental photography. I normally only used two f stops, one for close up(f32) and one for portraits(F8)
- Retractors, retractors, retractors. Over the many years I took dental pictures there has only maybe a dozen times I have not used two retractors and they where under unusual conditions.
I hope this help you make a decision.
Bruce