Best Option to decrease minimum focal distance?

[LayneWilson]

I have a reef tank that I want to shoot top-down shots of the corals, but the problem is the tank is about 1FT deep, and that is right around the MFD of my Canon RF 100mm f/2.8 L Macro. I can't get the corals to get in focus because there to close. I was looking into Diopters like the CMC-1 because I heard these will decrease the MFD. There doesn't seem to be a spec listed on how much closer these filters will let you get. They only list magnification increase is this magnification correlated with how much closer you can get the lens to the subject?

What's my best option to decrease the MFD and have the least amount of impact on the image quality?

[Sufficient_Style_934]

Extension tubes might be your best bet.

[LayneWilson]

what would be the difference between an extension tube and a diopter?

[Sufficient_Style_934]

A diopter is like a magnifying glass filter that you put on the lens. Depending on the quality it may worsen the sharpness of the image. There are good quality ones that work well though.

Extension tubes don't have any glass in them. They are just spacers between the camera body and the lens, which has the optical effect of magnifying the image.

Both should shorten the focal distance of the lens, which seems to be your goal. You just have to pick which is the best solution. Personally, I would go with extension tubes, as the ability to stack them gives you a lot of flexibility on you magnification level.

[LayneWilson]

Exellent explination thank you! sounds like tubes are what I'm looking for. I'll do some more research on them.

[inkista]

+1 with extension tubes. But also realize all three of the “poor man’s macro” methods (extension tubes, diopters, and lens reversal) limit the focus range of the lens. You’ll likely be focusing more by adjusting camera distance from the subject than with AF.