Diopter on Macro Lens?

I shoot with a Canon 60mm macro lens on a cropped sensor body.  Over the years people have told me to get a diopter, but I don't really understand what they would add to a lens that is already a macro lens.  Is there any benefit in adding a +5 or a +10 to the Canon 60mm macro?  Most of what I read basically says it would turn a normal lens into a macro allowing you to get closer to the subject, but that isn't a problem with the 60mm macro.

Thank you!

Most macro lenses can give you 1x magnification - i.e. its closest focus point, the lens will fill your frame (on a Canon crop sensor) with a 22.4x15mm subject. A diopter will allow you go achieve more magnification, although its usefulness on shorter macro lenses such as 60mm is limited, as that it doesn't add magnification by itself, but rather allows you to focus closer. With your 60mm EF-S lens, Nauticam port chart claims maximum 1.6x magnification with either CMC-2 or SMC-1. If you get a 100mm macro lens, an SMC-1 will get you 2.6x magnification (filling the frame with an 8x5mm subject), and an SMC-2 will get you 4.3x (5x3mm subject), although this latter scenario is extremely difficult to operate - your depth of field is a fraction of a millimeter thick, so you pretty much need a tripod and a completely stationary subject. Basically, you put a diopter on a macro lens when you get into shooting sandgrain-sized critters that you need a magnifying glass to find in the first place.

Thank you very much!  That largely confirmed my gut feeling that it just didn't make sense for the subjects I shoot.  Thank you for saving me some money!

33 minutes ago, peterclark said:

Thank you very much!  That largely confirmed my gut feeling that it just didn't make sense for the subjects I shoot.  Thank you for saving me some money!

yes, that's right you can get more magnification but the working distance is minimal with a 60mm plus diopter.  You working room from front element is 86mm at 1:1.   As mentioned the Nauticam port charts provide the magnification you get when adding a diopter and the working distance when achieving 1.6x magnification is 38mm ~usable but tight for access and lighting and depth of field is fairly minimal as well.  You don't of course need to use maximum magnification - it will allow you focus between 38-120mm (CMC-2)  so you can get a little more magnification than you currently do.  Only worth while if you routinely shoot critters that are say ~10mm or less in size.

I'm going to go a little against the grain here. I shoot a D500 cropped sensor and use both a 60 and 105 for macro. Personally, I find the 60 and a + wet diopter to be really a useful combo. The 60 is great for "close-ups" but I don't find it super useful as a macro lens for smaller things. I keep the diopter in a pocket and pop it on for tighter portraits and macro. At the same time, I can still use the 60 alone for some larger things. It's a great combo if you have commitment issues. 

I also use the diopter on my 105. That gives me "shrimp faces". I'd like to play with a +10 as well, but I suspect it would be a bugger to focus on the 105 with a cropped sensor.

This warbonnet is about "thumb-sized" and was shot with that combo.

Amazing shot Stoo!

Since I don't have an underwater tripod, I always handhold the camera which makes it hard to get very close to the subject and hold it steady.  The ebb and flow just moves it too much.  I'm thinking of trying something like a gorillapod attached to the bottom of the housing to see if that helps me keep it more steady.

What method do you use to manage it that close?

I fiddled with Gorilla tripods, but found they just can't support a full-sized housing. And then of course if you're shooting anywhere other than the bottom, tripods aren't much help. That warbonnet shot was at night, 90' deep on a wall in BC which I was being pushed along by a decent current. The D500 has amazingly fast focus capabilities.

Tripods have their places, especially for macro video, but I find I can get by with lots of light and a fairly fast shutter speed. Sadly, we need to also keep a small aperture to keep any sort of depth of field.

All this to say, "if it was easy, everyone would be doing it!"