Sorry if this is a repeated topic but I've searched and searched and couldn't find the answer - even google doesn't seem to know

I am looking into buying the MR-14EX ring light not only for macro but also as a fill in ring flash for portraits.
My question is, firstly will the unit be powerful enough - we're talking maby 6 feet away as just a fill flash?
Secondly what lenses will the unit fit? I know that it's designed to clip onto Canon's macro lenses, and that you can buy a 58mm screw thread adapter but what about larger lenses? Will it fit 67mm or even 77mm? Obviously I could buy the 58mm adapter and step down/up rings but won't this result in a vignette? How big is the centre hole?

I would normally just visit my local camera store and have a look myself but they don't have any instock

Thanks in advance for any help

I also forgot to add, with regards to off camera flash, the description mentions the master function but not slave - am I right in thinking that the mr-14ex can be used as a master unit but not an off camera slave - it can only fire other off camera slaves?

Thanks again

The adaptors come in 3 sizes, and the largest screws into a 72 mm thread. I bought the 72-77 mm adaptor to use it on my L's that have 77 mm threads & it can make the image look like it's shot through a pipe depending on whether you are shooting wide vs long. Plenty of power as a fill flash, and depending on ISO it can be the main flash in many uses. From reading the manual it seems to be usable ONLY as a master.

According to the manual you can attach it to the 180mm L Macro using the "72C" adapter.
I only have the MT-24EX (both units share the same manual), so I can only confirm this for the MT.

You definitely need a special adapter, since the flash does NOT fit to the filter thread but instead to its dedicated mount on the front of canons macro lenses. Canon also sells adapters for other filter threads including 58mm thread for use with non-Canon macro lenses.

I wouldn't try to fit it to anything larger than 72mm mount, though. At least for my MT it's opening is exactly as large as needed for the 180mm - not a millimeter more I think.

Thanks for clearing this up

Sounds good enough for me - I think I'll buy one

The 3 adapters available provide a screw thread to fit the lens and there is a section of metal with a groove that 2 lugs on the flash lock into. You press a release to install or remove the flash, and the groove goes all the way around the adapter so orientation isn't an issue. The Canon Macro lenses Canon lists as a direct fit have the groove built in, and therefore don't need any additional mounting hardware.

I might add that the only issue with lenses that have the built-in groove (i.e. 100mm) is that you cannot mount the flash if there's a filter on the lens. Kinda dumb...but life's like that sometimes. I'm guess that for those lenses that require an adapter maybe you can leave a filter on the lens.