Canon dioptric viewfinder lenses

[gblades]

I wear glasses and my prescription is around -6.5 in both eyes.
I received my Canon 600D yesterday and I have found than even when looking through the glasses I have to set the dioptric adjustment all the way to -ve (-3) and even then its perfectly clear for my right eye but I could do with a bit more adjustment in order to use my left eye which is preferable for me.

Canon do dioptric lenses for the viewfinder but they dont say what the actual adjustment they provide is.

The camera has a standard -3 to +1 adjustment (-1 center position and then +-2).

I would expect a (E-2) correction lens to adjust everything by -2 so the new range I can adjust would be -5 to -1. However Canon do a +0 lens but no -1 lens which makes me suspect the rating of the lens is actually the new center position. So a E-2 lens actually changes the center position from -1 to -2 and therefore adjusts the overall adjustment range to -4 to 0.

Does anyone know for sure?
I tried calling Canon UK but I managed to confuse the person in technical support and he has gone away to ask someone else.

Does anyone else find they still need the dioptric adjustment even when wearing glasses?

Thanks
Gareth

 

[Buck]

Gareth

Canon state that the lens is the new level of adjustment. See this article.

These lenses are available in graduations of 1 dioptre and provide the means to extend the range of adjustment built into the camera. The maximum lens available is marked -7 dioptres. It is, in fact, -4 dioptres, but it extends an EOS camera’s built in -3 dioptres range to -7.

http://cpn.canon-europe.com/content/education/technical/dioptric_adjustment_lenses.do