Resistance to Larger Filter Size, Kills Great Lenses?

[neuroanatomist]

Canon experimented with 2 different possible image stabilized f/2.8 zooms. There are patents for them available on both Canonwatch.com and egami.com, and canonrumors.com

Just did a search on the USPTO/google patent and there are no patents for anything related to a 24-70 f/2.8 IS. Loads of references to the 24-70 f/2.8 MKII and 24-70 f/4 IS. It could not be published yet, but I want to see the source material from the websites as nothing shows up in searching on them.

RMC33 - Your Google-fu is weak, Grasshopper. 

Radiating - Thanks, although a link would have been helpful.

http://www.canonrumors.com/2012/07/patent-canon-ef-24-70-f2-8l-is/

[RMC33]

Canon experimented with 2 different possible image stabilized f/2.8 zooms. There are patents for them available on both Canonwatch.com and egami.com, and canonrumors.com

Just did a search on the USPTO/google patent and there are no patents for anything related to a 24-70 f/2.8 IS. Loads of references to the 24-70 f/2.8 MKII and 24-70 f/4 IS. It could not be published yet, but I want to see the source material from the websites as nothing shows up in searching on them.

RMC33 - Your Google-fu is weak, Grasshopper. 

Radiating - Thanks, although a link would have been helpful.

http://www.canonrumors.com/2012/07/patent-canon-ef-24-70-f2-8l-is/

 
Thats the one. Upon searching it again it shows up in tandem with the MKII, f/4 IS and a few others. ~

[Rat]

Could someone explain why these specs indicate a need for 95mm filters? As far as I can tell, a 82mm thread would be enough...

[neuroanatomist]

Could someone explain why these specs indicate a need for 95mm filters? As far as I can tell, a 82mm thread would be enough...

They don't, necessarily.  But if you look at the 24-70 (both verisons), the front of the lens has a ring of reasonable diameter (sufficient to print the lens ID info) around the front element, meaning the filter diameter is a fair bit larger than the front element.  Not all lens designs have that much space (and some have a lot more). 

Does Canon have a reason for designing it that way? Probably.  Note that a quick comparison of this image suggests that the front element of both versions of the 24-70L is pretty close to the same size, but the MkII uses an 82mm vs. a 77mm filter.   Reasons could be to reduce chances of mechanical vignetting with a filter in place, to allow space for a more robust bracket setup to hold the front element, etc.

[helpful]

Image quality is affected by filters depending on the quality of the filter and on the surface area of the filter.

The larger the surface area of the filter, the greater the reduction in image quality. (You can see this with a softening filter--when your lens is stopped down, the effective diameter and surface area of the filter are reduced. When the surface area goes down, the image quality goes up, and hence there is less of a "softening" effect from the softening filter at smaller apertures (large f numbers).)

A filter with twice the diameter has four times the area. Large filters are bad in this way.

But ultimately, it is due to the expense--the larger the filter, the more expensive it is to make one the same quality as a smaller filter.

In fact, achieving that same level of filter quality isn't enough because even at the same level of filter quality the image quality will still be worse because of the larger area.