Canon Drop-in Filters

I was wondering about the drop-in filters used with some lenses like the longer tele lenses and some others like the 17-40 f4L.

What are the lenses supplied with, a clear glass filter element?
Is this part of the lens formula that should not be ommitted?
How are they fitted?

The long lenses come with a drop-in filter that is a clear glass. Something is required to fill the hole, and the clear glass is actually part of the optical formula.

The 17-40 and other such wide lenses do not actually use a drop-in filter, but rather a sheet of plastic (gel) that slides into a holder at the back end of the lens. They are not supplied with a filter.

Hope this helps.

Have Fun,

Thanks Rick

Regarding Canon's long telephotos,. just some additional info;

When Canon switched from there previous generation of long AF telephotos to the newer models that have Image Stabilization and weather sealing,. they changed the drop in filter holder,. and subsequent size of the glass filter required from 48mm to the current 52mm

I have lenses that require both types,. and it turns out that despite the differences,. there is some level interoperability.

For instance,. the 48mm drop in polarizer functions fine in the 500mm f/4L IS which is supposed to use 52mm drop ins.

Upon further investigation I found that despite the fact that the outer diameter of the glass filters installed differs .. the opening within the metal holders
for each of the clear glass "stock" units is an identical 40mm (yes 40mm... the extra 8mm or 12mm is the metal surround)

Also,. the distance to the center of the glass filter from the inner edge of the holders cap is the same,. ie: if the 48mm fits in the lens opening of a 52mm lens like the 500mm f/4L IS,. it not only just "fits" it fits in a way that the filter glass and that 40mm opening is placed exactly correctly .. it should not in any way impair the lens function or light gathering.

Now,. mind you the 52mm filters do not fit in the older lens,. well at least not into the 200mm f/1.8L that I have to experiment with.

I mention all this because this came as great news to me,. as I ha invested a significant sum in the 48mm drop in filters for the 200mm prior to getting the 500mm. It was greatly comforting to be spared having to purchase these filters all over again.
This came as great news to me

The 52mm is of course weather sealed,. the 48mm is not.