Step Down Rings

[steve torelli]

I've never used one of these before. I want to use my 72mm B&W CP on a 300mm f/4

which of course takes a 77mm. Would this combination possibly cause vignetting

on a FF at the wider apertures or any aperture for that matter. TIA, Steve

[mark u]

It will cause vignetting at any aperture. The narrower the aperture, the more pronounced the transition will be. I learned this the hard way many years ago, using a rubber lens hood on a zoom. Fine at the long end, but at wide angle and wide open the vignetting wasn't readily noticeable in the viewfinder (but easily seen in print): stopped down, it was readily visible and gave the impression I'd used a circular fisheye, with black image corners, ruining my nice Alpine landscapes.

[patrick j dempsey]

If its mounted on a crop-factor Rebel body you might not see it.

[francois_gauthier]

Unlike normals and of course wide angles, long tele like yours often take one size smaller without vignetting. 72 is one size from 77, so it is worth a try.

 

At least, i knew of some old 400mm that took 72 filters with step-down from 77.

[mark u]

http://www.vanwalree.com/optics/vignetting.html

 

http://www.vanwalree.com/optics/lenshood.html

 

The front element of a prime lens gets full useage into the corners on full frame, and while this is usually also true of a zoom, it's often the case that there is a wider collar around the front element to allow for the use of filters at wide angle (also with wide angle primes). With a telephoto lens, the collar is usually narrow. With the 300 f/4 IS, the built in hood might mean that there is a little latitude available:

 

http://www.canon.com/camera-museum/camera/lens/ef/data/ef_300_4lis_usm_bd.html

 

77mm filters (especially a good CP) can be expensive, but they have the advantage that they fit several of the most popular L lenses (only the new 16-35 II requires a larger 82mm IIRC), and can be used with step up rings on several other lenses (although you might want to consider how to handle the loss of use of the hood with these).

[steve torelli]

Thanks everyone for your comments. The reason I was looking into this is that all my other glass is L primes between 35 and 200mm and ,of course, are all 72mm. But, as Francois said, it only costs a couple of bucks to try it. Thanks again.