[plav1959]

Just had my T3i modified for full spectrum astrophotography. This requires the use of an EOS clip Luminance filter for use with refractive elements. The clip filter does not allow use of EF-S lenses due to clearance between back of lens and clip. So, I'm looking for a higher quality replacement. I've been looking at the Sigma 24-70mm f/2.8 IF EX DG HSM but am open to suggestions. The camera mod also allows IR photography which I am also interested in, using Hoya R72 IR filters. Most lenses in this range use 82 mm filters. Most of my lenses use 77 mm filters. Since I'm using an APS-C chip would I experience any vignetting if I use a step down ring?


First post and thanks for any help you can give me.


Paul

[Klaus]

> Since I'm using an APS-C chip would I experience any vignetting if I use a step down ring?

 

Sounds unlikely to me.

 

> I've been looking at the Sigma 24-70mm f/2.8 IF EX DG HSM but am open to suggestions.

 

Should be good on APS-C although the lens is not stellar on FF.

The Tamron 24-70/2.8 may be a tad better though.

[plav1959]

Any thoughts on the Canon 17-40 f/4? Wouldn't leave any gaps with my Tokina 11-16...