rear filters? i.e. Sigma 15-30mm

[cowman345]

Considering a purchase of a Sigma 15-30mm or Canon 17-40mm, but am concerned about the Sigma's rear filter slot.

Do they make circular polarizers for these filter slots? How to the prices compare to a (72mm) filter size?

-dave-

[scottbergerphoto]

I have the Sigma 500mm f/4.5. It uses the rear filter sytem. Mine shipped with the UV and CPL. I understand from other threads that they can be hard to come by. A search of B&H's web site bears that out.
Scott

[chris maddock]

Considering a purchase of a Sigma 15-30mm or Canon 17-40mm, but am concerned about the Sigma's rear filter slot.

Do they make circular polarizers for these filter slots? How to the prices compare to a (72mm) filter size?

-dave-

If the filter slot is like that on the 12-24mm Sigma (I'm only guessing, hopefully someone can confirm this), it is a holder for gelatin sheet filters right on the back of the lens.
This means that it is inaccessible without removing the lens from the camera, so (even if you could get CP gelatin material) it would be extremely impractical, if not impossible, to use.

KRs
Chris

[Canuck]

I am guessing it is like this picture at bottom, where you cut it to size slide it into the side bits it also takes a 77mm filter. This is the reason I stay with lenses I can put a filter on the front of it. This site may be of use to you, straight from the manufacturer: http://www.sigmaphoto.com/html/zoom_intro.htm
If you are in the market for a cheaper 17-40ish mm lens, I would look at the Sigma EX line. Lets see here from B&H...
Sigma Zoom Super Wide Angle 17-35mm f/2.8-4.0 EX Aspherical HSM Autofocus Lens Price: $ 439.00 (out of stock at moment)

Sigma Zoom Super Wide Angle 15-30mm f/3.5-4.5 EX Aspherical DG DF Autofocus Lens Price: $ 579.00

Sigma Zoom Super Wide Angle 12-24mm f/4.5-5.6 EX Aspherical DG HSM Autofocus Lens Price: $ 649.00

Sigma Zoom Super Wide Angle 20-40mm f/2.8 EX Aspherical DG DF Autofocus Lens Price: $ 649.00

Canon Zoom Super Wide Angle EF 17-40mm f/4L USM Autofocus Lens
Price: $ 699.95

Canon Zoom Super Wide Angle EF 16-35mm f/2.8L USM Autofocus Lens
Price: $ 1,369.95 This one was to show you how expensive F2.8 L glass can be.

This is the back of the Canon 16-35mm F2.8 L lens. The pic tells all...
http://images.fotopic.net/?id=2418964&outx=760&oq=0
-Canuck

[excessnoise]

I have a Sigma 15-30EX and I like it a lot ... (sound like Forrest Gump)
It uses a gel filter in the back just like Canuck's pic shows. It does come with a removeable lens hood that has a removeable cap. It has threads so you can screw in 82mm glass filters ; they are (huge and $$$$). I do have 3 glass filters but you WILL get vignetting at widest settings, even on a the 10D. I bought CC05B Kodak Wratten gel filters and they seem to do the trick. I read in another forum that the Sigma leans towards yellow so these slight blue color correction helps that, plus helps with the sky.

The lens is super sharp but IS slow to autofocus and has a fair amount of flair looking into the sun.

PS. If you do get the gels, make sure you use scissors not an razor knife to cut them. I wasted a few before I smartened up.

[scottbergerphoto]

The Sigma filters on some of their zoom lenses are not the gelatin filters you are describing. They are circular filters that screw onto a drop in filter holder at the rea of the lens barrel, not at the rear of the lens. The 15-30 does use gelatin filters as you describe.
Scott

[Canuck]

I forgot to mention that the abover pics of the 16-35mm F2.8 L lens was taken by a $80 Sigma 28-80 F3.5-5.6 lens and it had to be shrung from 3076x2048 to that size to get it looking as is. I couldn't get it to work the way I wanted. Needless to say, that lens really is pants! Now we know whay I wne to the 16-35mm F2.8L lens. It quite easily blows the cheapie Sigma out of the water. This isn't fair to compare lenses that have a $1300 price difference. There you have it.