Filter type for a Sigma 15-30?

[TomBarker]

Well, I've had the Sigma for a few weeks now, and I'm faced with a choice to make regarding filters. The ring that fits over the built-in lens hood is threaded and takes an 82mm filter, but there's also a holder at the back of the lens for a drop-in gel filter.

If I go for the screw-in filter, it'll be nice and easy to rotate a polarising filter but, will it show vignetting on such a wide lens?

Also, would I get an even polarising effect across the image with such a bulbous lens and a filter?

TBH, I expect a polarising filter to be the only filter I attach to this lens as I can do most things in Photoshop, but I can't take the glare off water with a computer.

[memobug]

Polarizing effect is best at 90 degrees to the sun. If your lens (like this one) is wide enough, the sky may show remarkably different saturation across the picture.

That may not be a big concern if you're not shooting a scenic.

Regards,

Matt

[Tom V]

I wouldn't worry too much about vignetting on the S2. The smaller sensor size (relative to film size) negates all but the worst vignetting.

Certainly, almost all the lenses you can put on the S2 are designed to work on film cameras. (The Nikkor 12-24mm zoom is the only exception I can think of). Since the lens has a front filter thread, there is not likely to be too much vignetting using a pie-plate sized 83mm filter. Using a thick filter (common on rotating polarizers) or a stack of filters will naturally increase the odds of vignetting (on film cameras).

Keep in mind that most lenses have light fall-off in the corners to some degree, even with no filters attached. It is more apparent on wide angle, zoom lenses, cheap lenses, and at wide apertures. It is more apparent on 35mm film format than in the reduced format of a digital sensor.

Vignetting occurs when the light is physically blocked by the obstruction of an offending filter ring that projects too far forward into the field of view. Offending filter rings are found on thick filters such as polarizers, on when stacking several filters. If you can't do without the filters, you can close the aperture to reduce the amount of vignetting (sometimes to apparently zero), in exchange for a harder sharper edge to the vignette (if it is still apparent).

You can check for vignetting and/or light fall-off by shooting an evenly lit, even toned wall wide open with and without filters. There is likely to be some fall-off in the corners even without the filter, but if there is vignetting, the fall-off would be more pronounced. You can reduce vignetting by using thinner filters, or shooting at a smaller aperture. Do some tests to see what the widest aperture is that does not reveal any vignetting. Often, stopping down a few stops reduces the lens’s natural light fall-off (if any).

If you get objectionable light fall-off or vignetting - you can always crop it out.

On the digital S2, this cropping is probably done for you already. Since the sensor is so much smaller in size than the film size the lens was designed for, it would take a lot of filters or a really thick filter to cause enough vignetting to be visible all the way into the corners of the digital sensor.

[TomBarker]

Thanks both. I think it's a nice front filter for me. Obvious that it's on, easy to rotate and could get adapter rings so it was the only polaring fillter I carried...

[Derek Byrne]

Re vignetting with Sigma 15-30 "lens hood":
I accidentally left the hood on my S2 one day and was delighted that there was no vignetting to be seen, so I've left it on ever since.
However - there's always a "however"- at an aperture smaller than f16 or f19 some slight shadowing may be seen at the corners.