Pentax 10-17 or Sigma 10-20

Anyone have any strong views on the comparison between these two fairly similarly priced lenses (for use on a K10D). And can anyone point me at a useful explanation of the significance of Pentax being a fisheye?
Thanks

Fisheye = curvilinear, which means that straight lines at the extreme edges of the image . . . are resolved as curves. A rectilinear lens resolves straight lines as straight lines.

Personally, I don't like the fisheye perspective and if the Sigma is rectilineaar, I would buy Sigma.

That sounds quite straightforward; and if it is that simple the Sigma gets my vote. But I have an idea it's a bit more complicated than that, and that in some circumstances a fisheye gives a truer reflection of real life. Anyone?

The fisheye lens is a creative tool which has immense possibilities. You can also use it to show no curvature say on ladscapes, as long as the horizon goes right through the centre of the frame. As you zoom towards the 17mm end of the lens the curvature diminishes.

Not true to life, but an interesting lens that tempts me constantly.

This Pentax fisheye has a much wide angle of view - up to a massive 180 degrees. Because of that you can't use filters at all (though the Sigma will require either a modified Cokin P holder, or a set of Lee filters).

The Sigma is a rectilinear zoom.

Both distort what you would consider a "normal" view, but a rectilinear is more suited to landscape work.

Hope that helps!
Matt

"......Both distort what you would consider a "normal" view..."

True, but a 'fisheye' design gives both geometric and optical distortion while a 'rectilinear' design only gives geometric distortion (ie., distorion due to the actual geometry of a wide view and not in any way due to any shortcoming of the lens design).....

And Matt it was who kindly helped me source Cokin P filters not so long ago! As chance would have it, someone has just posted a photo on dpreview demonstrating the degree of vignetting on a Sigma 10-20 at 10mm - it's bad! However, apparently it's gone by 12mm.

Does anyone have experience witrh the two lenses at issue here? I think I will prinicipally use whichever I buy for landscape work, so I'm still leaning Sigma-wards. Incidentally, I really appreciate the high signal-to-noise ratio of postings to this forum. People are so helpful, and only post when they have a contribution to make.

I suppose a fisheye lens would be perfectly true to life........for a fish!



Sorry, that wasn't much of a contribution, was it?

Re-reading my last post, I should have made it clearer - the vignetting at 10mm I was talking about is of the Cokin holder, not native to the Sigma lens. Actually, it's worse than vignetting, the holder itself is clearly visible.

There are two things that make a super wide vignette with Cokin P filters... and this is what you do (in true Blue Peter style ):

* We tried hacksawing off the front two slots so you have just the polariser and one slot let. It's better.

* It appears that the inside edge of the filter holder is visible in the corners, so get out a file and make 'em more square. No probs

This has worked well with a Cokin P, Sigma 10-20 and Canon 20D. I used a hacked Cokin P with the Pentax 12-24 and *ist-D for a while, but ended up with the Lee+Cokin Z. Better quality filters and a much nicer system, but stupidly expensive really

Actually, Cokin now do a wide angle holder for the P filters. It'll stop some of the problems - http://www.cokin.com/ico6-WIDE-ANGLE-HOLDER.html

HTH!
Matt

Yes, well, having just made a significant investment in the Cokin P system, you'll understand that I'm not hugely keen to embrace yet another!
The wide angle holder seems like the best solution at least for now. Or I just won't use filters at 10 and 11mm...

I also consider a wide-angle zoom and can't really decide whether I want a fisheye or not (though I'm leaning towards the Pentax).

Anyway, here is a comparison on pbase:
http://www.pbase.com/alinla/1017_vs_1020&view=tree

Some more samples of the Pentax are on Steves Digicams istDL review (scroll down to see the 10-17 pics)
http://www.steves-digicams.com/2006_reviews/istdl_samples.html

There were more samples of the Pentax on another site, I downloaded them to my computer but I don't remember where I found them. It's a series of 10 pics at different focal lengths. I could mail them to you but I'm hesitant to post them somewhere as they are not my images.

Hope this helps you to make the decision (hasn't really worked for me so far),
Prieni

FWIW, here's some interesting and useful links:
http://en.wikipedia.org/wiki/Fisheye_lens http://www.fisheyelens.de/index_e.html (mostly German)
http://wiki.panotools.org/Fisheye_Projection http://www.a1.nl/phomepag/markerink/fishyfaq.htm

Some Pentax images:
http://www.pentax.de/_de/photo/lenses/index.php?gruppe=41&artikel_nr=21580 (see at the bottom "Downloads"

HTH!
Matt

Matt,

your last link was the one I was looking for (i.e. the series of sample pics). Thanks for that (and the other links),
Prieni

Thanks again to all who have contributed. I really don't think, having looked at the test images, that a fisheye is what I'm after. Shame, since the Pentax is reasonably priced and a nice size. I think a Sigma may be on the way soon....