10-17 de-fishing resolution loss?

[nixcamic]

Wasn't sure if this should go in the slr lens forum or the software forum or here. I was wondering if anyone with a 10-17 fisheye could tell me how much resolution loss there is de-fishing at 10mm, including the crop needed to get a rectangular image. Also, how much FOV is lost when cropping to rectangular?

Thanks,
nixcamic

Edit: had square where it should have been rectangular.

[JJJPhoto]

I used to have that problem when defishing. Whether using the lens correction tool in CS3 or the PTLens plug-in, I had to compromise between removing distortion and loss of image detail ... the more distortion you remove using these "rectilinear" methods the more detail gets "smeared."

I read a post in this forum from a member who found this great plug-in called "Fisheye-Hemi" from Image Trends:

Image Trends - Fisheye-Hemi Plug-In - Corrects Fisheye Lens Distortion and retains Image Content Details

At first I was skeptical, but after downloading the demo I realized this plug-in really does work as well as it looks like it does in the advertising. Here is a link to a fisheye image I took with an 8mm Sigma fisheye:

JPG Magazine: Photos: "Original Tasty Jam" by Jerry Jackson

Here is the same image after removing the distortion with Fisheye-Hemi:

JPG Magazine: Photos: "Tasty Jam" by Jerry Jackson

[nixcamic]

very interesting program, available as an aperture plugin. I'll have to download the demo then dig up some pictures taken with the 10-17 online and see how well they come out. The reason for all this is that I'm looking to go wide, and cant afford any of the rectilinear wide lenses, and am not really interested in everything being fisheye.

[troyz]

Originally Posted by nixcamic

very interesting program, available as an aperture plugin. I'll have to download the demo then dig up some pictures taken with the 10-17 online and see how well they come out. The reason for all this is that I'm looking to go wide, and cant afford any of the rectilinear wide lenses, and am not really interested in everything being fisheye.

When considering a fisheye as a substitute for an ultrawide rectilinear, you should keep in mind that field of view (as a function of focal length) is different for a fisheye; you can get a 90-ish degree horizontal field of view (HFOV) on a crop sensor with a 12mm rectilinear or a 16mm fisheye.

Defishing to rectilinear works well at a 90-ish degree HFOV; I routinely get good 2400-pixel wide rectilinear images from a Zenitar 16mm fisheye on a K20D (84 degree HFOV).

As jjj notes, rectilinear de-fishing of images with a wider field of view (shorter focal length) becomes problematic due to excessive stretching of the corners of the image. Fisheye-Hemi (and other cylindrical projections) get around this problem by straightening vertical elements of the image but not the horizontal elements.

[nixcamic]

Originally Posted by troyz

As jjj notes, rectilinear de-fishing of images with a wider field of view (shorter focal length) becomes problematic due to excessive stretching of the corners of the image. Fisheye-Hemi (and other cylindrical projections) get around this problem by straightening vertical elements of the image but not the horizontal elements.

So fisheye-hemi just projects the image cylindrically and I could use any many free/open source programs that do cylindrical projections to defish images with similar effect? That would be interesting.

[JJJPhoto]

Originally Posted by nixcamic

So fisheye-hemi just projects the image cylindrically and I could use any many free/open source programs that do cylindrical projections to defish images with similar effect? That would be interesting.

Well, it depends on the subject, the distance of the subject from the lens, and the angle of view.

I took my 8mm fisheye to a cemetery this weekend and while I was able to de-fish most images very nicely, some close-up shots taken with an angled perspective didn't look right at all when I tried to use the fisheye-hemi plug-in to remove the distortion.

Even when I tried PTLens or CS3's lens correction tool it didn't look right.

Bottom line, you can de-fish a fisheye shot and "sometimes" it will look great ... but a fisheye lens and a fancy Photoshop plug-in is no replacement for a good non-fisheye wide angle lens.

I'm really looking forward to the new DA 15mm Limited that Pentax has on the roadmap. If it isn't a fisheye I'll probably be adding that lens to my kit.

[troyz]

Originally Posted by nixcamic

So fisheye-hemi just projects the image cylindrically and I could use any many free/open source programs that do cylindrical projections to defish images with similar effect? That would be interesting.

Short answer: the open source programs and Fisheye-Hemi produce similar, but not identical, results.

Long answer: Fisheye-Hemi isn't equivalent to the cartographic cylindrical projections (e.g. Mercator or Lambert) offered by panorama-stitching software; the cartographic projections will make your images bulge out at the top and bottom, forcing you to crop out these regions of the source image. Fisheye-Hemi doesn't bulge, so it preserves the top and bottom of your composition. (You lose the corners in any case; there's no free lunch in geometry.)

There are several packages out there worth trying; check out the "how do YOU de-fish" thread for examples. Try several programs, and choose the one that works best with your images and workflow.

(BTW, I'm also salivating over ultrawide rectilinear primes; could be a DA14/2.8, a 20mm-ish lens for film, or the new limited when it comes out.)