Wide angle C/Y conversion help!!!
/forum/topic/1130998/0



contas
Registered: Jul 21, 2010
Total Posts: 1048
Country: Vietnam

I did conversion C/Y 18mm to Sigma SA mount, went smoothly, far focus is fine. But on the right and left sides of the image has green bands :
http://farm8.staticflickr.com/7261/7554085588_537e15473b.jpg
http://farm8.staticflickr.com/7254/7554086414_e21be04486.jpg
They aren't disappeared when stepdown the diaphragm. As I did conversion several times, I never met this trouble before , so I firstly post this problem here for help , while am digging more to go out or return back.Thanks.



ZoneV
Registered: Nov 20, 2008
Total Posts: 949
Country: Germany

Supppose less a mount conversion problem, and more a sensor and light ray angel problem.
I could imaging that the Sigma / Foveon sensor has a problem like optical cross talk between the pixels and colours in the different pixel depth - most likely to happen with oblique rays.
But the not symmetrical behavior could probably be inducted by small tilt in the lens mount conversion.



contas
Registered: Jul 21, 2010
Total Posts: 1048
Country: Vietnam

Hi ZoneV, thanks for tips, I spent hours to disassemble and re-assemble to check all the possible faults , that may cause oblique, stray rays and other things thoroughly but sadly couldn't find.
I used OEM Pentax-K mount and 2 equal shims, I drilled more 3 holes to match C/Y lens's rear holes, everything seems done accurately.
That thing not happens to other converted lens like Apo-Makro-Planar.
Strangely that, when I couple converted C/Y 18mm to my Sigma SD9, no bands there.SD1 and SD9 cameras are almost the same in constructions, the main difference are : the sensor resolutions and maybe microlenses ( that SD9 doesn't have).
May my case becomes a warning about SA conversion? Thanks man.



contas
Registered: Jul 21, 2010
Total Posts: 1048
Country: Vietnam

Thanks RustyBug for PMs.Your suggestions are precious , I'll check my SD program that way. Thanks.



contas
Registered: Jul 21, 2010
Total Posts: 1048
Country: Vietnam

While testing C/Y 18mm between SD1 and SD9, I found that SD1 correct purple fringing very well.Before today I thought that the only cause CA mainly by lens.



contas
Registered: Jul 21, 2010
Total Posts: 1048
Country: Vietnam

It is busted!!!

This phenomenon is well decribed and a software named CORNERFIX was written for Leica M8 and now it could be used for other systems.
This is a certaint vignatting effect, happens when couple a wide angle to digital camera.
CORNERFIX supports .DNG only, but you can converse jpeg to .DNG in LR.
CORNERFIX is a freeware, so the quality isn't guaranteed.
At least the definition is done and a solution is on the way.