p.1 #1 · Zeiss 100/2 ZE Vignetting with Extension Tubes
I'm using Zeiss 100/2 ZE MP with Canon 5D IV for scanning/reproduction of film negatives. The lens has a native 1:2 magnification. At 1:2 magnification, the lens produces excellent results. When I add 25mm Canon extension tube (original Canon), the lens starts to vignette in the corners, when I add additional 25mm Canon extension tube for a total of 50mm extension to achieve 1:1 magnification, the corners vignette gets even stronger.
See photos below, I also provided a version with posterization effect to emphasize the vignette. I'm not expert on lens designs, my only theory here is that the rays of light exiting the rear of the lens at an angle end up being blocked in the corners by the extension.This has caught me completely by surprise as I did not expect this lens to vignette with extension tubes, considering it's a "macro" lens.
Since I'm using the lens to scan negatives and stitch multiple 1:1 shots into one final shot, the vignette is causing considerable problem and is fairly pronounced in the scanned negative. The only way around it is to crop, which means each camera shot covers less of the negative and I need more shots to cover the surface.
So, any theory on why would extension tubes cause vignette? Has anyone had similar experience with this particular lens?
p.1 #2 · Zeiss 100/2 ZE Vignetting with Extension Tubes
I use the CZ 100/2 ZE mostly for landscape shooting, and so I haven't encountered this. For tripod shooting at up to [1:1], I normally use the SMC Pentax-FA 50/2.8 Macro and Mamiya 645 A 120/4 Macro. I'd use the A 120/4 for this reproduction job.
I rarely use extension tubes, except to reduce MFD for super-teles. I much prefer using either, (i) a bellows system, for high mag (maybe with tubes), or (ii) a diopter auxiliary lens to increase mag on an existing lens. The Canon 500D diopter series is very clean, as its two-element design greatly reduces the CA at image edges, that you see with single-element diopter lenses. Using a 500D with the 100/2 ZE would probably get you to about [1:1.25] (mag. 0.8x) and a 1.4x Extender might get you to [1:1]. I could have a chance to try this, over the next couple of days. I'll report back here, if I do. FWIW, the EF 1.4x III does fit the CZ 100/2 ZE, although I've never actually used it (I just tried it, now).
