kidtexas
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thrice wrote:
kidtexas, I think the vignette on that 15/4.5CV shot is the result of the film/developer/scanning/colour-treatment. Otherwise this sort of behaviour would be documented and have a scientific foundation. Unless you can submit such an explanation forgive me if I don't accept one example as gospel.
I don't want to get in trouble, but as I assume you're not a Reid Reviews subscriber i'm going to share part of his 15mm CV review with you, here is a vignetting analysis without a filter on the lens, taken on the M8:
I'd say that reliably puts the argument to bed.
I never said (or implied) red corners occur without correction.
If the sensor isn't perfectly aligned to the lens flange then yes, symmetrical correction profiles would cause this problem, that remains to be proven in testing or measurement. I'll ask one question though, why doesn't it occur with the WATE if it's a sensor alignment issue?
The corners I showed are not due to scanning or color treatment - it's there on the slide. It could be Kodachrome's shadow rendering - it might shift to the blue. I don't know. However, I've seen it on many of my CV 15/4.5 shots on shot on Portra, so it's not limited to Kodakchrome. I didn't claim an explanation for it. I have it in several shots. It's either the due to the lens design and how it transmits light, or the way vignetting affects color on these films.
No, your picture does not put that argument to bed. I agreed with you that the IR filter over the sensor can cause cyan corners, but again, the bulk of the problem is due to the IR filter over the lens. I had a discussion with Sean Reid about the IR cut filters; he didn't understand how they worked at the time either. I don't know if he ever figured it out since I didn't follow up on the discussion. The CV 15/4.5 might get cyan corners without a lens mounted IR cut for the reason you state, due to its more symmetrical design, but almost ALL lenses greater than 35mm or so get really cyan corners with the IR filters.
I've been following the M8 since it came out, and it's well documented that without IR filters, your shots have IR contamination. The solution to that, adding IR filters on the lenses, caused another problem, cyan corners. It's in many of the reviews. Some lenses might additional have slight cyan corners due to the reasons you state.
I played around with an M9 yesterday. One of the things I specifically did was disable lens detection and look for color issues. I saw vignetting, but no cyan corners.
Lastly, look around for why Leica doesn't have corrections for the UV/IR filters on the M9. It's because the shift in the filter pass frequency, starting with 75mm or 50mm lenses, gets so extreme with wide angles that possibility of proper correction is low.
I said nothing about sensor alignment issues either. I don't know what causes the asymmetrical vignetting on the M9 and why symmetrical profiles don't correct for it. The best testing I've seen on the matter is by Sandy of Chromasoft, which I linked to earlier. It's also not red corners. It's a red left side.
I don't really have the time or desire to continue this. IR cut filters in front of the lens, as used on the M8, are interference filters. I use interference filters everyday at work. They block at the frequency they are design for at normal incidence. They cause the bulk of the cyan corners on the M8. The M9 should be largely free from this problem.
interference filters on wiki
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Two 24 mm lenses of different brand will of course not have the exact same exit pupil distance to the image plane.