6 Bit coding question

[ckchen72]

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I understand the fact of using IR filters to reduce the magenta cast, and then the subsequent need for the coding to compensate for the cyan drift. But if you are working soley in black and white, and you are using an ultrawide lens, do you still need the 6 bit coding. I guess my question is will the vignetting appear in the black and white photos?

 

Thanks!

Calvin

I've subscribed to Sean's site, but still wasn't clear whether the "vignetting" just applied to the cyan drift problem.

[marknorton]

When the 6 bit coding was announced, it was widely assumed to be there to deal with sensor vignetting. As it turned out, the parallel solution of the sensor microlenses dealt with it quite effectively, to the extent that people were questioning whether the lens coding was an unnecessary complexity.

 

Sensor vignetting is well handled even for uncoded lenses, coding the lens improves it a stage further.

 

Then along came the IR issue, the need for filters and the consequent cyan drift and Leica must have been breathing a sigh of relief that they had the lens coding available to them because the use of filters eliminates one problem - the effect of IR - which cannot be fixed in firmware and replaces it with one - the cyan drift - which can, providing you know the lens attached.

[scott kirkpatrick]

There are two generations of vignetting correction. With the first firmware versions, 1.06 and 1.09, and the "lens detection ON" setting, you see that coded lenses receive an overall lightening of the corners and a slight boost in red levels in the corners for wide angles (because the weak IR filter over the sensor contributes a small red vignette, visible on the widest angle lenses, such as the WATE or CV15).. This correction appears to even be somewhat aperture dependent, which is important for the faster lenses 50mm and longer, which only vignette at their widest apertures. With firmware 1.102 we got the "lens detection ON+UV/IR" setting, which gives a stronger correction of the red and very little effect on overall vignetting. The two settings are very different and could evolve in further firmware releases. For B/W photography I could imagine choosing to use a UV/IR cut filter for extra sharpness or leaving it off for slightly lighter shadow details and using "ON" without the red/green corrections.

 

scott

[sandymc]

Any lens vignettes, especially wide lenses. But on an M8, the extent of vignetting both in luminosity and chroma is greater than would be the case on a film camera. So to answer your question, yes, vignetting will appear in your B&W images. Whether it is enough to warrant lens coding or whatever else, only you can decide.......

 

Sandy

[carstenw]

Any lens vignettes, especially wide lenses. But on an M8, the extent of vignetting both in luminosity and chroma is greater than would be the case on a film camera. So to answer your question, yes, vignetting will appear in your B&W images. Whether it is enough to warrant lens coding or whatever else, only you can decide.......

 

Sandy

 

Sandy, do you mean with an IR filter on? Or for a given angle of view covered in the image?

 

There are two general factors with the M8 for vignetting: microlens angle on the pixels (more vignetting than film), and the crop factor, ie. the outside of the lenses aren't used (less vignetting than film). My feeling is that between these two factors, the M8 actually vignettes less than film *with a given lens*. However, the IR filter seriously emphasises the seriousness of the vignetting with wides, since it gains a colour tinge. Also, if you put a wider lens on the M8 to compensate for the crop factor (21 for 28, for example), then it is quite possible that the M8 vignettes more than film, even without IR filter.

[sandymc]

Sandy, do you mean with an IR filter on? Or for a given angle of view covered in the image?

 

There are two general factors with the M8 for vignetting: microlens angle on the pixels (more vignetting than film), and the crop factor, ie. the outside of the lenses aren't used (less vignetting than film). My feeling is that between these two factors, the M8 actually vignettes less than film *with a given lens*. However, the IR filter seriously emphasises the seriousness of the vignetting with wides, since it gains a colour tinge. Also, if you put a wider lens on the M8 to compensate for the crop factor (21 for 28, for example), then it is quite possible that the M8 vignettes more than film, even without IR filter.

 

Carsten,

 

Yes, agree on the two factors - I was coming at it from a "vignetting at a given angle of view" perspective, rather than with a given lens.

 

Sandy