6-bit M lenses vs old M lenses on M8

[biglouis]

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Can anyone explain to me - or direct me to the thread - which explains why it is desirable to have the new M lenses with their special electronic coding for use on an M8.

 

Reading between the lines some of the explanations do not make sense. I've read that the 6-bit code identifies the lens and amongst other things helps the camera to avoid vignetting. Surely, if the camera crops by 1.33 then there is no chance of vignetting?

 

I can understand the fact that the coding is needed for EXIF data but is there any other reason and would M8 users recommend only using 6-bit lenses or does it not really matter at all?

 

Just curious, is all

 

LouisB

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[Shootist]

The vignetting is caused by the way the light hits the sensor when using wider angle lenses.

With wide angle lenses the light is at a much greater angle in the corners.

[DaveEP]

Vignetting can still be seen on wider angle lenses which can be compensated for in-camera with a coded lens.

 

There is also a possible cyan drift that can be encountered when using the 486 filters. If you are using a coded lens, the camera could compensate for this also.

 

Exif data is often useful too, although less useful to me without the aperture.

[marknorton]

The M8 has four types of vignetting to deal with:

 

- The normal mechanical vignetting which is a reflection of the fact that the full diameter of the lens iris is not visible at all angles - take a lens at full aperture, look through the front of the lens and then move off axis. As you do, the shape and size of the "hole" changes which translates into reduced light making it on the sensor. This type of vignetting reduces as you stop down.

 

- Sensor vignetting which is the type of vignetting which originally caused Leica to believe that a Digital M would never be possible. The sensor is less sensitive to light striking it obliquely. To solve this, Leica have put offset microlenses in front of the sensor to increase the sensitivity of the sensor to oblique light. In addition, with a knowledge of the type of lens mounted (through the use of the coding) and a guesstimate (so it turns out) of working aperture, they can apply compensation in the firmware to boost the light levels into the corners of the image.

 

- Finally, there's red vignetting caused by both the IR filter in front of the sensor and any IR filter put on the front of the lens. Both attentuate red light as the angle of indicence increases and, again, the camera can compensate by boosting the red light level for both of these sources of vignetting if it knows the type of lens mounted.

 

TBH, if you have Leica lenses which can be coded, especially 50mm and down, it makes sense to do so.

[robsteve]

Louis:

 

I just mounted my old 1970's vintage 28mm Elmarit-M. It is coded. Below are examples with the coding disabled, and then Enabled. I shot at f2.8, with a B+W 486 UV-IR filter attached.

 

Here is coding disabled:

 

Here is coding enabled:

 

Finally, I run it through Panorama tools and the PTcorrect Radial luminance plugin to deal with the Cyan corners created by the filter.

[biglouis]

Rob

 

The links do not appear for me - did you put them in the document?

 

Louis

[biglouis]

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Must have been my PC.... the photos are appearing perfectly now. Hmmm. Don't want to sound like a complete dweeb but I really can't see any significant difference. What am I missing?

 

LouisB

[gravastar]

One way to see the differences between the images is to save them to your hard drive and then drag and drop each one, one after the other into the same internet browser window. Now use the browser's back and forwards buttons to quickly change between them. You'll see a progression of the corners being lighter and finally the cyan cast being removed from the corners.

 

Bob.

[wstotler]

Must have been my PC.... the photos are appearing perfectly now. Hmmm. Don't want to sound like a complete dweeb but I really can't see any significant difference. What am I missing?

 

LouisB

 

It can be a bit hard to see--I was scratching my head, also. I loaded all three images into Photoshop on layers and clicked them on and off to note differences. There is, incredibly, quite a bit of difference. I threw together a composite image so you can see roughly the same area of each photo together. Sample below.

[luigi bertolotti]

Louis:

 

I just mounted my old 1970's vintage 28mm Elmarit-M. It is coded. Below are examples with the coding disabled, and then Enabled. I shot at f2.8, with a B+W 486 UV-IR filter attached.

 

Here is coding disabled:

 

Here is coding enabled:

 

Finally, I run it through Panorama tools and the PTcorrect Radial luminance plugin to deal with the Cyan corners created by the filter.

 

Thank You really: I also have a 28 of the same age: finally, I have got a real example of what you earn by coding (when I get my M8...): difference is clear even in PC monitor view: I expect in printing it may result even more visible

[biglouis]

Will

 

Thanks, now I get it. I really must do something about my glasses :-)

 

I actually assumed that the sky was a darker blue as happens in mid winter in clear skies. To me it looked like the pictures were getting progressively lighter, as if the contrast was being lowered.

 

LouisB

[wstotler]

Will

 

Thanks, now I get it. I really must do something about my glasses :-)

 

I actually assumed that the sky was a darker blue as happens in mid winter in clear skies. To me it looked like the pictures were getting progressively lighter, as if the contrast was being lowered.

 

LouisB

 

 

NP. I really had trouble seeing the difference but I was sure what was being reported was happening. Vignetting--when it happens in a color photo--is easily missed by me unless it is quite severe. I think the subject also matters. To me, in these photos, the sky just looked "bluer"--I didn't really notice the vignetting until I could get the photos into Photoshop and really play. I am really happy about this post from Luigi (thanks, Luigi) because it made me really think about--and learn to notice--vignetting in a photo. Sure, I knew about it based on the "shot on gray" tests of Sean and company, but to really notice it in a color photo was another matter!