M8 lens coding question

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Nick De Marco

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Just back from a weekend in Italy with my brand new Leica Elmarit 28mm f2.8 lens. It's the first NEW Leica lens I have ever bought (Only been able to buy new Zeiss etc or used Leica before) so not only quite exciting, but the first lens I have with 6-bit coding.

So forgive the ignorance, but why does my camera efix say the photo I took was at f2.8 when it was more like f16? I am sure that maybe I have to set something different on the camera but having never used a coded lens before I don't know about it, and if I do set something will I have to reset every time I (frequently) change back to non-coded lenses etc?

Here is a photo taken from Atina with the lens, and you will see from the photo that there is no way this is f2.8

 
2.8?

2.8?

With the M8 on "A" you set the aperture and the body sets the speed. Perhaps you had the lens on 2.8 ? the data would indicate a super high shutter speed. The M8 does go up to 1/8000
Have you looked to see what shutter speed was used?
Rafael
 
Hi, The coding tells the camera what lens you have (28mm f/2.8). This allows the camera adjust the image file for the optic qualities of the lens/filter (if an IR filter is used (which you have to manually tell the camera)). The EXIF data will have the camera's settings (ISO, shutterspeed, flash) but the lens diaphram is not linked to the camera, really in any way, so the camera has no idea what f-stop you set the lens at.

For the typical SLR/DSLR, the lenses are coupled to the camera and the aperture information is sent to the camera (and the camera can ususally set the aperture on the lens). This ability very much preceeded digtal. With an modern SLR one views the image through the viewfinder at the maximum opening and the lens closes the aperture down when taking a picture. Initially the link between camera and lens was typically mechanical (rabbit ears on Nikkors) but is now usually electronic (accounting for some of the little electronic contacts on the lens mount.

My M8 files appear to only have the lenses max aperture listed. In looking at some M8 files in Lightroom and PSCS3, the f-stop line is blank but there is a second line called "Max Aperture" that does have the max opening of the lens in it but again it is the max for the lens, not what what used for the particular image. That is the only aperture information I can find or really expect to find.

Robert
 
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Nick, if your EXIF is showing you focal length and aperture then you must have detection turned on. The only question is, if you're using an IR filter, it should be set to ON-UV/IR not just ON, so the M8 will correct the cyan corner shift. In no case will the M8 report the actual aperture you used. I have a combo of coded and uncoded lenses (35mm and shorter are coded, above 35mm are not) and I leave the ON-UV/IR set permanently. One of my uncoded lenses required me to paint a screw head white to make it invisible to the reader, which thought it was a different lens and was applying too much correction which turned the corners red.
 
The M8 will record the actual aperture on coded lenses, or rather an estimate thereof, but normally EXIF will not show it, unless you run the image through Cornerfix or apply a dedicated EXIF reading program. Then you'll find it is there, and usually rather accurate too.
 
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Interesting,

I assumed that the M8 software had to make a guess at the lens aperture as changing the aperture should alter the amount of "cyan corner shift". I did not know it recorded that guess.

Capture 1, LR, PSCS3 and an EXIF viewer I had did not show it. They all list the lenses widest aperture as part of the Lens ID but have the f-stop field blank. I did look at what Corner Fix showed, and it is there, Leica's estimate and their estimate.

Would be interesting to see how they do it. I would guess it has to do with knowing the light transmission pattern on the sensor of each coded lens at each f-stop since the lens aperture ring is not directly coupled to the camera.

I still suspect the original poster saw the lens ID max aperture in the EXIF data he was viewing although it is a wide angle lens and the forground trees are not as crisp as the mountains so perhaps it really was taken at f/2.8.
 
The info data just records the focal length of the lens. If you are using a coded f2 lens it will say f2. The lens apperture is not coupled and it does not record this in the exif data. Your picture may well be f16, but the camera has no way of measuring directly your apperture setting.
Richard
 
Ah- but as I said, Richard, it does record its estimate of the aperture, as explained above. It can be read out too by several Exif readers. There have been several posts on the subject, one with a statistical analysis of the exactitude of the estimate. It was not too bad at all.
FYI It can be found in tag-id 0313 of the metadata. Here is an example of the full metadata; see line no. 9 from the bottom.

[Overview]
File name: 0160-0804.DNG
File type: Adobe Digital Negative
File size: 10.327,4 KB
Creation date: 21.02.2008 00:25
Last modification: 06.02.2008 12:52
Make: Leica Camera AG (http://www.leica-camera.com)
Camera: M8 Digital Camera
Lens: Summicron-M 35mm F2 ASPH.
Software: 1.201
Dimension: 3920 x 2638 px (10.3 MP, 3:2)
Focal length: 35 mm (equiv. 47 mm)
Exposure time: 1/180"
ISO speed rating: 160/23°
Program: Aperture priority
Metering Mode: Center-weighted average
White Balance: Auto
Flash: Flash did not fire, auto mode

[Image]
New subfile type: Reduced-resolution image data
Image width: 320 px
Image height: 240 px
Number of bits per component: 8, 8, 8
Compression scheme: uncompressed
Pixel scheme: RGB
Manufacturer: Leica Camera AG
Image input equipment model: M8 Digital Camera
Image data location: 0x00000F60, ...
Orientation of image: 0° (top/left)
Number of components: 3
Number of rows per strip: 68 rows
Bytes per compressed strip: 65280 bytes, ...
Image resolution in width direction: 72 dpi
Image resolution in height direction: 72 dpi
Image data arrangement: Chunky Format (Interleaved)
Unit of X and Y resolution: inch
Software: 1.201
Person who created the image:
SubIFD Pointer: 0x000001EE
Copyright holder:
Exif IFD Pointer: 0x000002FC
Self timer mode: Off
Date and time of original data generation: 2008-02-06 11:52:20
Focal plane X resolution: 3729 ppi
Focal plane Y resolution: 3764 ppi
Focal plane resolution unit: inch
TIFF/EP Standard ID: 0.0.0.1
DNG Version: Version 1.0.0.0
Unique Camera Model: M8 Digital Camera
Color Matrix 1: [1.0469, -0.5314, 0.1280], [-0.4326, 1.2176, 0.2419], [-0.0886, 0.2473, 0.7160]
Color Matrix 2: [0.7675, -0.2195, -0.0305], [-0.5860, 1.4118, 0.1857], [-0.2425, 0.4007, 0.6578]
Camera Calibration 1: [1, 0, 0], [0, 1, 0], [0, 0, 1]
Camera Calibration 2: [1, 0, 0], [0, 1, 0], [0, 0, 1]
As Shot Neutral: 0.470953462, 1, 0.791153605
Baseline Noise: 1
Baseline Sharpness: 1
Camera Serial Number: 3105328
Calibration Illuminant 1: 17
Calibration Illuminant 2: 21

[Additional Image Data]
New subfile type: Not set
Image width: 3920 px
Image height: 2638 px
Number of bits per component: 8
Compression scheme: uncompressed
Pixel scheme: CFA (Color Filter Matrix)
Image data location: 0x00039360, ...
Number of components: 1
Number of rows per strip: 16 rows
Bytes per compressed strip: 62720 bytes, ...
Image resolution in width direction: 300 dpi
Image resolution in height direction: 300 dpi
Image data arrangement: Chunky Format (Interleaved)
Unit of X and Y resolution: inch
CFA Repeat Pattern Dimension: Horizontal repeat pixel unit: 2, Vertical repeat pixel unit: 2
CFA Pattern 2: [Red, Green], [Green, Blue]
Linearization Table: <256 items>
White Level: 16383
Default Crop Origin: DefaultCropOriginH: 2
DefaultCropOriginV: 2
Default Crop Size: DefaultCropSizeH: 3916
DefaultCropSizeV: 2634
Bayer Green Split: 500
Relative strength of the camera's anti-alias filter: 0

[Camera]
Exposure time: 1/180"
Exposure program: Aperture priority
ISO speed rating: 160/23°
Exif version: Version 2.2
Date and time of digital data generation: 2008-02-06 11:52:20
Shutter speed: 7.5 Tv (1/181")
Exposure bias: ±0 EV
Maximum lens aperture: 2 Av (F2)
Metering mode: Center-weighted average
Light source: Unknown
Flash: Flash did not fire, auto mode
Lens focal length: 35 mm
Manufacturer notes: 0x0000090C
File source: Digital Camera
Scene type: A directly photographed image
White balance: Auto
Digital zoom ratio: Digital zoom was not used
Focal length in 35 mm film: 47 mm
Scene capture type: Standard
Unique image ID: 000000000000000000000000000012bb

[Manufacturer notes]
Selected User Profile: User profile 1
Camera Serial Number: 3105328
White Balance Preset: Auto or manual
Lens Name: Summicron-M 35mm F2 ASPH.
Frame Line Selector: 24/35mm frame lines engaged
Blue Dot Brightness: 8.293
TTL Brightness: 6.719
Estimated Aperture: F9.5
System Temperature: 14 °C
Color Temperature: Not set
UV/IR Correction: Active
CCD Sensor ID?: Rev. 1 of the Kodak KAF-10500 CCD
CCD Circuit Board ID?: Rev. 2
Controller Board ID?: Rev. 1
M16C Micro-Controller ID?: Rev. 1
Unique Image ID: 9795
Click to expand...
 
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I had a look at the exif of the original image; part of the exif was stripped, that is Mac for you 😀. You would have to look at the original DNG to find the real aperture. Btw, I notice you posted this image in aRGB. That means it can look a lot better on the Web by changing the output profile to sRGB in your CS3.
I guess the aperture must have been rather small too. Your shutter speed was 1/20th.
 
jaapv said:
Ah- but as I said, Richard, it does record its estimate of the aperture, as explained above. It can be read out too by several Exif readers. There have been several posts on the subject, one with a statistical analysis of the exactitude of the estimate. It was not too bad at all.
FYI It can be found in tag-id 0313 of the metadata. Here is an example of the full metadata; see line no. 9 from the bottom.
Click to expand...
Agreed dear friend. I was simply pointing out that the 2.8 referred to the lens biggest apperture and not the apperture set for the exposure.
I must say this is a pretty impressive amount of 'hidden' data. I am not suprised that the apperture is reasonably accurate. It should be fairly simple maths given that Ev is measured and shutter speed is known. Presumably the discrepancy from 'set apperture' might represent the limits of metering accuracy and also accuracy of shutter speed?
best wishes

Richard
 
Richard Marks said:
Agreed dear friend. I was simply pointing out that the 2.8 referred to the lens biggest apperture and not the apperture set for the exposure.
I must say this is a pretty impressive amount of 'hidden' data. I am not suprised that the apperture is reasonably accurate. It should be fairly simple maths given that Ev is measured and shutter speed is known. Presumably the discrepancy from 'set apperture' might represent the limits of metering accuracy and also accuracy of shutter speed?
best wishes

Richard
Click to expand...

I was wondering how the software would guesstimate the aperture since there is no electronic communication of data between the body and the lens😕. Thats really using the old "noggin". Sounds like a very reasonable explanation 😉. Tks

Rob
 
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