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Here's what the ON+UV/IR firmware does


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[geek alert]

 

I've been analyzing what the new routines do to see what sort of overall vignetting correction and red vignetting corrections are applied. In summary, setting ON+UV/IR provides a weak overall vignetting correction and fairly powerful correction of the red/green intensities to eliminate the "cyan drift" effect seen as you move radially out from the center of an image with light colored background.

 

To show this, I have analyzed white wall shots taken with a CV15/4.5 at f/4.5 with a Leica filter installed. The JM-LTM mount was encoded as a WATE. The light was indirect overcast daylight (around 5000K). Each frame was white balanced in C1 by clicking at the exact center of the frame (location 486,325 in C1's coordinates), and output as an sRGB JPEG with 900x603 pixels. A MatLab routine then averages each group of 3x2 pixels into a single r,g,b value and converts those levels to intensities by raising them to the 2.2 power, undoing the gamma correction that is part of sRGB. I then plot these intensities along a diagonal, averaging the diagonal from upper left to lower right with the diagonal from upper right to lower left. Things don't end up quite symmetric, as the top of the field of view is a little brighter (but less than 1/3 stop) than the bottom. The camera is set about 40 cm from the wall, with the lens focused on infinity to maximize vignetting and blur the image.

 

The focal length that is set in the WATE dialog box has a big impact. In the plot below I show the ratio of the red to green intensities as you move along the diagonal of the field, with lens detection OFF (bottom curve) and with ON+UV/IR at focal lengths set to 21, 18 and 16 mm, reading from bottom to top. The red/green ratio without correction on the CV15 is depressed by 60% at the corners of the frame, and corrected to within a few percent across the frame using the 16mm routines now provided.

 

However, if you forget to "SET" 16mm explicitly, and use the 18mm default that results from ignoring the dialog, pressing the shutter to get on with shooting, the 18mm correction leaves the red/green ratio depressed by 20% at the corners, which will be visible in some shots. I checked that when the default focal length appears in the EXIF and info data blocks, the 18 mm correction curve plotted here is the one being used, even though the focal length setting dialog remembers the value that you last have confirmed, which may be different. Similarly, if you have a WATE turned to 16 or 21 mm focal length (I don't have a WATE), the color error from using the default 18mm curve could be visible.

 

[/geek alert off]

 

scott

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[geek alert back on]

 

Here's the other side of the vignetting corrections for extreme wide angles. Again, I am using my CV15/4.5, this time with no filter. The first plot shows how the Green channel falls off due to normal vignetting (the lower curves at two apertures) and then is enhanced by the vignetting corrections that are designed into the ON routines. There is also some mild red vignetting occurring with the CV15 (and the WATE at its wider angles) even without a filter, and the ON firmware makes only a small correction to that.

 

[/geek alert off]

 

scott

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Guest guy_mancuso

It was pretty geeky Scott. LOL

 

Seriously it does give a good image of what is going on, nice job. May have to send you to Solms. LOL

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