Those Mean Ol' Cyan Corner Blues

[photolandscape]

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Just back from a great trip to So. America. Unfortunately, was too busy at work before leaving to do my homework on the cyan corner shift issue as it relates to using my CV15 on the M8.

 

Took about 1000+ photographs with the CV15 (a great lens for capturing the scene at Machu Picchu and for shooting the moai on Easter Island). Didn't have any way to view what I was shooting until I got home, so now I'm looking at hundreds of otherwise nice shots with serious cyan drift in the corners. So, I have two questions:

 

1) software to fix what I've shot--I've seen it mentioned here, and have downloaded it to my Mac. Want to fully employ it, but when I open it on my Mac, all I see is a simulated metal panel with a black dot in the middle. Can anyone tell me how to open and get into it? Are there any other programs which I should look at as well?

 

2) permanent fix--I have the Milich LT-M8 filter adapter/lens shade for the CV15. But does he or someone else make a different adapter (that would fit between the lens and the lensmount on the body) that can be coded and be used to prevent this from being an ongoing issue? Does Milich has a website or is there some way to contact him? I have lost that information.

 

I did a search but only found bits and pieces on these topics and am a little confused on how best to proceed. Thanks in advance.

[sandymc]

Can anyone tell me how to open and get into it? Are there any other programs which I should look at as well?

 

Umm, well, to ask the obvious, did you read the Quickstart guide that came in the ZIP file?

 

But to give the quick version, you need to do the following:

 

1. Build a lens profile: Take a photo of a grey card overexposed a few stops, then go File Open, then Profile Create, then save it with Profile Save.

 

2. Load an image you want to corrected by File Open, then load your lens profile, then save your corrected file..........

 

Sandy

[luigi bertolotti]

Sorry, not completely related to the thread : but anytime I see the "cyan drift" term there is a basic question that arises in my mind :

 

- "Cyan drift", FWIW is a term related to WAs used with Digital cameras (M8 in OUR case ... )

 

- When I used WAs with my old beloved M4, it was normal to speak about the well known phenomenon of "vignetting" = light falloff at the angles of the 24x36 film neg, caused, If I remember well by some of the usual lens abherrations.

 

Do arise the two phenomenons from THE SAME optical issue ? Or are they totally unrelated ? I saw a number of very fine explanations hereby, but do not remeber to have red something about this (trivial, admit) question...

[jlm]

i do make an adapter for the C/V lenses that has the recesses for coding; it allows the 15 to be coded as a 16mm WATE

 

jm@milich.com

[mwalker649]

i do make an adapter for the C/V lenses that has the recesses for coding; it allows the 15 to be coded as a 16mm WATE

 

jm@milich.com

 

I used my CV 15 yesterday with the adapter coded for the WATE, I had the setting for "UV/IR on" and got cyan drift in the corners too. What I'm i doing wrong?

[photolandscape]

Umm, well, to ask the obvious, did you read the Quickstart guide that came in the ZIP file?

 

Sandy, being impatient by nature and too busy too often, I must confess that I didn't read the Quickstart guide Partly because I didn't see it, and partly because I wasn't looking. But I will tonight. Thanks for pointing that out. I look forward to trying your program and I appreciate your efforts a great deal. I'd be happy to donate some $ if you would like.

 

Best, Steve

[ho_co]

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Do arise the two phenomenons from THE SAME optical issue ? Or are they totally unrelated ?

Totally unrelated.

 

Cyan drift occurs only when UV/IR-cut filters are used on wide angle lenses.

 

The UV/IR-cut filter uses multiple reflective coatings to block light of a specific frequency range.

 

First layer transmits the light, which reflects off the second layer, hits the first layer again from the inside; and the first layer now also reflects the light back to the second layer and so on, trapping the light and preventing its transmittance. That's obviously an impossible explanation but it brings us to the right place for the accurate one: The internal reflections among the partially transmitting multilayer coatings act to create destructive interference in the IR and UV. That is, the light's frequency causes it to be reflected 1/2 wavelength out of phase with the light entering, eliminating the transmission of those frequencies.

 

That's how these filters work, but light entering the filter from further off center has a greater distance to travel from one layer to the next because it is traveling at a greater angle to the normal of the surface. In other words, the light is traveling along a greater diagonal between the reflective surfaces. Because the reflections are now outside the optimum range, the light extinction moves into the visible range. That is, the different geometry of the reflection at these greater angles begins blocking visible rays as well as IR.

 

In other words, the UV/IR-cut filter blocks both UV and IR on axis. The further off axis the origin of the light, the more the same filter blocks red as well. Since cyan is opposite red on the color wheel, the absence of red causes a cyan tint. Because the effect is greater the further off axis we go, the cyan tint increases toward the edges of the image. Since the effect varies from none at the center to a maximum at the edges, it isn't a cyan cast but what S Reid calls a "cyan drift."

 

It's because the effect grows worse at wider angles that it doesn't occur with 50mm and longer lenses on the M8. And for the same reason, the effect grows worse the wider the angle of the lens.

 

Leica had designed the M8 to be programmed in firmware to compensate for vignetting. Luckily, that same design has allowed the camera to be programmed to compensate for the cyan drift.

 

Although the cyan drift looks like vignetting of a cyan color, the two are unrelated phenomena. Because the two look similar, it is tempting to refer to "cyan vignetting," but that is incorrect and Sean is right to keep pounding home the term "cyan drift."

 

There is a bit more specific information at Edmund Optics - Mounted IR Filters. The filter they call "UV/IR-cut" is a Schneider-branded 486. I don't know whether this product has a higher flatness grade that the consumer version sold under the B+W brand.

 

In astronomy, the same design is sometimes referred to as a "hot mirror."

 

Hope this helps.

 

--HC

[gravastar]

I used my CV 15 yesterday with the adapter coded for the WATE, I had the setting for "UV/IR on" and got cyan drift in the corners too. What I'm i doing wrong?

Whose filter were you using? Leica, B+W 486 or Heliopan etc. There's quite a difference between Leica and B+W in the corners with very wide angles, B+W tends to give green/cyan corners with the in camera correction which we're told is optimised for the Leica filters.

 

Bob.

[artur5]

I have a Zeiss 21/2.8 coded as Elmarit Asph 21 and I'm using the Leica I.R. filter. The cyan drift disappears completely, but I notice a mild overall reddish cast, not on the corners only. I don't know if it's a filter issue or a problem with the WB ( I always use manual WB but..).

The effect is easily correctable moving the tint slider a bit to the left on ACR., but it bothers me anyway.

Somebody else using a coded Zeiss 21/2.8 and Leica filters ?

[mwalker649]

Whose filter were you using? Leica, B+W 486 or Heliopan etc. There's quite a difference between Leica and B+W in the corners with very wide angles, B+W tends to give green/cyan corners with the in camera correction which we're told is optimised for the Leica filters.

 

Bob.

 

I just looked at the lens..I had no filter attached..duh

[gravastar]

I just looked at the lens..I had no filter attached..duh

Errrr..... no filter, I'd expect you to have red corners not green if the lens detection in the camera was working. I'm not sure how your filter (if it was mounted) was attached, maybe it was on the lens but it's fallen by the wayside between then and now?

 

I've just realised what your original problem with the green corners may have been due to. Assuming a filter was used and you've coded the adapter correctly as a WATE and the camera's lens detection is working. When you first turn on the camera with the WATE coded adapter mounted or you mount the adapter you should be presented with a menu. The menu asks for the focal length the WATE is set to - 16, 18 or 21mm, the default is 18mm. So for the 15mm lens you need to choose 16mm, the 18mm default is probably insufficient correction. Even the 16mm setting may not be enough with a 15mm lens, since I don't have the 15mm I'm not sure of this.

 

Bob.

[mwalker649]

Errrr..... no filter, I'd expect you to have red corners not green if the lens detection in the camera was working. I'm not sure how your filter (if it was mounted) was attached, maybe it was on the lens but it's fallen by the wayside between then and now?

 

I've just realised what your original problem with the green corners may have been due to. Assuming a filter was used and you've coded the adapter correctly as a WATE and the camera's lens detection is working. When you first turn on the camera with the WATE coded adapter mounted or you mount the adapter you should be presented with a menu. The menu asks for the focal length the WATE is set to - 16, 18 or 21mm, the default is 18mm. So for the 15mm lens you need to choose 16mm, the 18mm default is probably insufficient correction. Even the 16mm setting may not be enough with a 15mm lens, since I don't have the 15mm I'm not sure of this.

 

Bob.

 

No I had red corners. The filter was out to be cleaned and never replaced:o

[sean_reid]

Sorry, not completely related to the thread : but anytime I see the "cyan drift" term there is a basic question that arises in my mind :

 

- "Cyan drift", FWIW is a term related to WAs used with Digital cameras (M8 in OUR case ... )

 

- When I used WAs with my old beloved M4, it was normal to speak about the well known phenomenon of "vignetting" = light falloff at the angles of the 24x36 film neg, caused, If I remember well by some of the usual lens abherrations.

 

Do arise the two phenomenons from THE SAME optical issue ? Or are they totally unrelated ? I saw a number of very fine explanations hereby, but do not remeber to have red something about this (trivial, admit) question...

 

Beyond a certain angle of view (field of view) an IR-cut filter will begin to reflect not only infrared but also the color red itself. This begins at a certain radius from the center and increases in intensity with increasing distance from that center. This could be called "red vignetting". The wider the EFOV of a given lens, naturally, the more red vignetting will occur. In practice, its most noticeable on the M8 when 35 mm and wider lenses are used.

 

The visual consequence of red vignetting, in the actual picture file, is a color drift towards blue-green that I call "Cyan Drift". Like a boat drifting from its mooring, this color change drifts further and further from the neutral rendering it has on center. The drift follows the same pattern as the red vignetting, of course, but shows the colors that become more visible as red is removed.

 

"Shift" as in "cyan shift" suggests that the whole frame changes color, which it does not. "Cyan corners" implies that the problem occurs only in the corners whereas it begins much closer to the center and then radiates out with increasing intensity.

 

My site has many discussions, examples, etc. of this.

 

Cheers,

 

Sean

[ho_co]

Beyond a certain angle of view (field of view) an IR-cut filter will begin to reflect not only infrared but also the color red itself.

 

According to the Edmund link above, the effect Sean mentions comes into play from about 30° angle of incidence.

 

Note also that the layers of the multicoating reflect the involved wavelengths destructively, as I mentioned in post #7 above. That is, an IR-cut filter doesn't reflect IR back away from the filter, but prevents its transmission by destructive interference.

 

--HC

[luigi bertolotti]

Thanks to Sean and Howard... I was too lazy to surf for finding infos on cyan drift... and hadn't taken the basic info that is strictly related to the IRUV filters and their specific glass structure.